Solar Thermal Hot Water Systems FAQs

Here are a selection of commonly asked questions about solar thermal systems including general questions, pre-installation queries, and costs and savings questions.

What are solar thermal collectors and how do they work?

Solar thermal collectors cleverly extract the free energy from the sun and transfer this energy to heat a home's hot water system. The collector features serpentine pipework beneath the top layer of glass, through which a special solution flows - as this fluid passes through the collector, the fluid is heated up and then is transferred away from the collector to then heat up water stored within a cylinder which will fulfil hot water demands at the tap. Solar thermal collectors are efficient and an eco-friendly solution for heating domestic hot water, utilising energy from the sun and reducing a home's reliance on fossil fuels.

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Can solar thermal be used to heat my house?

Whilst solar thermal can be used to contribute to the heating of a house using a thermal store, it is more usually used to heat your domestic hot water cylinder and provide hot water to your taps. 

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Will the solar panels still work on a cloudy day?

Many people believe that solar collectors only work in the summer, however this type of free energy is available throughout the year. From May to September, solar thermal could produce 100% of the energy required for heating your domestic water. Grant collectors operate not just with direct sunlight, but also diffused sunlight, so they even work on cloudy days.

What is the difference between solar thermal and Solar PV?

A Solar PV system uses panels (usually called ‘modules’) that generate electricity in the presence of sunlight. The amount of electricity produced depends on the intensity of the sunlight. Solar thermal, on the other hand, uses sunlight to heat a fluid. In the case of Grant solar collectors, it heats a glycol/water solution within the collector. This heated fluid is then circulated from the collector to a cylinder where the heat is transferred to produce hot water.

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Does it matter what direction the solar thermal collectors are facing?

For installations in the UK, solar thermal collectors will perform best when facing due south at an angle of between 30 - 45°. However, collectors facing south west or south east will perform almost as well. Failing that a collectors facing due west will perform better than those facing due east. North facing solar thermal collectors are not usually used.

Can solar thermal collectors be mounted on any type of roof?
Grant solar thermal collectors can be fitted on many different types of roof, both flat and pitched. Collectors can be mounted either just above the roof covering or set into the roof, as required.
Can solar thermal be used to heat a swimming pool?
Yes. Solar Thermal collectors can be used to provide heat for a swimming pool.
What are the advantages of using solar thermal collectors?

There are multiple advantages and benefits of installing solar thermal collectors at your home. Firstly, a solar thermal system can fulfil a significant proportion of your annual hot water demand, reducing the demand on the heat source in your central heating system, whether that be a traditional boiler or heat pump. Secondly, the sun's energy is free so utilising this heat energy to heat the hot water in your taps can help reduce your energy bills. Solar Thermal systems, such as those supplied by Grant UK, are also incredibly straightforward to live with requiring minimal maintenance. 

Are solar thermal collectors suitable for residential use?

Yes, solar thermal collectors are suitable for installation at domestic properties, residential dwellings and residentials flats.

What factors should be considered when selecting solar thermal collectors?

There are several factors that need to be taken into consideration when selecting the right solar thermal system for your home. These include: size of property and its DHW demand, the orientation of the roof, the shape of the roof, and any objects obscuring the roof. 

Who can install Grant Solar Thermal?
The installation of the Grant Solar Thermal system must be carried out by a competent trained person in accordance with the relevant requirements for health and safety, local building regulations, building standards in Scotland and regulations and bylaws of the local water company.
Is planning permission required for solar thermal panels?

In most instances, the installation of a solar thermal system does not require planning permission. 

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Are there any certifications or standards I should look for when choosing solar thermal panels?

Solar water heating products can be certified under one or more standards, such as the Microgeneration Certification Scheme (MCS) or Solar Keymark. These are certifications issued to products that meet recognised standards relating to performance and quality build. Grant’s Solar Thermal Systems are both MCS certified and Solar Keymark approved.

Can solar thermal collectors be integrated into existing heating systems?

