Recent and planned improvements to the system advisor model

1. Recent and Planned Improvements
to the System Advisor Model
Aron Dobos
5th PV Performance Modeling Workshop
May 9, 2016

2. 2
Free software that combines detailed
performance and financial models to
estimate the cost of energy for systems
System Advisor Model (SAM)
http://sam.nrel.gov/download
Technologies
Photovoltaics, detailed & PVWatts
Concentrating solar power
Wind
Geothermal
Biomass
Solar water heating
Financials
Behind-the-meter
residential
commercial
Power purchase agreements
single owner
equity flips
sale-leaseback
Simple LCOE calculator

3. 3
Irradiance
Transposition using Isotropic, HDKR, or Perez
Measured plane of array (POA) input
Shading
Irregular obstruction shading from 3D scene
Self-shading for regularly spaced rows
External input from SunEye, Solar Pathfinder
Snow cover loss model
Module
Simple efficiency model
Single diode model (CEC database or datasheet)
Extended single diode model (for IEC-61853 tests)
Sandia PV Array Performance Model
Inverter
Sandia/CEC grid-tied inverter model
Datasheet part-load efficiency curve
System
Sizing wizard or electrical layout
Multiple subarrays
Fixed, 1 axis, backtracking, azimuth axis, 2 axis
Battery storage
Degradation
Extrapolated single year
Lifetime simulation of all years
Simulation
1 minute to 1 hour time steps
Detailed photovoltaic model
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Dobos, A.; MacAlpine, S. Procedure for Applying IEC-
61853 Test Data to a Single Diode Model. Proc. IEEE 40th
PVSC Conf. Denver CO, June, 2014

4. 4
Interactive drag-and-drop 3D scene editing
for positioning PV arrays and obstructions
Predefined boxes, cylinders, trees, roof panes
Calculates linear beam irradiance shading
losses and sky diffuse view factor loss
Imports 2D mapping underlays from online
maps
Outputs are diurnal or hourly/subhourly time
series linear shade loss percentages
You can group PV surfaces into subarrays
and specify parallel strings
Scripting to automate panel layout and
import/export geometry data
3D shading calculator

5. 5
More efficient way to estimate nonlinear impact of partial
shading than a bottoms-up electrical cell-by-cell model.
Nonlinear loss model for parallel strings
Bottoms-up
electrical model
At each time step…
Precalculate once.
Lookup table
Number of parallel strings
Shade fraction on each string
Fraction of diffuse irradiance
DC power loss due to shade (%)
Nominal DC kW
Shaded DC kW
~
MacAlpine, S.; Deline, C.; Simplified Method for Modeling the Impact
of Arbitrary Partial Shading Conditions on PV Array Performance.
Proc. IEEE 41th PVSC Conf. New Orleans, LA, June, 2015

6. 6
Nonlinear shade model results
Electrical Linear Nonlinear
3 kW, two trees 21.1 % 13.8 % 20.4 %
18 kW, row shading 15.8 % 14.5 % 15.0 %
Two systems in Denver, CO.
SAM
Linear
SAM
Nonlinear
PVsyst SunEye
NREL garage +4.1 % -0.1 % -1.5 % ---
Denver home +6.6 % -1.3 % +0.2 % -2.2 %
Boulder home +20.2 % -1.1 % -3.1 % ---
Comparison with measured performance data.
Notes
Models are quite sensitive to accurate placement of trees and obstructions in 3D.
Lookup table method is extremely fast, but limited to 8 parallel strings.
Efforts for additional validation are ongoing and should be published later this year.

7. 7
Scripting
Built-in scripting language to automate
simulations and post-process results
Macros
Ready-to-run scripts that are packaged
into SAM for nonprogrammers
Software development kit
Develop your own software that calls
the SAM models
Model plugins (next year)
Change the equations in SAM’s models
with your own functions
Extending SAM
SAM Simulation Core (SSC)
inputs outputs
C/C++ MATLABPython .NET Java
External applications
PV CSP SWH Financials
SAMprojectfileCode
SDK

8. 8
Plugins will let you to write your own
functions replace SAM’s built-in
model equations for:
1. Incidence angle modifier
2. Tracking angles
3. Shade losses/gains
4. Spectral response
5. Module power
6. DC and AC derates
7. Cell temperature
8. Inverter MPP tracking
9. Inverter efficiency
10. Battery voltage and current
11. Battery degradation
12. Battery dispatch
13. others…?
Model plugins (next year)
int pv_cell_temp( double *in, double *out )
{
out[CELLTEMP] = in[POA]*exp(
-in[A]+in[B]*in[WSPD] )
+ in[TDRY] + in[POA]/1000*in[DT];
return 0;
}
plugin.dll
SAM Simulation Core (SSC)
Photovoltaic model
inputs outputs
Function is called
at each time step
SAMcodeYourcode

9. 9
New complex utility rate model options
Additional net metering options have been added and implemented to help users
understand the impact of different scenarios currently implemented in several states.
New data browser categorizes and consolidates results.
Linkage with OpenEI rate database improved and expanded for some international rates.
http://www.openei.org

10. 10
Version 2016.3.14:
• Direct connection to the new NREL National
Solar Radiation Database (NSRDB)
• Lifetime PV+battery simulations
• Line-by-line debugging in scripting
• Parallel processing for batch simulations
• Simplified LCOE calculator using fixed
charge rate
• 1600+ bundled weather files in simple CSV
format
• Support for high-DPI screens and Linux x64
Coming up…
• Inverters with multiple MPPT inputs
• Improved spectral response models
• Utility scale battery storage systems
• 3D shading model comparison study
New features
30 years @ 1 min steps
http://nsrdb.nrel.gov
DC AC
Linux x64

11. Our team
Aron Dobos Project lead, software architecture, PV modeling
Nate Blair Emeritus lead, financials, costs, systems (on leave)
Janine Freeman Photovoltaic and wind models
Nick DiOrio Battery storage models
Steve Janzou Programming, utility rate structures (subcontractor)
Paul Gilman User support and documentation (subcontractor)
Ty Neises Concentrating solar power models
Mike Wagner Concentrating solar power models
http://sam.nrel.gov