According to a report by NI Energy, solar thermal panels, alternatively known as solar water heating collectors, are one of the most commonly used forms of solar energy in the UK. Further, the report stated that by installing the panels, households across the country could save up to £40 every year on their hot water and energy bills.

So, what are solar thermal panels, and what makes them so popular? In this guide, you will find everything you need to know about solar panels, their installation, their working principle, benefits, and more. Stay glued to our post till the end!

What are Solar Thermal Panels?

A solar thermal panel is not the same as a solar panel. While solar panels utilise the heat from the sun to generate electricity, the process is different in solar thermal technology. Here, sunlight is used to generate heat instead of electricity.

Solar Heating SystemUsually, the heat energy produced by solar thermal panels is used for water heating purposes. In short, this is how solar thermal technologies operate: the thermal panels installed on the rooftops of households function as sunlight collectors. The heat energy thus generated is then used to heat the water. Finally, the heated water is transported for daily use via connected tubes.

While solar thermal collectors are generally used for water heating, they also have other applications. For instance, you will find these collectors functioning as solar parabolic troughs, solar towers, and solar air heaters.

However, in the UK, solar thermal collectors are predominantly used in residential buildings and large households with significant domestic hot water needs.

What are the Different Types of Solar Thermal Systems?

There are two solar thermal systems types dedicated to heating water, and they are as follows:

Flat Plate Collectors

A flat plate collector is usually comprised of four main parts-

  • An enclosure
  • An absorber plate of dark shades
  • A transparent cover
  • Insulation on the front and back surfaces of the solar collector

The absorber plate’s function is to establish fluid circulation passageways. The absorbers can be made of polymers, copper, aluminium or steel. On the other hand, the purpose of the transparent cover is to facilitate optimum penetration of solar energy. To reduce the loss of heat energy, most flat plate collectors make use of a honeycomb structure.

In flat plate collectors, water is the ‘working fluid’. This type of thermal system works well in temperature ranges lower than 100 degrees celsius. The average lifespan of a flat plate collector is pegged at 25 years.

Evacuated Tube Collectors

While evacuated tube collectors, also known as ETCs, are not very common in the UK, they are widely used in other parts of the globe.

An ETC is comprised of the following parts:

Glass evacuated tubes

  • A heat pipe
  • A condenser
  • A collection tube
  • Heat transfer fluid
  • Insulation and aluminium casing

In ETCs, you will find rows of evacuated glass tubes arranged in parallel rows. Moreover, each inner glass tube usually comes with a heat pipe attached to it. By removing the air between two pipes, a vacuum is created. This vacuum is very effective in preventing heat loss. Due to their heat energy transfer efficiency, ETCs can function well in temperatures well above 200 degrees celsius.

Depending on the life span of the vacuum, an evacuated tube collector’s lifespan can last anywhere between 5 to 15 years.

The commonly used solar collectors are through-pass air collectors and unglazed transpired solar collectors for air heating purposes.

How Do Solar Thermal Panel Systems Work?

The working principle remains the same regardless of whether it’s a flat plate collector or an ETC. See for yourself:

  1. Depending on the purpose, the solar panels will be connected to a heater, collector or a boiler
  2. The solar collector will utilise the sunlight to heat transfer fluid. The collector, coated with an anti-freeze substance, will prevent the liquid from getting cold
  3. Once the water is heated, it gets transferred from the collector to a heat exchanger
  4. The heat exchanger then heats the water once again
  5. The heated water gets delivered to households
  6. If there is any unused water, it will be circulated back to the collectors for reheating
  7. The process is then repeated cyclically

What are the Components Found in a Solar Water Heating System?

Solar Water Heating SystemA solar water heating system’s structure is slightly different from the flat plate or tube collectors. Here are the components that play a significant role in the overall functioning of a solar water heating system:

  • Solar Thermal Panels: Usually, these panels are fixed on the roof or the ground
  • Heat Transfer Fluid: Like the two types of collectors, even a solar water heating system uses a heat transfer fluid
  • Heat Exchanger Coil: The dual coil plays a significant role, as it allows the heating system to provide extra hot water when required
  • Pump: The pump’s function is to circulate the transfer fluid from the panels to the cylinder
  • Piping: The flow piping and the return piping are involved in maintaining insulation between the panels
  • Control Panel: Displays all the information related to the water heating system’s performance
  • Heat Flow Generation Meter: This measures the overall output of the system. The reading can then be used to claim renewable heat incentive payments.

