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Solar Water Heating: What Is It and How Does It Work?

Solar panels have come a long way since the earliest inefficient models. There are more uses for solar energy now as well, such as turning cold water into hot!

Considering how much hot water we use throughout the year, it's not surprising that renewable energy has become more popular in recent years. It's sustainable and effective.

This guide will cover what you need to know about solar water heating systems and whether they're worth it for your needs.

Solar Water Heating: What Is It?

If you already own a conventional hot water system, you'll quickly understand why you need a solar water heating system.

Solar thermal panels in your home collect heat from the sun and keep it in a storage tank when it's not needed. They won't fully replace combi boilers, but they can help lower your heating costs once installed.

Whenever you need hot water, the solar collectors will pass heat down to your home without you needing additional energy. It's best to think of it as an energy-efficient hot water cylinder.

A solar thermal system has one purpose: to produce hot water and pipe it throughout your home. You can also heat your water with heat pumps, which draw heat directly from the air.

Solar thermal systems should not be confused with solar panels, which are meant to provide you with additional electrical energy throughout the day.

How Do Solar Water Heating Systems Work?

Solar thermal panels work in the following way. First, cold water from the mains passes through a coil to a hot water cylinder and remains there.

Next, a combination of water and antifreeze is pumped into the solar thermal panels installed on top of your roof.

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    These solar collectors look very similar to solar PV panels, which is why some people mistake them for electricity-producing panels.

    The sun's heat will warm your flat plate collectors or evacuated tubes and the anti-freeze solution until it reaches a temperature of about 90 degrees C.

    The now-heated solution will return to the hot water cylinder through a second coil, and your taps and baths will now have hot water!

    An immersion heater or conventional boiler can be used to supplement your solar thermal system on cloudy days and during the colder months when sunlight is less prevalent.

    What Are the Types of Solar Thermal Collectors?

    Solar thermal panels are also called solar collectors because they collect heat and use it to produce hot water as needed.

    There are two general types of solar collectors: flat plate and evacuated tube systems.

    Flat Plate Collectors

    Flat plate collectors look exactly how they sound. They're an arrangement of flat plates either affixed to the roof or integrated within the roofing itself.

    Flat plate collectors look like energy-producing solar panels with a dark surface for heat absorption and a transparent cover. The casing contains the anti-freeze fluid.

    Evacuated Tube Solar Collectors

    Evacuated tubes are an arrangement of glass tubes aligned in a parallel row.

    They're smaller and are considered to be more efficient than flat plate thermal panels, but they're also more expensive.

    There are also two different kinds of evacuated tube solar panels:

    • Heat Pipes - Each glass tube houses a small vacuum to reduce heat loss and is connected to a copper heat exchanger and a heat-absorbing reflector plate.
    • Direct Flow - The anti-freeze solution in these tubes flows directly to a hot water cylinder when activated.

    How Much Does a Solar Water Heating System Cost?

    Before you begin installing solar thermal panels on your roof, it's important to know that they cost more to install than to pay for electric immersion heating or gas heating.

    Solar hot water systems can help you save on fuel bills, but installation is expensive.

    Installing a solar thermal system can cost £3000 to £6000 for both the parts and the installation fee. Your solar water heating costs will depend on the type of heating system you choose and its size.

    There's also the question of whether your solar hot water cylinder will require minimal integration or if you will need an overhaul of your current water heating system.

    If your installers recommend installing a new hot water cylinder, your new system will cost more.

    Is Solar Water Heating Cost-Effective?

    We've previously mentioned that solar thermal panels will help lower your energy bills each month, but this is offset by the high installation costs.

    Depending on your current heating system setup, you can save £55-£95 per year.

    If the electricity grid is restructured to accommodate more renewable energy and fewer fossil fuels, green energy like wind and solar power may become more affordable in the future.

    And since fuel prices have risen, solar water heating has become a more cost-effective prospect, despite the current lack of government-backed financial incentives.

    Expect to save more money during the summer when your solar thermal panels will be most efficient.

    Conversely, you'll need to rely on your immersion heater or a heat pump as reinforcements once it gets colder.

    If you want more ideas on how to save money on energy costs throughout the year, visit the Energy Saving Trust website.

    Incentives for Solar Water Heating

    The government previously offered quarterly payments to homes and businesses with a solar water heating system. This programme was called the Domestic and Non-domestic Renewable Heat Incentive (RHI).

    Unfortunately, the RHI was discontinued in March 2022, so you can no longer get a pay-out for switching to solar thermal panels for your hot water needs.

    Despite the closure of RHI, you'll still save on gas and oil heating costs.

    What Are the Advantages of a Solar Water Heater?

    Here are some advantages of switching to a solar thermal system.

    Reduced Emissions

    Using gas or electricity for your hot water needs generates lots of CO2 but switching to renewable energy significantly reduces your carbon footprint.

    You can reduce the amount of CO2 you produce and save on gas and oil deliveries.

    If you're moving from coal to solar water heating, you can reduce your carbon footprint by up to 500 kg of CO2!

