The halting of climate change requires that fossil fuels be replaced; the CO2 must be stopped from entering the atmosphere. The consensus is to build wind and solar farms to generate electricity instead of using fossil fuels.
Since renewables are intermittent, there must be some way to store and supply electricity when renewables are not able to. The real capacity of wind and solar farms is less than 50%, typically somewhere around 30%. So during the daylight hours the amount of solar power has to be at least 3 times more than the daily needs so that 2/3 of the power can be stored for use during nighttime.
At this time (2021 May) there are several pumped hydro “water batteries” in the USA. There are a growing number of utility scale BESS – battery energy storage systems in the USA. Other forms of energy storage are being developed. One promising energy storage is to generate green hydrogen for use later.
Most of the pro’s and con’s of hydrogen are stated in another of my blogs. The one that I must explain is as follows.
Hydrogen
As I said, the renewables must be able to supply 3 or more times as much electricity as needed for the peak load. This is to allow enough power for when the sky is cloudy or during winter when days are shorter. This also applies to wind since there are times when there is no wind.
The result is that excess electricity will be generated and this must be stored for use at night or cloudy or windless days. The storage may need to be for longer than a few days, because of weather or seasonal periods of low light.
It’s not practical to spend huge amounts on adding excessive BESS – battery energy storage systems to the grid. One alternative is to use redox flow batteries. These batteries have capacities that are only limited by the size of storage tanks for the fluids. But it’s possible to generate hydrogen from the excess electricity.
Hydrogen can be stored in underground salt caverns just as natural gas (methane) is stored today. Enormous amounts can be stored. Another way to store hydrogen is to combine it with nitrogen from air, to make ammonia. This ammonia is already being made, stored and transported all over for use as fertilizer. It can be converted back to hydrogen with nitrogen as the byproduct, which is benign – the same as 79% of air.
This ‘excess’ hydrogen is being generated by the electricity of excess capacity, which is necessary but would otherwise be wasted (curtailed). The hydrogen should be viewed as an insurance policy or backup against the times when renewables are at a minimum. We humans can’t predict events, such as bad weather, that might cause a shortage of renewable electricity. So we have to have a backup that can supply power for a few days while the adverse weather or event passes. The backup may also be needed when the peak demand grows faster than renewables plus storage are being added. It’s likely that climate change will cause weather extremes that can’t be anticipated. This will be the times when stored hydrogen will be needed.
The amount of stored hydrogen has many uses other than for generating electricity. Large amounts of hydrogen can be used to make fertilizer. The hydrogen can be used to fuel ships, airplanes, trains or heavy trucks.
But one of the biggest uses of hydrogen will be to make synfuels such as diesel or gasoline AKA petrol. These fuels will be totally green – they will not be made from fossil fuels such as oil.
Hopefully in the next dozen years almost all of the fossil fueled ICEVs will be replaced by electric vehicles. But there will still be some transportation that needs a fuel with more energy per kg than hydrogen. The airplanes are one example, where batteries are too heavy at this time. Plus using hydrogen to make synfuel allows CO2 to be removed from the atmosphere.