This has been covered pretty extensively in several comment chains, eg https://news.ycombinator.com/item?id=29687522 https://news.ycombinator.com/item?id=296875

This has been covered pretty extensively in several comment chains, eg https://news.ycombinator.com/item?id=29687522 https://news.ycombinator.com/item?id=29687522. But basically, even down to below freezing it's still way above 100% efficient.