Solar Thermal Panels: Everything You Need to Know

Solar thermal panels on a rood

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Solar thermal panels use the sun’s energy to provide hot water for your home

They won’t provide all your hot water but they will make a modest dent in your bills

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Renewable energy is constantly evolving, and is significantly growing in popularity as years go by. And out of all the renewables on the market, solar panels still rank as the most popular choice for domestic use.

If you’re looking to heat your household water with renewable energy, solar thermal panels are for you – for starters, they can cut your bills by up to 60%. In this article, we’ll discuss the ins and outs of solar thermal energy, and whether it’s a suitable option for your home.

 

Solar thermal panels on a roof

What’s on this page?

 

What are solar thermal panels?

Solar thermal panels (also known as ‘collectors’) absorb the sun’s rays to heat up household water, which can then be used for showering, washing clothes, and other daily tasks. This renewable system will reduce your energy consumption substantially, and chop a few pounds off your monthly bills.

 

How does it work?

Just like solar PV, solar thermal panels are installed on your roof to allow optimal exposure to the sun. The water inside the panels is then heated naturally, stored in a hot water cylinder, and can be used throughout your home. 

Since these panels can be added to an existing water-heating system, installation isn’t complex. Conventional boilers and immersion heaters are both compatible with solar thermal panels, and can be used to make the water even hotter, or to collect the water for when solar energy is unavailable.

 

a diagram showing how solar thermal panels work

Types of solar thermal systems

There are four types of solar water heating systems, all varying in the way they absorb heat:

  • Active – Relies on external electric power to activate pumps (so not 100% renewable)
  • Passive – Relies on the natural transfer of heat from the sun to circulate the hot water, rather than electricity 
  • Direct – The water is heated directly by the solar panel/collector
  • Indirect – The water is heated by fluid (typically a mixture of water and glycol) being circulated between the rooftop thermal collector and a heat exchanger.

The two most common collectors for domestic use are flat plate panels and evacuated tube collectors.

Flat plate panels look similar to solar PV panels. A heat-absorption panel is attached to multiple copper pipes, which the water or transfer fluid passes through. A sheet of glass covers this panel, acting both as protection and insulation.

Evacuated tube collectors consist of multiple heat pipes, which are all surrounded by glass tubes. The glass tubes are all vacuumed, adding air-tight insulation. 

 

Pros and cons of solar thermal panels

Pros:

  • Cut down energy bills
  • Low maintenance
  • Most come with a 5-10 year warranty
  • Lower your carbon footprint
  • Cheaper than solar PV panels

X Cons:

  • You’ll still need a boiler to make water hotter
  • Not all boilers are compatible with solar water heating
  • Expensive
  • Dependent on the season

 

How much do solar thermal panels cost?

The average solar thermal panel system typically costs between £4,000 and £5,000 to install. We know, this is a hefty sum of money – but once the panels are installed, you can reap the renewable reward and watch your bills gradually decrease. 

 

Maintenance costs

After forking out the initial sum, you’ll be glad to hear that most solar water-heating systems require very little maintenance.

Unlike a boiler, solar thermal systems only need to be serviced every 3-7 years, unless you have any suspicious leaks that need checking out.

Over time, a few things may need tidying up, but minor tweaks won’t break the bank. The antifreeze that is used to protect the system in the winter months will need topping up. Keeping on top of this is important, as it can reduce the efficiency of your system – luckily for you, replacing the antifreeze needs to be done every 3-5 years, and will only set you back around £100.

As well as replacing the antifreeze, you’ll want to keep an eye on the system’s heat pumps. If the pumps are suffering from a bit of wear and tear, replacing them only costs around £90

So, despite the initial cost of installing solar thermal panels, you shouldn’t expect any nasty financial surprises along the way. 

 

How much can you save with a solar thermal panel system?

Existing boiler systemFuel bill savings (£/year)Carbon dioxide savings (kg CO2/year)
Gas£55260 kg
Oil£70340 kg
Coal£65520 kg
Electricity£65220 kg
Liquefied petroleum gas (LPG)£95300 kg

Data from the Energy Saving Trust

As you can see, if you’re switching from a fossil fuel-based system, solar thermal panels represent a worthwhile investment. 

