Now think if a solar energy farm with a battery like that were used to create bitcoin transactions. It's an infinite and free source or energy, right? At least after the investment is paid back. My doubt is how miners could return the fees to the transaction senders in this case. Would it be possible? Would you like to add any thoughts?
Energy will never be free. Bitcoin will push prices of energy extremely high. Right now Bitcoin not spend even 1% of all energy that is used on earth. When price of Bitcoin will be 20 times higher and many believes that will happen in only 5 years time, then more then 10 % of all energy used on Earth will be used to secure Bitcoin network. Of course only if price of electricity stays the same.