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Solar Thermal and Solar Collector installation FAQ

Q: How does a solar thermal system work?

  • A solar thermal system consists of; a solar collector, a pump station, a solar controller and an indirect hot water storage tank.
  • The solar collector collects the sun energy and transfers the heat to the storage tank via the tanks internal heat exchanger. The storage tank allows the hot water to be stored until it is used
  • The storage tank acts as a pre-heat tank for the existing hot water tank. As hot water is being drawn from the existing tank, hot water from the pre-heat tank replaces it.

Q: What is the life expectancy of a solar thermal system?
A: The life expectancy of a solar system is between 20 and 30 years. If a solar thermal system receives regular maintenance checks, they can last over 30 years. Although very little maintenance is required, it is recommended that a service contract be made with your solar installer.

Q: What is the payback period on a domestic solar installation?
This is the most frequently asked question by any customer considering any renewable technology. What they want to know is how long will it take to repay their capital investment based on the energy savings that a system will offer them. Inevitably this is not a simple question with a straightforward answer.
Talking to most customers, they seem reasonably satisfied if they can achieve a payback period in less than 10 years. The simplest way to calulate payback (ignoring the effects of interest rates) you will need to understand how much energy the system you are installing will save the customer in unburned fuel and a prediction of future energy price inflation. Of course we can't know exactly what energy is going to cost in the future, but a reasonable forecasting method would allow for a spread of constant annual increases at various percentages from 5%-30%.
Of course the simplest way to enhance the payback period is to be able to offer systems at a competitive and affordable price to everyone.

Q: Can a solar water heating system be used in place of a traditional gas or electric hot water system?
In order to ensure proper efficiency of your water heating system, a solar energy system must be used in conjunction with a traditional gas or electric hot water system rather than as an alternative.

Q: Is solar thermal suitable for my home?
A: The more hot water that you use, the greater the potential savings.  A family with typical hot water use will really make the most of the installation.  However, a very cost effective single panel type installation can serve a home with lower demand too.

Q: Can I combine solar thermal and an air source heat pump?
A: Yes. The ultimate low fuel cost system has both solar panels and air source. The air source heat pump will only come on if it needs to 'top up' the solar heat, so the system is very cheap to run.

Q: Do solar systems produce hot water in the winter?
Yes, but the amount produced will be less than in sunny summer months. Similarly, on cloudy days, solar thermal systems will still produce hot water, but less than when sunny.

Q: Can I use a solar collector with my existing hot water system?
A: Yes, but typically a 2nd hot water tank, or a larger replacement tank will be sensible. In most cases a 2nd heating coil is required in the tank. 

Q: How much hot water will Solar Thermal supply?
A: Solar Thermal systems are capable of producing 100% of your hot water requirements on an annual basis. A lower-cost and ideally-sized Solar Thermal system would supply 100% of your hot water during the summer months and a significant proportion during the winter.

Q: How safe is the Solar Thermal system?
A: It is totally safe.

  • The collectors continue to operate efficiently at temperatures far below freezing.
  • The only material in contact with the water is copper which is non-toxic.

Q: What can a Solar Thermal system be used for?
A: Solar Thermal systems have been chosen for a wide variety of domestic and commercial applications. These installations range from domestic hot water systems, space heating, pools and spas, 

Q: What about maintenance?
A: No collector maintenance is required. The glass tubes are round and perfectly smooth; any dirt or dust is carried away by the wind and rain. There are no moving parts to wear out. All components are made from high grade stainless steel, copper or non-corrosive materials.

Q: What is the difference between flat panels and the glass tube type collectors on the roof?
A: They both do the same job of heating the water, but the tubes are more efficient in low sun conditions.  Some people choose flat panel collectors based on the looks.

Q: Is the Solar Thermal Collector a proven product?
A: There are over two million tubes in every-day use in over thirty thousand locations worldwide. 

Q: Which type of panels/collectors are best, flat panel or evacuated tube?
A: The jury is still out with this question. Evacuated tube are easier to install they are better insulated and so lose less heat they are; better at absorbing solar radiation at different angles to the sun they are easier to clean with less maintenance
Flat plate collectors are typically cheaper, and some may perform better on cloudy days

Q: What is a Closed System?
A: A Closed System is one where the liquid warmed in the collector is used to warm the hot water tank via a heat exchanger or coil in the tank. An Open System directly heats the hot water, and are more common in warmer climates where freezing conditions are not common.
Solar thermal is one of the most cost-effective renewable energy systems. Solar thermal water heating systems collect the sun's energy in the form of thermal or heat energy. The system can save a major portion of your utility bill.

Q: How many solar thermal panels would I need to heat water for my home?
A: You can get the best answer to this by contacting a solar thermal dealer. This will depend on how many people in your household, on how much hot water you use and how much sunlight you receive.
However: a typical family of four might require four square meters, and we can roughly guess that a square meter per person is a fairly accurate estimate. But don't hold us to that!

Q: How does the conversion of solar energy to heat in a glycol-based system work?
A: Solar radiation hits the absorber (solar thermal panel) and is then transmitted to the heat transfer medium (glycol, usually) and converted to heat. The vacuum plus the insulation provided by layers of the absorber assure that heat remains in the solar thermal system.
Solar thermal systems with glycol use a composite tube that is made up of a jacket tube and absorber tube. Since these are made completely of glass, they are well-protected against degradation. 

Q: What are the benefits of a solar thermal system?

