What Is Solar Water Heating?

 

Solar water heating is a form of solar thermal technology.

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Roof-mounted collectors absorb heat from solar radiation.

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A heat-transfer fluid circulates through the collectors and carries this energy into the property.

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The heat is then transferred through a coil or heat exchanger into water stored within a hot-water cylinder.

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The process can be simplified as:

sunlight → solar collector → heated fluid → hot-water cylinder → hot water

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The water coming from your taps does not normally circulate through the panels themselves.

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Solar Hot Water

 

Solar hot water describes domestic or commercial hot water heated partly using solar energy.

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The solar system usually works alongside another heat source rather than replacing it completely.

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This might be:

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• a gas boiler

• an oil boiler

• an electric immersion heater

• an air-source heat pump

• another conventional heating system.

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When sufficient solar energy is available, the conventional system does less work.

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When there is insufficient solar energy, the normal heating system brings the water up to the required temperature.

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How Does a Solar Hot Water System Work?

 

A typical solar hot water system contains several main components.

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These usually include:

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• solar thermal collectors

• circulation pipework

• heat-transfer fluid

• circulation pump

• temperature sensors

• solar controller

• hot-water cylinder

• heat exchanger

• expansion vessel

• safety equipment.

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Sensors monitor the temperature of the collectors and the stored water.

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When useful solar heat is available, the controller operates the circulation pump.

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Hot fluid travels from the roof to the cylinder, transfers its heat to the stored water and then returns to the collectors to be heated again.

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Solar Hot Water Systems

 

Different solar hot water systems may use different collectors, cylinders and control arrangements, but the basic principle remains the same.

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The most suitable system depends upon:

the property's hot-water demand, available roof area, roof orientation, existing heating system and available space for a suitable hot-water cylinder.

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Correct sizing is particularly important.

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A system should be large enough to make a worthwhile contribution but not unnecessarily oversized for the household's hot-water requirements.

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What Is a Solar Water Heater?

 

A solar water heater is the complete system used to capture solar energy and use it for heating water.

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In everyday use, the term may also be used to describe the roof-mounted collector itself.

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In the UK, terms such as solar thermal system, solar hot water system and solar water heating system are more commonly used for professionally installed domestic systems.

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Regardless of terminology, the objective is the same:

use available solar energy instead of purchasing all of the energy required to heat water.

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What Is a Solar Heater?

 

The term solar heater can refer to several different technologies.

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It might describe:

a solar thermal water heater, a solar pool heater or sometimes an electrically powered heater supplied by solar PV panels.

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This distinction matters.

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A conventional solar thermal collector produces heat directly.

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A photovoltaic panel produces electricity, which can then be used by an electric heater, immersion heater or heat pump.

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Both involve solar energy, but they work in fundamentally different ways.

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What Is a Solar Geyser?

 

Solar geyser is a term commonly used in some countries for a solar water-heating system.

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The principle is essentially the same as solar thermal hot water.

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Solar collectors capture heat and use it to raise the temperature of stored water.

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The term is less common in the UK, where solar hot water or solar thermal would normally be used.

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If you encounter a solar geyser when researching systems internationally, check the exact design because equipment and installation methods can differ between countries and climates.

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Solar Thermal Panels for Water Heating

 

Solar water heating normally uses one of two principal collector types.

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Flat-Plate Solar Collectors

Flat-plate collectors resemble large dark roof panels.

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Sunlight passes through a transparent surface and heats an absorber beneath.

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Pipework incorporated into the collector transfers the heat into the circulating solar fluid.

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They can provide a relatively neat appearance and are widely used for domestic hot-water systems.

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Evacuated-Tube Collectors

Evacuated-tube systems contain a series of glass tubes.

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The construction is designed to reduce heat loss while capturing solar energy.

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They have a different appearance from conventional flat panels and can perform efficiently in certain conditions.

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The most appropriate collector depends upon the property and system design.

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Does Solar Water Heating Work in the UK?

 

Yes.

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Solar water heating does not require extremely hot outdoor temperatures.

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It requires solar radiation.

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Collectors can therefore obtain useful energy even when the air temperature itself is relatively cool.

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However, performance varies significantly throughout the year.

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Summer provides much greater solar availability than winter.

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A UK solar hot-water system should therefore be designed to supplement the main heating system rather than being expected to independently supply all hot water throughout the year.

