FAQ´s

Q. Why use solar technology?

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)?

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. What is a solar hot water system (i.e. solar thermal) & how does it work?

Solar water heating or solar thermal uses the radiation from the sun to heat a liquid (usually a mixture of water, antifreeze & a corrosion inhibitor) that flows through a solar collector, often sited on the roof of a building, which in turn heats water contained within a storage cylinder via a heat exchanger for use at the taps/shower etc within a building.  A solar hot water system does not produce electricity.  A conventional boiler or immersion heater is generally used as a back up to heat water within the hot water cylinder in order to reach the temperature set by the cylinder’s thermostat when the solar system is unable to heat water to that required temperature (for instance, during winter months).

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

•    Produce up to 70% of your annual hot water requirements from the power of the sun (up to 100% in the summer months, approx 15-20% in the winter months)

•    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. What are the components of a solar thermal system?

A solar hot water system includes the collectors (either flat plate or evacuated tubes), a new hot water cylinder (either to replace an existing cylinder or to be coupled with an existing cylinder) and control system as well as all the pipe work and connection with your boiler. 

Q. What is the difference between flat plate and evacuated tube panels?

The main component of a solar water heating system is the collector (often referred to as a solar panel) and its function is to collect the heat from the sun and transfer it to a fluid in the collector which in turn transfers it to the water in a hot water cylinder. In the UK the type of collectors fall into two main categories  – flat plate or evacuated tubes. Although there are variations available for each type of collector, the way they work is very similar. However, flat plate collectors can be either fixed onto the existing roof covering (slates/tiles etc) or integrated into the roof itself, whereas evacuated tubes must always be fixed onto the existing roof. Evacuated tubes are often considered to be slightly more efficient than flat plate collectors because the vacuum within the tube provides additional protection against heat loss. They are therefore generally more expensive than flat plates. This efficiency difference can be easily compensated for however, by installing a slightly larger array of flat plates. In essence, at the operating temperatures of the domestic hot water system, both types of panel can be considered to have similar efficiencies.

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. How does a solar thermal system integrate with my existing heating system?

In the UK a solar thermal system can never be the sole provider of hot water as there is simply 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, such as a gas, oil or wood fired boiler (or even just a back-boiler on a wood stove).  This is required to top up the heat from the solar system when necessary and to provide hot water and space heating in the winter. 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 (to allow for water heating from the solar system and from the conventional boiler) 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?

Combi boilers take water direct from the mains and provide instantaneous water and space 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 householder checks 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. 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. Do I need to have a new boiler for the installation of my solar thermal system?

This is purely dependent on the age and condition of your existing boiler and, in most cases, a new boiler is not required. However, if the boiler is old, it is likely that it will not be working very efficiently and a replacement with a modern efficient boiler would be recommended.  In any case you will need to have modern thermostatic and timer controls for the boiler in order to qualify for the government grant.

Q. How much will a solar thermal system cost?

The installed costs of a solar hot water system will depend on a number of factors, especially the size of the system installed (i.e. the collectors), the type of collectors used (i.e. flat plate or evacuated tubes) and the size of the new hot water cylinder. It should also be noted that most installations will require scaffolding to access the roof. A typical system for an average family will be in the region of £4,000- £6,000 depending on the factors mentioned above.

Q. Can I get a grant for installing a solar thermal system?

Yes, currently there is a grant of £400 available through the government’s Low Carbon Building Programme.  However, in order to qualify for the grant, you must have installed certain energy efficiency measures into your home. This ensures that energy use is minimised prior to installing solar thermal, to enable the most efficient use of the technology.  The measures required are loft insulation, to meet current building regulations e.g. 270mm (approx 11”) of mineral wool or suitable alternative, cavity wall insulation (if you have cavity walls),low energy light bulbs in all appropriate light fittings and basic controls for your heating system to include a room thermostat and a programmer or timer.

