The Institut fur Solare Energieversorgungstechnik (ISET) in Kassel has been developing scenarios for a future electricity supply entirely with renewable energies. Various concepts have been studied for providing renewable energies to Europe and neighbouring regions.

An extensive region (s. Fig. 9) with approx. 1.1 billion inhabitants and an electricity consumption of roughly 4000 TWh/a has been analysed to determine the available potentials for a future energy system. This process has taken into account ECMWF data as the meteorological basis and the population density as a restrictive factor for the wind energy potentials or estimated roof areas in all countries within the shown regions for determining the roof top photovoltaic potentials, combined with data on solar irradiation (ECMWF and NCEP/NCAR), wind speeds, and also temperatures used e. g. for photovoltaic electricity production and for solar thermal electricity production. Also other renewable resources such as biomass and hydropower have been investigated or included at the level of current knowledge. Mathematical optimisation routines have been applied to the question of which renewable resources with their individual temporal behaviour at different sites and with different yields should be used, and how selection should be made to achieve optimum cost performance. (A linear optimisation with roughly 2.45 million restrictions and about 2.2 million free variables is employed to find the best combination in each scenario.). The optimisation takes into account the temporal behaviour of the combined consumption of all countries within every individual region shown in Fig. 9 as well as all requirements imposed by resource-constrained production. Both sets of data, electricity demand and

temporal behaviour of the possible production, have been compiled for optimisation (using time series with three-hour intervals) for all of the 19 regions to be supplied. The optimisation process ensures that supply will meet demand at any time, while determining if and to which extent any potential source is to be used, and how every part of the supply system will operate, including the dimensioning and operation of a HvDc grid that is superimposed on the current grid infrastructure. The criterion of optimisation is the minimization of overall annual costs of electricity when fed into the regional high-voltage grids, enabling these costs to be compared directly with those from regular power stations feeding into the conventional AC-high-voltage grid. However, the economic optimisation of all power plant operations for a time frame greater than, or equal to, three hours has simultaneously been included using sets of time series extending over one year.

• 6.1 Base Case Scenario

The promising results for the base-case scenario — which assumes an electricity supply system implemented entirely with current technology using only renewable energies at today’s costs for all components (s. a. [Czi 01]) — indicate that electricity could be produced and transported to the local grids at costs below 4.7 €ct/kWh, which hardly differs from the case of conventional generation today. (At gas prices in 2002 of about 2.4 €ct/kWh for industrial consumers in Germany [EC 04], electricity from newly erected combined-cycle gas power stations had already reached significantly higher 5 — 6 €ct/kWhei.) In this scenario, nearly 70% of the power originates from wind energy produced from wind turbines with a rated power of 1040 GW. Biomass and existing hydroelectric power plants provide most of the backup requirements within the supply area, in which the individual regions are strongly interconnected via high-capacity HVDC transmission lines. Electricity is generated from biomass at 6.6 €ct/kWhel after proceeds from heat sales have been factored in. This result lies significantly above the average price level, yet the backup capability is essential to reduce the overall cost of the entire system. About 42% of the electricity produced is interregionally transmitted via the HVDC-System whereby the total transmission losses sum up to 4.2% of the electricity produced. Another 3.6% loss is production which neither can be consumed at the time it is produced nor be stored for later use within the pumped storage plants and therefore is produced in excess. These two losses may be considered quite acceptable for an electricity supply only using renewable energies.