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Hydrogen economy

From Wikipedia, the free encyclopedia

The hydrogen economy is a proposed system of delivering energy using hydrogen. The term hydrogen economy was coined by John Bockris during a talk he gave in 1970 at General Motors (GM) Technical Center.[1] The concept was proposed earlier by geneticist J.B.S. Haldane.[2]

Proponents of a hydrogen economy advocate hydrogen as a potential fuel for motive power[3] (including cars and boats) and on-board auxiliary power, stationary power generation (e.g., for the energy needs of buildings), and as an energy storage medium (e.g., for interconversion from excess electric power generated off-peak). Molecular hydrogen of the sort that can be used as a fuel does not occur naturally in convenient reservoirs; nonetheless it can be generated by steam reformation of hydrocarbons, water electrolysis or by other methods.[4]

A spike in attention for the concept during the 2000s has been repeatedly described as hype by some critics and proponents of alternative technologies.[5][6][7] A resurgence in the energy carrier is now underway, notably by the forming of the Hydrogen Council in 2017. Several manufacturers have now released hydrogen fuel cell cars commercially, with manufacturers such as Toyota and industry groups in China planning to increase numbers of the cars into the hundreds of thousands over the next decade.[8][9]

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  • What happened to the hydrogen economy? - Dr Paul Dodds - 20/02/2018
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  • Will Hydrogen Be the Fuel of the Future? Cars, Economy, Facts, Energy (2002)