Q. How much money will a solar thermal system save?

This is dependent on a number of factors, especially the size of the system installed and the type of fuel that traditionally heated your water but savings can be up to £170 per year.

Q. Is planning permission required to install a solar thermal system?

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 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.  See the following website for further information http://www.microgenerationcertification.org

Q. How long does it take to install a solar thermal system?

Depending on the size and type of system and the number of people employed, the installation can take between 1 and 3 days to complete.

Q. How long will the solar thermal system last and what are the guarantee periods?

The expected lifetime of a solar thermal system is at least 20-25 years. All solar collectors are guaranteed for 10 years, cylinders for 5 years and all other parts and labour for 2 years.

Q. What maintenance is required to the solar thermal system?

A well installed solar thermal system should only require servicing by an accredited installer at 3-5 year intervals although it may be advisable to couple this on a more regular basis with the general servicing requirements of your boiler. During the lifetime of the system (approx 25 years) it is possible that some minor components may need to be replaced (e.g. the pump) but these are not of significant cost.

Q. Can I use a solar thermal system to provide space heating for my home?

There is five times more energy from the sun in the warmest months of summer than in the coldest months of winter and therefore there is a problem that the vast majority of the energy received is during the period April to September, not during the winter months when it may be required for space heating. To provide any useful contribution to space heating when it is most required in the winter, the solar collectors would have to be massively oversized and this would simply be impractical on a cost basis.

Q. Will a solar thermal system work in the UK, and will it work during the winter?

Many parts of the UK have annual solar radiation levels equal to 60% of those experienced at the equator, and this means a solar thermal system in the UK can produce up to 70% of the annual hot water requirements for an average household. Most of the sun’s radiation will be received over the period of April – September when a solar thermal system can produce up to 100% of the hot water required within a household, but a system can still provide some useful hot water even on overcast days during the winter months.

Q. What are photovoltaics (solar electricity), or ´PV´?

First used in about 1890, the word has two parts: ‘photo’ derived from the Greek phos, which means light, and ‘volt’, a unit of measurement named after Alessandro Volta who was a pioneer in the study of electricity.  So, photovoltaic could literally be translated as light-electricity.

Q. How does solar PV work?

Solar PV generates electricity from daylight. The more light that shines on the PV panels the more electricity they produce. An inverter converts the electricity from direct to alternating current, for use in the home. When the solar energy system is producing more power than is needed within the home it is exported to the grid.  At night, when the solar system is not producing any electricity, or at a time when more electricity is required within the home than is being produced by the solar system, electricity is imported from the grid in the normal way.

A more technical explanation:  A PV cell is made up of two thin layers of semi-conducting material (silicon) that generate electricity when exposed to daylight and when light shines on a PV cell the material absorbs some of the light particles called photons. When a photon is absorbed, an electron is released within one layer of the semi-conducting material.  These ‘free’ electrons will be attracted towards the other layer of semi-conducting material so they move across the boundary between the layers and this movement creates a flow of electricity between the two layers within a cell.

Q. What are the benefits of a solar PV system?

•    Reduce and future-proof your fuel bills – sunlight is free so once you have paid for the initial installation your bills for producing electricity will be significantly reduced (depending on the size of the system) for the lifetime of the system (potentially up to 40 years)

•    Earn an income – with the UK government’s proposal to introduce a feed-in tariff from April 2010 you will be paid for the electricity your PV system generates at above-market rates (see questions relating to feed-in-tariffs)

•    Cut your carbon footprint – solar PV uses the renewable resource of the sun and does not release any harmful carbon dioxide or other pollutants

•    Solar PV requires very little maintenance, has no moving parts and is silent in operation and, once installed, you will have many years of free electricity with no running costs

Q. What are the components of a photovoltaic (PV) system?

A PV system is made up of a number of different components including the PV panels themselves (usually located on the roof of a building) plus the framework on which it sits; an inverter that converts the direct current (DC) produced by the solar panels into alternating current (AC) required by the electrical system within a home, a total generation meter, some switchgear and some wiring.

