What are the pros and cons of this renewable energy source for heating hot water in your home?

What is solar thermal?

Solar thermal heating systems use free sunlight to heat domestic hot water. On average, these systems can produce between 40% and 70% of hot water needed by a family of four, replacing a conventional boiler or electric immersion heater.

But is solar water heating suitable for your home? We take a closer look at the pros and cons.

How does it work?

Solar thermal technology is different to solar PV (photovoltaic). As the name suggest, solar thermal panels harness the free natural energy provided by the sun and use it to warm water. Solar PV, on the other hand, converts the sun’s rays into electricity.

Solar thermal systems work by collecting energy from the sun with solar panels, also known as collectors, on the roof of your property. These panels contain tubes of fluid (a mixture of water and anti-freeze) which absorb heat from the sun’s energy. The heated fluid is then pumped to a heat exchanger in your home’s water tank and heats the water stored within it. After the heat has been released from the fluid mixture, it is then pumped back to the collectors for reheating.

A conventional boiler or immersion heater can be used as a back-up heater to top up hot water on colder, cloudy days.

Types of solar thermal

There are two types of solar water heating panels:

The flat panel – also known as a flat plate collector, is the most common type and can be fixed on roof tiles. They look very much like solar PV panels.

Evacuated tubes – a series of glass tubes joined in a parallel row to form a panel and mounted on a roof. They are often considered the most energy efficient.

What are the costs?

Expect to pay between £3,000-£7,000, including VAT. This figure includes installation cost and parts (solar collectors, hot water tank, control panel and pipes). The price will vary with the size and type of system required for the hot water demands of your home, quality of panels and who you pay to do the job. If scaffolding is required, the cost could be considerably higher. A general rule of thumb is you need 1m2 for each person living in the building. Solar thermal collectors are round 2 to 3m2, so for a typical four-person household, you will need two collectors. The average person uses around 50 litres of hot water per day, so an average family will require a 200-litre water cylinder.

Is planning permission required?

In most cases, you don’t need planning permission for solar thermal panels on the roof as they are allowed under permitted rights. The exceptions are if you live in a conservation area or your home is a listed building. It’s always best to check with your local planning authority.

Pros of Solar thermal heating

Reduced energy bills

Your hot water costs will be lower - sunlight is free. While you’re likely to still need your boiler as back-up, the solar thermal panels will still generate some heat in cloudy and overcast weather, so the boiler won’t need to work so hard.

Typical savings from a well-installed and properly used system are around £55 per year when replacing gas heating and £95 per when replacing electric immersion heating, according to the Renewable Energy Hub. Some suppliers reckon you can save up to 60% on your domestic hot water energy costs.

Savings will vary depending on the energy source you are replacing, your property’s energy efficiency, geographical location and solar resource.

Earn money with the Renewable Heating Incentive

You can earn money through the UK Government’s Renewable Heat Incentive (RHI) for every unit of energy generated by your solar thermal system. The cash bonus is to boost take-up of renewable heating systems and reduce use of fossil fuels, like oil, gas and oil, and to cut the country’s carbon emissions. Homeowners receive RHI payments on a quarterly basis for seven years after installation. To be eligible, your solar water heating system needs to meet certain criteria. For more details and to work out potential earnings see: https://www.gov.uk/domestic-renewable-heat-incentive

Lower carbon footprint

As a green, renewable heating system, solar thermal can cut your home’s carbon dioxide emissions as you will be burning less fossil fuel. So, you will be doing your bit to save the planet.  An average household could save 260kgCO2/year by reducing use of a gas boiler, according to the Energy Savings Trust.

For homeowners with a planning condition on a building project that requires a percentage of your energy to come from renewables, solar thermal can be a solution.

Low maintenance

Most solar heating systems need little maintenance and are covered by a five-year or ten-year guarantee. Once the system is up and running, it needs servicing by an accredited installer around every 3-5 years. For peace of mind, some installers offer an annual service check. You may also find your boiler will last longer and need fewer repairs as it won’t be working so hard.

Cons of solar heating

Limited heating system

Solar thermal systems are for heating hot water only and seldom suitable for central heating. And while solar thermal will generate some heat in cloudy weather, they are most effective in sunny summer months, so it can be a variable. A solar thermal system won’t power cold-fill washing machines/dishwashers or power electric showers.

High upfront cost

A major obstacle for many is be the high upfront cost of installing a solar thermal system of between £3,000 and £7,000. This is offset by reduced heating bills and RHI payments, but it could be many years before you break even. Payback will vary with the amount of hot water that is used and the cost of fuel that you are replacing.

Not compatible with all heating systems

For the best use of solar thermal, a hot water tank is required. Solar thermal systems are often not compatible with combi boilers which are fed water directly from the mains and heat water on demand. Combi boilers don’t require a hot water cylinder.

The bigger the hot water tank, the more of your solar-generated hot water you will be able to store. Check with the manufacturer if your regular heating system is compatible with solar thermal.

Not suitable for all homes

Similar to solar PV panels, solar thermal panels work best on south-facing roofs. You will need at least five square metres of roof space with as much exposure to direct sunlight as possible - any shade will reduce effectiveness. The panels need to be angled at a 20 to 50 degrees pitch from the horizontal. In some cases, the panels can be fixed to a wall or mounted on the ground and orientated south for optimal performance.

Is solar water heating right for your home?

The financial payback on these systems is not great though the carbon savings can be considerable. However, a solar thermal system can be integrated into your home extension or conversion. For example, you may already be installing a new hot water cylinder to upgrade your heating and hot water system. What’s more, scaffolding may already be on site, which could further reduce the installation costs. If after weighing up the pros and cons, you decide solar thermal is right for your home, it’s a good idea to get multiple quotes for installation.    

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