Transcription

Good afternoon, everybody. My name is Paul Dodds. I'm from the UCL Energy Institute. I'll give you some background about myself first. My first degree was in physics. After that, I worked in the nuclear industry and consultancy. I then did a PhD in tropical agronomy, looking at crops and climate change in West Africa. These days, I work as an economist, on the boundary between engineering and social science, looking at economic modelling of energy systems and trying to understand how we achieve a low-carbon energy system in the cheapest way possible and what the transition might look like. One of the main areas of interest I have is hydrogen. We've done quite a lot of work on hydrogen, on trying to model hydrogen systems and trying to understand how hydrogen fits in to the wider picture as we go towards a low-carbon world. That's what I want to talk about today. My question is, what happened to the hydrogen economy? You might think the picture behind me is a bit odd if we're talking about hydrogen. Hydrogen disappeared out of our energy system in around the 1970s. Pretty much all the hydrogen we use in the world today is used to make ammonia for plants. This goes very well with my PhD. If we go back a bit, we find that hydrogen had a very early entry into our energy system or what we think of as the energy system today. It first became mainstream, in the year of 1812. The Gas Light and Coke Company was incorporated in 1812, to provide street lighting, public lighting in London. It did that using town gas. The gas was town gas, made from coal gasification. It had a number of by-products, which were important for the economic case. There's two fundamental reasons we keep coming back to when we think of hydrogen in the future. There was an economic reason. Until then, whale oil had been used. Town gas was around a third of the price of whale oil. There was an economic reason. Secondly, there was a quality of service reason. You got a brighter, safer flame using town gas, than you did using whale oil. I should say that town gas was about 50% hydrogen. It was a mixture of hydrogen, methane, carbon monoxide, carbon dioxide, but around 50% hydrogen. This was a huge success. In 1812, the first company was incorporated. By 1820, there was widespread adoption of street lighting across the UK. In only eight years, several hundred companies, some privately owned, some municipally, owned by local councils. It caused a social revolution. That's a bit of an aside. Until then, in most places, it was very dark at night and people wouldn't go out because they thought it wasn't safe. Once you had street lighting, people went out at night, so it changed what people could do. This is how hydrogen was used. It was part of town gas from around 1812 until 1875, when it started also to be used for cooking in many houses. Also in around 1880-ish, we started getting electric lighting. You might think electric lighting is what we use now. It's a much better technology than gas to provide lighting. Actually, it's surprising if you look at the statistics about how long it took for electric lighting to overtake gas in the UK. This is from 1920 onwards. In 1920, we're already 40 years after electric lighting has been demonstrated. Forty years later. Still, we have almost none in 1920. It wasn't until the 1950s when electric lighting started to replace gas in the UK. The changeover where electric lighting began to dominate wasn't until about 1960. Eighty years after electric lighting was first demonstrated. Again, it was for economic reasons. Gas was still competitive, even after electricity became available. Pretty soon after that, hydrogen disappeared out of our gas system, because in 1959 we discovered natural gas in the North Sea. We pretty quickly tested it in homes, worked out how to extract it, and in about 1966, the decision was made to convert the whole of the UK from town gas to natural gas. The programme started in 1967 and completed in 1977. Here's an example in Westminster, turning off the town gas. That also caused a change in how we use gas. Until then, town gas was rather expensive for heating, so people used coal. When natural gas became available, it was much cheaper, so heating became the primary market for natural gas. We greatly increased our gas consumption. The graph shows how in 1960 we had 10 gigajoules per customer per year and in 1980, with natural gas, we were up to 70 or 80. When we think of hydrogen today, we think of transport. Hydrogen has been used in transport before. Probably more infamously than anything else. On the left hand side, we have the Hindenburg disaster, which if you ask any hydrogen researcher what the public thinks of hydrogen, they'll say Hindenburg. It's not really true. If you do surveys on what people think of hydrogen in the UK, and people have done this, they found that people are quite interested in the idea, they're quite open to the idea, and want to know more. They don't think they will be sitting on top of a bomb, which is what a lot of researchers claim. There is a lot of controversy about the Hindenburg disaster and what actually caused it. I think they hydrogen all burned off in about 90 seconds. Hydrogen is very buoyant so it goes straight up at high speed. You can't see hydrogen flames visible. What you can see there is something else burning. Another place hydrogen was used a lot was in the Apollo programmes and in spacecraft in general. When you see one of the big rockets launch, you're not looking at hydrogen, it's jet fuel at the first stage. At the second and third stage, they use liquid hydrogen and oxygen to provide propulsion. Today, we're interested primarily in cars. The big interest in hydrogen in recent years is from fuel cell cars in particular. Nice, sleek, quiet, no-emissions, badly parked, they do all of it! Why fuel cells? Hopefully, this is going to work. A fuel cell looks like this. You put hydrogen and oxygen into it and we get an anode and a cathode out. They go through the anode and cathode, we get water out and electricity generated. Fuel cells can be up to about 60% efficient rather than 30%. There's lots of different ways you can provide that hydrogen. There are lots of uses for the fuel cells. We'll come to that a bit later. One interesting thing about fuel cells is they are scalable. You can go from very large to very small uses and they have the same efficiency. It's the only technology that produces the same efficiency at all scales. Most of them lose efficiency as you make small versions. What a lot of people think about is green hydrogen that comes from renewables, you have renewable electricity, that goes through an electrolyser to produce hydrogen, which has no emissions on the entire cycle. That's a vision many people have of what hydrogen could be in the future. So we get the green hydrogen economy. The term hydrogen economy became widespread in the 1970s and several visions have been proposed for hydrogen fuel cells in future economies. Quite a few people think of hydrogen as a clean energy carrier. It's the only energy carrier, other than electricity, which doesn't have carbon in it that we foresee using. Maybe ammonia. A few people talked about that, but we won't put it into houses as it's toxic. You might be able to use it in shipping and industry and places, maybe in electricity generation, but essentially we have the choice of hydrogen or electricity. Electricity can generally do more things, it's a hybrid fuel. Hydrogen is easier to store. You can make it more cheaply. We have trade-offs. A lot of people think of hydrogen as a clean energy carrier. They think of it as being produced from sustainable or renewable energy sources. Low-carbon. That's where the green hydrogen comes in. There's arguments over what green means. Does it mean renewable or low-carbon? People have been arguing this for electricity for many years. Every country has a different definition. Other visions people have had for hydrogen could be reducing import dependence and creating a more secure energy system. This is particularly in the US, where they look at import dependence on oil and see that's a big issue, they look at hydrogen as a way of having domestic energy resources that will reduce energy imports. It's very controversial whether reducing import dependence actually increases energy security. There's evidence it doesn't make a difference. That's a different conversation. Other people look at particular sectors. They foresee hydrogen in road transport or they see hydrogen supporting renewable electricity generation. For example, if you have excess generation in times of low demand, you produce hydrogen with that rather than lose electricity. They see decarbonising gas heating as well. Back to where we started. If we think about where hydrogen has gone, we need to think about the hydrogen hype cycle. This is a graph of the Gartner hype cycle. Time along the x-axis, and the visibility of technology along the y-axis. We start off with the technology trigger down here at the start. This is when it first becomes famous. People develop the new technology and they say it's going to change the world, it does all these amazing things, and the media becomes very interested. People set up companies, money goes into research, and a lot of hype builds up about it in a short space of time. We go up the hype cycle until we reach the peak of inflated expectations. At that point, we find that we still don't have a product that's commercially viable. It's too expensive and doesn't work well enough. We've had a lot of money put into a lot of companies so we're thinking about the tech boom type of thing. A number of those companies go bust. That happens with any new technology. People become disillusioned. They were expecting great things. They put money into companies. They all went bust. We then start going back down the visibility curve into the trough of disillusionment. At that point, people have forgotten about the technology. They think it's never going to work. It was yesterday's idea, which was good, but wasn't practical in reality. While you're down there, and through this whole process, in the first place you trained people to understand the technology. You still have a few companies that survived. They continue to develop if it was a good idea. Those people will work for the new companies, they will keep the networks they had going, and eventually they will overcome the problems. They'll do it in their own quieter way, which is more realistic than it was in the past. We then head to the slope of enlightenment. This sounds great to me because, as an academic, that's what I'm meant to do, enlighten. At that point, we are more realistic about the potential for the technology, but we are also getting to the point where it is economically viable. It becomes commercially viable for the first time. We eventually get to the plateau of productivity, which is when you start making and selling the thing, and when it might take off. This is the Gartner hype cycle. We see this hype cycle for a lot of different technologies. If I put on where I think we are for hydrogen. We started in about the late 1990s, when hydrogen became a big thing. Then, probably around 2002, at the same time as the tech boom, we hit the peak of inflated expectations. Since then, it's been a bit downhill. Particularly when electric vehicles have taken a lot of the limelight and a lot of the headlines in recent years. A lot of people have looked at battery electric vehicles and hydrogen fuel cell vehicles and said you're trying to pick one or the other. They're seen as competitors. Hence, a lot of people would say the battery electric vehicles have won. I think about 2013 we got to the trough of disillusionment. We're now somewhere heading up the slope of enlightenment. Probably more towards the bottom than the top. Do fuel cells work? How are they designed? Are they safe? Would you want one? Those are a few questions people often ask. All fuel cells look a bit like this, on the right hand side. They have a tank with hydrogen. Normally it's compressed to 700 bar. Really high compression. Hydrogen is not a dense gas. If you don't do that, you don't have enough for the range that you want. We tend to build these tanks out of carbon fibre. They're really strong. They have to go through a lot of safety tests. Out of that tank, we then supply a fuel cell. This generates electricity. That powers an electric motor, which powers the drive chain of the car. All commercial hydrogen vehicles are hybrids. They all have battery packs of various sizes. We also have batteries, which can power the electric motor. In some cars, they set up the fuel cell so it charges the batteries. Then the battery powers the electric motor directly. The fuel cell isn't connected directly to the motor. There's different ways of doing it. Fundamentally, these are electric cars. They have electric motors. The only difference to a battery vehicle is that in a battery vehicle, the battery provides all the energy, whilst here we have a fuel cell that also provides electricity. We tend to use proton-electrolyte membrane fuel cells in these cars. They have quite low operating temperatures, about 90 degrees. This means a little dribble of water comes out of your exhaust rather than gas. Also, they are exceptionally good at ramping up and down power levels as required and at high efficiency. This is what you need when you're using a car, because you get to a junction, you stop, the light goes green, you speed up afterwards and your power output has to ramp up. They're very good at that. I talked a bit about fuel cells being uniquely scalable and even small cells having high efficiency. That's great. As an example from Arcola Energy, I did promise a car, this is a fuel cell car, which they make out of Lego. It's powered by these. This is a hydrogen stick. This is a metal hydride hydrogen stick. It's filled full of metal and when you pump hydrogen in, it reacts with the metal and absorbs. When you open it up, the hydrogen will come out again. We don't tend to use these in cars because they're too heavy. In cars, we tend to compress the hydrogen in a strong tank. Here it's not compressed. That's a hydrogen tank, it's quite safe, it doesn't leak. You can build a car like this. This is a fuel cell here. This is a two watt fuel cell of the type you would use to charge a mobile phone. This is probably one of the cheapest fuel cells you can buy, in terms of the size. The power density can vary a lot between different fuel cells. This is very large for a two watt. For comparison, a car might have a 100 kilowatt fuel cell. You can imagine if you had to make this that much larger, it would take up your entire car. They have a much higher energy density. This is the exhaust pipe here, which gets the water out. This is a little 2 watt engine at the back under here. Theoretically, if I try, it'll work. In reality, we do have some fuel cell cars being commercialised. At the minute, you can buy two fuel cell cars in the UK. These became available for the first time last year. We have a Hyundai ix35, which was the first commercially available, 101 kW. It wasn't until the third generation of this car that they made them commercially available. Even then, their mass production was about 1,000 models. It was small but it was the first car that went into mass production. It wasn't built by hand. That was the first one that came out globally. The Toyota Mirai has had a lot of publicity in recent years. That's 113 kW and that's also available. The Honda's fuel cell Clarity is going to be released later this year. At that point, we will have three cars in the UK. Have battery vehicles already cornered the market? Worldwide, there's already 25 pure-electric cars, so only batteries powering an electric motor. Even within the UK, there's 70 types of plug-in cars and vans. When I say plug-in, you could have a car with a petrol or diesel engine, that also has an electric motor and has batteries as well. It can run off the engine or the motor. They are all hybrid cars. They have regenerative braking, but they could also be plug-in hybrid, where you charge them at home, run off the batteries for the first miles, and then move to the petrol engine when your batteries are empty. Also, we've been building infrastructure in the UK for battery vehicles. We have more than 15,000 charging points for plug-in vehicles. Electric vehicle sales do continue to grow over time. They're running at about 6,000 a month. It's interesting that hybrid vehicles have been dominating, not pure electric vehicles. Sales of pure-electric battery vehicles have reduced recently. There's a question about why that is and I don't know the answer. Those were sold in January 2018 and January 2017. Even those there were more electric vehicles sold in January 2018. There's a question of whether people are happy with the operating characteristics of the pure electric vehicles. This is quite a famous little chart, comparing useful transport energy derived from renewable energy. It's by Ulf Bossel in 2006, in a paper called, 'Does a hydrogen economy make sense?' He started with 100 kilowatt hours, 100 units of electricity from renewable sources, and said what proportion of that can we convert into useful energy for our car using different power trains. On the right hand side, we have electricity. Or battery vehicles. Essentially, you charge your batteries, and then you get down to your vehicle, and it's about 90% efficient, the motor, which means you end up with 69 kWh, 69% efficiency, 69 of your original 100 kWh, are used to provide motor force for your vehicle. If we then look at hydrogen fuel cell vehicles, on the left hand side, we have two different routes. On the far left, we have gaseous hydrogen. In the middle, we have liquid hydrogen. There's two routes you might supply and use a fuel cell vehicle. You can't put liquid hydrogen directly into a fuel cell, you have to gasify it, even if it was stored as liquid in the car. Fortunately, it gasifies at -250 degrees. That's not a problem. It happens automatically. We find that we convert the electricity into hydrogen using electrolysis, that loses about 29 units of our original 1,000. Then we have various steps where we need to compress the hydrogen and transport it and put it into the fuel cell and then go through the motor as