MEASURING DEGRADATION RATES WITHOUT IRRADIANCE DATA
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MEASURING DEGRADATION RATES WITHOUT IRRADIANCE DATA Steve Pulver Daniel Cormode Alex Cronin U of A Dirk Jordan Sarah Kurtz Ryan Smith NREL
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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 - PowerPoint PPT Presentation
Transcript of MEASURING DEGRADATION RATES WITHOUT IRRADIANCE DATA
MEASURING DEGRADATION RATES WITHOUT IRRADIANCE DATA
Steve Pulver Daniel Cormode
Alex CroninU of A
Dirk JordanSarah KurtzRyan Smith
NREL
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
TEP solar test yard
Missing POA irradiance sensors
Daily Final Yield, 2005-2009
Daily and annual insolation can vary by more than the degradation rate
Variation in daily insolation
Removing irradiance variation
Define Daily Relative Final Yield as:Daily Final Yield divided by field average final yield
Daily Final Yield Daily Relative Final Yield
Relative rates of change
Provides an easy comparison between systems, and can be calculated with low uncertainty
Rate of change (percent per year)2 systems
Example: only two systems…
relative
absolute
2 systems
5 systems
10 systems
There appears to be a higher probability of low degradation rates
Adding more systems…
Rate of change (percent per year)17 systems
Translating to absolute…
relative
absolute
In a large dataset, possibly there is a system that changes very little
Assume the best system doesn’t degrade?
Challenging scenarios
Best performing system degraded by 0.5 (percent / year)
Outlier at 2.0 (percent / year)
Normalizing by the best system may not be the best solution
Our analysis
Starting point: a PDF (Probability Distribution Function) to describe the absolute degradation rate.
Histogram of our dataset(relative rate of change)
Histogram of a much larger data set(absolute rate of change)
Comparison to histograms
Exponential PDF appears to be capable of handling both our dataset and the larger dataset
Results depend on the function used
Amount to shift relative rates
Consistent results between rates measured w/ and w/o irradiance data, and similar uncertainties between the two methods.
Absolute rates of change
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
