Solar Water Heating: Costs, Benefits & Types

picture of cartoon house with solar water heaters

A solar water heating system (or solar thermal technology) uses the sun’s free, renewable energy to heat water for your home. With every passing year the technology is becoming more effective, more popular and more affordable providing UK homes with a renewable alternative to traditional water heating systems.

We’ve taken a look at both the advantages of a solar water system and the things you need to consider before deciding if it’s the right choice for your home.

How Does Solar Water Heating Work?

A solar hot water system relies on solar thermal collectors. These collectors are similar to solar PV panels in that they absorb heat from the sun, but rather than converting the heat into electricity to power your home, solar thermal collectors use the heat 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

You will still need a boiler or immersion heater to provide a backup supply of hot water but you should be able to significantly reduce how often you need to switch them on. This means reducing the amount of energy you need to buy from your supplier which should not only save you money but also reduce your carbon emissions.


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Types of Solar Thermal Collectors

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 re-heated.

How Much Hot Water Could You Get?

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.

hot water from tap

Advantages

  • 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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Things to Consider

  • 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

Costs & Savings of Solar Water Heating

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 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.


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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 & Incentives

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.

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

Manufacturers

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 System Quotes & Installation

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.

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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