A solar thermal water heating system uses the sun’s energy to produce hot water for domestic consumption free of charge.

In Ireland, a solar water heating system can meet 50-60% of a household’s hot water needs per annum, potentially saving homeowners hundreds of euros on their heating bills.

Because this makes use of renewable energy in place of burning oil or gas boilers, it also helps homes to reduce their carbon footprint.

solar water heating systems take energy from the sun and converts it into heat

How Do Solar Thermal Panels Work?

Solar thermal systems work by trapping heat from sunlight in thermal collectors, and then channel that heat to a hot water cylinder. This is in contrast with burning fossil fuels such as oil or gas to heat a boiler.

The solar thermal panels work via a heat exchanger fluid, which is heated by the sunlight and carries that heat into a domestic hot water cylinder.

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Types of Solar Thermal Panels

There are two main types of dedicated solar thermal panels, Flat Plate Collectors and Evacuated Tube Collectors. Both of these work by pumping a heat exchange fluid in a loop from the rooftop panels to a heat exchanger coil located in the hot water cyclinder.

Active Solar Water Heating Systems

Active solar water heating systems have pumps and control systems to circulate hot water or the solar collectors heating fluid around the system.

  • Direct Circulation Systems pump water directly through the solar collectors array, and then pump the hot water around your house
  • Indirect Circulation Systems make use of a heat transfer fluid in a closed loop which will absorb the sun’s energy, and then uses a heat exchanger to heat the water. This is a more common type of solar hot water system in climates which are prone to freezing temperatures.

Passive Solar Hot Water Systems

A passive solar water heating system doesn’t use pumps to circulate water. Instead all that is needed is energy from the sun to heat water in the solar thermal collectors. Gravity and buoyancy between the different temperature water drives the circulation. These tend to be cheaper and more reliable, but are less efficient than active systems. They are also less suited to areas prone to freezing.

Flat Plate Collectors

Flat plate collectors are composed of a flat metal plate, coated in a material to help it absorb the sun’s heat. It is covered in a glass or plastic cover to protect it, surrounded by insulation to prevent heat loss, and a rigid frame for affixing it to the roof.

Either water or a heat transfer fluid is circulated through pipes underneath the metal plate and down to the hot water tank.

Evacuated Tube Solar Panels

Evacuated tube solar panels consist of glass vacuum tubes which have had the air evacuated from them to minimise the loss of heat. Inside of this is a metal pipe with an aluminium fin known as the absorber, which absorbs and transfers the heat into the fluid contained within the inner pipe.

The heat transfer fluid is then circulated to your hot water storage tank, where it heats the water via a coil.

Flat Plate vs. Evacuated Tubes

Evacuated Tube solar collectors are on average around 30% more efficient than Flat Plate solar thermal panels. This allows them to produce the same amount of hot water with a system that takes up less space, Ideal for homes that don’t have a large area of flat roof space.

A potential downside of using vacuum tubes is the larger amount of glass means that they can potentially be more vulnerable to damage.

Flat Plate solar thermal panels also tend to cost less, and their studier design makes them less likely to be damaged than evacuated tubes. The reduced efficiency can be made up for by installing more solar thermal panels if you have the roof space available.

Overall, Evacuated Tube solar thermal panels have become more popular due to their superior efficiency in retaining heat, an important benefit in lower temperatures which makes them ideal for the Irish climate.

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Augmenting Solar Thermal Panels

During summer months, a solar water heating system could be sufficient to provide you with enough hot water for the day. But in overcast weather, or during the winter when they will be far less efficient, solar thermal panels may not supply enough energy.

When that happens your solar thermal panels will need to be topped up using another system. This is best achieved through either an existing boiler, or with the electric immersion in the hot water cylinder.

Water Heating With Solar PV

Solar PV panels can also be used for hot water through the installation of a solar power diverter in your solar energy system. However, solar PV costs more to installed than solar thermal panels.

The primary purpose of photovoltaic solar panels, as opposed to a solar thermal system, is to generate electricity for use in that home. But that electricity can also be put to use making hot water when you have a surplus of power.

Many Irish homes use the immersion for hot water as a backup to gas and oil heating, but this can prove expensive by using a lot of electricity. A power diverter sends excess electricity generated by solar PV panels to top up a home’s hot water supply.

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What is a solar power diverter?

A solar power diverter, also known as an immersion diverter, monitors the power being used by your home, and when there is surplus electricity being generated by solar panels, diverts that to the immersion heater instead of allowing it to go to waste.

How Much Do Solar Thermal Panels cost?

The cost of a solar thermal system for your home is dependent on numerous factors. The number of panels you will need varies based on how many people are living in your home, how much sunlight you get, the type of panels you choose, and the direction your roof faces.

In addition, in order to qualify for the SEAI grant, you are required to install a system large enough for the average number of people that could live in your house, not the number that currently do.

Solar thermal panels generally cost between €800 and €1,200 per square metre, but that price could be even lower now with changes to VAT for domestic solar.

