By contrast, if interregional transmission is not allowed in a restrictive decentralised scenario, excess production increases significantly to 10% of the production, and additional backup power as well as backup energy employing other resources become necessary within individual isolated regions to meet the demand, leading to great additional expenses. In one scenario, fuel cells powered with renewable hydrogen produce electricity at about 20 €ct/kWhel (which is already quite optimistic if the hydrogen is produced from renewable energies), raising the net electricity costs to over 8 €ct/kWhel on the average. For Region 6 (Germany and Denmark), this restrictive "decentralized”

(insular) strategy would lead to costs of electricity greater than 10 €ct/kWh.

• 6.3 Scenarios with Reduced Costs for Individual Components

The effect of cost changes for individual technologies and components was also investigated in particular scenarios. This was used to find the costs at which PV could cost-effectively contribute to the supply. A major cost reduction for PV equipment would
enable this technology to provide a significant contribution to the electricity supply. If all other costs remained the same, a reduction to one-eighth of current PV costs would enable an economically viable 4% contribution to overall electricity generation to be provided. The generation would nevertheless be limited to the southernmost regions — particularly to regions 12,16, 17, and 18. If the cost were only one-sixteenth of present levels, PV technologies could account for about 22% of all electricity generation, reducing generation costs compared with the base case scenario by about 10% to 4.3€ct/kWh.

Even in this case, however, photovoltaic technologies would not be used in the northern regions 1, 2, 3, 6, 9, and 19, because they could not contribute to overall cost reductions.

If the costs of the mirror fields of solar thermal power plants were reduced by half — as is anticipated in the near future — solar thermal plants would already constitute about 13% of all electricity generation. In this case, the electricity costs lie at 4% below those of the base case scenario. Reducing the costs of the collector array to 40% and simultaneously lowering storage costs to two-thirds of current levels (still clearly above achievable storage costs according to the recent research mentioned above) would increase their contribution to 28% of the electricity produced, while the electricity generation costs would fall by about 10% to 4.3 €ct/kWh. These examples illustrate that solar thermal generation presents an economically attractive perspective for the future that can be realized fairly easily in view of minimal cost regression factors.