Irina Slav at Oilpro.com describes how surplus energy from solar and wind farms could be stored as hydrogen as an alternative to batteries.
….in Europe, renewable power is becoming so abundant that it could be used to produce cheap hydrogen without the need for any scientific breakthroughs. Last month Euractiv cited a report from a German analytical firm, Energy Brainpool, that said surplus electricity from solar and wind farms can be used to convert water into hydrogen through hydrolysis. Hydrogen is relatively easy to store and use when needed or fed into the hydrogen fueling station network, which, truth be told, is a very sparse network.
According to Energy Brainpool, using surplus electricity for hydrogen production can become cheaper with time as the efficiency levels of solar and wind installations rise and maintenance costs decline further. In fact, at some point in the future, hydrogen could become cheaper than natural gas, which would naturally have major implications for its adoption. Again, this is only a theory because power-to-gas facilities in some countries in Europe are subject to high feed-in tariffs and grid charges that make them uneconomical in the application outlined by Energy Brainpool.
Conversion of electricity to hydrogen through electrolysis is cheap but it’s not easy to store because of its low density. Liquid hydrogen requires temperatures of -253°C. One of the more promising options is to store vast quantities in underground caverns. ICI having been doing this in the UK for many years without any difficulties [Wikipedia].
It is also expensive to convert hydrogen back into energy. Costs of fuel cells are prohibitive. Scalability for smaller applications (e.g. motor vehicles) remains a problem.