Recent and Planned Improvements to the System Advisor Model

Nate Blair

Team: Aron Dobos, Janine Freeman, Paul

Gilman, Nick DiOrio, Steve Janzou

October 2016

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System Advisor Model

These calculations are done

using detailed performance

models, a detailed cash flow

finance model, and a library of

reasonable default values for

each technology and target

market.

Technologies SAM can model:- Photovoltaics

- Concentrating Solar Power

(Trough, Tower, Linear Fresnel,

Dish Stirling)

- Geothermal (power)

- Solar Water Heating

- Wind (Small + Utility scale)

- Biomass Power

The System Advisor Model (SAM) is a free user-friendly platform that calculates a

renewable energy system’s (sub-)hourly energy output, and calculates detailed

financial metrics for a renewable energy project over the life of the project.

Weather

Data

System

SpecsEnergy

Production Cost DataFinancing

Options

Utility Rates

&

Incentives

+ » + + + »

Annual, Monthly,

and Hourly Output,

LCOE, NPV,

Payback, Revenue,

Capacity Factor

Aron Dobos

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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

Non-linear shading algorithm

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 (with database)

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

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Ability to calculate losses due to snow cover

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• Techno-economic model for residential, commercial, and third-party ownership systems

o Lead acid & lithium ion battery chemistries

o System lifetime analysis including battery replacement costs

o Models for terminal voltage, capacity, temperature

o Multiple dispatch controllers available

PV with Battery Model Overview

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Battery Dispatch Visualization

Peak shaving for demand charge reduction Manual dispatch for energy arbitrage

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Parametric battery sizing results

• NPV maximized for no PV

system, battery bank

capacity of 70 kWh

• Illustrates simulation-based

method to approximate

‘optimal’ sizing.

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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

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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

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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. (% loss due to shading)

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 to measured data (% greater than measured)

ReferenceMacAlpine, S.; Deline, C.; Dobos, A.; Measured and Estimated Performance of a Fleet of Shaded Photovoltaic Systems

with String- and Module-level Inverters. Progress in Photovoltaics, forthcoming, 2017.

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.

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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

- Developing mobile platform versions

(iOS and Android)

Public Source Code

Working to publicly release source code

for PV and battery models such that

users can modify and recompile the

SAM Simulation Core

Extending SAM

SAM Simulation Core (SSC)

inputs outputs

C/C++ MATLABPython .NET Java

External applications

PV CSP SWH Financials

SA

M p

roje

ct f

ile

Co

de

SD

K

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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.

Note: This complexity now being used for projects in support of Mexico DG efforts

http://www.openei.org

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Current Version:

• Direct connection to the new NREL National

Solar Radiation Database (NSRDB) including

much of North and South America

• Lifetime PV+battery simulations

• Line-by-line debugging in scripting

• Parallel processing for batch simulations

• Simplified LCOE calculator w/ fixed charge rate

• 1600+ bundled weather in simple CSV format

• Support for high-DPI screens and Linux x64

Coming up…

• Direct link to India region weather data

• Inverters with multiple MPPT inputs

• Scripting enabled for 3D shading to program

trackers w/ arbitrary geometry

• Utility scale battery storage systems

• 3D shading model comparison study

• Source code for PV and Battery models

New features

30 years @ 1 min steps

http://nsrdb.nrel.gov

DC AC

Linux x64

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• Mexico: SAM is being used to help evaluate the cost-effectiveness (payback time) for regulators for DG PV.

• India: Developing templates for PV in India including minor adjustments to financial models and easier incorporation of India resource data

• China: Developing a China language version of the SAM manual (PV and CSP being of large interest)

• General: Accessing and distributing free resource data as available and better links to other data providers (NSRDB in particular)

Growing International Presence in Developing Countries

Our team

Aron Dobos Project lead, software architecture, PV modeling

Nate Blair Emeritus lead, financials, costs, international

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