What is a Renewable Heat Incentive (RHI)?

The RHI is a scheme by the UK government that was introduced to promote a switch to renewable heat energy sources. This scheme explicitly targets households and businesses and provides them with incentives to switch to renewable energy.

Currently, the RHI is paid every quarter, with payments spread across seven years. The incentive rate is fixed at 20.66p/kWh for energy generated by solar thermal panels and solar water heating systems.

How to Install a Solar Thermal System?

The installation of solar thermal systems involves elaborate steps and procedures:

Before Installation

  • In the UK, it is recommended that all households, before the installation, need to get their property inspected by personnel with MCS accreditation
  • Ideally, your property will be inspected for the roof’s orientation, inclination and other related factors
  • Depending on their findings, the surveyors will give you an estimate of the output of energy you can expect after installing solar thermal systems
  • Likewise, the surveyor will also try to determine the domestic water needs of your household

Solar Thermal Collector

  • The collector frames will be installed on the flat roof using stainless steel brackets
  • The brackets will be fixed directly to the roof to create a tight structure
  • The tiles of your roof might have to be removed but will be replaced once the solar thermal installation is complete
  • If you have opted for an ETS, a transfer unit will be juxtaposed atop the frames

Hot Water Cylinder

  • A dual coil water cylinder will be installed first, followed by a pump and system control panel
  • The installers will then install a hot water tank, required for solar energy storage purposes
  • The tank will be connected to various equipment like cold water mains, auxiliary heating, immersion heater, temperature sensors and an expansion vessel

Solar Thermal System Plumbing

  • The installers will first put in place a pumping station for the pump to be fixed
  • As a preventive measure, an expansion tank will be fitted in to monitor pressure changes
  • Insulated pipes will go in next, creating the flow and returning piping channel for the transfer fluid
  • The installers will ensure that there is enough distance between all the plumbing components

Controls and Display System

  • Finally, the solar thermal system’s display components will be setup
  • The installer will begin by fitting a heat generation meter, essential for RHI
  • An automatic control equipment will also be installed

Pumping of Transfer Liquid

  • As a final step, the installer will pump the transfer and anti-freeze liquid into the fully assembled solar thermal heating system
  • The liquid will be subjected to pressure, according to specifications

If you want to be eligible for RHI, there will be an extra step involved. Your installer will register your household’s solar thermal system with the MCS. You will be provided with all the necessary documentation to apply for the RHI.

In some cases, you might need to acquire planning permission before installing solar heating systems.

Planning Permission and When It’s Needed

Solar HeatingIn most cases, domestic and residential solar water heating systems can be installed without planning permission. However, permission will be required in the following cases:

  • If the panels are installed on the walls of a building containing flats
  • If the panels protrude from the edges of a flat roof
  • If the panels project upwards, i.e. if their height exceeds the limit
  • If the house or building is situated at a World Heritage Site
  • Solar panels should be installed without compromising the aesthetics of the building

What are the Benefits of a Solar Thermal System?

There are many benefits of installing a solar thermal system, and they include:

  • Less space: To install solar heating systems, you require less space, making it a convenient option for many households
  • Simple: The technology and processes involved are straightforward. As a result, the system is easy to understand and operate
  • Limitless Energy: Since solar energy is renewable and available in abundance, there’s no limit to the amount of energy that a solar thermal system can generate
  • Seamless Integration: Solar thermal systems can be easily paired with existing power sources
  • Increased Savings: It is a lot cheaper to heat water using a solar water heating system, leading to considerable savings in the electricity bills
  • Year-round Power Supply: With advancements in solar technologies, most solar thermal systems can work efficiently during the winter months as well, powering households and commercial establishments throughout the year
  • Environment Friendly: By using a renewable energy source for heating water and power generation, there’s no fuss about using fossil fuels
  • Reduced Carbon Footprint: With solar heating technologies, there are no instances of CO2 emissions. Besides, a solar hot water cylinder significantly contributes towards reducing the carbon footprint too. It is estimated that, on average, a UK household can reduce their carbon emissions by over 400 kg each year.

