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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 © 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 © 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 © 2013 SunPower Corporation
Soiling Loss Model
Central California
Hawaii
5 © 2013 SunPower Corporation
Soiling Loss Model
6 © 2013 SunPower Corporation
Snow Loss Model
Accumulation ∆𝑆𝐷𝑃𝑉𝑎𝑐𝑐𝑢𝑚= ∆𝑆𝐷𝐺 × 𝑐𝑜𝑠𝛽 (∆𝑆𝐷𝐺> 0)
Where:
∆𝑆𝐷𝐺 = change in snow depth on the ground, and
𝛽 = slope of the PV from horizontal
Melting ∆𝑆𝐷𝑃𝑉𝑚𝑒𝑙𝑡= ∆𝑆𝐷𝐺𝑚𝑒𝑙𝑡 ×𝑐𝑜𝑠𝜃
𝑐𝑜𝑠𝜃𝑧 (∆𝑆𝐷𝐺< 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 𝑆𝐷𝑃𝑉 = 𝑆𝐷𝑃𝑉𝑝𝑟𝑒𝑣𝑖𝑜𝑢𝑠 +∆𝑆𝐷𝑃𝑉𝑎𝑐𝑐𝑢𝑚 + ∆𝑆𝐷𝑃𝑉𝑚𝑒𝑙𝑡
Where:
𝑆𝐷𝑃𝑉 = current snow depth on the PV
𝑆𝐷𝑃𝑉𝑝𝑟𝑒𝑣𝑖𝑜𝑢𝑠 = previous snow depth on the PV (last iteration)
7 © 2013 SunPower Corporation
Snow Loss Model
Sliding
𝛽𝑐𝑟𝑖𝑡 = 𝑡𝑎𝑛−1 𝜇𝑠 = ~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 © 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 © 2013 SunPower Corporation
Snow Loss Model
T0 Tracker
10 © 2013 SunPower Corporation
Snow Loss Model
Fixed 0 degrees