A solar thermal system uses the energy from the sun to heat up water to use in the home. The way a solar thermal panel works is quite simple: it absorbs the heat from the sun with panels that are called solar collectors.
The heated water or heat-transfer fluid then runs from the collectors to your hot water cylinder. This way a solar water heating system can provide your home with free heated water.
Solar thermal panels are not to be confused with solar panels, which use the energy from the sun to generate electricity. As such, solar panels and solar thermals are two very different technologies.
Using solar energy has many advantages, among them the money saved on energy bills, the reduction of your carbon footprint and the low maintenance, making solar thermal a great investment.
When you choose to purchase a solar thermal, the costs of installing will vary between £4,000-5,000 (including VAT of 5% for a 3.6m2 system). Even though this sounds like a significant investment, the system can provide a fair amount of hot water throughout the year.
Luckily, to cover the costs of switching to this renewable energy system, the government compensates you for using renewable energy from a solar water heating system. This is called the Domestic Renewable Heating Incentive (RHI) and is paid over 7 years based on the amount of heat produced by your heating system.
An average detached house in the UK would receive the following support from the Renewable Heating Incentive:
| Household Size | Per Quarter | Per Year | 7 Years |
| Detached House | |||
| 2-person household - (2 bedrooms) | £43 | £170 | £1,190 |
| 3-person household - (2 bedrooms) | £45 | £180 | £1,260 |
| 4-person household - (3 bedrooms) | £48 | £190 | £1,330 |
The tariff is 20.66 pence/kWh for every application sent in before 1st of January 2019.
Next to that, you will also save money on your bill by using solar energy. How much you will save in costs depends on what system you have currently installed in your home.
| Existing System Gas | Oil | Coal | Electricity | LPG | |
| Fuel Bill Savings per Year | £50 | £55 | £65 | £80 | £95 |
An average solar thermal system in the UK covers around 40%-60% of the total hot water consumption of a household throughout the year. This includes hot water for showers, hot taps, etc. The specific amount of hot water that is produced depends on the time of year.
During the summer, the solar thermal panel can produce most or all of the hot water demand.
In the spring and autumn, by pre-heating the water in your cylinder, your solar thermal can reduce the amount of energy needed to heat your water.
Winter is a more problematic season for solar thermal panels because the sunlight is weaker and days are shorter. The solar thermal will make a smaller contribution to your water heating.
The solar thermal technology is designed in a way that the heated water is stored in a separate tank for preheating or a regular water tank until you need it. Even if additional heat is needed, the regular water heating system jumps in and provides the extra heat through electricity or fossil-fuel energy.
All solar thermal panels use solar collectors to absorb solar energy. There are 4 general types of solar water heating systems that differ in the way they use the solar collectors:
Active: electric power is needed to activate pumps.
Passive: relies on natural convection rather than electricity to circulate the hot water.
Direct: the potable water is heated in the collector.
Indirect: the transfer fluid is heated in the collector and transfers the heat to potable water.
Solar thermal systems can also be categorised based on the type of collectors:
A flat plate panel looks like a panel similar in a photovoltaic system. Its design includes an absorber panel attached to multiple copper pipes through which the water or transfer fluid passes. These copper pipes are encased in a metal frame that is surrounded by insulation to support the retainment of the collected heat. A sheet of glass or glazing protects this frame, which, at the same time, provides a space of air that works as insulation.
In comparison to flat plate panels, evacuated tube collectors are more efficient, especially in cold climates. On the downside, they lose efficiency in warmer seasons due to the risk of overheating. This is due to the vacuum tubes that are designed to avoid heat loss and therefore differ to flat plate panels that tend to lose some heat.
Evacuated tube collector is usually made of a heat pipe surrounded by a glass tube. These are under a vacuum. Having something under vacuum is a better heat retention than air space. In addition, the heat pipe is pressurised, which allows the fluid to boil rapidly.
In general, you need about 1m2 of solar collector area per person.
An average flat plate solar collector is sized between 2m2-4m2. This means you need between 1 or 2 of these collectors depending on the size of your households.
When you use an evacuated tube collector, you might need between 20-30 tubes to meet your hot water demand.
Even though, the advantages of solar PV panels are clear, the benefits of solar thermal panels are worth mentioning too.
Renewable Energy Source The most important benefit is that solar energy is a 100% renewable energy source. We will always have solar energy.
In the long run, it will save you a significant of money.
An average UK household can reduce their CO2 emissions up to 400 kg per year.
Solar thermal panels require little maintenance and only occasional planned servicing. You only have to keep them relatively clean. The only part that needs to be replaced is the inverter that works continuously to generate heat, which usually lasts for 5-10 years.
The cost of purchasing a solar thermal system is quite high, but it will be profitable in the long-run. You will also be eligible for the Renewable Heat Incentive (RHI) which supports you with yearly payments.
The summer is the best time to generate heated water. Nevertheless, a solar thermal can generate 40%-60% of your heated water throughout the year.
It needs both enough space and enough sunlight for it to cover your heat demand. Some homes don’t have the amount of space required. A solution in this case is to place them in the yard, as long as they catch enough sunlight.
It can only heat water but not to heat rooms or generate electricity. Yet, an average person uses between 90-160 litres of hot water a day which can be covered with an appropriately sized solar thermal system.
