The number of photovoltaic (PV) systems increases annually in Sweden and the installation rate increases every year. The Swedish Energy Agency predict more than a doubling of the amount of electricity generated from PV systems by the year 2025, compared with today’s numbers. There are certain challenges that arise when connecting PV systems to the electric grid, concerning quality of various grid parameters, including the voltage. First, there is a risk of voltage variations due to the lack of swing mass in the PV system, to counteract changes. Voltage variations can also occur due to the unpredictability of the power source which is solar radiation. Secondly, there is a risk of increased voltage when the power production from the PV system is maximized while the power demand is low.

The purpose of this report was to help network operators to understand how grid-connected PV systems affect grid voltage levels, and what measures may be necessary to strengthen the grid in the face of a continued increase in PV system installation.

A residential area in E.ON's low voltage grid in the municipality of Halmstad, Sweden, was studied, where approximately 20% of the customers currently have installed PV systems. The customers were distributed over 5 groups connected to the area’s substation. Measurements were carried out at the substation which showed that the power changed direction on sunny days. Measurements were also carried out at the customer's connection point, which showed voltage increases on sunny days.

In addition, future scenarios were simulated where the PV installation rate in the area was increased to investigate the hosting capacity in the area, before grid strengthening measures were necessary to manage the solar installations. The results showed a variation between the groups regarding how well equipped they were for an expansion of PV installations, which was probably due to a combination of the distance to the substation and the number of customers in the group. The simulations showed how the voltage level depended on the distance to the grid station and on the number of PV systems.

Network strengthening measures to cope with a future scenario with 100% installation rate were studied. Cable reinforcement was not a sufficient measure for two of the groups, a sectioning of the group was necessary.