Grid planning with a large amount of small scale solar power

Abstract: With an increasing interest for renewable power, photovoltaics (PV) have becomemore and more common in the distribution network. If a customer wants to install aPV system, or another type of distributed generation (DG), the distribution systemoperators (DSO) needs a good way to determine if it the grid can handle it or not. InSweden, a guideline to aid the DSO was published in 2011. However, this guidelineonly considers one connection without considering other DG units. This project isabout developing new guidelines for DG connections in grids with a large number ofDG units. Based on a literature study it has been concluded that one of the mostcritical issue is over-voltage, which is the main focus of this project. Two new methods have been developed; the first proposed method is based onneglecting reactance and losses in the grid, a simple linear relationship between thevoltage level, the resistance in the lines, and the installed power is obtained. Thisrelationship is then used to calculate the voltage level at critical points in the grid. Thesecond method is to find the weakest bus, with a connected DG unit. By assumingthat all power is installed at that point we get a very simple guideline; it is veryconservative but can be used before the first method. A simulation tool has been developed in order to analyze the voltage level in grids forvarious cases with connected DG units. The simulated results have proven that theproposed guidelines are, when considering voltage issues, very reliable and can beuseful. However, further work needs to be done to ensure that other problems donot occur.