Energy Production

How much energy you can generate from an array will firstly depend on the space you have available and how much you want to spend.

A typical sized domestic system would be 4 kilo watt; this would comprise 16 panels of 250 watts each.

16 x 250w = 4,000w = 4kw.

Microgeneration Certificated Scheme (MCS) companies should provide you with a legitimate report which factors:

  • Your roof orientation e.g. south or south east etc
  • Your roof angle
  • The size of the array
  • Losses in efficiencies from panels / inverter / cable
  • Shading
  • Your UK location

Your report will clearly illustrate the amount of electricity that you will generate through the course of a year.

There is an industry standard method for estimating how much a system will actually produce and it is called SAP 2005 (SAP = Standard Assessment Procedure).

In general, SAP estimates that the actual output for a system will be approximately 86% of its kWp size. Thus a 1kWp system will produce 860kWh of electricity in any year in the UK; notwithstanding different panel efficiencies.


Therefore an average performing system sited in good condition (south facing at 39 degrees pitch with no shading) should deliver 3,852 watts of electricity per annum.

High quality systems will produce more whilst low quality cheap systems will produce less.

Annual Energy Gain

Naturally, more hours of sunshine coupled with clearer days, the more solar radiation there is and the more you will generate.

The following graph illustrates the curve of electrical production through the course of a year.

Download Graph

Orientation and Tilt Angle

Orientation and Tilt Angle play a key role in the output of a Solar PV system.

The ideal orientation for Solar PV in the UK is South facing and the ideal tilt angle is between 30 and 45 degrees from the horizontal axis.

However, facing an Easterly or Westerly direction, or being at an angle of 65 degrees will still generate significant volumes of electricity but not a such as south facing at 30 degrees.

The following table shows performance levels for all types of system installations.

Download Table