The document summarizes recent updates to PVSim, a photovoltaic performance modeling software. It describes updates to the soiling and snow loss models. The soiling model now uses location-based classification instead of user-selected regions, considers system tilt, uses over 150 systems of validation data across 6 years instead of 46 systems over 1 year, and models soiling effects globally instead of just California. The new snow loss model accounts for snow accumulation and melting on PV modules based on weather data, models snow shedding effects based on panel tilt and coefficients of friction, and was validated using 3 years of data from 21 sites with 60 systems with different tilt angles.

1. PVSim Update
Mike Anderson
Presented at the 2014 Sandia PV Performance Modeling Workshop
Santa Clara, CA. May 5, 2014
Published by Sandia National Laboratories with the Permission of the Author

2. 2© 2013 SunPower Corporation
Recent Updates
Updated the
Soiling Loss Model
Added new
Snow Loss Model
• SunPower-designed simulator
• Free web-based access to:
– SunPower employees
– Partners and dealers
– External parties (upon request)

3. 3© 2013 SunPower Corporation
Dynamic Soiling Loss Model
Previous Model New Model
Environment User selection
(NorCal/SoCal/Central,
Urban/Suburban/Rural)
Based on Lat/Lon (Koppen-
Geiger classification)
- allows for user adjustment
System type No distinction System tilt dependence
Coverage California Global
Validation basis 46 systems, 1 year 150 systems, 6 years average
(~20x more data)

4. 4© 2013 SunPower Corporation
Soiling Loss Model
Central
California
Hawaii

5. 5© 2013 SunPower Corporation
Soiling Loss Model

6. 6© 2013 SunPower Corporation
Snow Loss Model
Accumulation ∆𝑆𝐷 𝑃𝑉𝑎𝑐𝑐𝑢𝑚= ∆𝑆𝐷 𝐺 × 𝑐𝑜𝑠𝛽 (∆𝑆𝐷 𝐺> 0)
Where:
∆𝑆𝐷 𝐺 = change in snow depth on the ground, and
𝛽 = slope of the PV from horizontal
Melting ∆𝑆𝐷 𝑃𝑉𝑚𝑒𝑙𝑡= ∆𝑆𝐷 𝐺𝑚𝑒𝑙𝑡 ×
𝑐𝑜𝑠𝜃
𝑐𝑜𝑠𝜃 𝑧
(∆𝑆𝐷 𝐺< 0)
Where:
𝜃 = incidence angle between the sun and normal to the PV (at solar noon)
𝜃𝑧 = incidence angle between the sun and normal to the ground (zenith angle) (at solar noon)
Combined 𝑆𝐷 𝑃𝑉 = 𝑆𝐷 𝑃𝑉𝑝𝑟𝑒𝑣𝑖𝑜𝑢𝑠 +∆𝑆𝐷 𝑃𝑉𝑎𝑐𝑐𝑢𝑚 + ∆𝑆𝐷 𝑃𝑉𝑚𝑒𝑙𝑡
Where:
𝑆𝐷 𝑃𝑉 = current snow depth on the PV
𝑆𝐷 𝑃𝑉𝑝𝑟𝑒𝑣𝑖𝑜𝑢𝑠 = previous snow depth on the PV (last iteration)

7. 7© 2013 SunPower Corporation
Snow
Loss
Model
Sliding
𝛽𝑐𝑟𝑖𝑡 = 𝑡𝑎𝑛−1 𝜇 𝑠 = ~8
Angle of repose for snow is approximately 38
-assumed 45 shed pile
Coefficient of
static friction
Coefficient of
dynamic friction
Waxed wood on wet snow 0.14 0.1
Waxed wood on dry snow 0.04
Non-waxed wood on snow 0.5 0.3

8. 8© 2013 SunPower Corporation
Snow Loss Model
• Validation based on 3 years of operation at 21
sites (60 systems)
– Tracker systems
– Fixed ground and roof systems ranging from 0 to 25
degrees

9. 9© 2013 SunPower Corporation
Snow Loss Model
T0 Tracker

10. 10© 2013 SunPower Corporation
Snow Loss Model
Fixed 0 degrees