Using storage to integrate renewables into the distribution system — A case study

In this paper the usage of a storage device to integrate a large amount of wind power into the existing distribution system of EWR is discussed. In the case study a wind power plant rated at 16 MW is to be connected to the existing distribution system. Normally the plant would be connected via a new cable to the substation, which is roughly 20 km away. In order to reduce the overall cost, EWR decided to find solutions that use only the existing infrastructure. System impacts such as harmonics, flicker, overloading, and voltage issues have been investigated. Almost all scenarios investigated turned out to have a high impact on the power quality of the distribution system and would be outside the allowed boundaries according to the German medium voltage grid code. Various solutions have been investigated; one of them is the usage of a storage device. Storage can be used to solve several issues at once, such as reducing the voltage increase during normal operation or reducing the fast voltage drop when shutting the turbines off. Further improvements can be made by reducing the loading on the lines and transformers and thus reducing the losses in the network. A reduction in system impact through flicker can also be achieved. In the case study it turned out that in order to reduce the system impact to allowed limits according to the German medium voltage grid code, a storage device of 2 MW and an energy capacity of 500 kWh is necessary.