the final step. Or we need to liquify the hydrogen and transport it, put it in the fuel cell and go through the motor. We end up with 19 kWh for the liquified route and 23 kWh for the gaseous route. Out of our original 100 kWh. 19% and 23%. This is a lot lower than 69% efficiency. Ulf Bossel's argument is why would you use hydrogen cars when if you look at the basic efficiencies, you should only use battery vehicles? We can be a bit picky with some of the numbers. We might say if we're going to use an electrolyser to produce hydrogen, we do it at a refuelling station, so there is no transport cost. Chop out that 80% efficiency loss there. We could argue with a few bits and pieces. All hydrogen cars are hybrids. Why does this one get regenerative braking and these don't? In the grand scheme of things, the argument still stands that these two are only a third of the efficiency of this one. What I'd call that efficiency on the previous graph is the power train efficiency. It's the efficiency of the motor force that comes through your car. That's not what we're interested in if we're interested in running a car. We're not interested in power train efficiency. We're interested in the vehicle efficiency. The vehicle efficiency is how many kilometres you get for a given amount of energy at the start. That's quite different to power train efficiency. We measure this in kWh per km, not as a percentage. The vehicle efficiency depends on the weight of the car. That's important because battery vehicles become increasingly heavy as the number of batteries increases. If you're happy to have a short range with your car, you won't have many batteries. If you want a longer range, you need to increase the number of batteries in order to increase the distance it can travel in one go. If you do that, you'll increase the weight. Pretty quickly, the majority of the weight in your battery car is the actual batteries themselves. That's important because if we want a long range car, you can keep adding batteries but you eventually get mass compounding. The more batteries you add, the less extra distance you get, and at a certain point, if you add more batteries, you'll reduce the range of the car because the weight outweighs the extra energy you have for storage. You end up with a graph like this. Your electric vehicles are much more efficient if you have a short range, but as you increase the range beyond a certain level, they become less efficient. Hydrogen vehicles, and today's internal combustion engine vehicles, are much less sensitive to increasing the amount of fuel stored on board, because the fuel is much lighter than it is in batteries. If range is important, then maybe it's not so clear cut, the differences between battery vehicles and hydrogen vehicles. Also you have to think that a lot of vehicles are quite heavy. For example, heavy goods vehicles or refuse vehicles or even very large cars. The larger the vehicle becomes, the more difficult it becomes to use batteries. If we look in the long-term, and think of what the costs of these technologies might be, this is a graph I produced in 2014. The idea was to compare the total cost of ownership of all of the different power trains. This is for a scenario where we meet our two degrees targets and we have carbon taxes on various fuels over time. This is why the gasoline ones become more expensive. The diesel ones become more expensive. This is assuming we have innovation in all the technologies, which brings all prices down to mass production level. We see that all of the costs lie somewhere between £50-70,000. There's a lot of crossover. Frankly, the uncertainty in all of these costs is far larger than the difference between the individual costs. If you were to ask , what's going to be the cheapest technology in 2040, if we can mass produce all of them, my answer is I have no idea. Anybody who tells you otherwise is guessing. If I was going to try to interpret this, I might say that we'd use battery only vehicles for city cars, because they're more efficient, and for long-distance or family cars, maybe we'd have hydrogen, plug-in hybrids. Hydrogen has batteries anyway, put a few more in and a plug on it, and it becomes a plug-in hybrid hydrogen vehicle. Of course, that could change if we have technological breakthroughs. Particularly on the battery side. If lithium air batteries could be made to work, they have a much higher energy density than existing lithium batteries then that could tip the balance. You could then greatly increase the range of battery vehicles. You might also want super-fast charging. At the minute, you can supercharge a car in about 30 minutes to do 100 km. If you're going long distances, that might be a pain. It won't be long before you're stopping for another half an hour and then another half an hour. You probably need something even faster than that. Hydrogen vehicles are essentially like existing vehicles. You get to a refuelling station, you fill up the tank in three minutes, you drive for 300 miles, you go to a refuelling station for three minutes. They're the business as usual option. There's a number of other markets that have been growing for hydrogen. Certainly, forklift trucks. They're becoming popular in the US in warehouses, because they can go for 8-10 hours without needing to be recharged. When you do need to refuel them, it takes three minutes as opposed to recharging them overnight. You get a much higher usage factor out of your forklift truck. That's also because you can't use petrol vehicles in warehouses, because of emissions. Depending which way you came, you could have come on a hydrogen bus. If you went on the RV1 route. There's a fleet of six buses in London, which have been running for a while. They've been running well, TfL are happy with them. In the longer term, we think of HGVs, hydrogen is one of the few options to decarbonise HGVs. Maybe even trains. This is a hydrogen train. They've been developed using fuel cells. Another area that's been getting interest recently in the UK is hydrogen for heating. Interestingly, heating is by far the biggest global market for fuel cells. Not transport. In Japan, there's now about 225,000, as of last October, fuel cell micro-CHP devices installed in people's houses. These generate electricity and provide heat for the house. There's been huge growth there. In comparison, there's only a few thousand vehicles being produced. We can see how this has happened. The Japanese government decided they were keen to promote this technology and promote innovation in it. For the first few, they had a Japanese industry shakeout, with the idea to reduce costs over time. You can see how they reduced from 2007 down to about 2011. On the blue line, that's Korea. Japan is the green line. It was about 2004. 2007 they broke them down and then they started putting them into competitive markets. The prices have continued to drop and drop. They started about £200,000 per unit and they're now down below £20,000 per unit. That's been achieved through year-on-year growth plus targeted investments and innovations within the country. There are interesting ideas. For example, if anyone is given a contract for research, they are required to share the insights they get with their competitors. There's been several companies involved in building the fuel cells. They compete with each other. They also help each other and collaborate a lot. They see a bigger picture of selling them. We have also started putting them into Europe, but we have far fewer. This is a logarithmic scale here. We have less than 1,000 at the moment. By Europe, you could write Germany. Almost all of them are there. Within the UK, there's been quite a bit of interest in hydrogen for heating. Partly because the plan before that of using heat pumps has proven to be quite difficult. We worry about whether the electricity system can cope. Here we have the gas demand compared to electricity demand. The gas demand is in orange. You can see there's very high winter demand and a lower summer demand. Both are much larger than current electricity demand. Electricity varies more between the evening peak and the overnight low than it does between seasons, at the moment. We worry about whether distribution networks will melt with the higher load, whether we can generate enough electricity for the winter peak at a low enough price with heat pumps. An alternative that's been suggested, this report in the top left, the Leeds City Gate h21 report, had a lot of publicity about this, was to instead use hydrogen, to convert the natural gas networks again and have a similar conversion programme to the 1970s but whereas in the seventies we went from town gas to natural gas, this time we'd go from natural gas to 100% hydrogen. The Leeds report looks at what the feasibility of doing that would be. It's a business-as-usual option. You can see it as a business-as-usual option for homeowners who have currently got natural gas heating because essentially you have a drop-in boiler, which does the same as your current natural gas boiler except it doesn't produce carbon dioxide emissions. We are looking at this in quite some detail. BEIS, the Department of Business Energy and Industrial Strategy, and Ofgem are investing more than £30 million between them in feasibility studies, to look at what happens with using hydrogen within your house and developing hydrogen boilers, looking at standards. Ofgem are looking at the gas networks themselves and what changes you need to make to use hydrogen in the gas networks. There is an open question about whether we would use gas boilers or fuel cells. I showed on the previous slide Japan is using all fuel cells. In that case, powered by natural gas. They have a built-in reformer that converts natural gas to hydrogen. If they move to a hydrogen grid, they could throw away the reformer. This would make the fuel cell cheaper Everybody would be happy. We could use either in this country. Maybe a mix of both. People have also done studies looking at whether you could use fuel cells to balance the electricity demands from heat pumps, if we had heat pumps in houses. All these technologies, although they're competing, they can be used to balance each other off. When a lot of people talk about hydrogen, they think about how are you going to produce hydrogen. That is the question you get a lot. How will you produce low-carbon hydrogen? We've already talked about producing hydrogen from renewables with electrolysis. This works. It's the most environmentally friendly. It's also the most expensive approach. Is still leaves the question of why you'd want to do that if you can use electricity directly in heat pumps or battery vehicles. There are lots of ways of making hydrogen. Similar to there being lots of ways of making electricity. The main way we make it worldwide is through natural gas. We have steam methane reformers, to produce hydrogen from natural gas. That's used to make ammonia in the Haber–Bosch cycle. That's 50%. Essentially, everywhere that has natural gas uses that. A few places with dams use electricity, everyone else uses coal to boost the hydrogen. In the future, you would need to use carbon capture and storage. There are some interesting designs as how you could build a module on the side of your steam reformer to capture the CO2, or just redesign it in a cleverer way to capture it in the process. Then you need to worry about how you get it from the production site to the point of use. You have pipelines that could do that. You could send them through tube trailers, which is a trailer with gas canisters on. Similar to this one, on the back. You drive it to refuelling station. If it's liquefied, you can put it in a road tanker. Similar to the oil tankers you see today. There are several ways. You have to think about how clean you want your hydrogen to be, how pure, what compression you need in different places. If you need it at 700 bar, you don't want to compress it from 2, because that's very example. You want a refuelling station from a high pressure pipeline, rather than low pressure. There's lots of issues about that. There's lots of options as you can see on here. I want to mention power-to-gas briefly. Power-to-gas generates hydrogen using excess renewable electricity. That power is not wasted in times of low demand. This assumes you have more renewables than we have at the moment. Probably more than 60% for it to make a difference. 60% of your total generation from renewables. According to the sums we've done. The economics of this depends on the cost of the electrolyser and the capacity factor, how often you are using your electrolyser. One issue is that the more electrolysers you have, the lower the capacity factor of all the electrolysers. The amount of excess varies over time. The more electrolysers you have, the greater amount of excess you get, but each amount of excess happens for a smaller period. You can only justify having a certain number of electrolysers on the system. We've done sums to see how much hydrogen you could supply to the UK using power-to-gas from excess renewables. How much of the demand you might supply. Let's assume that within the UK, virtually all the transport sector is supplied by hydrogen. All the road transport. All of the houses are supplied by hydrogen for heating. I talked about that previously. At that point, if we had 80% renewables, our excess renewable electricity could be used to produce 10% of needed hydrogen and about 90% of the hydrogen we'd need to produce using other technologies. This is not some sort of golden get-out-of-jail way of producing all the hydrogen we would need if we were using a lot of hydrogen. It's interesting. We could produce some hydrogen. It would make sense if we were going to produce hydrogen to use it as hydrogen rather than power-to-power storage and turn it back into electricity when we need more at times of high demand and low supply. The turnaround efficiencies are very low if you convert to hydrogen and then back to electricity. Depending on the timescale. You can store hydrogen for very long periods at low cost. You can't do that with batteries because they are too expensive. Essentially, it's not going to change things. You can see here the cumulative installed capacity. Most electrolysers have been alkaline electrolysers. We've been building those for 100 years quite happily. You can see the PEM electrolysers, similar to the PEM fuel cells, are becoming more common in recent years. That's because they are good at switching on and off to produce the hydrogen according to what your load is, which is ideal if you have excess renewables. Their generation is varying over time. There are five challenges for hydrogen fuel cells. The first one is to fund innovation. The only way you bring down prices for these technologies is through learning by doing to reduce fuel cell vehicle costs. I gave an example for that for the fuel cells for Japan, where they pulled the price down, but they did that through stalling 200,000. The same thing would be needed for fuel cell vehicles. You need to encourage people to try different methods of producing them in order to reduce the costs. That requires investment. Chicken-and-egg infrastructure is an issue. Whether you make the chicken or the egg. Do you build the infrastructure first or do you get the vehicles first? Actually, studies have shown you could build 60 small refuelling stations and that would cover about 80% of the population. It would cost £60 million, which in the transport sector is a drop in the ocean compared to what we generally spend. Working out purity and compression requirements is tricky. How they affect infrastructure development. The problem is that it's expensive compared to high carbon alternatives. Unless we have a carbon tax, we'll never justify building alternative vehicles. Maybe in the longer term, new demand patterns such as driverless vehicles could change how we use vehicles and that could change the economics. To summarise what happened to they hydrogen economy, the cars are being belatedly commercialised. There's a lot of technologies being pursued. I think there's a lot more realism now than in the past. I think the key drivers will be economics, user experience and air pollution. Personally, I think it's very hard to predict what's going to happen. Not least because hydrogen fuel cells can contribute in diverse ways across many sectors, which span the whole energy system. Thank you for listening. Thanks to the authors of these four papers here, whose work I used quite a bit. We have a minute or two for questions. Thank you. We have a microphone here. Hello, my name is Kim Leaper. I was reading in The Telegraph over the weekend, about a company by the name of High Tech, in Redmond, Washington who are very interested and have developed some technology of recognising that commercial vehicles are going to be the big problem in any kind of hydrogen economy and they have developed some injector technology to convert normal diesel engines into a hydrogen based fuel system. Are you familiar with this company and concept? I'm not familiar with the company. There is a company in London that's done something similar. You can convert internal combustion engines to run on hydrogen. BMW did a similar thing a few years ago when they had liquid fuels. The internal combustion engine efficiency is only 30%. Fuel cell is about 50-60%. You need twice as much fuel to go the same distance. BMW went for liquid fuel instead of gaseous fuel, but then the liquid fuel boils off and has problems. Nobody's doing that anymore. That's why people want fuel cells. If you have a short range, it can make sense. The ones in London that have been converted are all vans. For long distances, it doesn't work as well. We have time for one more. It's not a competition, electricity or hydrogen, but I'm interested in this question of AC/DC. Does that have an impact on the relative efficiencies? With all the different processes of using electricity to create hydrogen. You'll have some losses in the transformer. I don't imagine they are very large. [INAUDIBLE] I'm not sure whether people are using different engine designs to try and pick all AC or all DC, I guess it's possible. I'll have to talk to my electrical engineering colleagues. I'm afraid we don't have time for more questions. Thank you very much for coming.