What are the Disadvantages of a Solar Thermal System?

Nonetheless, there are a couple of disadvantages of solar thermal systems that you need to consider:

  • Weather-dependent: Poor local weather conditions can hamper the hot water supply in households. During the winter months, the solar water heating cylinder’s efficiency will be reduced
  • Singular Function: If you opt for thermal systems meant exclusively for water heating, that’s the only function it can perform. This singularity can be a dampener for many
  • Costs: It can take up to 20 years or so to see visible returns on investment. Nevertheless, schemes like the RHI make up for the long payback period
  • Expensive and Long-drawn Installation: The installation process takes time, and the cost is also high
  • Limited Availability of Installers: It’s hard to find installers for water heating systems that are solar-powered in the UK
  • Limited Storage Capacity: While all solar water heating systems do come with storage facilities, the hot water cannot be stored for long

Solar PV Panels vs Thermal Heating Systems

Many find it hard to wrap their head around the difference between solar PV panels and thermal heating systems. However, the differences are distinct and cannot be ignored:

  • Technology: Solar PV panels’ working principle is driven by the photovoltaic effect, while in a solar water heating cylinder, sunlight is used directly to heat the water
  • Complexity: In solar panels, the energy conversion process is rather complicated when compared with the procedures in a solar immersion heater or other thermal energy appliances
  • Use: While households use solar PV panels mainly for electricity generation, solar heating systems are used for domestic and industrial hot water supply and storage
  • Design: In terms of design and build, solar PV panels have a more straightforward structure and assembly procedure than solar heating systems
  • Lifespan: Domestic solar PV systems last longer than their thermal counterparts

Solar Thermal Systems and Energy Bills: The Equation

Solar ThermalHow much could a household in the UK save by installing a solar system? Here is what to expect.

To begin with, the savings will be directly influenced by daily hot water usage. Further, your savings will also depend, to a considerable extent, on the existing energy system you have installed.

However, it is estimated that a solar thermal system installation can save a household around £50 in a gas system, £55 in an oil system, £65 in a coal system, and £95 in an LPG system per year. Now, that’s a lot of savings in a year.

How to Choose the Right Type of Heating System?

While solar heating systems can be classified depending on the collector type they use, another classification is also possible. Here, the systems are classified according to how they make use of the collectors. They are as follows:

  • Active: In this type, you’ll need electricity to power the pumps
  • Passive: Passive systems usually make use of natural heating methods, like convection, to get the job done
  • Direct: The water is heated directly in the collector
  • Indirect: A two-step process is involved here. First, the transfer liquid is heated in the collector, and then the heat is automatically transferred to the water
  • While choosing a heating system for your household, keep in mind the two classifications: the collector type and how it’s being used.

Things to Keep in Mind Before Installing a Thermal System

If you are planning to install a thermal system, it will help if you ensure the availability of three things: a spot that receives plenty of sunshine, sufficient space, and a boiler. A sunshine spot is essential, as thermal power generation relies heavily on the availability of the sun’s energy.

Similarly, thermal systems require space for installation and maintenance. Moreover, the solar cylinder that’s a prerequisite will also take up some space.

At times, the existing boiler at home might not be compatible with a thermal system. In this case, you will need to get a new one installed, along with the system.

Wrapping Up

Solar thermal power generation systems bring a host of benefits to the table. With the UK government introducing the RHI scheme, many households and commercial establishments have started switching to solar thermal heating systems. There are different solar thermal systems, depending on the collector type and how it is being used.

A unique working mechanism powers them. In keeping with the same, every solar water heating system comes with a set of components that play a crucial role in daily functioning and operation. The installation of a thermal system is often elaborate and involves steps like plumbing and pumping of thermal transfer liquid.

The RHI scheme is a benefit that all UK households can take advantage of upon switching to a thermal system. While there are downsides to solar systems, they still hold an edge over solar PV panels. Upon choosing the system that’s a right fit for your household, you can save a lot on your energy bills. To read more about solar thermal systems, please reach out to us.