    Almost Free Energy and Consistent Hot Water

    A solar water heating system will help you reduce energy bills since it's powered by the sun. You almost don't need to pay for your hot water anymore!

    You don't need to pay for sunlight either, so a sunny day will see your energy bills shrink, and your savings will add up over time. You can also rely less on the electricity grid for your heating needs.

    However, remember that this will depend on your system's efficiency and daily water needs. Like solar panels, the larger the solar water heating array the more hot water it can produce.

    If your solar water heating system needs to serve a family of five, it may not produce enough hot water for your needs.

    Easy Integration

    Solar hot water systems can easily be installed alongside conventional combi boilers without needing a complete overhaul, provided you have the space required and your boiler can accept pre-heated water.

    They can also be installed in either new or old homes without major renovations. Remember to have your home inspected before installing solar thermal panels.

    Low Maintenance

    Though a solar water heating system is expensive to install initially, it requires little maintenance and can last for over 20 years!

    You'll also be covered by a warranty of 5-10 years on average when your system has been installed. However, this warranty will typically be unnecessary because of how little maintenance these systems need.

    This will depend on your model and your installer's instructions, but you'll normally only need to have your unit serviced every 3-5 years. You will also need to check whether the antifreeze has leaked.

    Remember to ask your installer to provide written instructions for any maintenance checks you'll need to conduct. And remember to keep a ladder handy for getting to the roof!

    No Planning Permission Required

    Needing planning permission before you install a solar hot water system, will depend on where your home or business is located.

    Contact your local planning authority to check whether your area has additional restrictions.

    What Are the Disadvantages of a Solar Water Heater?

    Solar water heaters are useful, but they're also not without their downsides. You should consider a few disadvantages before moving to this green energy water heater.

    Limited Range of Applications

    Unlike solar PV panels which can power your entire house, a solar water heating system is limited to water heating.

    If you need more energy for your appliances or want to power your cold-fill washing machine and electric showers, such a system will not suffice.

    Higher Installation Costs

    Solar thermal systems are more expensive to install than conventional electric or gas heating systems. We mentioned a price of £300-£6000, which is a significant investment.

    Even considering your energy savings, you'll need to wait a few years before seeing any major financial benefits.

    Things to Consider When Buying a Solar Water Heating System

    Here's what you should think about before getting a solar water heating system.

    Roof Space and Location

    Before making solar water heating work for you, you'll need to check if you have an appropriate area to place your solar thermal panels.

    These heaters are usually installed on a south-facing roof to ensure they receive maximum direct sunlight throughout the day, but you can install solar collectors on other parts of your home.

    If you don't have a south-facing roof, you can install them on a flat roof or even a wall, if needed.

    Consideration Regarding the Panel’s Location

    A solar water heating system can be quite heavy, whether you are using a flat plate or evacuated tube solar panels.

    Flat plate collectors can weigh over 40 kg, while evacuated tube systems can range from 19-52Kg.

    If your roof doesn't have adequate support, you may need to renovate it before installing any thermal panels.

    Hire a Reputable Installer

    Before installing a solar water heating system, ensure that your installer has been certified by the Microgeneration Certification Scheme (MCS).

    You can visit their website for a list of certified installers. This way, you can be certain that competent professionals are handling the installation.

    Limited Efficiency

    Don't expect your solar water heating system to operate at maximum efficiency throughout the year.

    That's because there's less usable solar heat as the year progresses, especially during the winter months.

    You'll need to use an immersion heater or a conventional boiler to compensate once it gets colder, which will raise your bills.

    Is Your Current Water Heating System Solar Compatible?

    Let's say you have a large home fitted with a system boiler. You've already got a separate hot water cylinder. So how can you integrate your solar water heating system with your current boiler?

    Alternatively, you may have a smaller home with a combi boiler instead. If your combi boiler is designed to accept pre-heated water, you can connect it to your solar hot water cylinder.

    Not all combi boilers have this feature, so remember to check with your manufacturer.

    Read the section to learn more about solar water heating systems!


    Solar water heating systems are great for producing hot water and for reducing your carbon footprint!

    These devices can provide you with hot taps and reduced bills without too many problems.

    Solar technology has progressed to the point where it can either generate electricity or heat water as needed, helping you save on your energy bills and minimise your environmental impact all at once!

    Did you know that Solar Panel Installation can match you with 3 local installers who will provide you with a free quote? Fill out our form today to get in touch with installers.

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    Mark McShane
    Content Writer
    Mark McShane is a seasoned professional in the solar industry and the owner of Skills Training Group, a leading provider of solar training and education. With years of experience in the field, Mark has developed a deep understanding of the latest trends, technologies and best practices in the industry. His expertise and passion for solar energy have helped countless professionals develop the skills and knowledge needed to succeed in the fast-growing field of solar energy. Whether you’re an aspiring solar professional or an experienced industry veteran, Mark is an excellent resource for anyone looking to enhance their skills and knowledge of the solar industry.
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