One of the most costly aspects of a renewable energy system is the method of storing excess energy for use at a later time. One option is to take the excess and dump it directly into the grid and hopefully be in a location that buys back that energy. That is an excellent option if you have a good buy back rate and the means to tie into the grid. The other current option is battery storage.
Batteries are great but have to be maintained in a somewhat controlled environment and will have to be replaced at the end of their life cycle. Not to mention the hazardous materials that go into batteries and the disposal problems associated with those materials. And everyone seems to be aware of their price.
What if you could store that energy in a form that would require very little to no maintenance, store indefinitely and have very little to any environmental impact. And possibly have a positive environmental impact.
How could we take any excess energy we produce and store it for later use in a cheaper and more environmentally friendly way. Store it as potential kinetic energy. Store it as water in a reservoir on a hill top or as compressed air. Some have suggested taking the excess energy produce and using it to produce Hydrogen. There would appear to be many options for long term storage with a minimal environmental impact at an equivalent price compared battery storage prices. Maybe even free or at least cheep.
Here are two potential methods for using air or water as a battery.
Water as a battery method
First the basic idea. Use an old fashion windmill to pump water up to an elevated storage tank or reservoir on a hill. When the energy demand is high allow the water to flow down through a water turbine to produce energy on demand. The water that exits the turbine can then be pumped back up to the reservoir or storage tank. Also A rain water collection system could augment the collection of water on the high side not to mention its free water falling from the sky. The old style water pumping windmill can be used or the excess electricity from a wind turbine or a solar array can power an electric pump to transfer the water from the low side to the high side.
Air as a battery method
Essentially the same technique used above but instead of pumping water it is compressing air into storage tanks. Then releasing the air through an air turbine to produce energy when needed.
Another method is referred to as wind storage.
I think these industrial scale methods could be done on a smaller scale as well. Compressed air could be stored in propane gas tanks. A good reuse of propane tanks that are just sitting around. As for the water, of course having access to a flowing body of water would be the best but not everyone has access or the rights to that option. Neither of these methods are ideal for continuous energy production but could be good for peak consumption times or long term back power.