Summary and Outlook

The use of Fresnel-Collectors in power plant configurations with low or zero CO2-emission has been analysed in this paper. Both, the solar-biomass hybrid plant and the solar-gas hybrid plant are very promising concepts with respect to technical, economical and ecological aspects. The hybrid operation would be very useful to handle the fluctuating solar resource and facilitate operation.

Depending on feed in tariffs the hybridisation of a solar thermal power plant with biomass or with small shares of natural gas can be economically very interesting. The ecological advantage of a solar-biomass power plant is evident, since it would be a zero CO2- emission plant. Beyond that biomass is a limited source, especially in regions with high solar irradiance.

More difficult to evaluate is the fossil hybridisation since it could be argued, that it would be better to fire the gas in a highly efficient combined cycle power plant instead of a low efficient steam cycle. It has been shown that it is favourable to build a hybrid solar plant, as from one kWh fuel over 200% electricity can be taken out in the configuration with 15% fossil share. In comparison a high-efficiency combined cycle will reach in maximum 60%. Of course in case it is technically and economically feasible to run a Fresnel plant without gas co-firing, from an ecological point of view this option should be realized, since a combined cycle can transform gas more efficiently.

Therefore the long term strategy should be working with very low gas shares or coupling solar fields to other steam plants than gas like coal or as described above to a biomass vessel. Another long-term option is thermal storage which is not yet feasible for direct steam generating systems.

The herein examined gas hybrid variants are by far more favourable than Integrated Solar Combined Cycle Systems (ISCCS), which have been previously examined. Since much higher solar shares can be reached this is a forward-looking technology. Furthermore the solar field does not act as a disturbing factor as opposed to the ISCCS concept, where the efficiency of the sophisticated CC system is reduced due to suboptimal dimensioning of components. In other words: It is better to build the suggested hybrid plant with low gas share and CC plants instead of ISCCS plants. The resulting solar levelised electricity costs of both options are approximately the same.

The calculated levelised electricity costs for the examined configurations of between 11 and 13 ct/kWh are very promising results. The calculations were made based on cost assumptions for the collector of 130 €/m2 which seems realistic not for the first project but for the »third« plant. As a next step in the commercialisation of the Fresnel-technology demonstration and test collectors must be built, such as by the Australian company Solar Heat and Power, to validate the technical and economic assumptions.