Evacuated tube solar panels are the most expensive but most efficient type of solar hot water system. They have a conversion rate of 90%, so they can produce more heat than other types of solar thermal panels.
How do evacuated tube panels work?
An evacuated tube is made up of a smaller glass tube which is kept in a larger tube. The air is pumped out of the space between the inner tube and the outer tube, which creates a vacuum thermal insulation layer. This layer reduces heat loss from the solar collector.
The inner glass tube is coated with a selective light absorber such as aluminium nitrate or titanium nitrate oxide. This helps maximise the absorption of solar radiation. An absorber plate runs through the inner glass tube. This is usually made of copper, and absorbs heat and transfers it to a heat transfer fluid.
When the transfer liquid gets hot, it evaporates and turns to steam, which rises to the top of the panel and the heat is transferred via a heat exchanger to another liquid. The cycle then starts all over again once the transfer fluid condenses and falls back down the evacuated tube.
Since evacuated tube solar panels are the most expensive, you might be unsure if they are right for you. Take a look at the pros and cons to help you decide.
You’ll produce more heat than other systems
As the panels are 90% efficient, you’ll produce more heat with evacuated tube panels than flat plate collectors. Although you may spend more on installation, you’ll be able to heat more hot water, which should save you more money.
You’ll save up to £60 per year on your gas bill
If you have gas heating, you should see a saving of £60 per year on your heating bill. Solar hot water is free to generate, so you’ll notice the difference on your bill within a few months.
Save 270kg CO2 compared with gas
Solar thermal panels are a great way to cut your carbon footprint. They generate heat from the sun, a renewable resource, so you’ll be doing your bit to reduce the use of fossil fuels and reverse global warming.
Get hot water throughout the year
Despite the UK’s winter being cold, you can still get some free hot water from your solar panels throughout the year.
Earn an average of £349 per year from the Renewable Heat Incentive (RHI)
As long as you get your system installed by an MCS-registered installer, you may be able to earn money for generating heat with your solar hot water system through the government’s Renewable Heat Incentive (RHI). A 2m2 system, which is usually sufficient for a 2 person household, will earn you £200 per year from the RHI, whereas a 4m2 system will earn you £345.
You may need a backup heater
During the winter, you may not be able to get your hot water to the desired temperature. That means you’ll need a backup heater, which of course will cost you money on electricity or gas.
Solar thermal panels aren’t compatible with combi boilers
Combi boilers provide instant hot water and don’t have a separate water tank. They’re not compatible with solar hot water systems, so if you want a solar system you will have to change your boiler. This will drive the cost up by at least £1000.
£3,000-£5,000 inc. installation
Advantages and disadvantages
- Save £60 per year compared with gas heating
- Save 270kg carbon dioxide compared with gas heating
- Get hot water throughout the year
- Earn between £200-£485 per year from the RHI
- You may need a backup heater in winter to get your water to reach the right temperature
- Solar hot water systems are not compatible with combi boilers
- You won’t save as much money on your hot water bill with solar thermal compared with your electric bill and solar PV (solar electricity)