What Is Solar Thermal?

 

Solar thermal is a technology that captures heat from sunlight and uses it to warm water.

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A typical solar thermal system includes:

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• roof-mounted solar collectors;

• insulated pipework;

• a pump;

• control equipment;

• a heat exchanger;

• a hot-water cylinder; and

• a conventional backup heat source.

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The solar collectors absorb heat and transfer it to fluid circulating through the system.

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That heat is then passed into the hot-water cylinder.

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The conventional heating system can provide additional heat when solar energy is insufficient.

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Solar Thermal Panels

 

Solar thermal panels are installed externally, most commonly on a roof.

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They look different from standard solar PV panels because their purpose is to collect heat rather than generate electricity.

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There are two principal forms of solar thermal collector commonly associated with domestic systems:

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• flat-plate collectors; and

• evacuated-tube collectors.

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Both perform the same basic function, but they have different designs and installation characteristics.

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Flat-Plate Solar Collectors

 

Flat-plate collectors consist of an insulated panel containing an absorber plate and pipework.

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Solar energy heats the absorber, which transfers heat to fluid circulating through the collector.

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Flat-plate systems can provide a relatively simple and neat installation and are widely used for domestic solar hot water.

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Evacuated-Tube Solar Collectors

 

Evacuated-tube collectors use rows of glass tubes designed to capture solar heat efficiently.

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They can perform well in a range of conditions and may be particularly suitable where available roof area is limited.

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The final choice between flat-plate and evacuated-tube systems should depend on the property, available space, system design and budget.

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What Is a Solar Water Heater?

 

A solar water heater uses solar energy to contribute towards domestic hot-water production.

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The term is often used to describe the complete solar thermal system rather than simply one piece of equipment.

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The system does not normally rely on solar energy alone.

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Instead, solar provides part of the heat required, while another source such as a boiler, immersion heater or heat pump provides additional heating when necessary.

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Solar Hot Water Systems

 

A solar hot water system is designed around the household's hot-water demand.

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A typical system may include:

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• solar thermal collectors;

• hot-water cylinder;

• circulation pump;

• controller;

• temperature sensors;

• expansion equipment;

• heat-transfer fluid; and

• backup heating.

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The size of the collector area and cylinder should be matched to the property and number of occupants.

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Installing unnecessarily large equipment does not automatically provide better value.

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How Does Solar Hot Water Work?

 

During daylight hours, the solar collectors absorb heat from the sun.

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A heat-transfer fluid carries this energy through insulated pipework to the hot-water cylinder.

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Inside the cylinder, a heat exchanger transfers the collected heat into the stored domestic water.

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If the solar energy is insufficient to reach the required hot-water temperature, the normal heating system provides additional heat.

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During brighter periods, solar thermal may contribute a substantial amount of the hot-water demand.

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During winter, the contribution will generally be lower.

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Solar Thermal Energy

 

Solar thermal energy is most useful when there is a regular demand for hot water.

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The technology captures heat directly rather than converting sunlight into electricity first.

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This direct use of solar heat can be effective for domestic hot-water production.

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However, the value of a system will depend on:

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• household hot-water demand;

• collector orientation;

• shading;

• roof area;

• cylinder capacity;

• existing heating system;

• installation cost; and

• how much solar heat can realistically be used.

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Is My Home Suitable for Solar Thermal?

 

Suitability depends on the individual property.

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Important factors can include:

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• roof orientation;

• roof pitch;

• shading;

• available roof area;

• roof condition;

• location of the hot-water cylinder;

• pipe routes;

• existing heating system;

• household hot-water use; and

• possible planning constraints.

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A Green Home Survey from APN Green Homes can help establish whether solar thermal appears worth further investigation and how it compares with other energy improvements.

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Solar Thermal Versus Solar PV

 

Solar thermal and solar photovoltaic panels use the same source of energy but produce different outputs.

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Solar thermal panels produce heat.

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Solar PV panels generate electricity.

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Solar PV electricity can be used by household appliances, battery storage, an EV charger, heat pump or immersion heater.

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Solar thermal is more specialised because it is designed primarily around water heating.

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This distinction is important when deciding which technology offers the best value for the available roof space.

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Should You Choose Solar Thermal or Solar PV?

 

There is no universal answer.

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Solar PV has become particularly flexible because electricity generated by the panels can be used in many different ways.

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Solar thermal may still be attractive where a property has significant and consistent hot-water demand.

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The decision should consider:

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• available roof area;

• electricity consumption;

• hot-water demand;

• battery-storage plans;

• EV charging;

• heat-pump plans;

• existing cylinder;

• installation cost; and

• long-term energy strategy.

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For some homes, solar PV may provide greater overall flexibility.

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For others, solar thermal can make useful use of available solar energy.

