Solar PV FAQs

Solar PV FAQs

Your guide to understanding Solar Photovoltaic (Solar PV)

How does Solar PV work?

Solar PV cells convert light into electrical power. They are made of a thin silicon wafer which is specially treated to form an electric field, positive on one side and negative on the other. When light energy strikes the solar cell, electrons are knocked loose from the atoms in the semiconductor material. If electrical conductors are attached to the positive and negative sides, forming an electrical circuit, the electrons can be captured in the form of an electric current How much electricity do solar PV systems generate?

A typical domestic system is between 1.5 to 3kWp. Each kWp should generate around 800 to 850kWh per year if unshaded and perfectly south facing with a tilt of around 30–50°. A solar roof array would typically generate 1200 to 2400kWh per year depending on size.

What do kWp and kWh mean?

Solar electricity systems are  sized in kilowatts peak (kWp). This is essentially the rate at which it generates energy at standard test conditions (Irradiance 1000 W/m², Cell Temperature 25°C, Air Mass AM1.5). The kWp of a  PV system will vary depending on the number and power of the individual modules used which in turn depends on how much a customer budget and the roof area available to accommodate the panels.

The total amount of electricity the system actually generates in a year is measured in kilowatt hours (kWh). This will depend on the system’s orientation, shading and how sunny your site is, as well as the size of the system (in kWp) that you have installed.

What size do Solar PV Systems come in?

PV systems are modular, allowing a great degree of flexibility in design and specification. In practice, the size of a system is determined by the power and number of modules fitted to the available roof space.

Why is shade a problem for Solar PV systems?

Any shading has a detrimental effect on the electricity your system generates. Shading may come from trees, chimneys or surrounding buildings. Shading is a very important factor in the solar PV output. However, if your panels are partially shaded in the early morning or late evening, the system will still generate acceptable yields. Installers assess and highlight any shading concerns and give a realistic electricity generation potential

Can I still install a Solar PV system on an old and deteriorating roof?

Although Solar PV systems are not normally heavy enough to cause structural problems, if your roof is in poor condition your installer would recommend that a structural survey be completed before proceeding with your installation.

What is the life expectancy of a Solar PV system?

Under normal conditions you can expect modules to operate for 25 years or more before they need replacing, although the inverter may need replacing earlier than this.

How long will my solar installation take?

A typical domestic solar installation will take place over two days but this may vary due to many factors . Depending on the building we access to erect and remove scaffolding will also be required. Your installer can advise the specific details for your property in his quotation.

How do I find an installer?

The installer must be certified under the Microgeneration Certification Scheme (MCS). You can find certified installers at www.microgenerationcertification.org. Rexel's service offering, Solar Energeasy has trustworthy MCS accredited installers signed up who have been fully vetted that will give you peace of mind.

How does the Feed in Tariff System operate?

There are three ways in which the owner of the technology can benefit from the scheme. These are:

  • Generation Tariff: in which your energy supplier gives money for every unit of electricity produced. The tariff varies depending on the capacity of the installed technology; for Domestic PV the rate is currently14.48p/Kwh 
  • Export Tariff: in this case, there is a payment of 4.77p/Kwh for all excess generated electricity exported to the grid. This payment is currently estimated at 50% of the amount of energy generated and homeowners receive an export payment along with the generation payment. 
  • Energy bill savings: by using the energy generated by the PV System, there is less dependence on the conventional electrical power from the grid thereby allowing savings on energy bills.
Read more on Government Feed-in Tariffs (FITs) and exporting electricity.