To limit the ongoing climate change and to meet the UN target for an increased temperature of maximum 2 degrees, governments worldwide strive for sustainable and fossil free power generation. Hence, Photovoltaic Solar Cells (PVs) are of great interest. The potential from sun is infinite; the annual solar radiation corresponds to 6.000 times the human energy demand (IEA, 2011).

In Sweden, the power generation from sun is 0.6 ‰ (Swedenergy, 2016). It is a very small, but strongly growing, share. In the municipality of Kristianstad, south of Sweden, the vision of power generation from sun is clear: by 2040, 5 % of the electricity consumption in the area is to come from PVs (Kristianstad kommun, 2016). Along with an increased interest from subscribers, more grid connected PVs are to be expected.

An increased share of grid-connected PVs, influences the power grid. The power quality must comply with legal requirements and maintain a certain voltage. This might be a problem in rural power grids where the distances are far; the grid is getting weaker and the voltage deviation grows. Never the less, the law requires the concession holder to compensate the subscriber in relation to the decreased losses in the grid. With power generation closer to the subscriber, the distances are shorter and the grid losses is decreased.

Mellersta Skånes Kraft (MSK) is a power distribution company located in Scania, south of Sweden. In the feeding 6 kV grid, a major part of the conductors are over-head lines, meaning a lot of interruptions caused by stormy weather and fallen trees. Hence, MSK is planning for isolated conductors to decrease the number of interruptions. 

At present, MSK have a few, sporadically placed, grid connected PVs and the power generation of today, regarding power quality, is not a problem. However, MSK sees an increased interest in PVs and more power generation the next few years are to be expected. The question is, how several grid-connected PVs will impact the power grid.

In this dissertation, the rural low voltage grid of Duckarp, Kristianstad municipality, has been studied. The grid is connected to the very last transformer in a radial grid. Two cases have been modulated: one with existing PVs of today, and one with PVs at all subscribers connected to the transformer T-640, Duckarp. As the feeding 6 kV grid is to be rebuilt, the study included the choice of cable cross section area in the 6 kV grid as well. The study included grid strength, voltage deviation, load in cables and transformer, and grid losses including compensation to subscriber.  

The study shows, that with present PVs and with the condition that a tap changing transformer is used, the grid is strong and capable of keeping the voltage required. Due to voltage deviation, more grid connected PVs make the grid weaker and require higher cable cross section areas on the feeding 6 kV grid. The load is not a problem, but still there is a risk of a high proportion of harmonics in the neutral and in the transformer. This, due to the low voltage grid being located in the weakest part of the grid. The reduced losses, due to local power generation, corresponds to a compensation to subscriber of 0.02 SEK/kWh.

Building strong power grids is expensive and alternative solutions, so-called smart grids, are of interest; Line Voltage Regulator (LVR), reactive power generation in the inverter, battery storage, or load regulations to mention some. But when there is an ongoing reconstruction of the grid, as in the case studied, it is appropriate to build a strong power grid to meet a future expansion of grid-connected PVs.