Solar Design

seasonal panel angle monthly optimum panel angle
Angle & Direction of the Roof

Obviously it is too expensive to install motorised panels that tilt towards the sun, so your options are limited by the direction and pitch of your roof. You could also use any flat ground or a flat roof and mount the panels on frames that can be positioned to the optimum angle and direction.


There are published tables that show how the direction and pitch of a roof affects the amount of electricity produced. The table on the right shows average % figures for the UK.


UK Irradiation Chart


The Power Inverter

One of the most important components in any system is the inverter. This combines all of the strings of panels and converts the direct electric current to AC current for domestic use. The efficiency rating of the inverter will directly affect the power output of the system. A good inverter will have an efficiency greater than 94% and even as high as 98%.

The more efficient inverters tend to require higher voltages from the panels (so more panels strung together). If there is a problem with shading and multiple strings are required then the most efficient inverters may not be an option.

Some now carry a 20 year warranty, but generally it is only 5 - 10 years, so it is likely that once in the 25 years lifetime that you will need to replace the inverter. Any Part P registered electrician could replace and test one of these in under 2 hours and the inverters are relatively inexpensive, so not a huge expense to replace, but you will lose part of your income in that year.




Shadows falling across solar panels are the biggest problem. The panels are strung together in a series, so if shadow falls on one of the panels the power produced by them all is affected, like squeezing one part of a hosepipe and stopping the flow of water along all of it. To reduce the effect of any shadows, the panels can be strung together in different loops so that areas shaded at the same times are grouped together, while panels with no shade are grouped separately. This ensures that as many panels as possible are working at full capacity at any one time.

Angle & Direction of the Panels

The angle and direction of the roof is also important. Ideally it should be a South facing roof, but East and West facing rooves also produce good electrical output. Even a North facing roof will still work at 68% capacity. In the Summer the best roof pitch in South East England is around 28 degrees but in Winter as the sun dips to the horizon this becomes 74 degrees. The charts on the left show the optimum angle each month and season for the Eastbourne/Crawley region.


UK Irradiance Levels

The current generation of solar panels do not require direct sunlight and work quite well with indirect light. You will find 'Irradiance' levels mentioned in relation to solar panels, this is a measure of the light intensity. Basically, the more light there is, then the more electricity the panels produce.

The chart below shows irradiance levels each month for the Eastbourne - Crawley region and the map shows the levels across the whole of the UK. Clearly the summer months are the most productive, but the winter still produces decent electrical output.



Crawley and Eastbourne Power Statistics

solar power inverter