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Solar Water Heating in Summer

 

Summer is when a solar hot-water system can make its greatest contribution.

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Longer daylight hours and stronger sunshine mean considerably more solar energy is available.

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During suitable conditions, the solar system may provide much of the household's hot-water requirement.

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This can allow the main boiler or other heating system to remain off for longer periods.

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The exact contribution depends upon collector size, orientation, weather and household hot-water consumption.

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Solar Water Heating in Winter

 

Solar water heating continues to operate during winter whenever useful solar radiation is available.

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However, production is substantially lower than in summer.

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Days are shorter, the sun is lower and weather conditions are generally less favourable.

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The boiler, heat pump or immersion heater therefore needs to provide a greater proportion of the required hot water.

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This seasonal difference should be understood before investing in a system.

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Solar Hot Water and Your Boiler

 

A solar hot-water system is commonly designed to work alongside an existing boiler.

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Solar energy heats the stored water first.

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If the water has not reached the required temperature, the boiler provides the remaining heat.

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The homeowner does not normally need to switch manually between solar and boiler operation.

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Correctly designed controls allow the systems to work together.

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Boiler Solar Systems

 

People sometimes search for boiler solar systems when looking for ways to combine solar energy with conventional heating.

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The usual arrangement is not that solar panels directly operate the boiler.

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Instead, solar thermal collectors heat water stored within a cylinder and the boiler provides backup heating when required.

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This reduces the boiler's workload during periods when useful solar energy is available.

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Solar Water Heating With a Combi Boiler

 

A combi boiler can make solar thermal installation more complicated.

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Combi systems commonly produce hot water directly when a tap is opened rather than storing a large quantity of hot water in a cylinder.

Solar thermal works most naturally with stored hot water.

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Installing solar water heating at a property with a combi boiler may therefore involve introducing an appropriate hot-water cylinder and adapting the existing heating arrangements.

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This needs to be assessed carefully before deciding whether solar thermal provides the best solution.

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Solar Water Heating With a System Boiler

 

A system boiler and existing hot-water cylinder can provide a more natural starting point for solar thermal.

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The existing cylinder may still need replacement with a suitable solar-compatible model.

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A solar cylinder can incorporate separate heat exchangers allowing heat to be supplied both by the solar collectors and by the boiler.

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The solar system is normally given the opportunity to contribute first, with the boiler providing backup.

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The Solar Hot Water Cylinder

 

The hot-water cylinder acts as the energy store for a solar water-heating system.

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Instead of storing electricity like a battery, it stores thermal energy as hot water.

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A properly insulated cylinder retains heat until the household requires it.

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Cylinder size is important.

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It needs to provide sufficient hot-water capacity while being suitable for the solar collector area and household demand.

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Do I Need a New Cylinder?

 

Many existing cylinders are not designed for solar thermal systems.

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A replacement cylinder may therefore form part of the installation.

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This is particularly relevant where the property is undergoing:

a heating upgrade, extension, major refurbishment or plant-room alteration.

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If the cylinder is being replaced anyway, that can be an ideal time to consider solar water heating.

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Solar Water Heating and Heat Pumps

 

Solar thermal can potentially work alongside a heat pump.

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However, it is worth comparing this arrangement with using solar PV to generate electricity for the heat pump.

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A heat pump uses electricity and can provide both heating and hot water.

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Solar thermal directly produces heat.

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Which approach works best depends upon the property, available roof area and overall energy strategy.

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This is increasingly a whole-house design question rather than a simple choice between individual products.

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Solar Water Heating or Solar PV?

 

For many homeowners, this is now the key comparison.

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Solar thermal converts sunlight directly into useful heat.

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Solar PV converts sunlight into electricity.

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Solar thermal is highly specialised: its principal domestic purpose is producing hot water.

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Solar PV electricity is much more flexible.

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It can be used for:

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• household appliances

• hot-water heating

• battery charging

• EV charging

• air conditioning

• heat pumps

• lighting

• cooking.

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This does not make solar thermal obsolete.

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It simply means that roof space has become valuable and homeowners should consider which technology gives them the greatest overall benefit.

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Using Solar PV to Heat Water

 

There is another way to create solar-powered hot water.

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Instead of installing solar thermal collectors, photovoltaic panels can generate electricity which is then directed towards an immersion heater or another electrically powered water-heating system.

