FAQs - PV Systems and Photovoltaic Installation

Below are the answers to some frequently asked questions? If you cannot find the answers you require here please feel free to contact us.

What is Solar PV?

Solar PV is a renewable energy system which uses photovoltaic modules, usually on the roof of a building, to convert daylight into electricity. Photovoltaic cells are made up of thin layers of semi-conducting material (usually crystalline silicon) which generate an electrical charge when exposed to direct or diffuse daylight.

How do photovoltaic’s work?

Sunlight hits the photovoltaic cells and is converted to clean electricity. The inverter converts the electricity from direct to alternating current, so that it may be combined with the electricity being imported from the mains, and used to power appliances in your home. When the solar energy system produces more power than is needed, it is exported into the electricity grid. At night, power is imported from the electricity grid in the usual manner.

Do we need Planning permission?

Generally roof installations fall under “permitted development” so you don’t require planning permission, however listed building, conservation areas, non domestic installations may require permission so we would always recommend you to contact your local Council to check prior to any installation taking place.

What is a unit or kWh (kilowatt hour) of electricity?

Units are how you are billed for electricity. To run a 100 watt lightbulb for 10 hours, you require 1,000 watt hours or 1 kilowatt hour (1 unit) of electricity.

What are the key benefits of a PV system?

Once installed and commissioned, you own the system, having control of a long-term free source of electricity that is exempt from price increases. You are not only saving money but actively saving the environment at the time. A PV system makes no noise, has no moving parts, requires minimal maintenance, has a long lifespan and generates no CO2 emissions. Basically, it produces clean energy for years to come.

Where can I install my PV modules?

The location of your PV array (group of PV modules) is vitally important. The modules should receive the maximum amount of daylight possible, so it is not advisable to install the modules in situations where surrounding buildings or trees may cast shadows. The best location for a PV array in the UK is on a south-facing roof angled at 30 degrees.

How do the panels perform at different angles and orientations?

Orientation Efficiencies of PV Solar Panels

If the optimum angle is not achievable, over 90% of the maximum annual energy can still be achieved at 10 degree and 50 degree tilts. South-facing vertical facades generate around 70% of the maximum.

What are the effects of shade?

Shading is critical. Minor shading can result in significant loss of energy. Since PV modules are linked together in series, the module with the lowest amount of irradiation falling upon it determines the operating voltage of the string in which it is connected. This is one of the factors considered in the DHR site survey carried out before any installation.

Does PV really work in the UK?

Yes. The PV modules only require daylight to work, and so will generate energy on cloudy and even rainy days. Temperature is also a factor when determining how much electricity a pv system will generate. The efficiency of a PV module decreases by a fraction for every degree the temperature is above 25 degrees Celsius. Therefore, a clear cold day is perfect, because PV modules operate better at cooler temperatures. The UK has similar irradiance levels to Germany where PV has proved extremely popular given their tariff structure, which is now also available within the UK under the Feed in Tariff.

What maintenance and cleaning do the PV systems need?

A Solar PV system is silent in operation, has no moving parts and requires minimal maintenance. Most of the time the rain will keep the modules clean. However, a build up of dirt can affect system performance. The degree of soiling will depend on the location but usually dust accumulation and self-cleaning reach a steady state after a few weeks if the array tilt is at least 15 degrees. In extreme cases, dust may cause a power reduction of about 10%. The design of the system should aim to minimise uneven soiling. The modules can be cleaned once a year if desired with either a hose or, if possible, soapy water and a non-abrasive cloth.

What size PV system do I need?

There is no simple answer to this question. It will depend on how much you want to invest, how much of your electricity you want to generate via PV, and how much south-facing, un-shaded roof space you have. It is not essential to provide ALL of your home’s electricity via solar PV (since you will still be connected to the national grid). If your PV system supplies half of your electricity, it will still make a serious reduction to your carbon footprint! After talking through your exact needs, DHR will be able to recommend the size of system you require.

How much energy do I need?

According to the Energy Saving Trust, the average three-bedroom house consumes 3,300 units of electricity (kWh) a year (cooking and heating using non electric supply). However, DHR always recommends that you look at your last few bills or call your electricity supplier to find out how many units you consume. You can then compare this to the output of the system which DHR recommends.

What if I produce more energy than I need?

Whenever your panels are producing more electricity than your home is using, it will flow back into the grid for other homes to use. As long as you have a meter that measures the amount of electricity exported, you are eligible to receive a credit for this electricity. This will lower your electricity bills and ensure none of your green electricity will be wasted.

