Solar photovoltaic modules convert the sun’s radiation into electricity even on a cloudy day

Solar electric panels, also known as Photovoltaic (PV) modules, convert sunlight directly into electricity. Each module consists of a number of PV cells made up of layers of semi-conducting material with a base, usually, of silicon. When light falls on the active surface, the electrons in a solar cell are energised in proportion to the intensity of the light they receive.  When their energy level exceeds a certain point a potential difference is established across the cell.  This is then capable of driving a current. The stronger the sunshine the more energy is produced, although they will still generate electricity on a cloudy day.

Solar Photovoltaic Modules

Modules fall into three categories based on the solar cells used, mono- crystalline, multi-crystalline and amorphous cells, also called thin-film. These differing types of modules vary in prices and efficiency. However, with increased global demand for PV technology, prices have been on a dramatic and continuing downward trend alongside large improvements in innovation and efficiency.

Currently PV can be installed for approximately £1000/kW.

Modules can be sited on roofs/walls of buildings or free standing. PV modules come in a variety of sizes and colours, from grey "solar tiles" that look like roof tiles to flat plates and transparent cells that can be used on conservatories and glass.

The capacity of a PV module is specified in Peak Watts (Wp), which is the measured maximum power rating at standard test conditions. Energy generated from solar PV is measured in kilowatt-hours (kWh). If a 12m2 array of 2kWp capacity, of 16% efficient monocrystalline PV modules are situated on a South facing roof in Leeds they will annually produce approximately 1400kWh. This is half the equivalent annual electricity consumption of an average household, giving a saving of 0.75 tonnes of CO2 per year. 

Feasibility and Development

There are a number of stages involved in assessing the feasibility of solar PV installations, including:

Siting and design considerations:-

Orientation – south facing roofs are preferred.  Efficiencies reduce by around 20% for an East or West facing roof.

Angle – inclined at an angle of 20-40 degrees is preferred for the modules to perform at their optimum.  In practical terms, this is not always possible on existing buildings, and some degree of flexibility between 10-60 degrees is acceptable at the expense of performance.

Mounting – The integrity of the building structure is important as it must be strong enough to take the additional weight, especially if the module is placed on top of existing tiles.

Shading – un-shaded areas are preferred as shadows cast from buildings, trees or other structures can significantly reduce PV module output. You can use a Sunpath diagram to help calculate shading effects.

Urban locations – urban areas provide opportunities for sites which may not be appropriate for other renewable systems.


Permitted development (PD) – For domestic dwellings, as long as the installation is not unusual in design, involves a listed building, and is not in a designated area, the Local Planning Authority (LPA) will generally regard it as a venture that does not need to submit a planning application.

If planning is required – For business applicants planning permission advice should be sort from the LPA and may need to include module design, photos of building environment, roof mounting arrangement and photomontages.

Management and maintenance

Maintenance – PV module performance degrades with age, typically reducing by 1% per annum, however manufacturers’ give up to 10 to 25 year production guarantees. They need minimal maintenance over their lifetime and can still generate electricity beyond their guaranteed lifetime. Consideration should be given to the replacement of the inverter which has a shorter design life than the modules.

Useful resources

See our guide to  - Feed in tariff

Planning Advice  -

Calculating generation potential:

Calculating revenue: Spread sheet

Useful 'how to' guides by Sharenergy:

Sharenergy - Community-Solar-Roof-Guide.pdf

Sharenergy - Solar-in-a-Box.pdf

Low carbon hub - School PV case study

Low carbon hub - Social housing

Low carbon hub - commercial project

Low carbon hub - making a solar PV project happen

Technical information:

Electrical Contractors Association: Guide to the installation of Photovoltaic systems

Microgeneration Certification MIS 3002 Issue 2.1pdf 

Useful PV tools: