Solar PV and shading

The benefits of installing solar PV into your home is widely reported, however the effects of solar PV’s biggest limiter isn’t. And this is the reason why so many consumers are not fully aware of the degree to which a partially or temporarily shaded solar PV panel will lose its full working potential.

According to some experts, homeowners could be losing as much as 40 per cent of the potential output of their solar PV installation because of shade. And that isn’t because the whole panel is being shaded. Just 10 per cent shading of a solar PV panel can result in a 50 per cent decline in efficiency according to some reports. And this is due to the way the solar cells are connected.

Traditional solar panel arrays are connected in a series of parallel ‘strings’. If one array is affected by shade, then the losses are passed onto the rest of the chain of cells. To prevent all the cells failing completely, the installation usually includes bypass diodes. These then reroute the current, bypassing the underperforming cells. However, despite stopping the array from failing all together – in the same way a set of Christmas tree lights go off when one bulb has gone – it does restrict the energy from the cells and lowers the entire strings voltage.

The inverter is left to decide whether to optimize the voltage for the underperforming string or to maximise the energy harvested from the strings that haven’t been affected at all. Either way, the inverter will be choosing one of two inefficient options as a result.

However, it has been argued that the impact of shading is sometimes over-exaggerated, especially during the periods of maximum yield. Well-situated solar PV panels on a property at midday and during the summer should only be minimally affected by shading as the sun is high and directly above.

With this in mind, shading is an obstacle for solar PV that needs to be considered and looked into by any potential consumer. The shading can come in many forms, can be seasonal and can be different depending on the objects that create the shade.

A professional solar installer should be able to notify you of potential shade issues when visiting your home to quote you on an installation. But it is worth investigating yourself beforehand, taking into account the changing seasons for trees, shading from the property and surrounding properties chimneys, potential high-rise buildings being erected in the coming years that could restrict your solar system and anything else that could obscure your panels from the sun.