Solar Water Heaters: Producing Hot water from the sun

Did you know that you can use the power of the sun to heat water for your home with a solar water heater?

Energy from the sun is abundant and free. So creating hot water from the sun is very common here in the UK and around the world.

We hear a lot about using solar panels to generate electricity, but you can also use solar energy to heat the water you use at home.  A solar thermal collector works on sunny days and days of relatively low sunlight. Even a small boost from the sun will help reduce the amount of energy you need from fossil fuels to bring your water tank up to temperature.

How Much do Solar Water Heaters Cost?

A typical cost of a solar water heater is around £4,500 installed with a hot water cylinder. 

Heating water accounts for around one quarter of a domestic energy bill, but you could save 30-60% on your annual water heating costs with a solar thermal collector. However, you can apply for a financial incentive from the Government to offset the cost.


The Benefits of Solar Hot Water Heaters

Like all renewable energy projects, there are many advantages of solar hot water heaters. Located on your roof, a solar thermal panel (or collector), will harness the natural energy of the sun to provide most of your hot water needs from March to September saving hundreds of pounds on gas or oil bills.

And because you will be using less fossil fuels to heat your water, you are also helping to reduce pollution and cut carbon dioxide emissions as well, which is good news for global warming.

Do Solar Hot Water Heaters Work on Cloudy Days and In Winter?

Solar panels work all year round, but they work best when the sun's radiation is strongest (generally during the warmer months).

During shorter winter days and cloudy days, solar thermal input will be reduced so you will still need a secondary source for heating water. Options could include biomass boilers or traditional gas boilers. Solar panels do not work at night, but hot water is stored in the tank. If you shower at night instead of the morning you can use the heat collected during the day.

Solar Thermal Panels Explained

The following table provides an overview of the pros and cons of solar thermal collectors for homes.

Solar Thermal Panels Heats hot water for your home for washing people, plates and pets.
Fuel Type and Cost Sunshine so the fuel is free forever.
Requirements Roof area (4m2) exposed to the sun (south-ish facing). A hot water tank with twin coils is preferable.
Equipment Cost Estimate £4,500
Government Money Available The Renewable Heat Incentive (RHI) at 20p per kWh.
Payback Eleven years plus (with the RHI).
Suppliers Accredited through the approved competent person scheme MCS.
Barriers If the solar water heater is shaded for most of the day by trees or other buildings.
Top Tips Save money if scaffolding is required by combining the installation with solar PV panels or maintenance work on your home.
The Geeky Bit Flat plate panels are cheaper but evacuated tube panels are more efficient. Choice depends on your budget.
Hassle Factor Very low with maintenance check required each year. Takes around two days to fit.

Is My House Suitable for Solar Thermal?

Dog being washed in the bathSolar thermal can be used on all sizes of home. It only requires around 4m2 of roof space. Ideally the solar thermal collectors should be mounted on a south-facing roof at a 30° angle. However, the angle and orientation can be adapted so even east and west roofs can work as well as south facing. Direct sunlight for the main of the day is a key factor, so large trees of adjacent buildings that block the midday sun might make your roof unsuitable.

Planning permission is generally not required as thermal solar panels are classed as a 'permitted development'. But, it's always worth checking with your local council planning office, particularly if your house is a listed building or you if you live in a conservation area.

Whilst not essential, a twin-coil storage tank will enable storage of hot water and will increase the benefit of the solar thermal system so you and all your family can enjoy plenty of hot water (and maybe even your pets).

Are Solar Thermal Panels Expensive to Maintain?

Solar thermal panels require very little on-going maintenance, so they are cheap to operate. Your installer will recommend a service every year or two years to maintain efficiency (£130). The panels can work even as temperatures plummet due to an anti-freeze solution which circulates around the loop of the thermal system to protect it from freezing. You should keep the anti-freeze topped up (£100) every ten years or so and you may need to replace the pump (around £90) once during the lifetime of the system.

Warranties of at least ten years are provided but your system should last much longer than this.

How Is A Solar Thermal Collector Installed?

The solar thermal system must be accredited and installed by a person approved by the Microgeneration Certification Scheme (MCS). You can find installers through specialist websites or via a web search for MCS certified installers.

The installer will initially need some details about your house including:

  • Your postcode - to view the roof on Google maps.
  • Details of your current heating system (gas boiler or a combi boiler that heats hot water on demand).
  • Information about your hot water cylinder if you have one, or if not the potential space to install one if required.
  • Do you have a water tank in your loft (gravity-fed system)?
  • Any planning restrictions.