Contents

Rationale

Elements of the hydrogen economy
Elements of the hydrogen economy

A hydrogen economy was proposed by the University of Michigan to solve some of the negative effects of using hydrocarbon fuels where the carbon is released to the atmosphere (as carbon dioxide, carbon monoxide, unburnt hydrocarbons, etc.). Modern interest in the hydrogen economy can generally be traced to a 1970 technical report by Lawrence W. Jones of the University of Michigan.[10]

In the current hydrocarbon economy, transportation is fueled primarily by petroleum. Burning of hydrocarbon fuels emits carbon dioxide and other pollutants. The supply of economically usable hydrocarbon resources in the world is limited, and the demand for hydrocarbon fuels is increasing, particularly in China, India, and other developing countries.

Proponents of a world-scale hydrogen economy argue that hydrogen can be an environmentally cleaner source of energy to end-users, particularly in transportation applications, without release of pollutants (such as particulate matter) or carbon dioxide at the point of end use. A 2004 analysis asserted that "most of the hydrogen supply chain pathways would release significantly less carbon dioxide into the atmosphere than would gasoline used in hybrid electric vehicles" and that significant reductions in carbon dioxide emissions would be possible if carbon capture or carbon sequestration methods were utilized at the site of energy or hydrogen production.[11]

Hydrogen has a high energy density by weight but has a low energy density by volume. Even when highly compressed or liquified, the energy density by volume is only 1/4 that of gasoline, although the energy density by weight is approximately three times that of gasoline or natural gas. An Otto cycle internal-combustion engine running on hydrogen is said to have a maximum efficiency of about 38%, 8% higher than a gasoline internal-combustion engine.[12]

The combination of the fuel cell and electric motor is 2-3 times more efficient than an internal-combustion engine.[13] Capital costs of fuel cells have reduced significantly over recent years, with a modeled cost of $50/kW cited by the Department of Energy.[14]

Previous technical obstacles have included hydrogen storage issues[15] and the purity requirement of hydrogen used in fuel cells, as with current technology, an operating fuel cell requires the purity of hydrogen to be as high as 99.999%. Hydrogen engine conversion technology could be considered more economical than fuel cells.[16]

Current hydrogen market

Timeline
Timeline

Hydrogen production is a large and growing industry, as of 2004. Globally, some 57 million metric tons of hydrogen,[17][18] equal to about 170 million tons of oil equivalent, were produced in 2004. The growth rate is around 10% per year. Within the United States, 2004 production was about 11 million metric tons (Mt), an average power flow of 48 gigawatts. (For comparison, the average electric production in 2003 was some 442 GW.) As of 2005, the economic value of all hydrogen produced worldwide is about $135 billion per year.[19]

There are two primary uses for hydrogen today. About half is used in the Haber process to produce ammonia (NH3), which is then used directly or indirectly as fertilizer. Because both the world population and the intensive agriculture used to support it are growing, ammonia demand is growing. Ammonia can be used as a safer and easier indirect method of transporting hydrogen. Transported ammonia can be then converted back to hydrogen at the bowser by a membrane technology.[20]

The other half of current hydrogen production is used to convert heavy petroleum sources into lighter fractions suitable for use as fuels. This latter process is known as hydrocracking. Hydrocracking represents an even larger growth area, since rising oil prices encourage oil companies to extract poorer source material, such as tar sands and oil shale. The scale economies inherent in large-scale oil refining and fertilizer manufacture make possible on-site production and "captive" use. Smaller quantities of "merchant" hydrogen are manufactured and delivered to end users as well.

If energy for hydrogen production were available (from wind, solar, fission or fusion nuclear power etc.), use of the substance for hydrocarbon synfuel production could expand captive use of hydrogen by a factor of 5 to 10. Present U.S. use of hydrogen for hydrocracking is roughly 4 Mt per year. It is estimated that 37.7 Mt/yr of hydrogen would be sufficient to convert enough domestic coal to liquid fuels to end U.S. dependence on foreign oil importation,[21] and less than half this figure to end dependence on Middle East oil. Coal liquefaction would present significantly worse emissions of carbon dioxide than does the current system of burning fossil petroleum, but it would eliminate the political and economic vulnerabilities inherent in US oil importation before the commercialization of tight oil in North America.[22]

As of 2004 and 2016, 96% of global hydrogen production is from fossil fuels[23] (48% from natural gas, 30% from oil, and 18% from coal); water electrolysis accounts for only 4%.[24] The distribution of production reflects the effects of thermodynamic constraints on economic choices: of the four methods for obtaining hydrogen, partial combustion of natural gas in a NGCC (natural gas combined cycle) power plant offers the most efficient chemical pathway and the greatest off-take of usable heat energy. (needs reference)

The large market and sharply rising prices in fossil fuels have also stimulated great interest in alternate, cheaper means of hydrogen production.[25][26] As of 2002, most hydrogen is produced on site and the cost is approximately $0.70/kg and, if not produced on site, the cost of liquid hydrogen is about $2.20/kg to $3.08/kg.[27]

Production, storage, infrastructure

Today's hydrogen is mainly produced (>90%) from fossil sources.[28] Linking its centralized production to a fleet of light-duty fuel cell vehicles would require the siting and construction of a distribution infrastructure with large investment of capital.[citation needed] Further, the technological challenge of providing safe, energy-dense storage of hydrogen on board the vehicle must be overcome to provide sufficient range between fillups.[citation needed]

Methods of production

Molecular hydrogen is not available on Earth in convenient natural reservoirs. Most hydrogen in the lithosphere is bonded to oxygen in water. Manufacturing elemental hydrogen does require the consumption of a hydrogen carrier such as a fossil fuel or water. The former carrier consumes the fossil resource and produces carbon dioxide, but often requires no further energy input beyond the fossil fuel. Decomposing water, the latter carrier, requires electrical or heat input, generated from some primary energy source (fossil fuel, nuclear power or a renewable energy). Hydrogen can also be produced by refining the effluent from geothermal sources in the lithosphere.[29] Hydrogen produced by zero emission renewable energy sources such as electrolysis of water using wind power, solar power, hydro power, wave power or tidal power is referred to as green hydrogen.[30] Hydrogen produced by non-renewable energy sources may be referred to as brown hydrogen. Hydrogen produced as a waste by-product or industrial by-product is sometimes referred to as grey hydrogen.

Current production methods

Hydrogen is industrially produced from steam reforming, which uses fossil fuels such as natural gas, oil, or coal.[31] The energy content of the produced hydrogen is less than the energy content of the original fuel, some of it being lost as excessive heat during production. Steam reforming leads to carbon dioxide emissions, in the same way as a car engine would do.

A small part (4% in 2006) is produced by electrolysis using electricity and water, consuming approximately 50 kilowatt-hours of electricity per kilogram of hydrogen produced.

Kværner-process

The Kværner-process or Kvaerner carbon black & hydrogen process (CB&H)[28] is a method, developed in the 1980s by a Norwegian company of the same name, for the production of hydrogen from hydrocarbons (CnHm), such as methane, natural gas and biogas. Of the available energy of the feed, approximately 48% is contained in the hydrogen, 40% is contained in activated carbon and 10% in superheated steam.[32]

Electrolysis of water

H2 production cost ($-gge untaxed) at varying natural gas prices
H2 production cost ($-gge untaxed) at varying natural gas prices

Hydrogen can be made via high pressure electrolysis, low pressure electrolysis of water, or a range of other emerging electrochemical processes such as high temperature electrolysis or carbon assisted electrolysis.[33] However, current best processes for water electrolysis have an effective electrical efficiency of 70-80%,[34][35][36] so that producing 1 kg of hydrogen (which has a specific energy of 143 MJ/kg or about 40 kWh/kg) requires 50–55 kWh of electricity. At an electricity cost of $0.06/kWh, as set out in the Department of Energy hydrogen production targets for 2015[37], the hydrogen cost is $3/kg. With the range of natural gas prices from 2016 as shown in the graph (Hydrogen Production Tech Team Roadmap, November 2017) putting the cost of SMR hydrogen at between $1.20 and $1.50, the cost price of hydrogen via electrolysis is still over double 2015 DOE hydrogen target prices. The US DOE target price for hydrogen in 2020 is $2.30/kg, requiring an electricity cost $0.037/kWh, which is achievable given recent PPA tenders[38] for wind and solar in many regions. This puts the $4/gge H2 dispensed objective well within reach, and close to a slightly elevated natural gas production cost for SMR.

In other parts of the world, steam methane reforming is between $1-3/kg on average. This makes production of hydrogen via electrolysis cost competitive in many regions already, as outlined by Nel Hydrogen[39] and others, including an article by the IEA[40] examining the conditions which could lead to a competitive advantage for electrolysis.

Experimental production methods

Biological production

Fermentative hydrogen production is the fermentative conversion of organic substrate to biohydrogen manifested by a diverse group of bacteria using multi enzyme systems involving three steps similar to anaerobic conversion. Dark fermentation reactions do not require light energy, so they are capable of constantly producing hydrogen from organic compounds throughout the day and night. Photofermentation differs from dark fermentation because it only proceeds in the presence of light. For example, photo-fermentation with Rhodobacter sphaeroides SH2C can be employed to convert small molecular fatty acids into hydrogen.[41] Electrohydrogenesis is used in microbial fuel cells where hydrogen is produced from organic matter (e.g. from sewage, or solid matter[42]) while 0.2 - 0.8 V is applied.

