Installing a solar thermal system for heating hot water is a good move for the environment. But before you go ahead, it’s essential to know all the facts so you can decide if a solar hot water system is the right choice.

First, it’s important to point out that there are two types of solar panel systems:

1. Solar PV panels that use energy from the sun to generate electricity
2. Solar thermal panels that use energy from the sun for heating and hot water.

This guide tells you everything you need to know about solar thermal panels: how solar thermal systems work, the cost of solar water heating, including installation and maintenance, and solar thermal hot water heating advantages and disadvantages.

View our range of solar thermal panels here

Solar thermal panels work by taking energy from the sun and transferring it into a hot water cylinder inside the home as follows:

Solar thermal panels are fixed to the roof of a house, and they contain a fluid made up of water and anti-freeze. These solar thermal panels are also called solar collectors because they collect energy from the sun and transfer heat to the fluid inside. This heated fluid is then pumped around a circuit inside the home. The circuit consists of:

• A solar controller and pump. The controller measures the temperature of the fluid in the solar collector and hot water tank, then automatically turns the pump off or on as needed to pump the fluid around the system.
• A hot water tank, which contains a heat exchanger (or coil) located at the bottom of the tank and heats the water. It also has a second heating coil at the top of the tank connected to the boiler. This kicks in when the energy collected from the sun isn’t sufficient to heat all the hot water.
• An expansion tank (this applies to an unvented system only. A vented system doesn’t require an expansion tank). The expansion tank prevents pressure changes in the system from damaging the components.
• A network of pipes that connect all the components in the system to each other.

The whole solar thermal system works on a loop. So, once the fluid releases its heat into the hot water tank, it flows back to the solar collectors for reheating.

As the amount of solar energy available varies throughout the year, a solar water heating system won’t provide all the hot water needed. Solar thermal panels can produce around 80-90% of hot water in summer and 20-30% in winter – that’s an average of up to 70% over a year. So, a boiler or immersion heater is needed to make up the difference.

It’s possible to use solar power for heating, as well as hot water. However, it only provides around 10% of a home’s heating needs, so it’s best to use other methods for heating instead.

When looking at the cost of solar thermal panels, it’s important to consider all the factors involved, not just the cost of the panels themselves.

Let’s look at the costs involved:

Solar thermal panels and installation costs

The cost of solar thermal panels themselves will depend on the brand, whether they are flat plate or evacuated tube solar collectors, and how many are needed. Evacuated tube solar panels tend to cost a little more than flat plate solar panels. And the quantity of panels required depends on how much hot water the household will use.

As well as the panels, a solar controller and pump will also need to be fitted, and there will be other small items required, such as valves and pipes. It’s easiest to buy complete solar water heating systems, where everything is included in one kit.

In addition to all the parts are the installation costs. Installation should always be carried out by a qualified installer.

According to the Energy Saving Trust, parts and installation costs combined are around £3,000 to £5,000.

Government grants for solar panels

There are currently no government grants available to help towards the cost of buying and installing a solar water heating system. However, the Renewable Heat Incentive (RHI) scheme rewards homeowners for switching to renewable energy sources, and flat plate and evacuated tube solar panels are included. People who join this scheme receive quarterly payments for seven years, based on the renewable heat they generate. It’s open to homeowners and private or social landlords in England, Scotland, and Wales.

Other costs

If hot water is currently supplied through a combi boiler, there probably won’t be a hot water tank in the house. If this is the case, you’ll need to factor in the cost of a new hot water cylinder and the extra installation cost.

You’ll also need to check whether the current boiler and hot water cylinder are compatible with a solar hot water system. Most are, but if not, you’ll need to include the cost of changing one or both of those too.

One other additional cost to the installation could be the price of scaffolding. If the roof is difficult to get to with ladders, scaffolding will need to be erected.

Maintenance costs

Maintenance costs for solar water heating systems are generally very low but can vary by location and how they were installed. The installer may suggest an annual service check, which would not take long. Other than that, a full service, costing about £100, to drain the system and replace the anti-freeze will be needed once every five years. The pump may need to be replaced after 10 years at the cost of around £90.