 

Renewable Heat Incentive (RHI)

If you’re worried about the cost of solar thermal panels, fear not: the Government has set up a scheme to support you.

The Renewable Heat Incentive (RHI) encourages homeowners to switch to renewables by offering quarterly cash payments over a seven-year period. The amount of money you receive will depend on a number of factors, including which green technology you install, the latest tariffs available, and in some cases, metering.

Check out how much money you can receive from the scheme if you install solar thermal panels:

Household sizeSolar thermal system sizeRHI payment (£/year)
2-person household2 m²£205
3-person household3 m²£285
4-person household4 m²£360
5-person household6 m²£435
6-person household6 m²£505

Data from the Energy Saving Trust

 

How to get the most out of your solar thermal system

  • Make sure your hot water cylinder and pipes are well insulated. This will reduce heat loss around the cylinder, and increase the overall efficiency of the system
  • Choose a large cylinder. During colder months, your panels won’t be able to absorb as much heat. By having a larger cylinder, you’ll be able to store more hot water for when the panels have stopped working for the day
  • Keep an eye on the temperature. Make sure the temperature of your cylinder reaches more than 60ºC at least once a week to avoid any build-up of bacteria in the water
  • Be smart with your water consumption. Simple things, like showering in the evening, will make a difference – this is much more efficient than letting your hot water lose heat overnight, then firing up the boiler for a shower the following morning

 

FAQs

How many solar collectors do I need?

There is no set guideline, but generally, you’ll need between 1-2 square metres of collectors (solar panels) per person living in the house.

 

Do I need planning permission?

You won’t need planning permission for most domestic solar water-heating systems in the UK, as long as they aren’t too big.

However, if you live in a listed building or a building in a conservation area, you will have to look into planning permission, which might not be granted.

Since standards vary across the UK, it’s worth contacting your council to see whether you need to apply for planning permission for your solar panels. It’s better to be safe than sorry! 

 

Are solar thermal panels right for my home?

Not all homes will benefit from solar thermal panels. Before you invest in any panels, ask yourself the following questions: 

  • Do I have a sturdy roof? – Solar panels can be heavy, so your roof must be strong enough to take their weight
  • Do I have the right boiler? – Not all boilers are compatible with solar-water heating. If your boiler doesn’t have a water tank, it won’t work with solar thermal panels. You can look into what equipment you need to make it work, but this can become quite costly
  • Do you have a south-facing roof? – For maximum efficiency, you need to put your solar thermal panels on a south-facing roof, at a 30-65 degree angle. You should also keep the panels away from any shadows, for example those caused by trees, buildings, or chimneys

 

How do I choose a solar panel installer?

Your installer should be certified under the Microgeneration Certification Scheme (MCS), a national quality assurance scheme, and use MCS-certified products.

You should also check whether the installer is a member of the Renewable Energy Consumer Code (RECC), or the Home Insulation and Energy Systems Quality Assured Contractors Scheme (HIES). These schemes make sure consumers are supported appropriately.

 

Solar thermal panels on a rood

 

What’s the verdict?

If you have the right type of property, solar thermal panels are a worthwhile investment – and can save you a considerable amount each year on bills.

However, one of the downsides to solar thermal energy is that it’s limited to just heating household water. Plus, in colder months, you are still reliant on your boiler to give your panels a helping hand. So, although you’ll be reducing your carbon footprint (and your bills), solar thermal energy is still quite limited.

Solar PV panels, on the other hand, can work much more effectively. If solar PV panels sound like a better option, our experts can pick out the perfect panels for your home. All you have to do is simply tell us a bit about your property, and our installers will be in touch shortly with quotes for you to compare. 

Beth Howell Writer

Beth is The Eco Experts’ newbie. She’s keen to use her writing skills, and passion for green living, to help the environment. Whether you’re after a new boiler, or just interested in how solar panels can improve your home, she’s got your back.