content: Batteries aren't the best choice and never will be for long term storage.      Chemical energy storage is better, Hydrogen, ammonia, carbonate, dehydration etc, and using excess power to produce products from CO2 such as simple hydrocarbons is another great choice.   (note: this excludes methane, because of subsidies no technology can ever compete with current natural gas production)    It is a great time to see that solar energy production is competitive, but solutions to deal with fluctuations both low and high output are required.