Solar Thermal Panels Grant

Grant funding is available from the Sustainable Energy Authority of Ireland for different solar water heating systems.

The SEAI grant has a fixed value of €1,200 regardless of the amount or cost of the solar thermal panels being installed.

The grant is open to all homes built and occupied prior to 2021, including private landlords renting out the property.

In order to qualify for the grant the solar thermal system must deliver a certain threshold of renewable energy per square metre of floor space in your home. Therefore, if you have a larger home, or get less sunlight, more solar thermal panels will be needed in order to receive the grant.

solar energy grants

How to Apply for and Manage your Solar Thermal Grant

  • Get a quote from one or more SEAI registered contractors. It’s recommended that you get quotes from at least four different companies.

  • Apply for the solar thermal grant with you chosen contractor, either online through the SEAI website, or by post.
  • Wait for your grant offer before installing any solar thermal panels. Once your grant has been approved you have 30 days to accept the offer before it expires.
  • Have the solar water heating system installed within eight months of accepting the grant offer.
  • Your chosen contractor can now go about installing solar thermal panels on your rooftop.
  • Have a post works BER assessment carried out on your home.
  • Complete the Declaration of Works and Request for Payment paperwork, and submit it to the SEAI by email or post. Your grant should be paid to you within 4 to 6 weeks.
apply for solar grant

You can also apply for the grant through an Energy Partner with the SEAI. The advantage of this is that they will handle the grant application and all paperwork. The grant money is paid directly to them, and they pass that on as a discount for the works.

7 Years

A typical solar installation is fully paid back within 7 years. All solar panels we recommend are under warranty for 25 years, so you will enjoy at least 17 years of free energy generation.

0% VAT

As of 10 May 2023, the government has removed all VAT on solar installation and solar panel supply. This means solar has never been more affordable!

Government Grants

There is a range of government grants available for all new solar installations. Our team will guide you through the application process.

Using Solar Energy for your Hot Water Needs

There are a multitude of financial and environmental reasons why you should make the switch to using solar thermal energy to heat water for your home.

Cutting Energy Bills

A solar water heating system can provide roughly 60% of the hot water used by the average home, and does so at no cost once it has been installed. Hot water makes up a significant portion of fuel bills for your average home, so this can result in significant savings.

Blackout Protection

Having solar water heating panels installed on your home can that you will still have an ample supply of hot water in the event of a power outage.

A passive solar thermal system which doesn’t require pumps or other controls can operate without the need for any electricity.

Reduce your Carbon Footprint

Switching to renewable energy has great potential to reduce a home’s carbon emissions by relying less on oil and gas for heating water.

The average Irish home emitted 3.86 tonnes of CO2 in 2021 from direct fuel use, not including electricity SEAI figures show.

Hot water accounts for a major portion of fuel use in Ireland, and using a solar thermal system in your home can offset a large portion of this.

Legionnaires Disease

In order to protect against Legionella, which causes Legionnaires Disease, it is important to heat the water in your water cylinder to at least 60° for an hour to kill off bacteria.

These temperatures are generally obtainable with solar water heating systems during the summer months. However, during winter you may have have to use an auxiliary system such an immersion heater.

If you have solar panels installed on your home, this would be an ideal use of a power diverter, most of which can be programmed to run a cycle to heat the entire contents of your hot water cylinder automatically.

Solar Water Heater FAQs

The best location for a solar water heating system is on a south facing roof, optimally one at a tilt angle of 30-45° to collect the most sunshine. If you don’t have a south facing roof, the next best option is southeast/southwest. East-West facing roofs are also usable, but you will need a larger system to compensate for less sunlight.

Planning permission is no longer required for homeowners to install a solar water heating system on their rooftop. The limit of 12m² or 50% of total rooftop space which had previously been part of planning regulations has also been lifted.

It remains the rule that solar thermal systems must be set back a minimum of 50cm from the edge of the roof.

Solar thermal panels will need to be topped up by some other heating system, whether a boiler or electric immersion. This is because they cannot meet all a household’s hot water needs, especially in Winter.

A Combi Boiler (Combination) draws water directly from the mains to supply your radiators and appliances. Therefore, if you do not already have a hot water cylinder in your house, then it is unlikely to be compatible with solar water heating. A lot of combi boilers also won’t accept pre heated water.

A power diverter can be an excellent way to further cut down on your energy bills if you have solar PV panels installed by reducing your heating costs as well. However, nowadays that surplus energy can also be sold directly back to the grid. You have to decide which will provide a better financial gain.

Solar thermal panels and solar PV are two different technologies which meet different needs. Solar PV is more expensive, but can also meet other needs than hot water. Solar PV panels can deliver greater savings over the course of their lifespan by reducing electricity bills.

Technically solar thermals panels can be used to help meet the space heating needs of a home, but this is not advised. Using solar thermal for space heating will typically save 1-4% of a household’s energy needs, resulting in a very long payback period.

Sensors installed on solar thermal panels will alert the controller for the system if there is heat available to use. This will then turn on the pump and begin sending heat to the hot water cylinder.

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