Biological hydrogen can be produced in an algae bioreactor. In the late 1990s it was discovered that if the algae is deprived of sulfur it will switch from the production of oxygen, i.e. normal photosynthesis, to the production of hydrogen.[43]

Biological hydrogen can be produced in bioreactors that use feedstocks other than algae, the most common feedstock being waste streams. The process involves bacteria feeding on hydrocarbons and excreting hydrogen and CO2. The CO2 can be sequestered successfully by several methods, leaving hydrogen gas. In 2006-2007, NanoLogix first demonstrated a prototype hydrogen bioreactor using waste as a feedstock at Welch's grape juice factory in North East, Pennsylvania (U.S.).[44]

Biocatalysed electrolysis

Besides regular electrolysis, electrolysis using microbes is another possibility. With biocatalysed electrolysis, hydrogen is generated after running through the microbial fuel cell and a variety of aquatic plants can be used. These include reed sweetgrass, cordgrass, rice, tomatoes, lupines, and algae[45]

High-pressure electrolysis

High pressure electrolysis is the electrolysis of water by decomposition of water (H2O) into oxygen (O2) and hydrogen gas (H2) by means of an electric current being passed through the water. The difference with a standard electrolyzer is the compressed hydrogen output around 120-200 bar (1740-2900 psi, 12–20 MPa).[46] By pressurising the hydrogen in the electrolyser, through a process known as chemical compression, the need for an external hydrogen compressor is eliminated,[4] the average energy consumption for internal compression is around 3%.[47] European largest (1 400 000 kg/a, High-pressure Electrolysis of water, acaline technology) hydrogen production plant is operating at Kokkola, Finland.[48]

High-temperature electrolysis

Hydrogen can be generated from energy supplied in the form of heat and electricity through high-temperature electrolysis (HTE). Because some of the energy in HTE is supplied in the form of heat, less of the energy must be converted twice (from heat to electricity, and then to chemical form), and so potentially far less energy is required per kilogram of hydrogen produced.

While nuclear-generated electricity could be used for electrolysis, nuclear heat can be directly applied to split hydrogen from water. High temperature (950–1000 °C) gas cooled nuclear reactors have the potential to split hydrogen from water by thermochemical means using nuclear heat. Research into high-temperature nuclear reactors may eventually lead to a hydrogen supply that is cost-competitive with natural gas steam reforming. General Atomics predicts that hydrogen produced in a High Temperature Gas Cooled Reactor (HTGR) would cost $1.53/kg. In 2003, steam reforming of natural gas yielded hydrogen at $1.40/kg. In 2005 natural gas prices, hydrogen costs $2.70/kg.

High-temperature electrolysis has been demonstrated in a laboratory, at 108 MJ (thermal) per kilogram of hydrogen produced,[49] but not at a commercial scale. In addition, this is lower-quality "commercial" grade Hydrogen, unsuitable for use in fuel cells.[50]

Photoelectrochemical water splitting

Using electricity produced by photovoltaic systems offers the cleanest way to produce hydrogen. Water is broken into hydrogen and oxygen by electrolysis—a photoelectrochemical cell (PEC) process which is also named artificial photosynthesis.[51] William Ayers at Energy Conversion Devices demonstrated and patented the first multijunction high efficiency photoelectrochemical system for direct splitting of water in 1983.[52] This group demonstrated direct water splitting now referred to as an "artificial leaf" or "wireless solar water splitting" with a low cost thin film amorphous silicon multijunction sheet immersed directly in water. Hydrogen evolved on the front amorphous silicon surface decorated with various catalysts while oxygen evolved off the back metal substrate. A Nafion membrane above the multijunction cell provided a path for ion transport. Their patent also lists a variety of other semiconductor multijunction materials for the direct water splitting in addition to amorphous silicon and silicon germanium alloys. Research continues towards developing high-efficiency multi-junction cell technology at universities and the photovoltaic industry. If this process is assisted by photocatalysts suspended directly in water instead of using photovoltaic and an electrolytic system, the reaction is in just one step, which can improve efficiency.[53][54]

Photoelectrocatalytic production

A method studied by Thomas Nann and his team at the University of East Anglia consists of a gold electrode covered in layers of indium phosphide (InP) nanoparticles. They introduced an iron-sulfur complex into the layered arrangement, which when submerged in water and irradiated with light under a small electric current, produced hydrogen with an efficiency of 60%.[55]

In 2015, it was reported that Panasonic Corp. has developed a photocatalyst based on niobium nitride that can absorb 57% of sunlight to support the decomposition of water to produce hydrogen gas.[56] The company plans to achieve commercial application "as early as possible", not before 2020.

Concentrating solar thermal

Very high temperatures are required to dissociate water into hydrogen and oxygen. A catalyst is required to make the process operate at feasible temperatures. Heating the water can be achieved through the use of concentrating solar power. Hydrosol-2 is a 100-kilowatt pilot plant at the Plataforma Solar de Almería in Spain which uses sunlight to obtain the required 800 to 1,200 °C to heat water. Hydrosol II has been in operation since 2008. The design of this 100-kilowatt pilot plant is based on a modular concept. As a result, it may be possible that this technology could be readily scaled up to the megawatt range by multiplying the available reactor units and by connecting the plant to heliostat fields (fields of sun-tracking mirrors) of a suitable size.[57]

Thermochemical production

There are more than 352[58] thermochemical cycles which can be used for water splitting,[59] around a dozen of these cycles such as the iron oxide cycle, cerium(IV) oxide-cerium(III) oxide cycle, zinc zinc-oxide cycle, sulfur-iodine cycle, copper-chlorine cycle and hybrid sulfur cycle are under research and in testing phase to produce hydrogen and oxygen from water and heat without using electricity.[60] These processes can be more efficient than high-temperature electrolysis, typical in the range from 35% - 49% LHV efficiency. Thermochemical production of hydrogen using chemical energy from coal or natural gas is generally not considered, because the direct chemical path is more efficient.

None of the thermochemical hydrogen production processes have been demonstrated at production levels, although several have been demonstrated in laboratories.

Hydrogen as a byproduct of other chemical processes

The industrial production of chlorine and caustic soda by electrolysis generates a sizable amount of Hydrogen as a byproduct. In the port of Antwerp a 1MW demonstration fuel cell power plant is powered by such byproduct. This unit has been operational since late 2011.[61] The excess hydrogen is often managed with a hydrogen pinch analysis.

Storage

Although molecular hydrogen has very high energy density on a mass basis, partly because of its low molecular weight, as a gas at ambient conditions it has very low energy density by volume. If it is to be used as fuel stored on board the vehicle, pure hydrogen gas must be stored in an energy-dense form to provide sufficient driving range.

Pressurized hydrogen gas

Increasing gas pressure improves the energy density by volume, making for smaller, but not lighter container tanks (see pressure vessel). Achieving higher pressures necessitates greater use of external energy to power the compression. The mass of the hydrogen tanks needed for compressed hydrogen reduces the fuel economy of the vehicle. Because it is a small molecule, hydrogen tends to diffuse through any liner material intended to contain it, leading to the embrittlement, or weakening, of its container. The most common method of on board hydrogen storage in today's demonstration vehicles is as a compressed gas at pressures of roughly 700 bar (70 MPa).

Liquid hydrogen

Alternatively, higher volumetric energy density liquid hydrogen or slush hydrogen may be used. However, liquid hydrogen is cryogenic and boils at 20.268 K (–252.882 °C or –423.188 °F). Cryogenic storage cuts weight but requires large liquification energies. The liquefaction process, involving pressurizing and cooling steps, is energy intensive.[62] The liquefied hydrogen has lower energy density by volume than gasoline by approximately a factor of four, because of the low density of liquid hydrogen — there is actually more hydrogen in a liter of gasoline (116 grams) than there is in a liter of pure liquid hydrogen (71 grams). Liquid hydrogen storage tanks must also be well insulated to minimize boil off.

Japan have a liquid hydrogen (LH2) storage facility at a terminal in Kobe, and are expected to receive the first shipment of liquid hydrogen via LH2 carrier in 2020.[63] Hydrogen is liquified by reducing its temperature to -253°C, similar to liquified natural gas (LNG) which is stored at -162°C. A potential efficiency loss of 12.79% can be achieved, or 4.26kWh/kg out of 33.3kWh/kg.[64]

Storage as hydride

Distinct from storing molecular hydrogen, hydrogen can be stored as a chemical hydride or in some other hydrogen-containing compound. Hydrogen gas is reacted with some other materials to produce the hydrogen storage material, which can be transported relatively easily. At the point of use the hydrogen storage material can be made to decompose, yielding hydrogen gas. As well as the mass and volume density problems associated with molecular hydrogen storage, current barriers to practical storage schemes stem from the high pressure and temperature conditions needed for hydride formation and hydrogen release. For many potential systems hydriding and dehydriding kinetics and heat management are also issues that need to be overcome. A French company McPhy Energy [3] is developing the first industrial product, based on Magnesium Hydrate, already sold to some major clients such as Iwatani and ENEL.

Adsorption

A third approach is to adsorb molecular hydrogen on the surface of a solid storage material. Unlike in the hydrides mentioned above, the hydrogen does not dissociate/recombine upon charging/discharging the storage system, and hence does not suffer from the kinetic limitations of many hydride storage systems. Hydrogen densities similar to liquefied hydrogen can be achieved with appropriate adsorbent materials. Some suggested adsorbents include activated carbon, nanostructured carbons (including CNTs), MOFs, and hydrogen clathrate hydrate.