It’s impossible to give an exact figure on savings and efficiencies of solar thermal systems because it depends on varying factors, such as:

• Whether flat roof or evacuated tube solar collectors are installed
• The size of the panels fitted
• The amount of sunlight the roof panels receive
• The hot water heating system it’s replacing
• That amount of hot water that’s used

However, a solar hot water heating system can provide roughly 70% of the hot water requirements annually – supplying nearly all hot water in the summer but less during the colder months.

According to the Energy Saving Trust, a 4m2 system could provide average annual savings of between £60 (if switching from gas) and £115 (when switching from LPG). The savings could be greater still if you join the Renewable Heat Incentive (RHI) scheme.

• They’re great for the environment – using a 100% renewable energy source and emitting zero carbon emissions
• They’re suitable for new builds and older homes
• They provide up to 70% of a home’s annual hot water
• They provide hot water throughout the year
• They help save money on energy bills
• The installation cost can be offset by Renewable Heat Incentive payments
• Installation requires minimal upheaval
• They’re low maintenance

• They can only be used to heat hot water or heating
• They won’t work as effectively on north-facing roofs or roofs that are in the shade
• A boiler or immersion heater is also needed to make the water hotter or provide hot water when solar energy isn’t sufficient

Installation of a solar thermal system should be carried out by a qualified tradesperson. It’s usually straightforward, but there are a few checks that need carrying out beforehand.

Here’s a guide to what you can expect:

• Check the boiler is compatible with solar water heating – standard boilers usually are, but if there is a combi boiler, a solar hot water cylinder must be added to the system, so you’ll need to consider if there is enough space and where to install it.
• Check the installation company is certified with the MCS (Microgeneration Certificate Scheme) – using an MCS certified installer ensures the solar thermal water system meets good performance standards and that the installer is technically safe and competent. You’ll also need to use an MCS-certified installer to qualify for the Renewable Heat Incentive payments scheme.
• Check the installation company are members of the Renewable Energy Consumer Code (RECC).
• Get the Energy Performance Certification (EPC) for the house. This can be carried out by the installer or an independent assessor and involves a full assessment of the house’s energy performance.
• Check the roof orientation – solar thermal panels should be placed on a south-facing roof or somewhere between east and west. They should not be placed on a north-facing roof or on a roof that’s in the shade.
• Check the roof size – you’ll need space on the roof of around 5m2 that receives about five hours of sunlight a day.
• Check the tilt angle of the roof – for best results, the panels should be mounted at an angle of 30-65 degrees. However, if that’s not possible they can be mounted into a frame on a flat roof or the ground. They can even be mounted to a wall if necessary.
• Check the quality of the roof from inside and out – solar thermal panels can be heavy, so the roof must be sound and in good condition.

It will take approximately 1-2 days to install a solar thermal system. The difference in time will depend on:

• How big the system is – a big system means more roof panels, which will take more time to fit
• Whether a new hot water cylinder will be installed or not.

Solar thermal systems and panels should always be installed by a qualified tradesperson, and we recommend you get at least three quotes. The installation process may vary slightly, depending on the installer, but in general, this is how the process works:

Step 1: Fitting the solar thermal panels
This work is carried out on the roof of the house, so the disruption to the home should be minimal. First, the solar thermal panel frames are mounted on the roof. They must be mounted to the roof rafters, so the roof tiles or slates are removed first. If flat plate solar collectors are installed, the panels will be bolted to the frames straight away. However, if the panels are evacuated tube solar collectors, the tubes won’t be fitted until after the work inside the house is completed.

Step 2: Installing or changing the hot water cylinder and boiler
If there is already a hot water cylinder and boiler that’s compatible with the new system in the house, then installing a new one won’t be needed. If a new tank and/or boiler is required, they will be installed now, and the water will be turned off at this stage.

