How does a solar water heater work?

A rooftop solar water heater has no pump and no motor, yet it turns sunshine into 100 litres of hot water a day. Glass, a vacuum and the simple fact that hot water floats do all the work. Sunlight brings about 1,000 watts to each square metre at a clear noon.

Read how it works: How does a solar water heater work? · The history of the solar water heater · More boxes on Glassbox

Chapters in this interactive model

1. What is on the roof?: A tank, a row of glass tubes, and not a single moving part.
2. Catching the sun: Where the sun is, how much light arrives, and how a black coating keeps it.
3. The vacuum trick: Heat escapes three ways. A vacuum blocks two of them.
4. Hot water rises, no pump needed: Why the tank sits above the collector, and how the water circulates by itself.
5. How much water, how hot?: Run a whole day on the roof for your city and month.
6. Living with it in India: Rules, hard water, monsoon, monkeys and hot-water safety.