Building sustainable power mix in small island grids: a multi-criteria analysis

Islands have traditionally experienced great dependency on external energy supply and many of them opted for diesel as fuel for power generation. This study tests scenarios of different levels of renewable penetration on the French Atlantic island Ouessant, facing the general problems of the energy planning such as grid reliability, the lack of economies of scale and reduced investor profitability. A complex model is built combining long-term investment routines with short-term hourly plant dispatching, following a parametric procedure. The energy mix is composed of wind - PV - tidal power plants and distributed battery storage. Their sizes adapt to the peaking loads, leading to an oversized infrastructure and to low usage rates due to loss of market opportunities during low demand hours. New evaluation criteria are necessary to policy makers in the selection of the energy mix, based on the performance of each plant and storage device, the cost of each power facility and the total system cost. From the investor perspective, the key indicator is the loss of energy generated, therefore storage will support the integration of intermittent renewables by avoiding the power curtailed and accurately sizing the generation mix. The final trade-off is between the reasonable rates of energy in excess to be curtailed, the cost of additional storage and the loss of load probability, which are socially and economically admitted by the regulator and by energy operators, having each conflicting interests and objectives.