BP neural network CI engine CO2 emissions avoided Covenant of Mayors Discrete Element Model EP4 GateCycle Power Take Off Research & information: general SDEWES 2018 Stirling engine airlift pump alternative fuels anaerobic digestion and composting bilevel modelling bioelectricity biofuel biomass borehole heat exchangers borehole thermal energy storage building location bypass carbon capture chicken manure circular economy climate change co-generation coefficient of performance cogeneration combustion