Yes, solar thermal collectors can be installed as part of a new heating system or they can be added to an existing heating system. Read more about Grant Solar Thermal Systems here.

Can solar thermal collectors be combined with other renewable energy technologies?

Yes, a solar thermal system can be installed alongside other renewable technologies such as air source heat pumps. A popular combination of Grant renewable products includes the installation of an Aerona³ heat pump, solar thermal system, and QR twin coil hot water cylinder.

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Can a solar thermal system be used with my existing hot water cylinder?

A Grant solar thermal system requires a cylinder with a solar coil. In many cases this will be a ‘twin coil’ cylinder with both a boiler coil and a solar coil. This may well mean that your existing hot water cylinder will have to be replaced by a suitably sized twin coil cylinder to maximise the performance of your solar thermal system.

Do I have to pay VAT when installing solar thermal?

Between 1st April 2022 through to 31st March 2027, the rate of VAT on the installation of certain energy saving materials, such as a solar thermal system, is 0%. If you have a solar thermal system installed at your home during this period and you live in Great Britain, you should not have to pay VAT.

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What is the cost of installing solar thermal collectors?

The cost of installing a solar thermal system will vary depending on the size of the system, the number of collectors required, and the complexity of the installation. The Energy Savings Trust estimates that the cost of installing a typical solar thermal water heating system is between £3,000 - £5,000. It is recommended that you approach more than one installer to obtain quotations specific for your home and its requirements. Find an installer here.

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How do solar thermal collectors contribute to reducing carbon emissions?

Solar thermal systems can help reduce carbon emissions because they capture the renewable energy from the sun and transfer this into heating the hot water within our homes, reducing the demand on fossil fuel appliances, such as oil or gas boilers, which have traditionally fulfilled both space heating and domestic hot water production in homes. 

What questions should I ask solar thermal panel installers?

When talking with solar thermal installers and obtaining quotations from them, consider asking the following questions:

  • Are you a member of a trade organisation such as the Solar Trade Association?
  • What options do I have in terms of panel size, type, and hot water storage?
  • What type of collector do you recommend? (e.g., flat plate panels or in-roof or on-roof mounting arrangements)
  • Do you have knowledge of applicable regulations and safety guidelines?
  • Will the system be eligible for any Government financial support?
  • What is included in the quoted price, such as removal and disposal of existing equipment and safe access to the roof?
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What can I expect to achieve by installing solar thermal panels?

Solar thermal panels can help you reduce your carbon footprint as well as your energy bills by utilising the sun's free energy to heat your home’s water. Each property’s carbon and cost savings will vary but the Energy Savings Trust has shared a useful infographic which details an example summary of savings made throughout the year.

Can I get any grant funding towards the cost of installing a solar thermal system?

To find out if there is financial support for the installation of a new solar thermal system and to check whether you are eligible, we would recommend speaking to your local authority or you could visit the Energy Saving Trust website.

What proportion of my hot water would be heated by a solar thermal system?

Solar thermal collectors work in both direct sunlight and diffused sunlight so even on cloudy days, they will work, providing your home with hot water. During the summer months between May and September, solar thermal can produce 100% of the energy required to meet a home’s domestic hot water needs.

Do I need a special hot water cylinder for a solar thermal system?

To incorporate a solar thermal system into a new or existing heating system, you will need a cylinder that has dedicated solar coil. A solar thermal system will typically be installed with a twin coil hot water cylinder so that the heat held within the solar thermal system can be transferred into the contents of the cylinder via the lower coil and so that the main heat source (a boiler or heat pump for example) can feed the heat it generates into the cylinder via the top coil. Grant UK supply twin coil hot water cylinders and you can read more about these cylinders here.

Will a solar thermal system work on cold days, for example in the winter?

Yes, a solar thermal system will work all year round. However, during the winter months, when there is less energy and warmth produced by the sun, the amount of solar gain will be less than that available during the summer. Therefore, on cold days, a solar thermal system will take longer to heat up the water in the system compared to on a hot day and this is when products such as the Grant WinterSOL can help boost any shortfall.

