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Solar Thermal

  1. What is Solar Thermal?
  2. How Does It Work?
  3. Types of Solar Panels
  4. How does it work?
  5. What are the benefits?
  6. Grants Available?
  7. Frequently Asked Questions about Solar Thermal 

Sol2o offer consultation, design, installation and maintainance for Solar Hot Water systems

For a Solar Hot Water evaluation or a complete energy performance assessment of your property call us now on 0800 2800 020, or click here to register with us.

What is Solar Thermal?

Water heating accounts for approximatley 6% of the total national delivered energy use. Running a boiler with a continously burning pilot light, and un-insulated hot water pipe runs for small quantities of hot water reduces effciency considerably. Solar water heating systems use heat from the sun to work alongside your conventioal water heater.

How Does It Work?

Solar thermal systems create energy by converting daylight, which is absorbed by the panels, into heat. The system then uses this to heat water in an insulated cyclinder. A highly insulated copper pipe connects the panels to the lower heat coil in a sealed circuit. The upper coil connects to the boiler as usual, acting as a back up system. Sensors are installed in the panels and the new cyclinder, which communicate to a digital controller. This turns on a pump when the heat is needed and the solar energy is available, directing heat from the panel to the cyclinder. When the water is heated suffciently the pump is switched off.

Sol2o solar thermal systems use extremly effective insualtion methods to ensure the heat loss is very slow, meaning you still have hot water long after the sun has set. The solar thermal system will typically provide 90% of a familys hot water requirements during the months of April to September and make a very useful contribution during the rest of the year. In a typical year the system will provide up to 70% of a family's annual domestic hot water needs.

Types of Solar Panels

The two main types of collectors that can be used in cold climates are flat plate collectors and evacuated tube collectors.

Flat plate collectors

These can either be integrated into a roof or mounted onto the roof or other structure. They consist of a transparent, glazed, insulated and weatherproofed panel. Flat plate collectors are less expensive and slightly less productive than evacuated tube collectors, but they are a proven technology.

Evacuated tube collectors

These feature parallel rows of transparent glass tubes that each use a partial vacuum to assist with heat transfer. Evacuated tubes are slightly more efficient, however, they are more expensive and more susceptible to breakage.

How does it work?

There are three main components:

Solar Collectors:

These are mounted on the roof or other structure. The surface within the panels is coated with a special material made from aluminium oxide. When light strikes the coating it causes the molecules of the substance to vibrate, this is designed to occur in all types of light conditions as well as in below freezing weather conditions. That vibration causes friction, which produces heat, which is absorbed through the collector. In the collector is a system of pipes filled with a heat transfer fluid.

Solar Circuit:

The heated fluid is now transported through the pipe work that forms a closed heating pipe that connects to a coil in your domestic hot water cylinder. This is managed by means of a digital controller, which is connected to a pump.

Hot Water Cylinder:

The heat transfer system goes straight into the domestic hot water circuit by methods of a second coil in the Hot Water Cylinder. There is a primary coil that is connected to the boiler as a form of back up when solar energy is low or insufficient. The Hot Water Cylinder stores the hot water that heated during the day and supplies it for use later.

Which system is most suitable for your property or project depends on a number of factors that Sol2o will take into account prior to designing a solution, these include:

Suitable Space

Mounted panels range in size, but for the average three to four bedroom house you would ideally need 4m2 for a flat plate collector or 3m2 for an evacuated tube collector.

Orientation of the Panels

Ideally the collector should be on a roof within 45 degrees of South and with a pitch between 30 degrees and 60 degrees to allow it to absorb the most light.


Roofs that are shaded for much of the day or are obstructed may not be suitable for Solar Thermal systems. A solar shading analysis would be done by a Sol2o Green Energy expert to assess the roof's suitability.

Hot Water Cylinders

It is often necessary to install a twin coil hot water cylinders that forms part of the system. These cylinders are generally taller/narrower than single coil cylinders. With this in mind it is important to consider additional space required or alternative locations for the cylinder may need to be located.

Pipe Insulation

It is very important that great attention is given to fully insulating the pipelines within the solar loop to prevent unnecessary heat loss when transporting the heat transfer fluid to the cylinder.

What are the benefits?