Underground hydrogen storage

'Available storage technologies, their capacity and discharge time.' COMMISSION STAFF WORKING DOCUMENT Energy storage – the role of electricity
'Available storage technologies, their capacity and discharge time.' COMMISSION STAFF WORKING DOCUMENT Energy storage – the role of electricity

Underground hydrogen storage is the practice of hydrogen storage in underground caverns, salt domes and depleted oil and gas fields. Large quantities of gaseous hydrogen have been stored in underground caverns by ICI for many years without any difficulties.[65] The storage of large quantities of liquid hydrogen underground can function as grid energy storage. The round-trip efficiency is approximately 40% (vs. 75-80% for pumped-hydro (PHES)), and the cost is slightly higher than pumped hydro.[66] Another study referenced by a European staff working paper found that for large scale storage, the cheapest option is hydrogen at €140/MWh for 2,000 hours of storage using an electrolyser, salt cavern storage and combined-cycle power plant.[67] The European project Hyunder[68] indicated in 2013 that for the storage of wind and solar energy an additional 85 caverns are required as it cannot be covered by PHES and CAES systems.[69] A German case study on storage of hydrogen in salt caverns found that if the German power surplus (7% of total variable renewable generation by 2025 and 20% by 2050) would be converted to hydrogen and stored underground, these quantities would require some 15 caverns of 500,000 cubic metres each by 2025 and some 60 caverns by 2050 – corresponding to approximately one third of the number of underground gas caverns currently operated in Germany.[70] In the US, Sandia Labs are conducting research into the storage of hydrogen in depleted oil and gas fields, which could easily absorb large amounts of renewably produced hydrogen as there are some 2.7 million depleted wells in existence.[71]

Power to gas

Power to gas is a technology which converts electrical power to a gas fuel. There are 2 methods, the first is to use the electricity for water splitting and inject the resulting hydrogen into the natural gas grid. The second (less efficient) method is used to convert carbon dioxide and water to methane, (see natural gas) using electrolysis and the Sabatier reaction. The excess power or off peak power generated by wind generators or solar arrays is then used for load balancing in the energy grid. Using the existing natural gas system for hydrogen Fuel cell maker Hydrogenics and natural gas distributor Enbridge have teamed up to develop such a power to gas system in Canada.[72]

Pipeline storage

A natural gas network may be used for the storage of hydrogen. Before switching to natural gas, the German gas networks were operated using towngas, which for the most part consisted of hydrogen. The storage capacity of the German natural gas network is more than 200,000 GW·h which is enough for several months of energy requirement. By comparison, the capacity of all German pumped storage power plants amounts to only about 40 GW·h. The transport of energy through a gas network is done with much less loss (<0.1%) than in a power network (8%). The use of the existing natural gas pipelines for hydrogen was studied by NaturalHy[73]

Infrastructure

Praxair Hydrogen Plant
Praxair Hydrogen Plant

The hydrogen infrastructure would consist mainly of industrial hydrogen pipeline transport and hydrogen-equipped filling stations like those found on a hydrogen highway. Hydrogen stations which were not situated near a hydrogen pipeline would get supply via hydrogen tanks, compressed hydrogen tube trailers, liquid hydrogen trailers, liquid hydrogen tank trucks or dedicated onsite production.

Because of hydrogen embrittlement of steel, and corrosion[74][75] natural gas pipes require internal coatings or replacement in order to convey hydrogen. Techniques are well-known; over 700 miles of hydrogen pipeline currently exist in the United States. Although expensive, pipelines are the cheapest way to move hydrogen. Hydrogen gas piping is routine in large oil-refineries, because hydrogen is used to hydrocrack fuels from crude oil.

Hydrogen piping can in theory be avoided in distributed systems of hydrogen production, where hydrogen is routinely made on site using medium or small-sized generators which would produce enough hydrogen for personal use or perhaps a neighborhood. In the end, a combination of options for hydrogen gas distribution may succeed.

While millions of tons of elemental hydrogen are distributed around the world each year in various ways, bringing hydrogen to individual consumers would require an evolution of the fuel infrastructure. For example, according to GM, 70% of the U.S. population lives near a hydrogen-generating facility but has little public access to that hydrogen. The same study however, shows that building the infrastructure in a systematic way is much more doable and affordable than most people think. For example, one article has noted that hydrogen stations could be put within every 10 miles in metro Los Angeles, and on the highways between LA and neighboring cities like Palm Springs, Las Vegas, San Diego and Santa Barbara, for the cost of a Starbuck's latte for every one of the 15 million residents living in these areas.[76]

A key tradeoff: centralized vs. distributed production

In a future full hydrogen economy, primary energy sources and feedstock would be used to produce hydrogen gas as stored energy for use in various sectors of the economy. Producing hydrogen from primary energy sources other than coal, oil, and natural gas, would result in lower production of the greenhouse gases characteristic of the combustion of these fossil energy resources.

One key feature of a hydrogen economy would be that in mobile applications (primarily vehicular transport) energy generation and use could be decoupled. The primary energy source would need no longer travel with the vehicle, as it currently does with hydrocarbon fuels. Instead of tailpipes creating dispersed emissions, the energy (and pollution) could be generated from point sources such as large-scale, centralized facilities with improved efficiency. This would allow the possibility of technologies such as carbon sequestration, which are otherwise impossible for mobile applications. Alternatively, distributed energy generation schemes (such as small scale renewable energy sources) could be used, possibly associated with hydrogen stations.

Aside from the energy generation, hydrogen production could be centralized, distributed or a mixture of both. While generating hydrogen at centralized primary energy plants promises higher hydrogen production efficiency, difficulties in high-volume, long range hydrogen transportation (due to factors such as hydrogen damage and the ease of hydrogen diffusion through solid materials) makes electrical energy distribution attractive within a hydrogen economy. In such a scenario, small regional plants or even local filling stations could generate hydrogen using energy provided through the electrical distribution grid. While hydrogen generation efficiency is likely to be lower than for centralized hydrogen generation, losses in hydrogen transport could make such a scheme more efficient in terms of the primary energy used per kilogram of hydrogen delivered to the end user.

The proper balance between hydrogen distribution and long-distance electrical distribution is one of the primary questions that arises about the hydrogen economy.

Again the dilemmas of production sources and transportation of hydrogen can now be overcome using on site (home, business, or fuel station) generation of hydrogen from off grid renewable sources.[4].

Distributed electrolysis

Distributed electrolysis would bypass the problems of distributing hydrogen by distributing electricity instead. It would use existing electrical networks to transport electricity to small, on-site electrolysers located at filling stations. However, accounting for the energy used to produce the electricity and transmission losses would reduce the overall efficiency.

Natural gas combined cycle power plants, which account for almost all construction of new electricity generation plants in the United States, generate electricity at efficiencies of 60 percent or greater.[citation needed] Increased demand for electricity, whether due to hydrogen cars or other demand, would have the marginal impact of adding new combined cycle power plants. On this basis, distributed production of hydrogen would be roughly 40% efficient. However, if the marginal impact is referred to today's power grid, with an efficiency of roughly 40% owing to its mix of fuels and conversion methods, the efficiency of distributed hydrogen production would be roughly 25%.[77]

The distributed production of hydrogen in this fashion would be expected to generate air emissions of pollutants and carbon dioxide at various points in the supply chain, e.g., electrolysis, transportation and storage. Such externalities as pollution must be weighed against the potential advantages of a hydrogen economy.

Fuel cells as alternative to internal combustion

One of the main offerings of a hydrogen economy is that the fuel can replace the fossil fuel burned in internal combustion engines and turbines as the primary way to convert chemical energy into kinetic or electrical energy; hereby eliminating greenhouse gas emissions and pollution from that engine. Although hydrogen can be used in conventional internal combustion engines, fuel cells, being electrochemical, have a theoretical efficiency advantage over heat engines. Fuel cells are more expensive to produce than common internal combustion engines.

Some types of fuel cells work with hydrocarbon fuels,[78] while all can be operated on pure hydrogen. In the event that fuel cells become price-competitive with internal combustion engines and turbines, large gas-fired power plants could adopt this technology.

Hydrogen gas must be distinguished as "technical-grade" (five nines pure, 99.999%), which is suitable for applications such as fuel cells, and "commercial-grade", which has carbon- and sulfur-containing impurities, but which can be produced by the much cheaper steam-reformation process. Fuel cells require high-purity hydrogen because the impurities would quickly degrade the life of the fuel cell stack.

Much of the interest in the hydrogen economy concept is focused on the use of fuel cells to power electric cars. Current hydrogen fuel cells suffer from a low power-to-weight ratio.[79] Fuel cells are much more efficient than internal combustion engines, and produce no harmful emissions. If a practical method of hydrogen storage is introduced, and fuel cells become cheaper, they can be economically viable to power hybrid fuel cell/battery vehicles, or purely fuel cell-driven ones. The economic viability of fuel cell powered vehicles will improve as the hydrocarbon fuels used in internal combustion engines become more expensive, because of the depletion of easily accessible reserves or economic accounting of environmental impact through such measures as carbon taxes.

Other fuel cell technologies based on the exchange of metal ions (e.g. zinc-air fuel cells) are typically more efficient at energy conversion than hydrogen fuel cells, but the widespread use of any electrical energy → chemical energy → electrical energy systems would necessitate the production of electricity.

