Solar hot water
Here are two solar hot water heaters that are quite similar. They produce pretty hot water (note, measurements are in Fahrenheit - we use Celsius). How could you make these even better?
Here's a scaled up version (parts 1&2)...
Here's the story of an unhappy customer who lives in the UK. He has a solar hot water heater installed, but he says it doesn't work! A big part of the problem is that he is in England which generally has a much colder climate than ours. Does he have a point? Is solar hot water only ever good for certain climates (climates that don't really need lots of really hot water)?