Efficiency and Cost
Solar hot water systems can be extremely efficient, reducing costs and energy consumption. For a solar system to work, all they need is daylight as they can collect both direct radiation, direct sunlight on clear days, and diffused radiation, light which is present on cloudy days.
Both flat plate collectors and evacuated tube collectors have selective and non selective surfaces. In terms of which collector has best efficiency, it is dependant on your domestic use. At low temperatures the efficiency for all the collectors is very similar, but as temperatures increase all the collectors show a slight reduction in efficiency. For lowest temperatures an unglazed non-selective surface flat plate collector can be seen as most effective, hence use in swimming pools, however for highest temperatures there is a very marginal difference between selective surface evacuated tubes and selective surfaces flat plate collectors, with the former being the most efficient.
In terms of costs you would expect to save between 50 -70% on your annual heating costs, as the more hot water used the greater the saving. For a family of four, a well designed solar water heating system should contribute around I,500kWh and 2,000kWh, which will be equivalent to 50 to 65% of the household’s water heating energy needs. The monetary value of this saving will depend on the type of energy displaced.
Typically, solar water heating systems installed into existing households are priced in the region of £4,000, though this will depend on the size and type of collector and storage system. For DIY or new build system installations, costs can be reduced – particularly in the case of large scale new building projects.
DTI Test
This study was undertaken in 2001 to compare eight solar water heating systems on the market in the UK side by side at a test site in Bedfordshire. A pdf file of the document ' Side by side testing of eight solar water heating systems' may be accessed by clicking here.
EST Test
The Energy Saving Trust are currently undertaking a field study of 100 installed solar thermal systems across the UK. The findings of this study should be published in 2010 and give a clearer indication of the realistic outputs of installed systems.