Why is it a problem? Well, firstly, it makes a significant difference to the production of electricity and efficiency of the PV, and this ultimately means over-shadowing costs you money because it reduces how much electricity can be produced, used, or fed back into the National Grid.

Secondly, during the life-span of a PV Module, the surroundings can alter dramatically. For example, a sapling in Year 1 can be a 40 foot Leylandii in year 10. This means the efficiency of the PV Module requires forward-thinking planning and monitoring.

What can be done to reduce the risk of over-shadowing?

For the majority of standard construction buildings, there are 3 common problems:

1. Trees and chimneys
2. Birds
3. Wiring / Linking

Chimneys:

During the course of the day, the shade of the tall chimney depicted in Image 1, will overshadow several of the PV panels. Each time there is overshadowing on the PV, the efficiency is affected, which means the output is significantly reduced.

Nature dictates that our feathered friends perch on aerials and satellite equipment, and over time nature takes it course, and the bird droppings fall onto the PV panel - thereby causing ‘black-out' areas on the PV panel where sunshine or daylight can't penetrate. This will affect the whole panel and will either cause a reduction in output or mean a regular clean is necessary.

Trees:

Within the life-span of a PV Module, surrounding trees will mature and may grow tall, causing overshadowing for part or all of the Modules.

Wiring/Linking:

A device called an ‘inverter' is used to link the PV Module back to the house meter. An inverter can be used to control a single PV Module or a whole arrange of PV Modules, and they differ in size accordingly. Usually a series of small inverters is more expensive than one large inverter, and the usual Guarantee is 5 years.

Please note that the effect of the PV Module is significantly affected by the way the Inverter links the array of PV Modules together. For example, in Box 1, if there is a single inverter for the whole array of PV Modules, then the overshadowing affects not just the Modules in shadow, but the whole array. This could reduce the output by up to 90%. By contrast, if this array had individual inverters, wiring the PV Module to the house meter, then the reduction of output caused by the overshadowing would be limited to the Modules in shadow.

 
How will PV impact your SAP or SBEM Calculation?

The SAP (for domestic) and SBEM (for commercial) Calculations work out the expected CO2 emissions from your building, taking into consideration fuel used for heating, lighting and general occupancy. By installing PV panels to your building you can dramatically cut the amount of grid electricity you use over the course of a year, lowering the overall emission rate.

Electricity is seen to be a ‘carbon heavy' fuel due to inefficiencies in the way it is created (mainly at power stations) and transported (via pylons) to your building. By creating your own electricity, and exporting the surplus back onto the National Grid, you have the potential to cut your CO2 levels as well as lowering your utility bills.

The Energy Performance Certificate (EPC) measures the running cost and environmental impact of your building. Because of this, installing PV can give you a better rating on the EPC certificate, which can make your home more appealing to potential buyers.

This information was written in March 2011. We work hard to keep the information up to date, however, it is not our specialist area and our intention is for the information to be used only as a Guide.