Integrating renewables into stand-alone hybrid systems meeting electric, heating, and cooling loads: A case study
School of Engineering
The complex interplay between cost, energy, and exergy, in trigeneration and cogeneration systems when compared to power only systems, is yet to be resolved under varied proportions of heating to cooling loads. After an overview of research on the modelling and optimisation of cogeneration systems, the effects of satisfying highly dynamic electric, heating, and cooling loads are analysed in stand-alone hybridised mode, a concept not commonly tackled in the literature. The sensitivity of performance in this Micro Gas Turbine/PV system under, multi-objective (double, triple) optimisation functions is also addressed in terms of Cost of Energy (COE, $/kWh), overall energy efficiency (η, %), and exergy efficiency (ηex, %). Varied capacities of Micro Gas Turbines (30 kW and 65 kW) are included in the MATLAB based Genetic Algorithm under CHP or CCHP mode. The COE and efficiencies are dependent on the configuration, but CHP systems appear most competitive when efficiencies (as well as costs) are considered. The energy efficiency (η) of power only systems is of the order 40% but rises to ∼51% (CHP) and 55% (CCHP) for the same electric to thermal load ratio (30:70). There is a minimal effect on the COE using either triple (COE, η, ηex) or double (COE, η or COE, ηex) objective functions. The energy efficiency (η) of CCHP systems is largely unaffected by the breakdown of heating (Pther,h) and cooling (Pther,c) loads. The study also highlights that stand-alone CHP or CCHP solar-PV systems can have renewable penetrations of the order 50% and 70%.