  • You can produce up to 70% of your annual hot water requirements
  • Reduce & future proof your fuel bills – sunlight is free so once you have paid for the initial installation your bills for producing hot water will be significantly reduced for the lifetime of the system (around 25 years)
  • Cut your carbon footprint – solar hot water uses the renewable resource of the sun and does not release any harmful carbon dioxide or other pollutants (other than from using a very small amount of electricity for powering the pump)

Q: How does a solar thermal system integrate with my existing heating system?
A: In the UK a solar thermal system can never be the sole provider of hot water as there is insufficient sunshine in the winter months to heat water to the required temperature and you therefore need to have a conventional water heating system as well,. . You can add a solar thermal system to most existing hot water systems, although you will usually have to change your existing hot water cylinder to a twin coil cylinder system or, as an alternative, add an additional water cylinder to pre-heat the water from the solar system to feed into the original cylinder. You will also need a pump to circulate the water around the solar system and some regulating equipment to prevent overheating.

Q: Will a solar thermal system work with a combi boiler?
A: Combi boilers take water direct from the mains and provide instantaneous water and heating without the need for a hot water storage cylinder and most combi boilers are not designed to take pre-heated water from a solar system. Connecting a solar system, although not impossible, can present some problems and it is always recommended that the you check with the manufacturer of the combi boiler to establish if it can be used with a solar thermal system. Generally there will be an increase in cost for installing a solar hot water system with a combi boiler.  All solar systems require a hot water storage cylinder

Q: Why use solar technology?
A: It is widely accepted that the increase in so-called greenhouse gases, such as carbon dioxide (CO2), from the burning of fossil fuels, is having a major impact upon the planet’s climate and there is now a growing imperative to reduce our dependence on fossil fuels and the amount of carbon dioxide within the Earth’s atmosphere. A solar thermal system collects heat from the power of the sun producing no CO2 emissions and this is used to heat water stored in a hot water cylinder. A solar photovoltaic system produces purely clean energy from the power of the sun with no CO2 emissions and can transform a building from being an energy consumer into one that is an energy generator.

Q: What is the difference between solar thermal and solar power (i.e. solar PV)?
A: Solar thermal uses the heat of the sun to warm a liquid that flows through solar collectors (usually situated on the roof) which in turn heats water in a storage cylinder producing hot water at the taps or for a shower. Solar power (PV) uses solar cells to convert the energy from the sun into electricity to power electrical appliances within a building or to be exported to the national grid.

Q: Where is the best place to install the solar collectors (i.e. panels/tubes)?
Ideally the collectors should be south facing, usually on the roof of a dwelling or they can be mounted on a frame attached to a wall of a dwelling or even ground mounted.  However, there is a good deal of tolerance with solar thermal systems and their efficiency will only decrease by a small amount if the collectors face anywhere between south east and south west. If you only have east and west facing roofs, collectors can still be installed on each of these roofs but costs will increase as you will require more collectors than would be the case on a south facing roof.  North facing roofs are not acceptable for solar thermal systems.

Q: How much space is required for the solar thermal collectors and can I still use my loft?
A good rule of thumb is that, for each occupant of the household, approximately 1m2 of solar collector is required.  Therefore, for the average family, the solar thermal collectors will require 3-4m2 of roof space   (NB  usually sited on the roof but can be wall or ground mounted).  Although pipework from the collectors will normally have to run through the loft space, this will not prevent you using your loft.

Q: Do I need a new hot water cylinder to install solar thermal, and if so, how big does it need to be?
In the majority of solar thermal installations the existing hot water cylinder (where the heating is from a conventional boiler or possibly an immersion heater) is replaced with a new twin-coil cylinder so that the water it contains can be heated by the solar system and by the conventional boiler when that is required as a back-up (e.g. in the winter months).  The twin-coil cylinders are generally taller than a normal cylinder so you will need to have sufficient space (usually in an airing cupboard) to house it.  An alternative is to fit a new ‘pre-heat’ dedicated solar cylinder alongside the existing cylinder though this will require more space and is also considered to be slightly less efficient than using just one cylinder

Q: Is planning permission required to install a solar thermal system?
A: Most domestic properties do not require planning permission provided the solar collectors do not project more than 200mm above the surface of the roof covering and do not project above the ridge of the roof. However, you may need permission if the panels are of an unusual design, they project significantly beyond the roof slope, or your house is a listed building or is situated in a National Park, an Area of Outstanding Natural Beauty or in a conservation area.

Q: Who will install the system?
We recommend you only use fully MCS (Microgeneration Certification Scheme) accredited installers for the installation of solar thermal and solar PV systems. The Microgeneration Certification Scheme is an independent scheme that certifies microgeneration products and installers in accordance with consistent standards and is designed to evaluate microgeneration products and installers against robust criteria providing greater protection for consumers. An MCS approved installer must be used in order for the householder to qualify for the government grant.  

A: The RHI is similar to Feed-in Tariffs, which have done more than anything else to accelerate the installation of renewable energy capacity in Europem. in April 2011 the Renewable Heat Incentive will come into force.

  • You may earn a regulated income from every kilowatt hour of heat produced
  • The Tariff level is set by the government - based on technology and size
  • All renewable heat qualifies for Household and business users,No maximum size.
  • It is planned that Solar thermal will earn around 6p for every kilowatt of heat produced.
  • All income will be tax exempt.

Q: How does the reduced 5% VAT rate for solar installations work?
A: There are three requirements in order to offer your customers the reduced 5% VAT rate on solar installations:

  • Your business will need to be VAT registered
  • The equipment that you are installing should be to heat a domestic system
  • You have supplied and installed all of the equipment
  • Check with HMRC or your Accountant if you are uncertain when to apply the reduced rate.

For print friendly version, you can download a copy of Solar Thermal and Evacuated Panel FAQ document.

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