Solar Water Heating: Pros, Cons, & Costs

picture of cartoon house with solar water heaters

A solar water heating system (solar thermal panels) uses the natural heat from the sun to heat water for your home. Solar thermal technology is an increasingly popular renewable alternative to traditional water heating systems, but is it the right choice for your home?

We've taken a look at the pros, cons, and cost of installing a solar water heating system to help you decide.

NOTICE: Under the government's Green Homes Grants scheme, between September 2020 and March 2021 you can apply for a grant to cover two-thirds of the cost of installing solar thermal panels. Click here for more information.

How does solar water heating work?

A solar water heating system uses solar thermal collectors, also known as solar thermal panels. These panels look a lot like solar PV panels and work in a similar way, i.e. they capture energy from the sun, but rather than converting the heat into electricity, solar thermal collectors use the energy to produce hot water.

The process is very simple:

  1. Solar thermal collectors are panels which are (usually) fitted onto your roof. The panels contain tiny tubes of water which are heated by the sun.
  2. This heated water can reach up to 90 degrees C. It is passed down into your home where the heat is transferred to water in a storage tank or cylinder via a coil.
  3. Pipes then transport this hot water for use in your home.

solar thermal diagram

Most properties will need a boiler or electric immersion heater to provide a backup supply of hot water during times of peak demand, but you should be able to significantly reduce how often you need to use them so you can lower your heating costs and carbon emission.

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Pros of solar thermal panels

  • By providing up to 70% of a household's hot water through free energy from the sun a solar water heating system can reduce your annual energy bills.
  • Solar water heating systems could earn you money for every unit of renewable energy you generate under the government's Renewable Heat Incentive (RHI) scheme.
  • Using more renewable energy from the sun rather than buying fossil fuels like gas or oil from a supplier will reduce your carbon footprint.
  • Other than the initial installation cost and a little maintenance, there are no running costs to budget for with a solar water heating system as it's free energy.
  • Solar thermal systems are very low maintenance. Aside from an annual check by you, your system should only need professional servicing every 3-5 years.

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Cons of solar thermal panels

  • A solar thermal system is not a complete solution; you will still need a boiler or immersion heater to supply hot water through the winter and to supplement your supply on cloudy days.
  • The cost of installing an average solar water heating system tends to fall between £3,000 – £5,000 which is a significant investment.
  • Ideally solar thermal collectors need to be installed on a roof facing due south at a 20-50 degree angle from horizontal. However, they can work effectively when positioned between south east and south west. They can also be installed on the ground in some circumstances but any shade will reduce their effectiveness.
  • Solar water heaters will not power electric showers or cold-fill dishwashers / washing machines.
  • Solar water heating systems are not always compatible with Combi boilers as they heat water directly from the mains supply on demand; you will need to check with the manufacturer if your Combi boiler will accept pre-heated water.
  • If you have a Regular heating system which is gravity fed you will need an extra valve or pump so the system can work effectively in winter when the heating is running at the same time.
  • You will need to install a solar compatible water cylinder which is large enough to hold around 2 days of hot water.

calculator and money

Solar water heating costs & savings

The cost of installing a solar water heating system in the home of a family of 4 could cost between £3,700 - £4,200 but this can increase to around £5,500 depending on the size of the system needed. Industry recommendations suggest that you will need around 1m2 of panel per person living in the home.

Size of System People in Household Average Cost of Installation
2m2 2 £2,500 – £3,000
3m2 3 £3,100 – £3,600
4m2 4 £3,700 – £4,200
5m2 5 £4,300 – £4,800
6m2 6 £4,900 – £5,400

These costs will also be impacted by the complexity of the installation, i.e. how simply the solar technology will integrate into your existing plumbing and whether or not scaffolding is needed. The size and brand of your solar water cylinder will also have an impact on the cost of your system.

Remember, you need to weigh up the cost of installation against the potential savings that a solar water heating system could deliver. The Energy Saving Trust gives the below figures as an estimation but specifies that savings will vary from user to user.

Existing Heating System Potential Fuel Bill Savings per year Potential CO2 Savings per year
Gas £50 270kg
Oil £55 350kg
Coal £65 5450kg
Electricity £80 390kg
LPG £95 310kg

Grants and incentives for solar water heating

Green Homes Grants

Under the government's Green Homes Grants scheme, between September 2020 and March 2021 you can apply for a grant to cover two-thirds of the cost of installing solar thermal panels.

Many UK homeowners want to reduce their heating bills and carbon footprint by installing solar thermal panels, but most do not have the money available to cover the upfront costs. To address this, the government is introducing the Green Homes Grants scheme which will give UK homeowners up to £5,000 (£10,000 for the lowest income households) towards the cost of installing a solar thermal heating system.

