Photovoltaic (PV) cells and modules are only part of the picture when you consider the efficiency of a solar electricity generating station. Key to an effective PV system is an efficient inverter, which converts the direct current (DC) electricity produced to AC (alternating current or mains equivalent).

For small systems connected to the national grid (rated up to around 4 kWp) you will need a G83/1 approved inverter. This makes connection to the grid simple and makes sure that the system operates safely. If the inverter detects a mains failure, your system will shut down so that there is no danger to anyone carrying out repairs on the electricity network.

Grid connected inverters are typically in the region of 93 per cent efficient. This will depend on the design of the inverter. To maximise efficiency, inverters typically have a MPPT feature (this stands for maximum power point tracking). It optimises the operating voltage point of the inverter so that the maximum power is extracted from the PV system as the light levels vary.

When putting a system together you need to make sure that under fluctuating light levels the output voltage range from the string of PV modules  is greater than the inverter's minimum input voltage range. If it is lower for a significant amount of the time the system will lose efficiency. It is equally important never to exceed the maximum voltage permitted by the inverter, as this may permanently damage it.

If you plan a large system, you may need to connect under G59/ regulations. The procedure is much more complex, so it is worth discussing this with the local electricity network operator (DNO) as they will often make exceptions. I have come across cases where they have allowed 10 kWp generators to be connected on a single phase.

photo by mountain ash

About the author: Graham Eastwick is a director of Encraft, and manages renewable energy installations for home owners, community organisations and small businesses across the UK.

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