Does the system need batteries?

No. DHR’s PV systems are connected to the national grid. In the night, when the cells are not generating energy, electricity is bought from the utility company in the normal way. Any excess electricity generated during the day – for example, when you are at work – is sold back to the utility company.

What happens if there is a power cut?

DHR’s PV systems for homes are entirely grid connected. If there is a power cut, your system is automatically switched off. This is 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.

Which electricity supplier should I use?

Due to the Feed-in Tariff, all electricity retailers will be obliged to offer the same generation and export credits for microgeneration systems to their customers so you may choose whichever electricity retailer you prefer.

Can I sell the electricity I make?

Yes. You are able to sell any electricity you generate and don’t use back to the grid.

How soon will a PV system pay back the cost of installation?

DHR estimates that a system installed during the Feed-in Tariff Scheme will be paid back in eleven years. However, in addition, you will carry on receiving a tariff for a further fourteen years and you will benefit from free electricity for years to come after that.

What is the cost of a solar PV system?

The cost of installation is dependent on a DHR detailed survey and will vary according to how easy or difficult it is to access the roof space and the type and size of the PV system chosen. Please contact us for current pricing.

A Solar PV installation adds as little as 4% to the build cost of an average new three- bedroom home, but this can be added to its final value when sold. It also helps ‘future proof’ a home against rising fuel prices making properties doubly attractive to price- conscious house buyers. As fuel prices continue to rise, energy-efficient renewably powered homes will continue to sell at a premium.

How long will it take to install my system?

PV systems can be installed and ready to produce electricity in 2-8 weeks from the time the design has been agreed. The actual installation will take approximately one day to install depending upon your building type.

What are the lifetimes of PV products?

Most panels have a manufacturer’s warranty of 25 years and a working lifetime of 40 years and beyond.

Does DHR service the whole of the UK?

Yes. DHR’s Installation Engineers, accredited to Microgeneration Certification Scheme (MCS) standards, are fully trained to install photovoltaic systems throughout the whole of the UK dependant of the project size.

Doesn't the glazed front reflect light away from solar PV modules?

No. Solar PV modules constructed with a glass front have two characteristics that reduce light reflection. In order to optimize electrical yield, the glass is treated with an anti-reflective coating which greatly increases the transmittance through the glass, maximising the amount of light reaching the solar cells. Secondly, the outer face of the glass has a slight granular texture. The result is a matt-like finish – rather than mirrored. Again, this is actually intended to maximize yield. These two characteristics greatly reduce reflection from the glazed front face of solar PV modules when compared with conventional glazing.

Are there disadvantages to using solar PV energy?

Solar energy technologies often have a higher investment cost. This means that a person is likely to pay more money initially to purchase and install a solar PV system. Still, in nearly all cases, the high initial cost is recovered through substantial fuel savings within the life of the product (40+ years). This time is significantly reduced by any government incentives in place such as Feed-in Tariffs. Free installations options are also available, although with these systems you will only receive the free electricity you generate and not the governments Feed in tariff.

What happens if something goes wrong?

Most Panels come with a 25-year performance warranty so, in the unlikely event that you experience problems, DHR will be on hand to diagnose your problem and, if necessary; arrange a home visit to ensure that everything is working as it should be. The installation comes with a one-year warranty so you can be sure your service will be of the highest standard.

Can I use PV to power my business?

PV systems can be blended into virtually every conceivable structure for commercial buildings. You will find PV being used outdoors for security lighting as well as in structures that serve as covers for car parks and bus shelters, generating power at the same time. PV systems are also used to offset and operate all kinds of electrical systems, including lights, cooling systems, and appliances.

Most work units have a large roof area that is ideal for solar PV to be installed to generate free electricity for your business.

Can I design and install a PV system myself?

Maybe! However, unless you are very handy or experienced in home wiring, we suggest using experienced professionals such as DHR to design and install, for the following reasons:

- You have to pay 15% VAT on the PV cells rather than the 5% through accredited dealers.

- You must be certified via the Microgeneration Certification Scheme in order to be eligible for the government’s feed-in tariff.

- You might void the manufacturer’s warranties.

- You might not have a functional system after spending your hard-earned money on the system.

How can PV glass laminates and flexible thin film PV be used architecturally?

PV glass laminates are attractive and well suited to facades and transparent roof tops. They can be fitted to standard curtain walling structures and are suitable for any application where glass is used, as long as there is a reasonable level of light present.