This is why it's not called efficiency. >100% efficiency is the realm of perpetual motion machines and other such quackery. The metric is Coefficient of Performance. A CoP of 3 means for every W ...
Buying decent quality LiFePO4 rack batteries (52v, 100ah) you can get 66kwh for around $12,000. You’d need to add charge controllers and inverters to that. But depending on the size, if you are ...