What is the pay back for solar thermal systems? Well, first and foremost it does have a payback.

If you buy coal, oil, electricity or gas the supplier does not offer you any pay back at all. No matter how much you buy and no matter how long you buy it for, you never get your money back. You have to service, maintain and renew your fuel burning equipment all at additional cost. 

Various government bodies sometimes define payback as the annual fuel bill savings divided by the capital cost.  This is simply inaccurate, misleading and incorrect.

To take a precise view of payback, you have to factor in future energy increases, inflation, savings in boiler servicing, the increase in lifespan of the boiler itself, savings in future fuel costs, value added to your property, then add in the parasitic losses that a solar thermal system suffers.

Doing the sums properly, most thermal systems typically offer a payback of 5 years, depending on the fossil fuel displaced, the future fuel inflation factor you use and the amount of hot water you use.

Although payback is one way of looking at the cost, it is perhaps more accurate to look at the return on your investment that solar thermal offers. Typically the financial savings of a good solar thermal system will be equivalent to a tax free return on investment of between 8% and 12%.

The solar system represents a home improvement that saves money and will generate a higher sale value when the property is sold. People don’t ask what the payback time is for a new kitchen, bathroom, or extension – also home improvements -  (projects that add value but certainly don’t save money) so why do they ask about solar heating, a carbon saving technology?

Sit back and enjoy. Think of what you're saving. The potential for solar energy is spectacular. In half an hour, enough sunlight reaches the Earth's surface to meet the world's energy demand for a year. New materials offer the prospect of converting this more efficiently - prototype plastic solar cells now being developed could reduce the cost per watt by 95 per cent, for example. Be an advertisement - a missionary, even - for the solar age. At the very least, you'd be in at the start of something big.