Recent and Planned Improvements to the System Advisor Model

Aron Dobos

5th PV Performance Modeling Workshop

May 9, 2016

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

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

֍

֍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

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

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

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

NonlinearPVsyst 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.

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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

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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

SA

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ur

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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

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

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