What do you think about solar panel water heaters? I had a discussion today in shopping center with solar panel company and they say I can save up to 30% on my gas bill (which will take about 10 years to repay the cost, BTW). However, as gas prices are going up, it could be better if I had "gas-less" water heater.
What do you think about these things? Are they efficient taking British sun into account?