Energy Engineering - Power Production from Renewable Energy

Ex 6 - DESIGN AND ECONOMIC FEASIBILITY OF A CONCENTRATED SOLAR PLANT - Text

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DESIGN AND ECONOMIC FEASIBILITY OF A CONCENTRATED SOLAR PLANT Power production from renewable energy – A.Y. 20 20 /21 Prof. Paolo Silva – Ing. Dario Alfani Design of collector field A parabolic trough collector is used to heat up 1 kg/s of HTF at Tin to a given T out. Determine the required collector length and the efficiencies (optical and thermal) for di fferent concentration ratio (CR equal to 50, 80 and 100) assuming a DNI of 900 W/ m2 and a n ambient temperature of 30 °C. HTF data are reported in Table 1, while c ollector data are reported in Table 2. Table 1: HTF thermodynamic properties and conditions Synthetic Oil Solar Salts Collector inlet temperature (Tin) 290 °C 290 °C Collector outlet temperature (Tout) 390 °C 550 °C Mean density () 760 kg/m 3 1’800 kg/m 3 Mean specific heat (cp) 2.5 kJ/kg K 1.5 kJ/kg K Table 2: Collector properties COLLECTOR Mirror Reflectivity ( m) 0.905 Absorber Absorptivity ( abs) 0.95 Intercept factor ( ) 1-0.001*CR Absorber outer diameter (D ext,abs ) 70 mm Glass envelope Trasmittance ( g) 0.97 Thermal losses (W/m) 0.00826× T2 - 3.81× T + 554 Design of the CSP plant Figure 1 : Simplified parabolic trough CSP plant layout Design a parabolic trough CSP plant with a power block of 50 MW el 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 aper ture of 5.75 m. The design DNI is 900 W/m 2 and a design ambient temperature of 30 °C. The power block efficiency is 0.66 with respect to the Lorenz efficiency (computed between the HTF source and a heat sink at T= Tamb) . Table 3: plant data HTF return T from PB 290 °C p solar field 15 bar HTF collector outlet T 390 °C hydr, SF PUMP 0.85 Collector aperture 5.75 m el-mec h, SF PUMP 0.94 Collector thermal losses @ mean HTF T Piping thermal losses 1 °C (both for the hot and cold side) Calculate the optical, thermal, piping, power block and the solar field auxiliaries nominal efficiencies toget her with the collectors aperture area . Assum e a distance between parallel rows of 2.5 times the aperture and compute also the solar field land occupation . Annual simulation Calculate the yearly optical and thermal performance (based on 3 representative days) of the designed CSP plant with the following assumptions: - Site: Sevilla, 37.42° N, 5.9° W, STZ = 1 - Solar field inlet and outlet temperature can be considered constant . - ������������������ (������)=cos ������−5.251 ∙10 −4������−2.8596 ∙10 −5������2, with  in degrees . - Collector end losses can be neglected. - Solar field pressure drops are proportional to the square of the HTF mass flow. - Piping efficiency is assumed constant through the year and equal to 92% . - The power block efficiency can be computed as: ηPB = (1-%Reduction)· ηPB_nom , where %Reduction = 0.191 - 0.409· (Q ̇PB/Q ̇PB,NOM )+0.218· (Q ̇PB/Q ̇PB,NOM )2 In case of N -S oriented collectors (as in this case), the incidence angle can be computed as: �������� = cos −1√cos 2(������������)+cos 2(δ)·sin 2(ω) Compute the difference in the yearly electric energy yield and in the NPV , IRR and LCOE assuming a 7, 8 or 9 hours indirect two -tanks Thermal Energy Storage ( TES ) systems with molten salts as storage medium . The main economic assumptions are reported in Table 4. Table 4: Economic assumptions Power block cost 750 €/kW el TES cost 25 €/kWh th Solar Field Cost 220 €/m 2 Engineering and installation costs 21% of the direct plant costs Contingencies 12% of the Engineering and Procurement costs Tax rate 20% Infla tion rate 1% Rate of return on capital 4% Operating life 30 years Electric energy selling price 50 €/MWh O&M costs 0.75 €/MWh Optional : How the plant operation, the NPV and the yearly electric energy yield would change if a time -variable electric energy selling price is considered? In the attached .xls file : DNI and ambient temperature for Sevilla , hourly electric energy selling price. Equations for the solar position : ������= 23.45∙�������� (360 284 +� 365 ) ������������=229 .18∙(0.000075 +0.001868 ∙�������� (360 �−1 365 )−0.03277 ∙�������� (360 �−1 365 )−0.014615 ∙�������� (2∙360 �−1 365 )−0.04080 ∙�������� (2∙360 �−1 365 )) �������=�−(�������������� −�������������������� ) 15 +������������60 ������=(�������−12)∙15 ������������=�������������� (�������� ������������������� ∙�������������� ∙�������������� +�������� ������������������� ∙�������������� )