Solar PV

Introduction to Solar Photovoltaic (PV)

Solar PV utilises free energy from the sun to generate electricity. It relies on daylight (rather than radiation) to generate power through the use of photovoltaic cells within roof-mounted modules.

The modules are simple to install, as they fix to a roof in the same way as Solar Thermal panels in an on-roof, in roof and flat roof arrangement, both landscape and portrait.

The electricity produced by Solar PV can be used to drive an appliance that is powered by electricity. An inverter (usually situated in the loft) converts the DC current into usable AC current that can be used as power.

A 1.80kW Solar PV System (10 modules) should produce around 1,693kWh of electricity per annum (this figure may vary, depending on location). To put this into perspective, the average household usage is 9 - 10 kWh per day.

Typical energy usage

Everyone consumes energy, but sometimes it is hard to know just how much power is really being used. A good way to understand is to look at kilowatts in a different way, like everyday human activities.
A kWh of electricity means:

  • 1200 electric shaves
  • Drying your hair 15 times
  • Listening to 15 Cd's
  • Using a small refrigerator for 24 hours
  • Microwaving 20 meals
  • 4 evenings of light with 60W incandescent lamps

Also keep in mind that for each kWh produced with fossil fuel, about 1.5lb (0.68kg) of CO2 is released into the atmosphere.

Feed-in Tariff (Clean Energy Cashback) scheme for PhotoVoltaics

Introduced in April 2010 the FIT is available if your system is installed by an MCS registered contractor, click here for more information.

In addition to this the UK Government has now announced the introduction of the Renewable Heat Incentive (RHI) from 2011/12 as part of their Comprehensive Spending Review. The Renewable Heat Incentive (RHI) is designed to provide financial support that encourages individuals, communities and businesses to switch from using fossil fuel for heating, to renewables such as wood fuel. Click here for more information.

Location of collectors

The location of PV modules is vitally important. They must receive the maximum amount of daylight possible, so it is not advisable to install them in situations where surrounding buildings or trees may cast shadows.

The best location for a PV solar module is on a south-facing roof or side of a building.

Solar PV System

Diagram of Solar PV system


How effective is solar electricity in the UK?

Solar PV systems rely on sunlight not heat so produce sufficient power even on a cloudy day. The optimal weather can actually be during colder seasons, when it can be very cold and very sunny.

Is there a difference in the effectiveness of solar panels for different parts of the UK?

The solar radiation received on a collector facing due south at an incline of 30° varies from approximately 900 kWh/m2 per year in Scotland and the North of England, to approximately 1,200 kWh/m2per year in the South West.

UK map outlining solar effectiveness
Can I increase the size of the array of panels at any time?

As the components of a P.V. system are carefully matched, it is normally not possible to add panels to an existing array unless the inverter (a major component) is also changed. It is often more cost effective to add a complete new system alongside the existing one and join their outputs before the generation meter.

How much would a typical system cost for the average family home?

A typical good quality system of 2.1 kWp would cost around 10,500 and would give total payback benefits of around 950 per annum. However if you have the space on the roof and have access to capital, you should install the biggest system you can afford, up to 4 kWp as the return on capital should exceed 9% per annum.

What direction does my roof need to face in order for solar panels to provide maximum efficiency?

For maximum efficiency, solar panels should be mounted on a south facing roof at an angle of 30° - 50° with the horizontal and away from trees, surrounding buildings and chimneys. Fortunately, the average tilt of a UK house roof is about the optimum for receiving solar energy in the UK.

However, if your roof faces east or west solar panels can be installed, although this angle will have some effect on the efficiency. The same applies to the pitch of the roof which, provided it is between 30° and 50°, should still be suitable.

Diagram showing change in performance due to panel orientation
Are some types of Solar PV panels more efficient than others?

There are 3 basic types of solar PV panel - Monocrystalline, Polycrystalline and Thin Film. Monocrystalline panels are slightly more efficient than Polycrystalline by around 1.5% and have an overall efficiency of around 16%. Thin Film panels are used in specialist locations and have a much lower efficiency.

How long do they take to install?

A 12 panel system installed on a typical roof would normally be completed in 4 days.

What types of roof are suitable?

Fixing systems and brackets are available for almost all types of roof structure, and panels can be mounted vertically on walls or on angled supports on the ground or flat roofs.

Is planning permission required?

From April 2008 new government rules state that providing the solar installation does not protrude more than 200mm from the roof slope and is not in a conservation area or on a listed building, installation of solar panels are considered a permitted development, meaning that no planning permission is required.