Distributed generation: Thermodynamic model for a solar-dish micro-gas turbine system

Abstract

[EN]In this work a thermodynamic model that describes the performance of a power plant based on a hybrid recuperative Brayton-type parabolic dish is presented. The model is capable to analyse the performance of such plants at off-design conditions. One of the characteristics of parabolic dishes operating in hybrid mode is that they can work uninterruptedly, since the energy necessary for their operation comes from two different sources: a renewable one, the solar system, and a conventional one, the combustion of a fossil fuel. The use of a renewable energy source allows for the reduction of the fuel consumption and consequently of the emissions of pollutant gases. The distributed generation of electrical energy (that is, the installation of electricity production sources near where it is going to be used) motivates the development and optimization of these systems. The transformation of thermal energy to mechanical one is carried out by means of a Brayton thermodynamic cycle. The irreversibilities taking place in all subsystems (solar part, combustion chamber, micro-gas turbine, and the corresponding heat exchangers) have been considered in the model with home-software elaborated using Mathematica. The model is validated by comparing with several results from the literature. Subsequently, an analysis is made for two operating conditions: with and without solar contributions. Four days are analysed, each of them corresponding to a season and for four different micro-turbine power outlets (30, 23, 15 and 7 kWe). In addition, an off-design study of the behaviour of the system is made for a representative day. An estimation of the greenhouse effect emissions is made, comparing the operation with and without solar power input.