Renewable Heat Incentive

In addition to the potential fuel savings, if your solar water heating system is installed and used correctly you could actually earn money through the government's Renewable Heat Incentive (RHI) scheme.

For every unit of energy you generate through your solar water heating system you are rewarded financially based on the government's current tariff. The payments are made to you on a quarterly basis over 7 years. The below table gives an indication of the kind of payments available to solar water system owners based on the tariff between 1st January 2018 - 31st March 2018. NOTE: The RHI scheme closes to new applications 31st March 2021.

Size of Household/strong> Size of Household/strong> Renewable Heat Incentive Payment per year
2 person 2m2 £200
3 person 3m2 £270
4 person 4m2 £345
5 person 5m2 £445
6 person 6m2 £485

Solar water heating efficiency

Generally, a solar water heating system can produce between 40-70% of the hot water needed by an average family of 4 annually. Exactly how much hot water you will benefit from is difficult to estimate, however, as there are a number of factors to consider:

  • How much sunlight is available? In the sunnier UK months between April - September your collectors will absorb more heat from the sun and therefore generate more hot water. On cloudy days the system will not produce as much hot water.
  • How much hot water does your family use? Obviously the busier your household the higher demand you will be placing on the system and the more likely it is you will need to supplement your supply with a boiler or immersion heater.
  • Are you prepared to adapt your routine to suit the system? For example, taking showers in the evening when the hot water supply is at its highest is a great way to make the most of the hot water available.
  • The capacity of your hot water cylinder will impact how much hot water you can store. If the cylinder can only hold one day's worth of hot water, more than one cloudy day will mean you need to supplement with an immersion heater or boiler.
  • If your heating and hot water are not set up with separate controls, when the heating is on your hot water supply may be reduced.
  • It's important to ensure that both your cylinder and pipework are adequately insulated to prevent heat loss.
  • Keep in mind that you may not need the system to heat water to the highest possible temperature at all times. You can reduce the need for backup water heating by lowering the temperature of the water.
  • Types of solar thermal panels

    There are 2 types of solar thermal collector: flat plate or evacuated tubes.

    flat plate collector

    Flat Plate Collectors:

    Flat plate collectors look more like traditional solar panels. They have a flat, glazed, dark-surfaced absorber plate which contains metal tubing. The plate covering the tubing, which is normally copper or aluminium, absorbs the solar energy and the casing stops heat from escaping from it. A fluid is constantly run through the tubing which is heated up by the solar power captured from the sun.

    evacuated tube collector

    Evacuated Tube Collectors:

    Evacuated tube collectors have a very different look. The panel is a collection of glass tubes in a parallel row which have an absorber insulated by a partial vacuum. They are generally more expensive than flat plate collectors but provide an alternative aesthetic option and are argued to be the more efficient option.

    There are two different types of evacuated tube solar panels:

    Direct Flow, where the fluid flowing in the absorber also flows through the pipes to the hot water cylinder.

    Heat Pipes which have fluid in them that evaporates at a low temperature. When the fluid evaporates it rises up in the tube and condenses, transferring the heat it was carrying and the latent heat of condensation into the pipes into the hot water cylinder. The fluid then runs back down the tube again ready to be reheated.

    Best solar thermal manufacturers

    We have listed some of the best solar thermal manufacturers on the market here, but you can find more information in our Best Solar Thermal Panels article.

    Manufacturer Flat Plate Panel Collectors Evacuated Tube Collectors
    Viessmann Vitosol 100FM or 200FM Vitosol 200T, 300T, 200TM, 300TM
    Worcester Bosch Greenskies Solar Lito or Greenskies Solar Lifestyle N/A
    Kingspan Kingspan Flat Plate Panels Thermomax HP400/DF400 or Varisol

    Solar water heating installation & maintenance

    In most cases, you don't need to apply for planning permission for a solar water heating system as it's categorised as a 'permitted development'. Some homeowners in conservation areas or listed buildings may need to contact their local authority before proceeding.

    Once the system is in place you should be covered by a warranty. Warranties tend to cover a 5 or 10 year period and require very low maintenance. Aside from noticing problems with the performance of the system, other potential issues could be a faulty pump or an antifreeze leak. However, if everything is running smoothly, you simply need a professional to check the system over every 3-5 years.

    Get free solar water heating quotes

    If you think a solar water heating system could be the right choice for your home, your next step is to get multiple quotes for installation. This is the best way to compare prices and professional advice ensuring you get the right size and type of system.

    We can put you in touch with up to 3 of the UK's leading solar installation professionals for free, no obligation quotes. Use our simple online form and get solar thermal quotes from trusted traders in your area.

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