Concentrated solar power

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EXERCISE ON CONCENTRATING SOLAR POWER Solar and biomass power generation – AA 2018/19 Prof. Giampaolo Manzolini – Ing. Marco Binotti Preliminary exercise A parabolic trough collector is used to heat up 1 kg/s of HTF at Tin to a given Tout. Determine the required collector length for different concentration ratio (CR=50, 80 and 100) assuming a DNI of 900 W/m2. HTF data are reported in Table 1, while collector data are reported in Table 2. Table 1: HTF thermodynamic properties and conditions Name Synthetic Oil Solar Salts Collector inlet temperature (Tin) 290 °C 290 °C Collector outlet temperature (Tout) 390 °C 550 °C Mean density () 760 kg/m3 1800 kg/m3 Mean specific heat (cp) 2.5 kJ/kg-K 1.5 kJ/kg-K Mean internal convective heat transfer (m=1kg/s, D=64 mm) (hint) 750 W/m2-K 600 W/m2-K Table 2: Collector properties MIRRORS GLASS ENVELOPE Reflectivity (m) 0.905 External diameter (Dext,v) 125 mm Intercept factor () 1-0.001*CR Thckness (sv) 3 mm ABSORBER TUBE Conductivity (kv) 1.04 W/m-K External diameter (Dext,abs) 70 mm Trasmittance (v) 0.97 Thickness (sabs) 3 mm Absorptivity (v) 0.02 Conductivity (kabs) 21 W/m-K Emissivity (v) 0.86 Absorptivity (abs) 0.95 OTHER DATA Emissivity (abs) 2.64E-07*T2 + 1.25E-05*T + 5.40E-02 (T in °C) External convective heat transfer (hext) (radiation+conduction) 18 W/m2-K In the analysis, the convective heat transfer between the absorber tube and the glass envelope and the thermal losses in the brackets can be neglected. Case study Design a parabolic trough CSP plant with a power block of 50 MWel net power. The solar field has synthetic oil as heat transfer fluid and a solar multiple equal to 2. The selected collectors have the same properties reported in Table 2 and an aperture of 5.75 m. For simplicity a constant internal…