Q. What types of PV panel are available?

•    Poly-crystalline cells are effectively a slice cut from a block of silicon, consisting of a large number of crystals. The panels have a speckled reflective appearance.  These cells are slightly less efficient than mono-crystalline cells and are therefore usually less expensive

•    Mono-crystalline cells are cut from a single crystal of silicon and have a smooth texture. These cells are slightly more efficient than the polycrystalline panels and are usually more expensive

•    Hybrid photovoltaic cells are comprised of a mono-crystalline PV cell covered by an ultra-thin amorphous silicon PV layer and will perform at slightly higher efficiencies than conventional silicon PV cells. They are therefore more expensive than the other types of PV panels

NB All panels are rigid and require mounting in a frame which, in most cases, is mechanically fixed to the roof of a building.

Q. Definition of ´power´ terms relevant to PV systems

A kilowatt (kW) is a unit of power, 1kW = 1,000 watts.
A kilowatt hour (kWh) is the amount of energy used when a kilowatt of power works for one hour.
Kilowatt peak (kWp) refers to the peak performance of a solar panel working under ideal conditions and is a standardised test for panels across all manufacturers so that the performance of solar panels can be compared.

Although it is impossible to predict the amount of electricity that a solar PV system will generate on any particular day, the government has developed a formula based on experience which states that a system will generate approximately 850kWh per year for each kWp of solar PV installed.  This figure is often higher in places with greater solar radiation such as Cornwall.

Q. How much electricity will solar panels produce?

This is dependent on a number of factors, especially the total size of the solar panels installed, the type of panels used, the orientation of the solar panels (due south facing is best), the angle of the solar panels from the horizontal (ideally 30°-45°), and whether the proposed location for the solar panels is subject to any shading. According to the Energy Saving Trust, the average 3-bedroom house uses 3,300 units or kilowatt hours (kWh) of electricity per year although this is an average and will vary from property to property. Each kWp (kilowatt peak) of solar PV produces between 800 and 1,200 kWh per year depending on the factors listed above. Therefore, to produce all of the electricity required for an average household, the PV array would need to be around 3-4 kWp.  However, it is not essential to provide all of your homes electricity needs from solar PV as you will still be connected to the national grid.

Q. Does the solar PV system need batteries?

No, the system is connected to the national grid. During the night, when the cells are not generating energy, electricity is imported from the national grid in the normal way. Any excess electricity generated during the day, for example when you are at work, is exported back to the grid.

Q. How is the solar PV system connected to the national grid?

This will all be done for you as part of the installation. Permission is required to connect a PV system to the distribution network but this is usually not a problem for any system up to 4kWp.

Q. Can I get paid for the electricity produced by a solar PV system?

Yes you get paid. The current position is that all electricity suppliers in the UK are obliged to provide more and more of their electricity from renewable sources and will purchase the electricity generated by householders. At the current time the rates paid are different from supplier to supplier. However, the government will be introducing a new ‘feed-in tariff’ in April 2010 when the electricity suppliers will be obliged to buy renewable electricity at fixed above-market rates and the rate will be the same for all suppliers.

Q. What is the feed-in tariff and when is it being implemented?

The government are introducing a new feed-in tariff (FIT) to provide an incentive to encourage householders and businesses to install microgeneration technologies and this comes into force in April 2010. Fuel utility companies will be obliged to purchase renewable electricity at fixed above-market rates which are set by the government. The proposed structure of the new feed-in tariff is as follows (based on a domestic installation of less than 4kW):

The householder will receive a payment for all electricity generated, whether consumed within the home or exported to the grid – this is known as the generation tariff and the proposed rate is 36.5 pence per kilowatt hour.  The rate of the generation tariff is set & guaranteed for a 25 year period.  However, households installing PV systems in future years will get a reduced rate as the government intends to decrease the tariff year on year from 2011 onwards because they expect the cost of PV systems to fall as a result of the increased demand.  In order to receive the best possible feed-in tariff rate a PV system will need to be installed before April 2011 as rates will be reduced after that time (probably at 7% per year).