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Solar-diversion equipment can potentially detect surplus PV generation and redirect suitable electricity into a hot-water cylinder.

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In effect, the hot-water cylinder becomes another form of energy storage.

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This arrangement can be particularly attractive where solar PV is already being installed.

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Solar-Powered Heater

 

The phrase solar-powered heater can therefore describe two very different ideas.

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A solar thermal collector uses sunlight directly to produce heat.

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An electrically powered heater can instead operate using electricity generated by photovoltaic panels.

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For modern homes considering solar PV, batteries, EV charging and cooling, the second approach can provide greater flexibility because the electricity can be redirected according to what the property needs.

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Solar Hot Water and Battery Storage

 

A solar thermal installation does not normally connect to an electrical battery.

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The energy is already being stored as heat within the hot-water cylinder.

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Solar PV, on the other hand, can charge a battery.

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The battery can then supply electricity for many different purposes.

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This is another reason homeowners should consider both technologies within the wider energy strategy.

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Solar Water Heating and EV Charging

 

Solar thermal cannot charge an electric vehicle because it produces heat rather than electricity.

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Solar PV can.

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If the household is likely to purchase an electric car, this can affect how valuable the available roof area becomes for photovoltaic generation.

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A roof covered substantially with thermal collectors cannot use the same area for PV panels.

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This should be considered before the system is designed.

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Solar Water Heating and Air Conditioning

 

The same principle applies to air conditioning.

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Solar thermal cannot directly provide electricity for an air-conditioning unit.

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Solar PV can.

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Cooling demand can also correspond particularly well with solar generation because air conditioning is normally needed most during warm, bright weather.

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For homeowners planning a wider solar + battery + EV + cooling system, maximising photovoltaic generation may therefore be more attractive than dedicating a large amount of roof space exclusively to hot-water heating.

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Solar Water Heating for Large Families

 

Solar thermal can become particularly attractive where a property has high and consistent hot-water consumption.

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A large family may use substantial quantities of hot water for:

showers, baths and everyday washing.

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This gives the solar system somewhere useful to send the heat it produces.

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A small household with very low hot-water consumption may gain less benefit from a large collector installation.

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System design should therefore begin with demand.

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Solar Hot Water for Hotels

 

Properties with consistently high hot-water demand can offer particularly good opportunities.

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Hotels may require substantial quantities of hot water for:

guest bedrooms, kitchens, cleaning and leisure facilities.

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Demand can continue throughout summer when solar thermal output is strongest.

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The commercial case can therefore be very different from that of an ordinary house.

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Solar Water Heating for Care Homes

 

Care homes and similar residential facilities can also have substantial year-round hot-water demand.

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Where roof area and building configuration are suitable, solar thermal may contribute towards that demand.

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Large systems require careful hydraulic design, storage capacity and integration with existing heating plant.

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Solar Heater for Pools

 

Solar heaters for pools are another major application of solar thermal energy.

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Swimming pools require substantial amounts of heat, and demand often corresponds with sunny weather.

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Outdoor pools can be particularly suitable because the period of greatest use coincides with stronger summer solar energy.

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Swimming-pool solar systems may use different types of collectors from domestic hot-water installations.

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The system should be designed specifically for the pool and expected operating season.

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Solar Water Heating for Indoor Pools

 

Indoor pools require heating throughout a much longer period of the year.

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Solar thermal can contribute, but the seasonal relationship becomes more complicated because winter heating demand remains high while available solar energy falls.

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The building's complete heating strategy should therefore be assessed.

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For leisure facilities with significant electrical consumption, solar PV may also form an important part of the overall energy solution.

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How Much Roof Space Does Solar Water Heating Need?

 

A domestic solar thermal system generally requires much less roof area than a large photovoltaic installation.

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The appropriate collector area depends upon:

number of occupants, hot-water demand, collector performance, roof orientation and storage capacity.

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Installing more collectors does not automatically provide better value.

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Once the hot-water cylinder has reached its required temperature, additional summer heat may have little useful purpose.

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Correct sizing is therefore essential.

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Which Roof Is Best for Solar Water Heating?

 

Collectors need good solar exposure.

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A broadly south-facing roof can provide strong annual performance.

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South-east and south-west orientations can also work effectively.

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Roof pitch, shading and available area should all be considered.

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Collectors should ideally avoid significant shading from:

chimneys, trees, dormers and neighbouring buildings.