Since the 2003 State of the Union address, when the notion of the hydrogen economy came to national prominence in the United States, there has been a steady chorus of naysayers. Most recently, in 2013, Lux Research, Inc. issued a report that stated: "The dream of a hydrogen economy ... is no nearer." It concluded that "Capital cost, not hydrogen supply, will limit adoption to a mere 5.9 GW" by 2030, providing "a nearly insurmountable barrier to adoption, except in niche applications". Lux's analysis speculated that by 2030, PEM stationary market will reach $1 billion, while the vehicle market, including forklifts, will reach a total of $2 billion.[80]

Use as an automotive fuel and system efficiency

An accounting of the energy utilized during a thermodynamic process, known as an energy balance, can be applied to automotive fuels. With today's technology, the manufacture of hydrogen via steam reforming can be accomplished with a thermal efficiency of 75 to 80 percent. Additional energy will be required to liquefy or compress the hydrogen, and to transport it to the filling station via truck or pipeline. The energy that must be utilized per kilogram to produce, transport and deliver hydrogen (i.e., its well-to-tank energy use) is approximately 50 MJ using technology available in 2004. Subtracting this energy from the enthalpy of one kilogram of hydrogen, which is 141 MJ, and dividing by the enthalpy, yields a thermal energy efficiency of roughly 60%.[81] Gasoline, by comparison, requires less energy input, per gallon, at the refinery, and comparatively little energy is required to transport it and store it owing to its high energy density per gallon at ambient temperatures. Well-to-tank, the supply chain for gasoline is roughly 80% efficient (Wang, 2002). Another grid-based method of supplying hydrogen would be to use electrical to run electrolysers. Roughly 6% of electricity is lost during transmission along power lines, and the process of converting the fossil fuel to electricity in the first place is roughly 33 percent efficient.[82][83] Thus if efficiency is the key determinant it would be unlikely hydrogen vehicles would be fueled by such a method, and indeed viewed this way, electric vehicles would appear to be a better choice. However, as noted above, hydrogen can be produced from a number of feedstocks, in centralized or distributed fashion, and these afford more efficient pathways to produce and distribute the fuel.

A study of the well-to-wheels efficiency of hydrogen vehicles compared to other vehicles in the Norwegian energy system indicates that hydrogen fuel-cell vehicles (FCV) tend to be about a third as efficient as EVs when electrolysis is used, with hydrogen Internal Combustion Engines (ICE) being barely a sixth as efficient. Even in the case where hydrogen fuel cells get their hydrogen from natural gas reformation rather than electrolysis, and EVs get their power from a natural gas power plant, the EVs still come out ahead 35% to 25% (and only 13% for a H2 ICE). This compares to 14% for a gasoline ICE, 27% for a gasoline ICE hybrid, and 17% for a diesel ICE, also on a well-to-wheels basis.[84]

Hydrogen has been called one of the least efficient and most expensive possible replacements for gasoline (petrol) in terms of reducing greenhouse gases; other technologies may be less expensive and more quickly implemented.[85][86] A comprehensive study of hydrogen in transportation applications has found that "there are major hurdles on the path to achieving the vision of the hydrogen economy; the path will not be simple or straightforward".[11] Although Ford Motor Company and French Renault-Nissan cancelled their hydrogen car R&D efforts in 2008 and 2009, respectively,[87][88] they signed a 2009 letter of intent with the other manufacturers and Now GMBH in September 2009 supporting the commercial introduction of FCVs by 2015.[89] A study by The Carbon Trust for the UK Department of Energy and Climate Change suggests that hydrogen technologies have the potential to deliver UK transport with near-zero emissions whilst reducing dependence on imported oil and curtailment of renewable generation. However, the technologies face very difficult challenges, in terms of cost, performance and policy. [90]

Hydrogen safety

Hydrogen has one of the widest explosive/ignition mix range with air of all the gases with few exceptions such as acetylene, silane, and ethylene oxide. That means that whatever the mix proportion between air and hydrogen, a hydrogen leak will most likely lead to an explosion, not a mere flame, when a flame or spark ignites the mixture. This makes the use of hydrogen particularly dangerous in enclosed areas such as tunnels or underground parking.[91] Pure hydrogen-oxygen flames burn in the ultraviolet color range and are nearly invisible to the naked eye, so a flame detector is needed to detect if a hydrogen leak is burning. Hydrogen is odorless and leaks cannot be detected by smell.

Hydrogen codes and standards are codes and standards for hydrogen fuel cell vehicles, stationary fuel cell applications and portable fuel cell applications. There are codes and standards for the safe handling and storage of hydrogen, for example the standard for the installation of stationary fuel cell power systems from the National Fire Protection Association.

Codes and standards have repeatedly been identified as a major institutional barrier to deploying hydrogen technologies and developing a hydrogen economy. To enable the commercialization of hydrogen in consumer products, new model building codes and equipment and other technical standards are developed and recognized by federal, state, and local governments.[92]

One of the measures on the roadmap is to implement higher safety standards like early leak detection with hydrogen sensors.[93] The Canadian Hydrogen Safety Program concluded that hydrogen fueling is as safe as, or safer than, compressed natural gas (CNG) fueling.[94] The European Commission has funded the first higher educational program in the world in hydrogen safety engineering at the University of Ulster. It is expected that the general public will be able to use hydrogen technologies in everyday life with at least the same level of safety and comfort as with today's fossil fuels.

Environmental concerns

There are many concerns regarding the environmental effects of the manufacture of hydrogen. Hydrogen is made either by electrolysis of water, or by fossil fuel reforming. Reforming a fossil fuel leads to a higher emissions of carbon dioxide compared with direct use of the fossil fuel in an internal combustion engine. Similarly, if hydrogen is produced by electrolysis from fossil-fuel powered generators, increased carbon dioxide is emitted in comparison with direct use of the fossil fuel.

Using renewable energy source to generate hydrogen by electrolysis would require greater energy input than direct use of the renewable energy to operate electric vehicles, because of the extra conversion stages and losses in distribution. Hydrogen as transportation fuel, however, is mainly used for fuel cells that do not produce greenhouse gas emission, but water.

There have also been some concerns over possible problems related to hydrogen gas leakage.[95] Molecular hydrogen leaks slowly from most containment vessels. It has been hypothesized that if significant amounts of hydrogen gas (H2) escape, hydrogen gas may, because of ultraviolet radiation, form free radicals (H) in the stratosphere. These free radicals would then be able to act as catalysts for ozone depletion. A large enough increase in stratospheric hydrogen from leaked H2 could exacerbate the depletion process. However, the effect of these leakage problems may not be significant. The amount of hydrogen that leaks today is much lower (by a factor of 10–100) than the estimated 10–20% figure conjectured by some researchers; for example, in Germany, the leakage rate is only 0.1% (less than the natural gas leak rate of 0.7%). At most, such leakage would likely be no more than 1–2% even with widespread hydrogen use, using present technology.[95][96][97]

Costs

In 2004, the production of unit of hydrogen fuel by steam reformation or electrolysis was approximately 3 to 6 times more expensive than the production of an equivalent unit of fuel from natural gas.[98] When evaluating costs, fossil fuels are generally used as the reference. The energy content of these fuels is not a product of human effort and so has no cost assigned to it. Only the extraction, refining, transportation and production costs are considered. On the other hand, the energy content of a unit of hydrogen fuel must be manufactured, and so has a significant cost, on top of all the costs of refining, transportation, and distribution. Systems which use renewably generated electricity more directly, for example in trolleybuses, or in battery electric vehicles may have a significant economic advantage because there are fewer conversion processes required between primary energy source and point of use.

The barrier to lowering the price of high purity hydrogen is a cost of more than 35 kWh of electricity used to generate each kilogram of hydrogen gas. Hydrogen produced by steam reformation costs approximately three times the cost of natural gas per unit of energy produced. This means that if natural gas costs $6/million BTU, then hydrogen will be $18/million BTU. Also, producing hydrogen from electrolysis with electricity at 5 cents/kWh will cost $28/million BTU — about 1.5 times the cost of hydrogen from natural gas. Note that the cost of hydrogen production from electricity is a linear function of electricity costs, so electricity at 10 cents/kWh means that hydrogen will cost $56/million BTU.[98][when?]

Demonstrated advances in electrolyser and fuel cell technology by ITM Power[99] are claimed to have made significant in-roads into addressing the cost of electrolysing water to make hydrogen. Cost reduction would make hydrogen from off-grid renewable sources economic for refueling vehicles.

Hydrogen pipelines are more expensive[100] than even long-distance electric lines. Hydrogen is about three times bulkier in volume than natural gas for the same enthalpy. Hydrogen accelerates the cracking of steel (hydrogen embrittlement), which increases maintenance costs, leakage rates, and material costs. The difference in cost is likely to expand with newer technology: wires suspended in air can use higher voltage with only marginally increased material costs, but higher pressure pipes require proportionally more material.

Setting up a hydrogen economy would require huge investments in the infrastructure to store and distribute hydrogen to vehicles. In contrast, battery electric vehicles, which are already publicly available, would not necessitate immediate expansion of the existing infrastructure for electricity transmission and distribution. Power plant capacity that now goes unused at night could be used for recharging electric vehicles. A study conducted by the Pacific Northwest National Laboratory for the US Department of Energy in December 2006 found that the idle off-peak grid capacity in the US would be sufficient to power 84% of all vehicles in the US if they all were immediately replaced with electric vehicles.[101]

Different production methods each have differing associated investment and marginal costs. The energy and feedstock could originate from a multitude of sources, i.e. natural gas, nuclear, solar, wind, biomass, coal, other fossil fuels, and geothermal.

Natural Gas at Small Scale
Uses steam reformation. Requires 15.9 million cubic feet (450,000 m3) of gas, which, if produced by small 500 kg/day reformers at the point of dispensing (i.e., the filling station), would equate to 777,000 reformers costing $1 trillion and producing 150 million tons of hydrogen gas annually. Obviates the need for distribution infrastructure dedicated to hydrogen. $3.00 per GGE (Gallons of Gasoline Equivalent)
Nuclear
Provides energy for electrolysis of water. Would require 240,000 tons of unenriched uranium — that's 2,000 600-megawatt power plants, which would cost $840 billion, or about $2.50 per GGE.[102]
Solar
Provides energy for electrolysis of water. Would require 2,500 kWh of sun per square meter, 113 million 40-kilowatt systems, which would cost $22 trillion, or about $9.50 per GGE.
Wind
Provides energy for electrolysis of water. At 7 meters per second average wind speed, it would require 1 million 2-MW wind turbines, which would cost $3 trillion, or about $3.00 per GGE.
Biomass
Gasification plants would produce gas with steam reformation. 1.5 billion tons of dry biomass, 3,300 plants which would require 113.4 million acres (460,000 km²) of farm to produce the biomass. $565 billion in cost, or about $1.90 per GGE
Coal
FutureGen plants use coal gasification then steam reformation. Requires 1 billion tons of coal or about 1,000 275-megawatt plants with a cost of about $500 billion, or about $1 per GGE.

