For ballpark numbers, I am not worrying about 15%. e.g. will your batteries last 10yrs, 20yrs, or more, is a bigger unknown. But to try answering your questio

For ballpark numbers, I am not worrying about 15%. e.g. will your batteries last 10yrs, 20yrs, or more, is a bigger unknown. But to try answering your question, here [0] the UK govt says it is 5% for battery banks for wind power, and for hydro power. Solar is not mentioned, my guess would be that the rate on the battery we are discussing is 5%. [0] https://www.gov.uk/government/publications/vat-notice-7086-energy-saving-materials/vat-notice-7086-energy-saving-materials https://www.gov.uk/government/publications/vat-notice-7086-e...