Islands and other isolated power systems depend on thermal power generation from Diesel or other fuels to supply their electric loads. This type of power generation is a reliable and well-known established technology but brings a lot of undesired side effects such as exhaust gas pollution, noise and a lot of preventive maintenance demand [1,2]. Moreover, rising fuel costs and the cost of transporting fuel to remote islands are putting additional economic pressure on energy costs, making electricity generation from renewable energy sources an interesting competitor today.

Especially in remote locations, electricity from renewable energies (PV and wind) can often be produced at lower costs. To enable large renewable energy shares in those systems, a sophisticated and fully integrated power flow and energy management system is installed. In addition, more grid support functions have to be provided by each renewable component [3]. Large-scale grid-forming inverters can act as the backbone for genset-free grid operation and allow higher shares of renewable energy. The large-scale integration of inverter-controlled renewable generators into isolated power grids poses significant challenges for local grid operators as the proportion of conventional synchronous generators connected to the grid is gradually reduced or even eliminated. To mitigate the aforementioned challenges while enabling greater integration of renewables, isolated grid operators have established new grid code requirements for renewables and installed battery energy storage systems (BESS) to provide power frequency control. In isolated systems with close to 100% renewable integration, the BESS converter control mode can be based on grid-forming structures as these provide better performance to mitigate grid frequency fluctuations.

A rising number of projects are proving the concept to work and providing experiences about the impacts on grid operation. This chapter describes the experiences with large grid-forming inverters on the Caribbean island St. Eustatius and the hybrid power system in Madeira.