The fifth topic in our solar series explores how to avoid damage to solar panels from electrical surges and lightning strikes.
Earthing is paramount to the design of new solar farms and associated electrical grid infrastructure, both in order to keep people safe by preventing electric shocks and in avoiding damage from overloading caused by excess currents running through the circuit. Such damage can reduce the efficiency of the solar panels, and even cause them to fail completely, leading to costly repairs or replacements and impacting operational efficiency.
Through full understanding the site’s electrical property, an appropriate earthing system can be designed which may include earthing plates, earthing rods, or earthing pits.
The Method: Soil Resistivity Testing
The electrical properties of a site are measured through soil resistivity testing, which measures the capacity of the ground to pass an electrical current. The procedure involves putting four electrodes into the ground in a fixed configuration array. A low frequency electrical current is applied across the outer electrodes and the voltage is measured between the inner electrodes.
Above : Soil resistivity testing in progress on a new solar farm development.
A series of depth readings are acquired using different electrode spacings, allowing the apparent resistivity of the ground to be recorded at regular depths to 50m or more at any given point. The resultant data is presented in tabulated form (below) as well as in graphs, listing the electrode spacing, nominal testing depth; electrical resistance for each electrode spacing (R1, R2); average resistance (Rav) and apparent resistivity for each position.
As a general rule, lower resistivities make the design and installation of an earthing system simpler.
Above : Tabulated soil resistivity testing results at standard electrode spacings.