Weather-Corrected_Performance_Ratio NREL(5)

WSi = wind speed corrected to 10 m height for period i [m/s]

Tm_i = module back surface temperature for period i [°C]

Tcell_i = cell operating temperature for period i [°C].

4. Temperature-Corrected Theoretical DC Energy Generation

Temperature-corrected theoretical DC energy will be calculated with averaged values for each 15-minute data interval using Equation (8):

(8)

Where:

i = defined above

ENDCi = temperature corrected theoretical DC energy over time step i [kWh]

PSTC = summation of nameplate ratings for all installed modules in given power blocks during the acceptance test [kW]

GPOAi = POA irradiance averaged over time step i [W/m2]

GSTC = STC irradiance [1,000 W/m2]

δ = temperature coefficient of power (negative in sign) that corresponds to the installed modules [1 / °C]

Tcell_typ_avg = average annual cell temperature for the project weather file calculated by Equation (5)

Tcell_i = cell operating temperature for period i calculated with Equation (7) [°C]

TimeStepi = date/time interval for each data record i (15 minutes = 0.25 hour) [hr]. ENDCi = (PSTC) * [GPOAi /GSTC] * [1 - δ(Tcell_typ_avg – Tcell_i)] * (TimeStepi)

5. Determine Corrected Measured PR

For the test period, the temperature-corrected PR is determined by summing up the measured AC energy and the temperature-corrected theoretical DC energy over all eligible 15-minute periods (i).

(9)

Where:

PRcorr = weather-corrected PR for the test period

ENACi = measured AC energy generation [kWh]

ENDCi = temperature-corrected theoretical DC energy [kWh].

Eligible periods are defined in the contract as well as in the “Test Requirements” section of this document.

6. Compare with Guaranteed Values

The test will be deemed a success if the corrected PR is greater than or equal to the guaranteed value with 95% tolerance (or the tolerance specified in the contract) due to uncertainty applied — and if the availability guarantees have been met:

(10) PRcorr ≥ (ContractTolerance) * PRguar

Where:

ContractTolerance = tolerance to account for measurement uncertainty, as specified in the contract (95% is recommended as a default value)

PRguar = guaranteed PR defined in the contract.

PRcorr = ∑ [ENACi] / ∑ [ENDCi]

References [1] IEC 61724. "Photovoltaic system performance monitoring – Guidelines for measurement, data exchange and analysis." 1998.

[2] N.H. Reich, et al. "Performance ratio revisited: is PR?>?90% realistic?" Progress in Photovoltaics: Research and Applications, 2012.

[3] B. Decker and U. Jahn. "Performance of 170 grid connected PV plants in Northern Germany? Analysis of yields and optimization potentials." Solar Energy, 59 (4-6), 1997; pp. 127–133.

[4] T. Ishii, T. Takashima, and K. Otani. "Long-term performance degradation of various kinds of photovoltaic modules under moderate climatic conditions." Progress in Photovoltaics: Research and Applications, 19 (2), 2011; pp. 170–179.

[5] T. Ishii, K. Otani, and T. Takashima. "Effects of solar spectrum and module temperature on outdoor performance of photovoltaic modules in round-robin measurements in Japan." Progress in Photovoltaics: Research and Applications, 19 (2), 2011; pp. 141–148.

[6] Y. Ueda, et al. "Performance Ratio and Yield Analysis of Grid Connected Clustered PV Systems in Japan." Proc. Photovoltaic Energy Conversion, Conference Record of the 2006 IEEE 4th World Conference on Photovoltaic Energy Conversion; pp. 2296–2299.

[7] W.G.J.H.M. van Sark, et al. "Review of PV performance ratio development." World Renewable Energy Congress; 2012, Denver, CO.

[8] S.J. Ransome, J.H. Wohlgemuth, S. Poropat, and R. Morgan. "Can Grid Tied PV Systems Be Characterised with Only Monthly Average Values of PR?" Proc. 19th PVSEC; 2004, Paris, France; pp. 5BV-1-56.

[9] B. Marion, et al. "Performance Parameters for Grid-Connected PV Systems." Proc. 31st Photovoltaic Specialists Conference; 2005, Lake Buena Vista, FL.

[10] D.L. King, W.E. Boyson, and J.A. Kratochvil. Photovoltaic Array Performance Model. SAND2004-3535. Albuquerque, NM: Sandia National Laboratories, August 2004.

[11] F.P. Incropera and D.P. DeWitt. Fundamentals of Heat and Mass Transfer. 4th Edition. New York: John Wiley & Sons, 1996; p. 347.