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Solar Thermal and Heat Pumps

 

Solar thermal can potentially work alongside a heat pump.

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The solar system may contribute towards hot-water heating during brighter periods, reducing the amount of energy the heat pump needs to provide.

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However, the system needs to be designed carefully so that the hot-water cylinder, controls and heat sources operate together properly.

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A Green Home Survey can help identify whether combining these technologies is likely to make practical sense.

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Solar Thermal and Gas Boilers

 

Solar thermal can also work with a conventional gas boiler.

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The solar system preheats or heats the stored water, while the boiler provides additional heat when necessary.

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This can reduce the amount of gas used for domestic hot water.

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The benefit will depend on the age and efficiency of the boiler, household hot-water use and solar contribution.

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Solar Thermal and Immersion Heaters

 

Many hot-water cylinders include an electric immersion heater.

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A solar thermal system may operate alongside this arrangement, with solar heat providing part of the hot-water demand and the immersion heater used as backup where appropriate.

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The overall control strategy should avoid unnecessary heating and make the best use of available solar energy.

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Solar Thermal and Hot-Water Cylinders

 

Most solar thermal systems require a suitable hot-water cylinder.

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The cylinder may include separate heat exchangers for:

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• the solar thermal circuit; and

• the main boiler or heat source.

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Where the existing cylinder is old or unsuitable, replacement may form part of the project.

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Cylinder size is important because the system needs enough storage to make effective use of solar heat without creating unnecessary standing losses.

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Solar Thermal Hot Water System

 

A solar thermal hot water system should be designed around real household demand.

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A family using substantial amounts of hot water may benefit more than a household with very low consumption.

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The system should therefore take account of:

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• number of occupants;

• bathing habits;

• cylinder capacity;

• collector area;

• backup heating; and

• seasonal variation.

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The objective is to match the system to the home rather than install equipment based on a generic package.

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Solar Water Heater for Home Use

 

A solar water heater for home use can be particularly relevant where the property has regular daytime or year-round hot-water demand.

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Possible applications include:

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• family homes;

• larger households;

• homes with multiple bathrooms;

• properties with significant bathing demand; and

• some rural or off-grid properties.

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The economics will vary considerably from one property to another.

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Solar Thermal System Cost

 

The cost of a solar thermal system depends on the equipment and complexity of the installation.

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Factors affecting cost can include:

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• collector type;

• collector area;

• roof access;

• scaffolding;

• hot-water cylinder;

• pipework;

• control equipment;

• pump station;

• roof construction;

• existing heating system; and

• installation complexity.

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A simple installation on a suitable roof may be relatively straightforward.

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A system requiring extensive cylinder replacement, difficult pipe routes or significant roof work can cost considerably more.

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Solar Hot Water System Price

 

Homeowners searching for solar hot water system prices should compare the entire installation rather than the price of the collectors alone.

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A quotation should make clear whether it includes:

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• solar collectors;

• mounting equipment;

• hot-water cylinder;

• controls;

• pumps;

• pipework;

• insulation;

• scaffolding;

• electrical work;

• commissioning; and

• removal or alteration of existing equipment.

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This makes it easier to compare different proposals accurately.

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Solar Water Heater Price

 

The price of a solar water heater will vary according to the system size, collector type and property.

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The lowest quotation is not necessarily the best value.

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System design, equipment quality, workmanship, warranties and future servicing all deserve consideration.

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A poorly sized or badly installed system may never provide the expected benefit.

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How Much Hot Water Can Solar Thermal Provide?

 

Solar contribution varies throughout the year.

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During brighter summer months, a well-designed system may provide a substantial proportion of domestic hot-water demand.

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During winter, solar output will be lower and the main heating system will provide a greater share.

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The system should therefore be judged on annual performance rather than peak summer output.

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Does Solar Thermal Work in Winter?

 

Yes, solar thermal systems can collect heat during winter, but output is generally much lower than during summer.

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Shorter days, lower solar intensity and colder conditions reduce the available energy.

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The backup heating system therefore remains important.

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Solar thermal should be viewed as a way of reducing conventional energy use rather than completely replacing the normal hot-water system.

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Solar Thermal and Roof Orientation

 

Roof orientation can significantly affect performance.

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South-facing roofs generally provide strong solar exposure, but other orientations may also be workable depending on the property.

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Shading from:

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• trees;

• chimneys;

• neighbouring buildings; and

• other roof features

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can reduce performance and should be considered before installation.

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Solar Thermal on Flat Roofs

 

Flat roofs can provide opportunities for solar thermal collectors because the panels can be mounted at a suitable angle.

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The design needs to consider:

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• orientation;

• wind loading;

• fixing or ballast;

• roof waterproofing;

• access;

• shading between collectors; and

• structural capacity.

