Analysis of Alternatives for a Multiproduct System Using Geothermal Energy Under Cascade Utilization Concept

Geothermal energy is one of the no fossil energy sources that has been utilized mainly for electricity generation, by using the so-called high enthalpy geothermal resource. Nevertheless, low and medium enthalpy geothermal resources are most abundant, but utilized in less extension due mainly to technological barriers or the thermal match between temperature of energy resources and the technology requirements. This work presents the analysis of alternatives for integrating a multiproduct system, producing sequentially electricity, ice and useful heating. For the purpose, the cascade utilization concept is considered for geothermal energy, utilizing low and medium enthalpy resources. To carry out the analysis, it is assumed availability of geothermal hot water with different temperatures typical of already drilled geothermal wells or studied geothermal reservoirs in Mexico. In order to produce electricity, ice and heating for further use (dehydration process or greenhouse heat supply), three cascade levels are proposed to operate sequentially and simultaneously. For electricity generation Organic Rankine Cycles are considered, and for ice production, thermally activated technologies are the best candidates. If necessary, supplementary heat is provided as a mean of geothermal energy upgrade; among the technologies to integrate are parabolic trough collectors, linear Fresnel collectors and biomass boiler. Particularly, with regard to Organic Rankine Cycles, are considered the ones that works with geothermal hot water in the range of 90 °C to 125 °C with rated power output between 25 kWe to 250 kWe. For ice production, two type of machines are under study, i.e. single-effect absorption machines with coefficient of performance around 0.6, and half-effect absorption machines with a value around 0.3 for the coefficient of performance. Absorption machines can be activated thermally with geothermal hot water with temperature in the range of 70 °C to 90 °C. Afterwards, a number of alternatives are proposed to integrate the multiproduct system, which are analyzed and compared both from the energy and economic point of view, obtaining in this way the main energy interactions of the systems, including electricity produced, amount of ice produced and heat availability. In the model, economic indicators are evaluated, obtaining for each alternative the capital cost, simple payback and net present value. Results shows quantitatively that cascade use of geothermal energy is a viable concept to increase the use of low and medium enthalpy geothermal resources with increase of energy performance and improvement of economical profit.