Get detailed written quotes from three installers, ask for recent references and check they are quoting on a similar scope of work and offering comparable warranties. Check their products are approved under the Microgeneration Certification Scheme as you will need the MCS certificate to claim the Renewable Heat Incentive.

Installers may also participate in other schemes to provide additional reassurance, such as the Renewable Energy Consumer Code, Which? or advertise on You Gen.


Do I Need A Hot Water Tank for Solar Thermal Energy?

Ideally your home will have room for a hot water cylinder. If you don't have space for a hot water tank, solar thermal systems can work without a hot water cylinder.  Major manufacturers of combi (combination) boilers, which provide hot water on demand, can accept preheated water directly from solar thermal systems.

Can I Get Financial Support to Install a Solar Water Heater?

The Renewable Heat Incentive (RHI) is a Government scheme which encourages and enables the use of renewable energy. It provides financial support to homeowners or landlords who have invested in renewable heat technologies. Of all the technologies the RHI supports, solar thermal for the provision of hot water is paid at the highest rate (currently 20.06p/kWh). 

The solar thermal system must meet eligibility criteria* and the householder must apply for RHI via Ofgem within 12 months of the system being commissioned.

The RHI payments are paid quarterly, for seven years. They are tax-free and RPI linked. The payment is based on the estimated annual generation which will be listed on the Microgeneration Certification Scheme Certificate provided by your installer. As an example, a 4m2 installation could receive £345 a year.

Where RHI is claimed, most thermal systems offer a pay back of between 10 and 15 years, depending on the fossil fuel displaced, the future fuel inflation factor and the amount of hot water used.

Uniquely within the RHI, solar thermal is also eligible for support as a second technology, if installed in combination with biomass boilers or heat pumps. This means homeowners can receive financial support for both systems.

To be eligible for RHI a valid Energy Performance Certificate is required for your home and you must have installed insulation in the loft and cavity walls (if the EPC recommends this). The thermal solar system must be accredited and installed by a person approved by the Microgeneration Certification Scheme (MCS).

Can I Install A Solar Pool Heater?

Kids jumping in to outdoor swimming poolIf you have an outdoor swimming pool to heat, then solar thermal is an amazing fit. Pools are normally heated to at least 21°, but often hotter and this consumes a lot of energy.

Because solar water heaters work most when the sunlight is strongest, typically the summer months, this coincides nicely with when an outdoor pool will be used the most. Solar heaters will save you money on gas or oil bills and reduce carbon dioxide emissions in the process. So, if you want to heat your pool with renewable energy then solar panels on the roof of your house or alongside the pool may be a good solution. However, RHI payments are not available for solar thermal systems used to heat swimming pools.

How Does A Solar Water Heater Work?

Solar thermal panels, called collectors, use the power from the sun to heat hot water for your home. A solar thermal system can generally meet up to 70% of your hot water needs.

Solar thermal collectors are generally fixed onto a roof and as the sun rises during the day the liquid (glycol) in the collector is heated. The hot glycol is pumped through a heat exchanger where the heat is passed to the water and stored in the hot water cylinder. The heated water is stored ready to use whenever you turn on the shower or taps.

Solar thermal systems do not heat the hot water for your radiators. A suitably designed system can contribute to your space heating through an under-floor heating system (as this works at lower temperatures than wall mounted radiators). However, this requires a larger solar collector area on the roof as well as a big hot water cylinder (1200 litres), making it quite an expensive option. People generally use other sources of energy for space heating, such as biomass boilers, heat pumps or gas boilers.

There are two types of solar thermal panel; flat plate and evacuated tube. Evacuated tubes are best but will cost more.

  1. Flat plate: are based on a thin sheet of copper or aluminium, backed by a fluid carrying tube system. They are relatively thin, highly insulated with a glass cover on the front. They are cost effective, fitted either on top of, or integrated into the roof if building a new roof and can reach efficiencies of 75-80%.
  2. Evacuated tube panels are made up of multiple vacuum glass tubes. The vacuum provides extremely efficient insulation and these tubes can reach very high temperatures and an efficiency of around 90%. They are therefore slightly more expensive but require a smaller area for installation.

As you can see, there are plenty of ways that you can use the power of the sun to heat water for your home, using a solar water heater. Creating hot water from the sun is very common around the world, so why not take a closer look at Solar Panel Heaters for your home?



This information is provided for guidance only. Please see the full disclaimer in our terms and conditions.

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