Another interesting idea for smoothing out the inevitable irregularity of renewable energy is to convert excess power into gas, as espoused by Chris Goodall in Carbon Commentary. He starts with some figures for Germany showing the live generation over a week, and points out that at times there is more supply than demand, which means the cost of electricity is zero. The prices are the wavy lines at the bottom, which you can see dipping to zero and beyond.
Converting electricity into hydrogen is usually expensive, and hydrogen is usually produced from methane. If the power is free, then the economics change, at least according to the article. The hydrogen can be converted into methane, which is the main ingredient of natural gas.
Gas has the advantage over batteries that it can be stored, so for example gas generated in the summer could be stored for winter use. It can also be transported and there is already an infrastructure for using gas as a fuel, from power stations and vehicles to domestic heaters and cookers. If renewable energy is being used to generate gas, and taking carbon dioxide out of the air in the process, then this could replace fossil fuel gas and help our carbon accountancy.
This idea may come unstuck when you look at energy returns on energy invested (EROI) and how much extra energy you need to make the infrastructure to convert the power to gas. Also we have to be very careful that we don't get an unvirtuos non-cycle of the electricity being converted to hydrogen, then the hydrogen to methane, then the methane leaking into the atmosphere, since methane is much more powerful as a greenhouse gas.
On the other hand, if something like this doesn't start happening, then the power prices that have been driven down by renewables are going to have interesting economic consequences. Lower prices may mean that investments in energy become financially unviable.
