The DTI commissioned a 2 year monitoring programme of 4 domestic hot water solar systems in differing locations. The results showed that systems provided an average of approximately 70% of the annual hot water requirements at the 4 locations. All 4 systems worked in winter as well as summer with 16-17% of hot water needs being met in January and December and almost 100% of hot water needs being met in both July and August.  Download report (PDF - 496KB)

Elsewhere on our website we have discussed the financial and ecological impact a solar thermal system has and here we describe the practical benefits that you should expect.

Solar radiation is an energy force radiated in all directions by the sun and of that energy an output of 1.36kW/m², called the solar constant hits the outer earths atmosphere. This solar radiation is reduced through reflection, dispersion and absorption in dust particles and gas molecules. The portion of radiation which passes through the atmosphere and strikes the earth’s surface directly is known as direct radiation. That part of the solar radiation which is reflected and/or absorbed by dust particles and gas molecules, irradiated back and strikes the earth’s surface indirectly is known as diffused radiation. The sum total of all direct and diffused solar radiation is called global radiation and is illustrated in this chart.

The global radiation under optimum conditions amounts to a maximum of 1000 w/m². With solar panels, as much as 75% of this global radiation can be utilised, depending on the type of collector and the system size.

The amount of global radiation available at any location is a function of latitude. There is a widely held opinion that the UK does not have enough sun to make solar systems worthwhile. In fact parts of the UK have annual solar radiation levels equal to 60% of those experienced at the equator. This map, prepared by the European Commission Joint Research Centre, shows the levels of solar radiation across the northern hemisphere.