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The installation should be coordinated carefully with the roof construction.

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Solar Thermal on Listed Buildings and in Conservation Areas

 

Solar thermal installations can affect the appearance of a property and may require more careful consideration in sensitive locations.

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This is particularly relevant to:

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• listed buildings;

• conservation areas;

• prominent roof slopes;

• historic properties; and

• properties subject to additional planning controls.

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Alternative locations or less visible roof areas may sometimes provide a better solution.

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APN Green Homes can help identify where planning or design advice may be required before installation.

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Does Solar Thermal Need Planning Permission?

 

Many ordinary domestic solar installations may be possible without a full planning application, subject to relevant conditions and limitations.

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However, additional considerations can arise with:

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• listed buildings;

• conservation areas;

• unusual installations;

• flats;

• ground-mounted systems; and

• prominent or sensitive locations.

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Where there is uncertainty, the planning position should be established before equipment is ordered.

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Solar Thermal Installation

 

A solar thermal installation requires specialist plumbing and roof work.

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The installer may need to deal with:

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• roof fixings;

• weatherproofing;

• insulated pipework;

• collector mounting;

• cylinder connections;

• pumps;

• controls;

• expansion vessels;

• heat-transfer fluid; and

• commissioning.

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Good installation is essential because the system combines high temperatures, pressurised fluid and roof-mounted equipment.

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Solar Thermal Maintenance

 

Solar thermal systems require periodic maintenance.

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This can include:

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• checking system pressure;

• inspecting the heat-transfer fluid;

• checking pumps and controls;

• reviewing collector condition;

• inspecting pipe insulation;

• checking expansion equipment; and

• reviewing cylinder performance.

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The heat-transfer fluid may also need replacement at intervals depending on the system.

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Homeowners should consider future servicing when comparing installations.

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Solar Hot Water Service

 

A solar hot water service can help maintain system performance and identify faults before they become more serious.

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Possible signs that maintenance may be required include:

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• reduced hot-water contribution;

• unusual pump noise;

• pressure changes;

• control faults;

• leaks;

• damaged insulation; or

• overheating problems.

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Older solar thermal systems may benefit from specialist inspection where maintenance history is unclear.

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Solar Thermal During a Renovation

 

Major renovation can provide a good opportunity to consider solar thermal.

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If the hot-water cylinder, heating system, roof or plumbing is already being altered, the solar system can potentially be incorporated more efficiently.

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The project can also be considered alongside:

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• solar PV;

• heat pumps;

• underfloor heating;

• insulation;

• new bathrooms; and

• future household energy demand.

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Planning these elements together can reduce duplicated work.

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Solar Thermal as Part of a Green Home Plan

 

Solar thermal is one of several ways a home can use renewable energy.

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Solar thermal contributes directly to hot-water heating.

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Solar PV generates electricity.

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Battery storage stores electricity.

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Heat pumps use electricity for heating and hot water.

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Insulation reduces overall heat demand.

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At APN Green Homes, we consider how these different systems might work together rather than assuming that one technology is always the best answer.

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Independent Solar Thermal Advice

 

Solar thermal installers naturally concentrate on designing and installing solar hot-water systems.

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APN Green Homes takes a wider whole-home approach.

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Through a Green Home Survey, we can consider whether solar thermal appears suitable, whether solar PV might provide greater flexibility, whether the existing hot-water system needs upgrading and how renewable technologies fit into the wider energy plan for the property.

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The aim is to establish where your investment is likely to provide the greatest benefit before you commit to equipment.

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Start With Your Hot-Water Demand

 

The best solar thermal system begins with understanding how much hot water your household actually uses and how that demand changes throughout the year.

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Before choosing solar collectors or replacing a cylinder, it makes sense to consider the roof, existing heating system, available space, solar PV potential and other green home improvements you may be planning.

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NEXT STEPS

Every home is different, so the right next step depends on your property, your budget and what you want to achieve. APN Green Homes can help you turn the information you have just read into a practical plan for your own home. Whether you are considering one improvement or looking at a complete whole-home energy upgrade, we can help you understand what is suitable, what should be prioritised and where your money is likely to make the greatest difference.

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Choose one of the options below to get the ball rolling:

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BOOK A GREEN HOME SURVEY
Get a detailed assessment of your home with practical, property-specific recommendations and a clear plan for the improvements worth considering.

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BOOK A PHONE CONSULTATION
Talk through your property, ideas and priorities with us and get some initial direction on the best way forward.

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EMAIL US
Send us details of your property, photographs or any questions and we can advise you on the most appropriate next step.

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GIVE US A CALL
Prefer to speak to someone? Give us a call and tell us what you are hoping to achieve.

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Your greener, more efficient home starts with understanding the right improvements for your property — and putting them in the right order.