Energy and environmental assessment of integrated biogas trigeneration and photovoltaic plant as more sustainable industrial system

Abstract

The biogas fired tri-generation system for cooling, heating and electricity generation (BCCHP+PV) supported by a photovoltaic system (PV) is discussed and analyzed from energetic and ecological effectiveness point of view. Analyzed system is based on the internal combustion engine and the adsorption machine. For the evaluation of primary energy savings in the BCCHP aided by PV system, the indicators of the total primary energy savings (TPES) and relative primary energy savings ΔPES were defined. Also an analysis is carried out of the reduction of greenhouse gases emission. In the ecological potential evaluation, the environmental impact as an indicator of the total greenhouse gasses reduction (TGHGR) is taken into account.The presented detailed algorithm for the evaluation of the multigeneration system in the global balance boundary can be applied for the analysis of energy effects (consumption of primary energy) as well as ecological effect (emission of greenhouse gasses) for real data (e.g. hour by hour through the year of operation) taking into account random availability of renewable energy. It allows to take into account a very important factor characterized for renewable energy systems (RES) which is the variability or random availability (e.g. in the case of photovoltaic – PV) of primary energy. Particularly in the presented work the effects of the analysis and the application of the discusses algorithms have been demonstrated for the hour-by-hour availability of solar radiation and for the daily changing availability of chemical energy of biogas. Additionally, the energy and ecological evaluation algorithms have been integrated with the methods offered by exergy analysis. In the case of cogeneration systems there is a problem of the allocation of fuel between useful products (heat and electricity). The commonly applied methods of “energetic division” don’t take into account different quality of products generated in the cogeneration unit. Moreover, these methods require subjective assumptions and it can lead in some cases to non-physical results of fuel allocation. It is commonly known that exergy losses decide on the amount of consumed energy driving the production process. If in the considered process two or more products are generated these losses should be proportionally allocated between these products. For this reason the correct allocation also should be done with the application of the exergetic allocation, what has been proposed in the algorithm presented in the paper.