The environmental awareness has led to many political decisions and initiated laws that regulate the market towards responsible energy usage. The demand of sustainable power has led to an increasing integration of renewable energy sources to the electric grid. Solar power is the 3rd largest renewable power source after wind and bio-power.
One of the main reasons to this fast expansion is the German renewable energy act that has motivated households to install PV systems in their houses. This has led to a large amount of producers on the low-voltage network. The small scale producers receive compensation for electricity generated from the PV systems, both when it is used directly in the producer’s home and when it is sold to the grid due to low usage. The systems can be more profitable by storing the energy instead of selling it on the grid. In this way the amount of bought electricity can be reduced.
There are concerns regarding the connection of renewable sources to the grid. This project aims to examine the impact from single-phase PV systems on the low-voltage grid. The focus of this bachelor thesis is understanding problems such as harmonic distortion and grid asymmetry. Simulations have been carried out using the software MATLAB in order to study harmonic distortion in the output of a single-phase PV system. Grid asymmetry is examined through calculations and simulations of a worst case scenario in the software NEPLAN. This scenario contains a low voltage grid with a star-star connected transformer, where all PV-systems are connected to the same phase.
The simulations in combination with a literature review have provided the conclusion that harmonic distortion caused by the inverter becomes higher when the voltage supply is too low. Integration of battery energy storage systems together with PV systems does not cause additional harmonic distortion. The results also show how single-phase systems contribute to the asymmetry in the grid. When the production from the PV systems is high, and all systems are connected to a certain phase, the current and voltage will also have an impact on the other phases in the worst case scenario.