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MEASURING DEGRADATION RATES WITHOUT IRRADIANCE DATA

MEASURING DEGRADATION RATES WITHOUT IRRADIANCE DATA. Steve Pulver Daniel Cormode Alex Cronin U of A Dirk Jordan Sarah Kurtz Ryan Smith NREL. Outline. Goal: Measure degradation rates for systems that don’t have irradiance data Approach: Use 20 PV systems from TEP

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MEASURING DEGRADATION RATES WITHOUT IRRADIANCE DATA

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  1. MEASURING DEGRADATION RATES WITHOUT IRRADIANCE DATA Steve Pulver Daniel Cormode Alex Cronin U of A Dirk Jordan Sarah Kurtz Ryan Smith NREL

  2. Outline • Goal: Measure degradation rates for systems that don’t have irradiance data • Approach: Use 20 PV systems from TEP • Step 1: Quantify relative degradation rates • Challenge: Relative vs. absolute rates • Step 2: Bayesian statistics to derive absolute degradation rates

  3. TEP solar test yard Missing POA irradiance sensors

  4. Variation in daily insolation Daily Final Yield, 2005-2009 Daily and annual insolation can vary by more than the degradation rate

  5. Removing irradiance variation Daily Final Yield Daily Relative Final Yield Define Daily Relative Final Yieldas: Daily Final Yield divided by field average final yield

  6. Relative rates of change Provides an easy comparison between systems, and can be calculated with low uncertainty

  7. Example:only two systems… relative absolute Rate of change (percent per year) 2 systems

  8. Adding more systems… 2 systems 5 systems 10 systems There appears to be a higher probability of low degradation rates

  9. Translating to absolute… relative Assume the best system doesn’t degrade? absolute Rate of change (percent per year) 17 systems In a large dataset, possibly there is a system that changes very little

  10. Challenging scenarios Outlier at 2.0 (percent / year) Best performing system degraded by 0.5 (percent / year) Normalizing by the best system may not be the best solution

  11. Our analysis Starting point: a PDF (Probability Distribution Function) to describe the absolute degradation rate.

  12. Comparison to histograms Histogram of our dataset (relative rate of change) Histogram of a much larger data set (absolute rate of change) Exponential PDF appears to be capable of handling both our dataset and the larger dataset

  13. Amount to shift relative rates Results depend on the function used

  14. Absolute rates of change Consistent results between rates measured w/ and w/o irradiance data, and similar uncertainties between the two methods.

  15. Conclusions • We determined degradation rates without irradiance data. • Relative degradation rates provide a useful comparison between systems • Absolute degradation rates can be obtained from relative rates

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