Optimised inverter sizing for photovoltaic systems in high-latitude maritime climates

Inverters are typically sized based on guidelines. These do not consider the specifics of a maritime climate as seen in the UK, i.e. a high percentage of diffuse irradiance, fast moving weather fronts and a smaller variation in inter-seasonal module operating temperatures compared to continental climates. The existing UK-guidelines are shown to be sub-optimal. A more appropriate sizing methodology is presented. The first influence considered is the sampling rate. It is shown that high irradiances are underestimated in hourly models, resulting in a significant skewing in the inverter sizing. The use of datasets with time resolutions higher than 10 minutes is recommended to avoid this effect in the future. Variations of module operating temperature influence the DC voltages achieved by systems. It is shown that neglecting this in the sizing might result in several percent reduced annual output. The presented model considers the voltage dependence of the inverter efficiency which is affected by the temperature induced variation of the DC voltage. Different inverters are assessed and it is shown that no general rule of thumb can be given as the sizing depends strongly on the detailed inverter characteristics.