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Verification of the PVToolbox against Measured Data, WatsunPV, and RETScreen for the Iqaluit Grid-tied PV System

Michael M.D. Ross
GPCo Inc.

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Link to GPCo Inc
Link to CETC-Varennes

Note on Authorship:

This technical report was authored by the principal of RER Renewable Energy Research when he was an employee of GPCo Inc.


Research conducted on behalf of the Photovoltaics and Hybrid Systems Program at the CETC-Varennes (Natural Resources Canada) with partial funding from the Panel on Energy Research and Development (PERD).


Ross, Michael M. D. Verification of the PVToolbox against Measured Data, WatsunPV, and RETScreen for the Iqaluit Grid-tied PV System. Report to CETC-Varennes (Natural Resources Canada). Varennes, Québec, 2002.


Monitored data from the Iqaluit grid-tied PV system was used to verify the accuracy of the PVToolbox weather, PV array, and inverter routines. The hourly horizontal insolation measurements were used as input; the output of PVToolbox was compared with the measured data for insolation in the plane of the array, system DC output, and system AC output. In addition, the Iqaluit system was simulated using the RETScreen photovoltaic project model and WatsunPV, and the output from these systems was compared with PVToolbox.

The mean bias error of the PVToolbox, in terms of converting insolation data from the horizontal to the plane of the array, the calculation of the system DC output, and the calculation of the system AC output, is roughly similar to that of WatsunPV for the Iqaluit grid-tied PV system. The mean bias error is roughly 22 to 26% for these tools. RETScreen is significantly less accurate, with a mean bias error of about 72%. The most troubling source of error for these hourly tools is introduced in the conversion of horizontal insolation data to the plane of the array.

The PVToolbox output matches that of WatsunPV quite closely. This suggests that the PVToolbox is functioning correctly.

The PVToolbox is sufficiently flexible that, despite being a hybrid simulation tool, it can model grid-tied systems with relatively minor modifications. The development of a grid-tied inverter model did not require changes to other component models, demonstrating that a user can make changes to individual components as necessary, without being too concerned about how this will affect the rest of the simulation components. This type of modification would be much more complicated with a tool such as WatsunPV.