Principal Solar Institute

A community for development and installation professionals in the solar industry

The Principal Solar Institute Module Ratings

The Principal Solar Institute’s scientifically designed and certified combination of tests and performance standards provide an unbiased, comprehensive rating system – the PSI PV module rating. Seven essential characteristics related to initial and long-term PV module performance are combined to create the PSI Rating:

  • Actual Tested Maximum Power vs. Advertised
  • Temperature Coefficient at Maximum Power
  • Power at Low Irradiance to Power at High Irradiance Ratio
  • Normal Operating Cell Temperature (NOCT)
  • Total Area Efficiency
  • Negative Power Tolerance
  • Annual Power Reduction

These ratings allow you to make comparisons when analyzing PV modules and help you select the optimal PV module.

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PSI Ratings – PV Solar Modules from Watton Solar

Here are the PSI Ratings for modules from Watton Solar, calculated based on initial performance test data. If you don’t see a solar module that you are considering, contact us and we will try to add it.

Rank Manufacturer Model Type Power
(W DC)
PSI Rating Percentile
1Watton SolarWTM240PPolycrystalline2407.47*46
2Watton SolarWTM185MMonocrystalline1857.34*38
3Watton SolarWTM235PPolycrystalline2357.30*36
4Watton SolarWTM230PPolycrystalline2307.16*28
5Watton SolarWTM180MMonocrystalline1807.14*27
6Watton SolarWTM225PPolycrystalline2257.00*21
7Watton SolarWTM175MMonocrystalline1756.93*18
8Watton SolarWTM220PPolycrystalline2206.84*16
9Watton SolarWTM170MMonocrystalline1706.73*12
10Watton SolarWTM215PPolycrystalline2156.67*11
11Watton SolarWTM165MMonocrystalline1656.54*8
12Watton SolarWTM210PPolycrystalline2106.52*8
13Watton SolarWTM205PPolycrystalline2056.36*6
14Watton SolarWTM160MMonocrystalline1606.34*5
15Watton SolarWTM200PPolycrystalline2006.21*4

* Modules denoted with an “*” use estimated values for one or more characteristics. Manufacturers can contact us to provide the missing data for these PV modules.

NOTE: PSI Ratings are based on publicly available data, and are subject to change as additional data and proprietary analyses become available for long-term performance.