The construction of a large hydroelectric plant at an extremely favourable location in the Democratic Republic of Congo near Inga was also investigated for one proposed scenario (s. also [Kan 99]) The construction of a hydropower plant with a capacity of 38 GW was the decision resulting from computational optimisation. This would lower the costs of electricity by 5.3% compared to the base-case scenario due to more economic generation and incidental system benefits. A primary reason for the low costs of the electricity produced at Inga is the high average load of the hydropower plant of about 6900 FLH and the relatively low anticipated investment costs at this very advantageous site. Two-thirds of the electricity produced at Inga is transmitted over a HvDc system with 26GW capacity, connecting the generating station with Region 17, with the remainder conducted in equal amounts over two HVDC systems with a combined capacity of 12 GW, joining Inga with Regions 16 and 18.

• 6.5 Electricity Transmission within the Scenarios

In all scenarios — with the exception of restrictive and expensive insular configurations — electricity transmission is of significant importance. The necessary conversion capacity for the HVDC grid exceeds values of over 750 GW in some cases. (This level corresponds to about one-half of the installed generation capacity of all production facilities in the scenario regions.) The grid is used to achieve smoothing effects among different resource — dependent generation capacities using renewable energies, and to provide access to hydroelectric plants and to distributed biomass power plants with associated storage media for wide-area backup applications. In the base case scenario, for instance, about 42% of the electricity generated is transmitted over the HVDC system between the regions within the supply area. Measured against the total electricity costs the cost of the transmission system amounts to 7% of which the main part of 5% is contributed by the transmission lines and cables. HVDC transmission has a higher intrinsic system stability than AC lines. Furthermore the transmission system of the base case scenario is highly redundant due to the fact that the thermal limit of the transmission lines is about twice the
rated power and due to the fact that between almost al regions two or more systems are designed to be built parallel. But nevertheless if further redundancy was seen as desirable this could be relatively inexpensively achieved. A somewhat extreme idea would be to erect two whole systems of transmission lines in parallel. This would mean that the costs of transmission lines and cables would double but at the same time the losses would decrease and thus the overall cost increase would only be about 3% ensuring a degree of immunity against faults, which is by far higher than stipulated for today’s systems.

• 7 Conclusions Drawn from the Scenarios

The fundamental technical prerequisites for an electricity system realized entirely with renewable energies have already been fulfilled. Even at today’s prices, the price of electricity need not to be higher than from a newly erected combined-cycle gas power plant when all costs are included. The annual difference in cost compared with the current national bill for electricity, which accounts for roughly 2.2% of gross national product, would impose less than a 3%o additional burden e. g. in the case of Germany, thereby constituting a highly rational alternative to the predictable consequences of climate change and declining fossil fuel resources. Foreseeable cost reductions — particularly for renewable energy technologies — make a comprehensive renewable energy system both conceivable and potentially more economical than all current means of providing electrical energy. The problem of converting our electricity system to one that is both globally competitive and environmentally benign is therefore hardly a financial or technical issue, being instead almost entirely dependent on political attitudes and governmental priorities. Responsible political decisions are now imperative for allocating the necessary technical, scientific and economic resources to achieve this goal.