The householder will also receive an additional payment for every kilowatt hour exported to the national grid – this is known as the export tariff and the proposed minimum rate is 5 pence per kilowatt hour.

There is also a further additional benefit when consuming the electricity generated on site which provides a saving due to the avoided costs of not having to purchase that amount from the grid.  The cost of purchasing electricity from the national grid varies from supplier to supplier but a current average is around 12 pence per kilowatt hour.

These tariffs & savings will provide a real incentive for householders to take up renewable technologies that generate electricity, particularly solar PV, and will significantly reduce the payback times for such systems.  However, please note that at the time of writing the tariff levels and exact conditions are still under consultation and hence not fixed.  However, it is not expected that they will change significantly from the amounts set out above.

To illustrate what this might mean to a householder investing in a solar PV system, it may be useful to consider the following example:

A typical 3-bedroom house with several occupants consuming 3,500kWh (kilowatt hours) of electricity annually

Example 1:     No microgeneration i.e. all electricity is purchased from the grid

Annual electricity bill = 3,500 x 12p/kWh = £420

Example 2:    Householder installs a 2.5kW solar PV system that generates 2,000kWh per year (based on government statistics that a 1kW solar PV system will generate at least 800kWh per year, though the amount generated could be as high as 1,200kWh per year depending on the location within the UK).  As a solar PV system will generate electricity during the day but a proportion of the electricity use will be during the evening and at night, some of the electricity generated will be used within the home and some exported to the grid – this example assumes that 50% is used & 50% exported.  Also this example assumes the cost of imported electricity to be 12p/kWh

Generation tariff = 2,000 x 36.5p/kWh = £730/year

Export tariff (50% exported) = 1,000 x 5p/kWh = £50/year

Total income = (generation + export) = £780/year

Less cost of imported  = 2,500 x 12p/kW = £300/year
electricity

Total income to householder = (income - import cost)
= £480/year

So, in this example, the householder has gone from paying the electricity supplier £420/year to getting paid £480/year by the supplier – a saving of £900 per year (every year!).  It should be noted that the cost of purchasing electricity from the grid will inevitably rise in future which means even greater savings.

NB The approximate cost of installing a 2.5kW PV system is £12,500 (including the government grant of £2,500).

Q. Will I be eligible for the feed-in tariff if I have a solar PV system installed before April 2010?

Yes, all systems installed between the announcement of the feed-in tariff on 15 July 2009 and the start of the new scheme on 1 April 2010 will be eligible to receive the new tariff.

Q. What if I produce more electricity through my PV system than I need?

Whenever your panels are producing more electricity than your home is using, it will exported back to the national grid. As long as you have an arrangement with your energy company, you will be paid for this power so you can be sure that your energy bills will be even less and none of your clean, green electricity will be wasted. You can speak to your electricity provider for details or check at www.uswitch.com to check which energy companies offer arrangements like this. Please note that when the new feed-in tariff comes into operation in April 2010 all exported electricity will be paid at an agreed set rate irrespective of the energy supplier who purchases that electricity. This is in addition to the tariff for the total amount generated by the PV system.

Q. How much will a solar PV system cost?

The installed costs of a PV system will depend on a number of factors, especially the size of the system installed and the type of panel used. It should also be noted that most installations will require scaffolding to access the roof. Current industry prices indicate an average of approximately £6,000 per kWp installed (excluding any grant). However, at the present time there is a government grant of £2,500 towards the cost of installation and you will also be eligible for the feed-in tariff when it is launched in April 2010. A typical 2kWp system which will produce approximately 50% of an average household’s electricity needs will therefore cost around £12,000 less the grant. With fuel costs certain to rise over its lifetime, a solar PV system can be seen as an economic investment as well as an environmental one. Please note that prices will vary from property to property and a more exact quote can be provided for any specific dwelling once a full assessment has been carried out.