Reduce Your Energy Bills

In a domestic installation, a well-designed solar thermal system will provide 100% of a households hot water during the summer months and deliver an annual average contribution of approximately 70%. In winter months Solar Thermal can still contribute significantly to your domestic water requirements.

Reduce Your Impact On The Environment

With almost 40% of all UK carbon emissions coming from 24 million dwellings in the UK there are many opportunities to install solar thermal systems to help reduce these emissions. Fossil fuel use has a particular detrimental effect to the environment as when these fuels are burned, carbon dioxide is released into the atmosphere contributing significantly to global warming. Energy from the sun is environmentally friendly, it's clean and it doesn't pollute. A typical domestic solar thermal system will generate 1500kWh of useful heat per year. This equates to a CO2 reduction of between 325kg and 700kg per year depending upon your current fuel type.

Lower Maintenance And Servicing Costs

The technology used is proven and established. The solar collectors are very durable and have no moving parts and as such there is very little that can go wrong with them. Unlike fossil fuel systems there is no need for regular servicing and maintenance is minimal. This means that the actual running costs are reduced further when compared to fossil fuel systems.

Reduce Your Dependency On Fossil Fuel Imports

The sun is a plentiful and free source of energy and is estimated to be secure for the next 4 billion years. This can provide you with the peace of mind that a significant proportion of your energy is under your control and will not increase in price as a result of foreign government actions or the prevailing economic climate.

Easy To Use As A Fossil Fuel System

A modern solar thermal system dovetails seamlessly into your existing hot water heating system and is self regulating, meaning that when the sun is shining it is silently contributing to your energy requirements without you having to lift a finger.

Grants Available?

Sol2o can offer advice on appropriate grants available to you and help you in the application process.
Government grants are available to help you cover the cost of a Solar Thermal installation. For domestic properties the maximum grant available from the Low Carbon Building Programme is £400, providing you meet the following criteria:

  • Install a minimum of 270mm of loft insulation to meet the current building regulations
  • Have Cavity Wall Insulation (if you have a cavity wall)
  • Install low energy light bulbs in all appropriate light fittings
  • Install basic controls for your heating system, they include a room stat and a programmer or timer.

The rationale for this is that all these measures are more cost effective ways to reduce carbon emissions than simply installing a solar water heating system and should be done first.

For more information on grants please click here

Frequently Asked Questions about Solar Thermal

Will the system still work in very cold weather?

Yes, the system will work in much colder temperatures than we experience in this country. However it will not work if the panel is covered in snow, as this will prevent the light striking the absorber plate. Some of our collectors are fitted to Alpine Hotels where really cold weather is experienced and they work perfectly in conditions of up to minus 30°C.

What should I do if it snows?

Nothing. If snow collects on the glass surface of the collector it will rapidly melt. In fact the design is such that it will melt more rapidly from the collector surface than it will from other parts of the roof.

It is not very sunny today. Will the system work?

Although they work best in direct sunlight, very good performance will be given in the indirect light of a cloudy day.

How much of my hot water will the system provide?

The amount of hot water produced by a solar thermal system will depend upon the weather over the year, but on average the system will provide you with up to 70% of your hot water annually.

Why do I need a new hot water cylinder?

Your present cylinder has only one coil, connected to your boiler, in order for the system to work in conjunction with your existing boiler the cylinder must have two coils. One is connected to the solar collectors the other is connected to your boiler as normal to act as a backup.

How long will it take to pay for itself?

How long the system takes to pay for itself depends on many different factors. The weather, how much water you use and how well the panels are positioned all have an impact on the efficiency of the system so it is impossible to quote an exact payback period but with a life expectancy of over 35 years you can be sure it will pay for itself many times over.

Where is the best place to put the panels?

Your solar collectors should be facing south as we are in the northern hemisphere. An experienced Sol2o surveyor will advise you on the best place to site the panels and due to the design of the panels, they can be mounted horizontally or vertically to best suit the available space.

I have heard that global warming is caused by carbon dioxide and other greenhouse gases. How much of these emissions does my solar hot water system produce?

Your solar hot water system produces no emissions whatsoever. It is entirely without any discharge of greenhouse gases or other pollution. So installing a solar thermal system will help to combat Global Warming and Climate Change.

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