Power plants generally serve for net-power production. In geothermal power plants the provided net-power results from the produced gross power output, from which auxiliary power needs to be deducted due to power consuming components in (i) the binary conversion cycle such as pumps and valves, (ii) the cooling cycle such as pumps and fans, and (iii) the thermal water cycle such as down-hole pumps. The resulting net-power output therefore depends not only on plant-specific parameters but also on geological reservoir characteristics and - concerning the cold end - on site-specific ambient conditions.
The poster addresses the different auxiliary power characteristics of geothermal power plants and derives recommendations for a holistic approach to power plant design. As in conventional power plant design, plant-specific parameters such as component efficiencies and temperature differences in heat exchangers, which allow a general statement on the quality of particular components, need to be considered. In addition, reservoir-productivity and the choice of thermal water flow rate, injection temperature and condensation temperature have a decisive impact on the net-power output. An example of a reference plant in the North-German Basin shows that the maximum net-power output cannot be achieved by striving for the maximum gross-power.
For the reasons outlined above, a detailed analysis of the particular site-specific characteristics of the net-power output needs to be carried out for each site in order to optimise project development. Beyond the approach presented here as example, further constraints (such as seasonal cycle of ambient temperature and humidity, availability of cooling water, cooling water treatment) need to be considered. Depending on the plant site, non-technical aspects (such as noise emission, land use) can be further limiting factors for power plant design. A successive development of geothermal power generation is hence related to the development and implementation of appropriate planning instruments.