Q. Can I get a grant for installing a solar PV system?

Yes, in the vast majority of cases you can and the grant is worth up to £2,500 towards the total cost of installation through the government’s Low Carbon Buildings Programme. (Please note that the grants are allocated on a first come first served basis). However, in order to qualify for the grant, you must have installed certain energy efficiency measures into your home. This ensures that energy use is minimised prior to installing solar PV, enabling the most efficient use of the technology.  The measures required are loft insulation, to meet current building regulations e.g. 270mm (approx 11”) of mineral wool or suitable alternative, cavity wall insulation (if you have cavity walls), low energy light bulbs in all appropriate light fittings and basic controls for your heating system to include a room thermostat and a programmer or timer.

Please note that the government intends to phase out the grants in 2010 and to replace them with a new system of feed-in tariffs. Until that time, households installing PV systems will qualify for the current grant and will also receive the feed-in tariff, as long as the system is installed by a MCS accredited installer.

Q. Is planning permission required to install a solar PV system?

Most domestic properties do not require planning permission. However, there are some exceptions to this if the property is a listed building or is situated in a National Park, an Area of Outstanding Natural Beauty or in a conservation area. In all cases the local authority will need to be contacted for clarification.

Q. How much space is required for the solar PV panels?

Each kWp requires an area of approximately 8m².

Q. What are the effects of shade on a solar PV system?

Shading is critical and even minor shading can result in a significant loss of energy being produced by the solar array, so it is best to avoid shading wherever possible, especially from any trees or buildings to the south of the array. This is because the cell with the lowest illumination determines the operating current of the series string in which it is connected and shading to even just one cell can reduce the power output to 50% of its full available value. This is one of the areas covered in the survey carried out before any installation, to ensure that the building is suitable for a solar PV installation.

Q. How long does it take to install a solar PV system?

Once a survey has been completed and the householder agrees to proceed, an average domestic installation takes approximately 2-3 days on site to install, depending on the size of the installation.

Q. How long will a solar PV system last and what are the guarantee periods?

Most solar PV system panels have a manufacturer’s warranty of 25 years with an expected lifetime of up to 40 years. It is estimated that the performance of the PV system will decrease by less than 1% per year and the manufacturers guarantee that the PV system will still perform at 80% of its installed efficiency 20 years after installation. Inverters are generally guaranteed for at least 5 years, although this is extendable, and workmanship is guarenteed for 2 years.

Q. What maintenance and cleaning does a solar PV system need?

Solar PV systems are silent in operation, have no moving parts and require very little maintenance. However, during the lifetime of the system, the inverter (which converts the DC electricity produced to AC electricity) may need to be replaced.

Q. What happens to the solar PV system if there is a power cut?

In most cases solar PV systems for homes are entirely grid connected. If there is a power cut the solar PV system is automatically switched off as a safety measure, designed to stop electricity leaking on to the national grid and to protect individuals who may be working to restore the power supply.

Q. What if I need to expand the solar PV system in future years?

If your demand for electricity should increase in future years a solar PV system can be expanded with the inclusion of additional panels although some other components of the original system may also need to be upgraded. 

Q. Will a solar PV system work in the UK, and will it work during the winter?

Yes, the important thing to bear in mind is that solar power depends on the intensity of light, not necessarily direct sunlight, and electricity will still be generated even on cloudy days though at a lesser rate than on days with full sun.

Q. How much carbon dioxide will a solar PV system save?

By installing a PV system you will be producing your own clean electricity, therefore offsetting the production of carbon dioxide from electricity generation using fossil fuels such as gas, oil and coal. The amount of CO₂ saved is dependent on the size of the system installed - a typical 2kWp solar PV system will save almost 1 tonne of carbon dioxide each year (based on the emission factor used by the UK government of 0.43kg of CO₂/kWh).