A few words about Solar Power - or in this instance, Solar Water Heating.
We've had a Photovoltaic solar panel for some years now to provide electrical power for the 12v systems on the caravan - its a large 50 watt panel, so produces loads of useful power and drives the numerous 12v systems in our van even on a cloudy day. The concept of "free" energy is a non-starter of course as manufacturing these systems and buying them are quite costly on many levels. However, the photovoltaic panel does give us the freedom to stay at many small caravan sites for long periods of time without having to worry about the battery going 'dead' and leaving us without light and water pumps. We are not keen on sites that have mains electric hook-ups because they tend to attract those with massive vans who spend 90% of their time sat in their vans in front of the telly... Why bother going away?