How it Works
In the UK, every square metre of land receives 800-1200kWh of solar thermal energy every year, whilst the average home here spends about 20-25% of their annual energy bills on water heating. A correctly designed solar hot water system can use the free energy from the sun to produce all your hot water requirements in the summer and provide up to 70% of hot water requirements over the year.
Solar thermal collectors work best when installed on a south facing roof. This allows them to collect the largest amount of availble solar energy whilst minimising the chance that the collectors will be overshadowed by surrounding buildings and trees.
Both the flat panel and evacuated tube solar collectors work best on a south-facing roof but can also be used in an east/west configuration with an array on each side of the roof pitch if a south-facing roof is unavailable.
Both types can be are mounted over the roof tiles on a mounting frame, or on a flat roof with an adjustable A-frame. The flat panel collectors also have the option to be mounted ‘in-roof’ (like a Velux™ window) if required.
Solar thermal systems collect heat from the sun using flat plate or evacuated tube collectors that have a special selective coating designed to absorb as much infrared heat as possible. This heat is transferred by conduction to the water in the collector. Flat plate colletors heat water directly using pipes connected to the back of the absorber, whilst our evacuated tube collectors utilise a special heat pipe to transfer the heat from the absorber surface to water passing through the top of the collector.
A digital solar controller monitors the temperature of the water in the collectors as well as the temperature of the water in the solar hot water storage cylinder. When the collectors are warmer than the storage cylinder, the controller turns on the solar pump to move the heat from the collector array to the hot water cylinder.
Flat panel vs. evacuated tube collectors
The type of collector chosen will depend on the availability of suitable roof area as well as the project’s aesthetic requirements. Whilst the flat panel tubes can be recessed into the roof for a neater installation, the evacuated tube collectors can provide significant performance boost in systems that do not face south.
Both the evacuated tube and flat panel collectors will give a similar peak output if installed on a directly south-facing roof. For projects where the array is more than 15° from true south, or in east/west systems, evacuated tubes will perform significantly better than the flat panel collectors because of their ability to collect light from a wider angle.
The vacuum insulated tubes are also subject to lower heat losses during the colder months than the flat panel collectors to give useful output on more days of the year, as illustrated in the diagram above.
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