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Solar Water Heating on Flat Roofs

 

Flat roofs can accommodate solar collectors on mounting frames.

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This allows the orientation and angle of the collectors to be controlled independently of the roof itself.

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The design needs to consider:

wind loading, roof structure, waterproofing, access and drainage.

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The condition of the roof should also be established before installation.

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Solar Water Heating on Pitched Roofs

 

Solar collectors can be installed on tiled, slated and other pitched roofs using an appropriate mounting system.

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They can either sit above the existing roof covering or potentially be incorporated more closely into the roof construction.

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Fixings must be securely connected to the supporting structure.

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Weatherproofing around the installation is critical.

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Roof Condition Before Installation

 

Solar thermal collectors are intended to remain on the building for many years.

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It makes little sense to install them on a roof approaching the end of its useful life.

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If substantial roof repairs or replacement are expected soon, it may be better to carry out this work first.

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Where a new roof is already being constructed, the collector installation can potentially be coordinated with the roofing work.

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Solar Water Heating During an Extension

 

An extension provides an excellent opportunity to consider renewable-energy systems.

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The new roof may provide suitable space for solar collectors or photovoltaic panels.

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The heating and hot-water system may already be undergoing alteration.

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New pipe routes can be incorporated before ceilings and walls are finished.

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A new utility or plant area may also provide space for a larger cylinder.

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It is therefore considerably easier to consider solar water heating during the design stage than after the extension has been completed.

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Solar Water Heating During Refurbishment

 

The same applies to major refurbishment.

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Where a property is already being rewired, replumbed or upgraded, it makes sense to consider future energy requirements before everything is closed up and redecorated.

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This might include:

solar thermal, solar PV, battery storage, EV charging, air conditioning and heat pumps.

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Even where all of these technologies are not installed immediately, appropriate provisions can sometimes be incorporated for later.

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Solar Hot Water System Price

The solar hot water system price depends upon considerably more than the roof collectors.

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The total cost can be affected by:

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• collector type and size

• roof access

• scaffolding

• hot-water cylinder

• pipe routes

• controls

• pumps

• existing heating system

• structural considerations

• installation complexity.

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A straightforward property already containing suitable plant space may cost less to adapt than a house requiring extensive changes to its hot-water system.

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What Determines Solar Water Heating Cost?

 

Two apparently identical houses can have very different installation costs.

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One might already have a suitable cylinder positioned immediately below the solar collectors.

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Another may have a combi boiler and no existing hot-water storage.

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The second property could require substantially more plumbing and internal alteration.

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For this reason, meaningful quotations usually require an assessment of both the roof and the existing heating system.

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Is Solar Water Heating Expensive?

 

Solar thermal should be judged over its working life rather than purely according to initial installation price.

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The system can reduce the energy required to produce hot water, but the financial benefit depends upon:

existing fuel costs, hot-water consumption, system efficiency, installation cost and maintenance.

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A large household using considerable hot water may see a very different financial case from a one-person household.

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Solar Water Heating Maintenance

 

Solar thermal systems contain more mechanical elements than photovoltaic panels.

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Maintenance may involve checking:

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• solar fluid

• circulation pump

• pressure

• expansion vessel

• temperature sensors

• controls

• pipe insulation

• collectors.

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The heat-transfer fluid may require periodic checking or replacement according to the system manufacturer's requirements.

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Can Solar Hot Water Systems Overheat?

 

Solar collectors can become very hot during strong summer sunshine.

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If little hot water is being used, the system needs to manage the excess heat safely.

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This is one reason why an excessively large system is not necessarily desirable.

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Correct design should consider periods when the household is away or hot-water demand is particularly low.

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Solar Water Heating Controls

 

A solar thermal controller monitors temperatures within different parts of the system.

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The circulation pump normally operates only when the collectors are warm enough to deliver useful heat to the cylinder.

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If the cylinder is already hotter than the collectors, circulating fluid would serve little purpose.

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The controller therefore manages the system automatically.

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Monitoring Solar Hot Water

 

Some modern systems provide useful monitoring information showing solar temperatures and system operation.

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This can help homeowners understand how much solar contribution is being achieved.

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Monitoring can also make faults easier to identify.

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However, solar thermal performance is often less immediately visible than electricity generation from a PV system.

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Solar Water Heating Lifespan

 

A good solar thermal installation can operate for many years.

