Increased dimensioning requirements from an elevated degree of installed distributed photovoltaics

This study aims to examine the hosting capacity (the maximum amount of distributed generation possible to add to a current grid) of Mälarenergi’s distribution networks. The three areas examined are a rural network, a modern suburban grid and an older suburban grid. The networks are modelled in PowerWorld Simulator with data mainly from Mälarenergi’s NIS (Network Information System). The basic models include calculated minimum loads based on load profiles, combined with 0 kW, 2 kW, 4kW or 5 kW installed photovoltaics (PV) systems at each consumer. The compensating models are based on the previous ones but with reduced transformer voltages to lower the risk of grid over-voltages. A high load case is also examined to make sure there are no under-voltages for these models. The results show that the rural network is strong enough to handle the biggest available PV system at 5 kW, if the transformer voltage is lowered from 1.03 p.u. to 1.005 p.u. The modern suburban grid can host 4 kW solar panels together with a lowered voltage level of 1.005 p.u. The larger package of 5 kW leads to overloading at the transformer when used. The older suburban grid has the largest issues with both overvoltages and overloading and can only handle 2 kW distributed generation with a voltage reduction to 1.005 p.u. The models are fairly sensitive because of assumed transfomer parameters and, in the case of the modern suburban grid, some lines being removed due to limitations in the software. Regardless, the results are robust enough that they can be considered correct