Step 3: Fitting the controls and plumbing the system in
Once the tank is in place, all the other parts will be fitted, and the whole system will be connected. This involves fitting and/or connecting:

• the mains cold water
• the heating system (i.e., the boiler)
• the solar collectors
• the hot water cylinder
• the solar controller that manages the whole system
• the pump that circulates fluid around the system
• an expansion vessel (if an unvented model is being fitted)

The controller and pump run on electricity, so some electrical work will be necessary at this stage, and the electricity will be switched off. If evacuated tube solar collectors are being used, the tubes themselves will be fitted to the frames on the roof at this stage too.

Step 4: Getting the system started
The special heat transfer fluid (a mix of water and anti-freeze) will be pumped into the system and pressurised to approximately 2 bar, or as per the manufacturer’s specifications. The system is now ready to use.

Solar hot water systems are low maintenance, but always check the installers and manufacturer’s guidelines. If you have used an MCS installer, the work will come with a five-year warranty, and the solar thermal panels will have a warranty of at least 10-years.

The solar thermal panels themselves are low maintenance and can last for 20 years or more. You may just need to give them an occasional clean.

Some installers offer an annual service check that typically lasts around 10-20 minutes. Other than that, the heat transfer fluid will need to be drained and replaced by a qualified tradesperson once every five years. And the pump may need to be replaced after 10 years.

One other main thing that needs to be checked is the pressure gauge. If the pressure is too low, there could be a leak in the system that will need to be repaired by a qualified tradesperson.

We advise that anyone considering solar thermal panels should always do their research before deciding on what to buy to ensure it’s right for them, their situation and setup.

Here are five things to consider:

1. House suitability

Whether they’re a new build or an older house, most homes are suitable for solar thermal water heating systems. But there are a couple of things to consider:

• The direction of the roof – solar thermal panels should be placed on a south-facing roof, or somewhere between east and west. Although they will still generate some energy, it isn’t recommended to place solar thermal panels on a north-facing roof, or a roof that’s in the shade as they won’t perform as well.
• The boiler – if a combi boiler is installed, it will need to be changed to a standard boiler
• The hot water cylinder – if the house currently has a combi boiler, there won’t be a hot water cylinder. This system requires a hot water cylinder, so you’ll need to consider if there is a suitable space inside the house to install one.

2. Current energy usage

Work out how much energy and money a solar thermal system could save by checking energy and water usage over a year. If water usage is very high, the savings will be lower since the solar thermal system won’t supply all the hot water needed.

Also, check how the appliances in the house use hot water. For example, does the washing machine or dishwasher take a hot water feed? If so, changing to cold water feed appliances instead will lower the hot water usage considerably and increase the cost savings of a solar thermal system.

3. Home insurer checks

Before installing a solar thermal system, check the home insurance policy to make sure the new system will be covered, including any other changes that are made to the house. If it doesn’t, get in touch with the insurer to adjust the policy.

4. Number of solar panels needed

The number of solar panels needed depends on the hot water usage. On average, each person uses around 50 litres of hot water per day, and that volume of water can be heated by 1m2 of solar panel.

Solar panels vary in size depending on the manufacturer and type, but they are usually around 2-3m2. So, for a 3-4 bedroom house, two panels will be needed.

5. Planning permissions for solar panels

Before installing solar thermal panels, it’s essential to check if planning permission is needed. In most cases, solar thermal panels are considered a ‘permitted development’, meaning no planning permission is required. However, if the property is a listed building or in a conservation area, planning permission may be needed. But whatever the circumstances are, it’s always best to check.

• Always use a reputable installer, preferably registered with the MCS. This is essential if you are applying for the Renewable Heat Incentive (RHI) scheme.
• Get at least three quotes and ensure the installation requirements are verified by a surveyor, not just a salesman.
• Always do your own research before inviting a company to the house and watch out for sales tactics such as exaggerated financial savings and putting you under pressure to buy.
• Check the size and position of the solar thermal panels that are recommended. There should be at least 30-40cm between the panels and the roof edge. They should not overhang.

Installing a solar thermal system is a significant investment, and it’s important to ensure you have all the facts available to make an informed decision about the best type of solar water heating system to install and how they work. But once installed, solar thermal systems are an excellent investment due to their long lifespan, energy savings and environmental benefits.

If you’re considering installing a solar thermal system, check out our solar thermal panel range here.