3E analysis of a hybrid renewable energy system

A micro combined heat and power (micro-CHP) unit generates simultaneously heat and power from a single fuel source at high efficiency for buildings. The micro-CHP unit can be fuelled by renewable energy sources, such as solar or biomass. The photovoltaic-thermal (PVT) collector converts solar energy to electricity and heat, simultaneously. On the other hand, the Stirling engine powered micro-CHP unit produces, in a controlled manner, energy from biomass. To support fluctuating solar based cogeneration, a hybrid renewable energy system (HRES) is formed by combining the PVT collectors and controllable Stirling engine micro-CHP unit with multi-port thermal energy storage. In addition to support fluctuating solar energy production, the hybridization enables high efficient and 100 % renewable energy production, increased reliability and flexibility, and a reduction in CO2 emissions, primary energy use and costs. However, the HRES based on the different micro-CHP units requires further analysis, especially, in terms of dynamic simulation due to highly dynamic behaviour of the PVT collectors and thermal load of the building. In this paper, a dynamic model of the described HRES is presented and built to Matlab/Simulink in order to perform energy, exergy and exergo-economic analysis of the system. The system produces domestic hot water (DHW), space heating and electricity for residential building use under climate conditions of Strasbourg, France. The hourly demand and weather data are used to simulate the operation of the HRES. In addition to energy and exergy analysis, the exergo-economic analysis is performed which combines exergy with economic analysis. This method is used to allocate the investment and operation costs of the system to the energy products. The exergo-economic method is extremely useful when the energy system has multiple inputs and outputs with different exergy levels. In addition to the 3E analysis, a sensitivity analysis is conducted to see how the number of the PVT collectors and the size of the storage tank will influence on the exergo-economic costs of the thermal and electrical energy products. As a result, the seasonal variations on the energy and exergy efficiencies are presented on the component and system level. Additionally, the monthly fuel exergy, exergy destruction in the components and exergy products of the system are presented. Finally, the monthly variation of the exergo-economic costs of the energy products is presented and discussed. The results showed that combining the free solar energy production with costly biomass energy conversion reduced the specific cost of electricity and increased the electricity production capacity of the system. The specific costs of the energy products varied seasonally and the specific cost of electricity was relatively high compared to the electric grid price due to high initial investment costs of the HRES.