Examples and pilot programs

A Mercedes-Benz O530 Citaro powered by hydrogen fuel cells, in Brno, Czech Republic.
A Mercedes-Benz O530 Citaro powered by hydrogen fuel cells, in Brno, Czech Republic.

Several domestic U.S. automobile manufactures have committed to develop vehicles using hydrogen. The distribution of hydrogen for the purpose of transportation is currently being tested around the world, particularly in Portugal, Iceland, Norway, Denmark, Germany, California, Japan and Canada, but the cost is very high.

Some hospitals have installed combined electrolyser-storage-fuel cell units for local emergency power. These are advantageous for emergency use because of their low maintenance requirement and ease of location compared to internal combustion driven generators.[citation needed]

Iceland has committed to becoming the world's first hydrogen economy by the year 2050.[104] Iceland is in a unique position. Presently, it imports all the petroleum products necessary to power its automobiles and fishing fleet. Iceland has large geothermal resources, so much that the local price of electricity actually is lower than the price of the hydrocarbons that could be used to produce that electricity.

Iceland already converts its surplus electricity into exportable goods and hydrocarbon replacements. In 2002, it produced 2,000 tons of hydrogen gas by electrolysis, primarily for the production of ammonia (NH3) for fertilizer. Ammonia is produced, transported, and used throughout the world, and 90% of the cost of ammonia is the cost of the energy to produce it. Iceland is also developing an aluminium-smelting industry. Aluminium costs are driven primarily by the cost of the electricity to run the smelters. Either of these industries could effectively export all of Iceland's potential geothermal electricity.

Neither industry directly replaces hydrocarbons. Reykjavík, Iceland, had a small pilot fleet of city buses running on compressed hydrogen,[105] and research on powering the nation's fishing fleet with hydrogen is under way. For more practical purposes, Iceland might process imported oil with hydrogen to extend it, rather than to replace it altogether.

The Reykjavík buses are part of a larger program, HyFLEET:CUTE,[106] operating hydrogen fueled buses in eight European cities. HyFLEET:CUTE buses were also operated in Beijing, China and Perth, Australia (see below). A pilot project demonstrating a hydrogen economy is operational on the Norwegian island of Utsira. The installation combines wind power and hydrogen power. In periods when there is surplus wind energy, the excess power is used for generating hydrogen by electrolysis. The hydrogen is stored, and is available for power generation in periods when there is little wind.[citation needed]

United States has a hydrogen policy with several examples. A joint venture between NREL and Xcel Energy is combining wind power and hydrogen power in the same way in Colorado.[107] Hydro in Newfoundland and Labrador are converting the current wind-diesel Power System on the remote island of Ramea into a Wind-Hydrogen Hybrid Power Systems facility.[108] A similar pilot project on Stuart Island uses solar power, instead of wind power, to generate electricity. When excess electricity is available after the batteries are full, hydrogen is generated by electrolysis and stored for later production of electricity by fuel cell.[109]

The UK started a fuel cell pilot program in January 2004, the program ran two Fuel cell buses on route 25 in London until December 2005, and switched to route RV1 until January 2007.[110] The Hydrogen Expedition is currently working to create a hydrogen fuel cell-powered ship and using it to circumnavigate the globe, as a way to demonstrate the capability of hydrogen fuel cells.[111]

Western Australia's Department of Planning and Infrastructure operated three Daimler Chrysler Citaro fuel cell buses as part of its Sustainable Transport Energy for Perth Fuel Cells Bus Trial in Perth.[112] The buses were operated by Path Transit on regular Transperth public bus routes. The trial began in September 2004 and concluded in September 2007. The buses' fuel cells used a proton exchange membrane system and were supplied with raw hydrogen from a BP refinery in Kwinana, south of Perth. The hydrogen was a byproduct of the refinery's industrial process. The buses were refueled at a station in the northern Perth suburb of Malaga.

The United Nations Industrial Development Organization (UNIDO) and the Turkish Ministry of Energy and Natural Resources have signed in 2003 a $40 million trust fund agreement for the creation of the International Centre for Hydrogen Energy Technologies (UNIDO-ICHET) in Istanbul, which started operation in 2004.[113] A hydrogen forklift, a hydrogen cart and a mobile house powered by renewable energies are being demonstrated in UNIDO-ICHET's premises. An uninterruptible power supply system has been working since April 2009 in the headquarters of Istanbul Sea Buses company.

Hydrogen-using alternatives to a fully distributive hydrogen economy

For other energy alternatives, see

Hydrogen is simply a method to store and transmit energy. Various alternative energy transmission and storage scenarios which begin with hydrogen production, but do not use it for all parts of the store and transmission infrastructure, may be more economic, in both near and far term. These include:

Ammonia economy

An alternative to gaseous hydrogen as an energy carrier is to bond it with nitrogen from the air to produce ammonia, which can be easily liquefied, transported, and used (directly or indirectly) as a clean and renewable fuel.[114][115] For example, researchers at CSIRO in Australia in 2018 fuelled a Toyota Mirai and Hyundai Nexo with hydrogen separated from ammonia using a membrane technology. [116]

Hydrogen production of greenhouse-neutral alcohol

The methanol economy is a synfuel production energy plan which may begin with hydrogen production. Hydrogen in a full "hydrogen economy" was initially suggested as a way to make renewable energy, in non-polluting form, available to automobiles. However, a theoretical alternative to address the same problem is to produce hydrogen centrally and immediately use it to make liquid fuels from a CO2 source. This would eliminate the requirement to transport and store the hydrogen. The source could be CO2 that is produced by fuel-burning power plants. In order to be greenhouse-neutral, the source for CO2 in such a plan would need to be from air, biomass, or other source of CO2 which is already in, or to be released into, the air.[117] Direct methanol fuel cells are in commercial use, though as of August 2011 they are not efficient.[citation needed]

The electrical grid plus synthetic methanol fuel cells

Many of the hybrid strategies described above, using captive hydrogen to generate other more easily usable fuels, might be more effective than hydrogen-production alone. Short term energy storage (meaning the energy is used not long after it has been captured) may be best accomplished with battery or even ultracapacitor storage. Longer term energy storage (meaning the energy is used weeks or months after capture) may be better done with synthetic methane or alcohols, which can be stored indefinitely at relatively low cost, and even used directly in some type of fuel cells, for electric vehicles. These strategies dovetail well with the recent interest in Plug-in Hybrid Electric Vehicles, or PHEVs, which use a hybrid strategy of electrical and fuel storage for their energy needs. Hydrogen storage has been proposed by some[citation needed] to be optimal in a narrow range of energy storage time, probably somewhere between a few days and a few weeks. This range is subject to further narrowing with any improvements in battery technology. It is always possible that some kind of breakthrough in hydrogen storage or generation could occur, but this is unlikely given that the physical and chemical limitations of the technical choices are fairly well understood.[citation needed]

Captive hydrogen synthetic methane production (SNG synthetic natural gas)

In a similar way as with synthetic alcohol production, hydrogen can be used on site to directly (nonbiologically) produce greenhouse-neutral gaseous fuels. Thus, captive-hydrogen-mediated production of greenhouse-neutral methane has been proposed (note that this is the reverse of the present method of acquiring hydrogen from natural methane, but one that does not require ultimate burning and release of fossil fuel carbon). Captive hydrogen (and carbon dioxide from, for example, CCS (Carbon Capture & Storage)) may be used onsite to synthesize methane, using the Sabatier reaction. This is about 60% efficient, and with the round trip reducing to 20 to 36% depending on the method of fuel utilization. This is even lower than hydrogen, but the storage costs drop by at least a factor of 3, because of methane's higher boiling point and higher energy density. Liquid methane has 3.2 times the energy density of liquid hydrogen and is easier to store compactly. Additionally, the pipe infrastructure (natural gas pipelines) are already in place. Natural-gas-powered vehicles already exist, and are known to be easier to adapt from existing internal engine technology, than internal combustion autos running directly on hydrogen. Experience with natural gas powered vehicles shows that methane storage is inexpensive, once one has accepted the cost of conversion to store the fuel. However, the cost of alcohol storage is even lower, so this technology would need to produce methane at a considerable savings with regard to alcohol production. Ultimate mature prices of fuels in the competing technologies are not presently known, but both are expected to offer substantial infrastructural savings over attempts to transport and use hydrogen directly.

It has been proposed in a hypothetical renewable energy dominated energy system to use the excess electricity generated by wind, solar photovoltaic, hydro, marine currents and others to produce hydrogen by electrolysis of water then combine it with CO2 make methane (natural gas).[118][119] Hydrogen would firstly be used onsite in fuel cells (CHP) or for transportation due to its greater efficiency of production and then methane created which could then be injected into the existing gas network to generate electricity and heat on demand to overcome low points of renewable energy production. The process described would be to create hydrogen (which could partly be used directly in fuel cells) and the addition of carbon dioxide CO2 possibly from BECCS (Bio-Energy with Carbon Capture & Storage[120]) via the (Sabatier reaction) to create methane as follows : CO2 + 4H2 → CH4 + 2H2O.

Note: After combusting methane in CCGT the CO2 would again be captured, i.e., CCS and used to produce new methane.

See also

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