| Abstract |
The efficiency of any thermal cycle depends on the temperature differential of the working fluid in the boiler and the condenser. As such, it depends not only on the temperatures of the geo-liquid, but also on the temperature of the condenser. Most of Australia’s geothermal energy resources are found in arid or semi-arid regions where day-time ambient temperatures are high, and where limited access to water will almost certainly prevent the use of cooling towers. This leaves air cooling through large fin and tube heat exchangers (analogous to large automotive “radiators”) as the only established alternative option for cooling. However, air cooling in the desert will lead to degraded performance when ambient temperatures are high. The extent of this degradation is illustrated by way of example, based on a flash cycle with a re-injection pressure for the geoliquid of 10MPa and a geo-liquid temperature of 210 °C. It is estimates that a change in ambient temperature from 15 °C to 45 °C, will reduce the output power of this cycle by 44 %, and that this percentage reduction increases with re-injection pressure (Langman et al., this volume). While the magnitude of this effect will depend on the type of cycle and local conditions, it will be significant for all geothermal cycles. Furthermore, the degradation will be most significant during the period of peak summer demand, at precisely the time when the price of electricity is greatest. As such, it could have a significant adverse impact on the commercial return of the plant. To address this problem it is proposed to undertake a preliminary assessment of the potential to use under-ground cooling for the plant. |