بهینه سازی سیستم بهره برداری از آنتالپی سفره آب زمین گرمایی کم همراه با مناطق درجه حرارت مختلف

Market penetration of renewable energy sources, such as geothermal energy, could be promoted even by small cost reductions, achieved through improved development design. This paper deals with optimization of the exploitation system of a low enthalpy geothermal aquifer, by means of the method of genetic algorithms, which has been successfully used in similar problems of groundwater resources management. With respect to water flow, the aquifer consists of two zones of different transmissivities, while from the thermal point of view it may bear any number of zones with different temperatures. The optimization process comprises the annual pumping cost of the required flow and the amortization cost of the pipe network, which carries the hot water from the wells to a central water tank, situated at the border of the geothermal field. Results show that application of the proposed methodology allows better planning of low enthalpy geothermal heating systems, which may be crucial in cases of marginal financial viability.

Soft and renewable energy sources, offer, in medium and long term, the best, if not the sole, solution to the world's energy problem, for the following reasons: a) impact of their use on the environment is much smaller than that of conventional energy sources and b) nature provides them continuously. Still, we have to use them in a sustainable way. Regarding geothermal energy in particular, Earth will provide us with heat for the next million years at predictable rates [1], but sustainable management of geothermal resources is required to preserve both their temperature and the means of transporting their heat content to the ground surface, namely the water (or steam) capacity of geothermal aquifers. It should also be mentioned that increased share of renewables in the energy market promotes global stability, since it reduces the dependence of energy consumers on big oil companies, remote oil and natural gas producers and the respective transport means (tankers or pipes) and routes. Moreover, renewable energy sources have no military applications. This paper deals with low enthalpy geothermal resources. Much more abundant than the high enthalpy ones, and more evenly distributed around the Globe, they can provide heat for space heating and other direct uses, thus covering an important part of energy demand. Analysis of their financial performance is rather complex. A comprehensive report is offered by Lund et al. [2]. Their current contribution to the energy balance is probably underestimated, since very often their use is not adequately recorded, at least quantitatively. It is certain, though, that their share can be substantially increased in many areas of the world, including the energy importing part of Europe. Greece is one of the countries with large unexploited potential [3] and [4]. As the financial performance of geothermal energy applications is still in most cases marginal (when environmental cost is not taken into account), its optimization is very important. It may even decide whether an investment plan will be materialized. This paper deals with cost minimization of a geothermal district heating scheme. Two major cost components are taken into account: a) annual pumping (operation) cost and b) amortization of the construction cost of the pipe network, carrying hot water from the wells to a central water tank, at the border of the geothermal area.

Despite the renewable character and the environmental advantages of geothermal energy, its market penetration is still restricted, due to financial reasons. In this paper, the possibility of reducing cost of a geothermal district heating scheme, through optimizing its design by means of genetic algorithms, has been investigated. Two major cost items have been taken into account, namely: a) annual pumping cost and b) amortization of the pipe network, which carries the hot water from the wells to a water tank, situated at the border of the geothermal field. The proposed methodology has been applied to a geothermal aquifer with two zones of different transmissivities and four zones of different temperatures, which are not affected by pumping. For such a case an analytical solution exists for the hydraulic head level drawdown, which, although complex, does not introduce excessive computational load. While the simulation model is rather simplified, the respective optimization problem, which includes distribution of total required flow rate to existing and new wells and determination of the locations of the latter, is rather difficult. Pumping cost is smaller when the new wells are placed in the higher transmissivity zone and away from each other. On the contrary, pipe network cost is reduced, when the wells are concentrated close to the central tank. Total required flow is reduced, when more water is pumped from the highest temperature zone, but the latter might not be included in the higher transmissivity zone. Nevertheless, application of the method of genetic algorithms has produced pumping schemes with substantially reduced cost. Such cost reductions may be crucial for the financial sustainability of a geothermal district heating scheme.