Novel hybrid CSP-biomass CHP for flexible generation: Thermo-economic analysis and profitability assessment

This paper focuses on the thermo-economic analysis of a 2.1-MWe and 960 kWt hybrid solar-biomass combined heat and power (CHP) system composed of a 1.4-MWe Externally Fired Gas-Turbine (EFGT) and a 0.7-MWe bottoming Organic Rankine Cycle (ORC) power plant. The primary thermal energy input is provided by a hybrid Concentrating Solar Power (CSP) collector array covering a total ground area of 22,000–32,000 m2, coupled to a biomass boiler. The CSP collector array is based on parabolic-trough concentrators (PTCs) with molten salts as the heat transfer fluid (HTF), upstream of a 4.5–9.1 MWt fluidized-bed furnace for direct biomass combustion. In addition, two molten-salt tanks are considered that provide 4.8–18 MWh (corresponding to 1.3–5.0 h) of Thermal Energy Storage (TES), as a means of reducing the variations in the plant's operating conditions, increasing the plant's capacity factor and total operating hours (from 5500–6000 to 8000 h per year). On the basis of the results of the thermodynamic simulations, upfront and operational costs assessments, and considering an Italian energy policy scenario (feed-in tariffs, or FiTs, for renewable electricity), the global energy conversion efficiency and investment profitability of this plant are estimated for different sizes of CSP and biomass furnaces, different operation strategies (baseload and modulating) and cogenerative vs. electricity-only system configurations. Upfront costs in the range 4.3–9.5 MEur are reported, with operating costs in the range 1.5–2.3 MEur annually. Levelized costs of energy from around 100 Eur/MWh to above 220 Eur/MWh are found, along with net present values (NPVs) from close to 13,000 to −3000 kEur and internal rates of return (IRRs) from 30% down to almost zero when prioritizing electrical power generation (i.e., not in cogenerative mode). In all cases the economic viability of the systems deteriorate for larger CSP section sizes. The results indicate the low economic profitability of CSP integration in comparison to biomass-only plants, due to high investment costs of the former, which are not compensated by the higher global energy conversion efficiency and energy sales revenues.