Optimisation of stand-alone hybrid CHP systems meeting electric and heating loads
Energy Conversion and Management
School of Engineering
Most research published into stand-alone energy systems, hybridised by supplementing PV with combustion-based prime movers, considers meeting an electric load demand. This paper goes further by studying the role of both electric and heating loads on the optimisation of hybridised stand-alone Combined Heating and Power (CHP) systems. The role of both the load following strategy in these systems (electric only FEL, versus electric and thermal FEL/FTL) as well as the relative magnitude of the heating load is analysed on system cost and performance. The conceptual CHP systems modelled also consider waste system derived from either multiple Internal Combustion Engines (ICEs) or Micro Gas Turbines (MGTs). The research uses MATLAB-based Genetic Algorithm (GA) optimisation throughout and features detailed hardware characteristics as well as temporally fluctuating meteorological (solar irradiance, temperature) and load (electric, heating) data. The outcomes are also tested in relation to CHP systems sized whilst optimising either single (Cost of Energy-COE, $/kW h) or multiple functions (COE and overall system efficiency, ηCHP,%).
Results indicate that whilst the power management strategy used in CHP systems (FEL or FEL/FTL) has minimal effects on the COE, it can appreciably affect other performance indicators. For example, in CHP systems sized based on FEL/FTL, whilst COE = ∼0.20 $/kW h the resulting ηCHP is 66% for PV/Bat/ICE and 44% for PV/Bat/MGT. This is compared to using a PMS of the FEL type which results in similar COE = ∼0.21 $/kW h but with ηCHP = 50% in PV/Bat/ICE systems and 34% in PV/Bat/MGT. In relation to overall environmental impact expressed though Life Cycle Emission-LCE (kg CO2-eq/yr) when heating demand is around 50% of the electric (Electric to Thermal Load Ratio = 60:40), a PMS of the FEL/FTL results in up to 30% lower LCE compared to those with FEL in some CHP systems.