My copy dates from the '70's. It's a handy bok on home made power. everything to solar hot water heaters, wind turbines to water wheels, it's all in here. Contains explanations of how it works, how to build/design one yourself. Prices provided are completely out of date, but it's funny to see that to build a solar hot water heater would have cost you less than a £1. If you find a copy pick it up, it's so handy. ( )