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Description
Solar panels, usually mounted on the roof, deliver warm water heated by solar energy. Two basic types of solar collector are used, 'flat plate' and 'evacuated tube'. Flat plate collectors work by circulating water through the whole panel and are cheaper but are less efficient than evacuated tube types. Evacuated tubes utilise a vacuum to retain heat in the system but also work on a different principle. The panel comprises a number of separate tubes each being separately sealed and containing a small amount of a fluid. Heat is extracted by evaporating the fluid in the tube which then condenses at the top, releasing the heat to the fluid circulating in the closed loop. The delivery temperature for evacuated tube is higher than conventional flat panels, and they operate more efficiently particularly in diffuse solar radiation.
There are also two methods of heat transfer, 'direct' where the water that will be used for bathing etc. is heated directly by being passed through the solar collector and 'indirect' whereby the water passing through the solar collector is in a closed loop and transfers heat to the hot water cylinder via a heat exchange coil.
Unit cost of installation
£2,000 - £3,000 for a flat plate system. £3,000 - £5,000 for an evacuated tube system.
Bulk cost of installation
Discounts may be available. For example in 1998 - 2000 on a 100 house installation in Wales cost £1400 per dwelling - see General Information Report 88 'Solar hot water systems in new housing - a monitoring report'
Indicative energy cost and carbon emissions
Savings will depend on the size and type of solar collector, and the orientation of panels. Ideally solar panels should face face somewhere within the south east to south west direction. A dual coil cylinder and additional controls are required for indirect systems.
£/yr saving
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kgC/yr saving
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90
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Maintenance
Solar collectors may need periodic cleaning, and electromechanical components (e.g. circulation pump) will need to be replaced periodically. Direct systems may require periodic descaling in hard water areas.
Lifetime
20 years.
Technical suitability
A suitable site is required for the solar panel (i.e. correct orientation with minimal shading), which means that the technology may not be suitable for all dwelling types. With indirect systems the hot water cylinder requires two coils, one for heating via the domestic boiler, the other for heating via the solar collector.
With direct systems the water that passes through the collector will be used within the dwelling, anti-freezing agents cannot be added. Thus other methods of preventing freezing must be employed, such as designing the system to drain down automatically when the pump switches off.
Non-technical constraints
There may be planning issues in some areas. Evacuated tube systems are more easily modified to increase the capacity of the system.
Potential concerns with fuel poor
No specific issues.
Trigger points for work
Repairs to roof and/or major works to hot water system.
Performance Limitations
Flat plate types are less efficient than evacuated tube types, and last effective in overcast conditions.
Technical Guidance Available
» Solar Trade Association - 01908 442290: www.solartradeassociation.org
» CADDET Renewable Energy - 01235 436806: www.caddet-re.org
» GIR 88 'Solar hot water systems in new housing - a monitoring report'.
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