Can I still have a solar thermal system if my roof does not face south?

Yes, a solar thermal system can be installed on most roofs that are not south facing. While solar thermal collectors installed on south facing roof will perform best, collectors facing south west, south east, west and east will still work albeit with lower performances due to the reduced exposure to the sun. It is rare for solar thermal collectors to be installed on a north facing roof.

Will a solar thermal system produce electricity?

No, a solar thermal system uses the sun’s free energy and transfers this into a fluid that can heat hot water. A solar PV system, which is different to a solar thermal system, will use the sun’s energy to generate electricity.

How many solar collectors (panels) are required?

The number of solar collectors required will depend on the hot water demand of the property and the number of occupants. On average, 1.0-1.3m² of nett collector area is needed per person and the Grant Sahara Collectors have a nett (also known as absorber) area of 2.14m². And for each m² of nett collector area, approximately 50-60 litres of cylinder capacity is required. For example, a two collector solar thermal system installed alongside a 200-250ltr cylinder would be sufficient for a four people and could satisfy up to 70% of the household’s annual hot water demand.

This table you can download here demonstrates how to calculate the number of solar collectors a system may need. Please note, other variables (such as the angle of the roof and any shading) must be factored in when designing a solar thermal system.

Can a solar thermal system be used with a combi boiler?

Yes, provided you install a Grant CombiSOL with your solar thermal system, the system will work alongside your combi boiler. The Grant CombiSOL is a clever but simple solution that enables the integration of a mains pressure combination boiler with a solar thermal system. Read more here.

Will a solar thermal system still work if partly in shade?

A solar thermal system will work in partial shade but it is important to note that it will not perform as well compared to a system that is installed on a roof with no shade obscuring the collector(s). It is therefore recommended that any trees that do grow near a roof are regularly cut back to limit the amount of shade that can cover the collectors.

Can solar collectors be fitted on a flat roof?

Yes, if you have a flat roof, you will need to install a solar thermal system kit that has a flat-roof mounting arrangement. Grant UK’s flat-roof system features mounting rails that are fitted to a rigid inclined frame structure that the solar collectors are positioned onto.

What is the best roof angle for fitting solar thermal collectors?

A solar thermal system will perform best when the collectors are facing due south at an angle of between 30 - 45°.

Will it be necessary to remove any tiles from the roof to fit solar thermal collectors?

This will depend on the type of roof mounting arrangement you use. If you opt for an on-roof mounting arrangement that Grant UK supply, the Sahara collectors will be fitted above your existing roof tiles or slates using brackets and a mounting rail that will attach directly to the roof trusses. If you choose an in-roof mounting arrangement (which Grant UK also supply), the Sahara collectors are set into the roof ensuring a low-profile appearance and for these types of installation, any existing tiles or slates will need to be removed where the collectors will be positioned.

How much energy can solar thermal collectors produce?

A well designed system can be expected to collect useful energy greater than 450 kilowatt hours per year per square metre (kWh/y/m²). However, performance is dependent on the location and orientation of the collector.

Can solar thermal collectors be used for both heating and cooling purposes?

No, solar thermal collectors are designed to heat hot water for DHW production only and not for cooling purposes.

How does the efficiency of solar thermal collectors impact their performance?

The more efficient a solar thermal collector is, the greater its ability to transfer heat energy from the sun into the fluid within the collectors and transfer this quickly into the hot water stored in the cylinder without losing too much heat energy between the collector and cylinder.

How cost effective are solar thermal panels?

The installation of a solar thermal system will be an initial cost for homeowners who choose to add this renewable energy system to their home. However, a suitably designed solar thermal system should provide around 50-70% of the domestic hot water requirements of the average home, representing a generous saving on annual hot water heating costs.

To discover more about the benefits you can access with a solar thermal hot water heating system, please visit our Knowledge Hub. 

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