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Different components have different expected lifespans.

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Collectors can remain serviceable for a long period, while pumps, controls and valves may require replacement earlier.

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Regular maintenance can help identify issues before they result in complete system failure.

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Solar Water Heating Planning Permission

 

Many straightforward domestic roof installations may be possible without a conventional planning application, subject to the relevant planning rules and limitations.

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However, additional considerations may apply to:

listed buildings, conservation areas, prominent roof locations and unusual installations.

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Where there is any uncertainty, the planning position should be checked before work proceeds.

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Solar Water Heating on Listed Buildings

 

Solar collectors can sometimes be installed on listed properties, but the effect upon the historic building needs careful consideration.

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Prominent alterations to important roof slopes may be difficult to support.

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Less visible roofs, outbuildings or alternative locations may provide better opportunities.

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Listed Building Consent may also be required where works affect the character or fabric of the listed building.

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Solar Water Heating in Conservation Areas

 

Conservation-area properties can require greater attention to appearance.

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A collector installation on a prominent street-facing roof may have a different impact from one positioned on a less visible rear roof.

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Performance and visual appearance therefore need to be considered together.

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Choosing a Solar Water Heating Installer

 

Solar water heating involves both roof work and plumbing.

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A competent installer should therefore understand:

solar collectors, hot-water cylinders, controls, pipework and integration with the existing heating system.

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The installer should assess the property rather than recommending equipment solely from photographs.

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A quotation should explain exactly what is included and whether alterations to the existing cylinder, boiler or heating controls are required.

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Comparing Solar Hot Water Quotations

 

When comparing proposals, look beyond the headline price.

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Check the:

collector type, collector area, cylinder specification, controls, warranties and anticipated contribution to hot-water demand.

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Also establish whether the quotation includes:

scaffolding, plumbing alterations, commissioning and any associated electrical work.

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Two quotations describing a "solar hot-water system" may in reality contain very different equipment and scopes of work.

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Is Solar Water Heating Worth It?

 

Solar water heating can still be a very effective renewable-energy technology.

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It can be particularly attractive where:

hot-water demand is high, suitable roof space is available and the existing heating system can accommodate solar thermal efficiently.

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However, homeowners now have more options than they did when solar thermal first became widely available.

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Solar PV has become central to a broader home-energy system because electricity can be used for almost anything.

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That makes it sensible to compare the alternatives before committing valuable roof space.

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Solar Water Heating or a Whole-Home Energy System?

 

This is perhaps the most useful question for anyone planning a significant home upgrade.

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One approach is:

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solar thermal → hot water.

Another is:

solar PV → household electricity + battery + EV charging + hot water + air conditioning + heat pump.

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The second solution provides much greater flexibility, although solar thermal may still outperform it for particular hot-water applications.

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The correct answer depends upon the property.

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Planning for Future Electricity Demand

 

Home electricity consumption is changing rapidly.

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A property that currently uses relatively little electricity may eventually need much more because of:

electric vehicles, cooling, electric heating and other equipment.

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If substantial roof space is available, homeowners should therefore think beyond today's electricity bill.

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A solar system being installed now may remain on the building for decades.

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Designing around likely future demand can be much more sensible than designing only around current consumption.

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The Modern Solar Home

 

Solar technology is increasingly becoming part of a complete home-energy strategy rather than a stand-alone addition.

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A modern property might combine:

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solar PV for electricity

battery storage for evening use

EV charging for transport

air conditioning for summer cooling

heat-pump technology for efficient heating

smart controls managing energy automatically

efficient hot-water storage.

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Solar water heating can form part of that strategy where appropriate.

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The key is deciding which combination of technologies makes the best use of the property and the available roof area.

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Planning a Solar Water Heating System?

 

A successful solar water heating system starts with understanding how much hot water the property actually uses.

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Roof orientation, collector space, shading, existing boiler arrangements, hot-water storage and future energy plans should all be considered before deciding upon the system.

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It is also worth comparing solar thermal with solar PV, particularly if you are considering battery storage, an electric vehicle, air conditioning or electrically powered heating.

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For homeowners undertaking an extension or major refurbishment, this can be the ideal time to review all of these technologies together rather than adding them individually over the following years.

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APN Solar can help homeowners and property owners connect with experienced renewable-energy specialists who can assess the property and provide quotations for solar water heating, solar PV and wider home-energy improvements.

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