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Talking Tech: Maximising power generation under the 3.68 kWp limit

Problems problems: Lee Summers, Spitfire Wholesale, highlights an issue that has arisen within the current solar boom

We are currently in the midst of a British solar boom. Market conditions dictate that it is now the right time for homeowners, farms, businesses and community organisations to harness the power of small scale solar energy systems. The Feed-in Tariff (FiT) scheme launched by the government has made renewable systems more attractive for all concerned.

Trying to maximise the lowest tariff band of 4 kWp or less, installers are beginning to encounter the strict enforcement of engineering requirements G83/1 by certain District Network Operators (DNOs).  The requirements do not allow a grid connected renewable energy system to export more than 16 Amps per phase without prior permission, effectively limiting the nominal power of the system to 3.68 kWp.

This enforcement is due to the DNOs being tasked with maintaining the balance of the local electricity network. Due to the recent upsurge in installation rates of embedded generator systems in theUK, such as PV, DNOs are concerned that the balance is being disturbed.

So what does this mean for the future of sub 4 kWp installations?  The performance of the inverter at low irradiation levels such as in the UK can have a significant effect on the overall system efficiency. Thus, the size of the inverter should be circa 80 per cent of the arrays’ nominal capacity in order to achieve high inverter efficiencies at low power levels. By over dimensioning the capacity of the PV generator, the overall losses of the system are taken into account, resulting in a more efficient system.

The low availability of inverters that meet the UK G83/1 requirements of 16 Amps connected to PV systems of up to 4 kWp’s power, has spurred manufacturers to begin production of these inverters. The Swiss manufacturer, Sputnik Engineering, has recently been certified after limiting the output current to 16 Amps of its SolarMax S-series string inverters. This will allow solar panel installations of up to 4 kWp the opportunity to take full advantage of FiT and nominal power, without additional procedural costs

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