Download - Sam How to Rev j July 2012
tenKsolar – Production Projections using NREL SAM
Overview
In this “How to” guide you will be walked through the key assumptions necessary to model the energy output of a tenKsolar RAIS Wave using the US National Renewable Energy Lab’s (NREL) System Advisor Model (SAM). Commonly it is referred to as “SAM”.
First couple slides give background on SAM.
Next slides cover the inputs needed to SAM for tenKsolar’s RAIS Wave system
SAM is a complex program and incorporates many ways and facets in which to model renewable energy. What is shown here are the necessary and known variables to model a tenKsolar RAIS Wave. There are some variables, such as cost, levelized cost of energy, etc that are not addressed here at this time. Where those are pertinent to making a wise solar system purchase, those will be addressed in future efforts.
And as with any model, the results are only as good as the inputs. The user is guided to verify all assumptions used are relevant to their specific decision.
Also included at the end of the package is the procedure for designing a conventional solar array in SAM. This can be used to compare the energy production relative to a tenKsolar array.
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Solar Energy
Solar Energy is the world’s most abundant energy resource. Enough solar energy hits the earth in one hour to power the entire world for a whole year.
The growth in solar energy installations continues to expand worldwide.
One key to making good investment decisions is for the solar system owner to know that they are receiving the level of production they expect from the system.
A number of modeling tools, such as PV Watts, or PVSyst, or NREL’s SAM are used to model the energy production, taking into account the climate where the system is installed, the size of the system, the technology used.
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Modeling Energy Production for a tenKsolar
RAIS Wave using NREL SAM The tenKsolar RAIS Wave uses static reflection in a way unlike
another solar array. As such, generating energy production
estimates from tools like PVWatts v1 using standard PV
assumptions will yield inaccurate results.
NREL’s SAM (System Advisor Model – formerly known as Solar
Advisor Model) promotes the use of a consistent methodology for
analysis across all solar technologies, including financing and
cost assumptions.
NREL’s SAM can be downloaded from
https://www.nrel.gov/analysis/sam/download.html
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Background on SAM
SAM allows users to investigate the impact of variations in
physical, cost, and financial parameters to better understand
their impact on key figures of merit. Figures of merit related to
the cost and performance of these systems include, but aren't
limited to:
• System output
• Peak and annual system efficiency
• Levelized cost of electricity
• System capital and operating and maintenance (O&M) costs
• Hourly system production
More information about SAM can be found at
https://www.nrel.gov/analysis/sam/background.html
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Benefit of Using NREL SAM
Provides for consistent comparison between differing
technologies
Use of a 3rd party software
Ability to model practically unlimited locations
Maintain pace with other developments in solar industry
modeling
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Approved SAM versions
Given the development of SAM at NREL, a new version is
typically released on a twice yearly cycle.
However, to maintain synchronization with assumptions and
practices with tenKsolar’s system design, tenKsolar has only
approved the following versions of SAM
• SAM version 2011.12.2
Do not use any versions of SAM not listed above.
tenKsolar will issue an update to this document when the
qualification of newer versions are completed.
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Before modeling your array
To model the energy output of a tenKsolar RAIS Wave array in
SAM you need to have identified the following
• The layout of the array
• number of front row non-reflector modules
• Number of interior row reflector modules
• The location where the array will be installed
• In this picture, there are 12 front row modules, and 48
interior row modules
Front Row Modules Interior Row Modules
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What’s new in this Guide
REV I (June 13, 2012)
• Derate array production to account for module fresnel losses
during very early morning, late afternoon/evening periods
p.20
REV H (October 2011)
• Updated system availability assumption. p. 15
• New guidelines for soiling derates to account for wider
representation of possible sites and weather types. p. 22
• New guidelines for accounting for reflector edge effects. p. 32
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Creating a file in SAM
Open System Advisor
Model from the
Windows program list.
Go to the file menu
and select “File-New”
The dialog box as
shown to the right will
appear.
Make the selections as
highlighted.
A new file dialog will
appear. Provide a
descriptive name name
for your file. – i.e.
“tenKsolar 250KW
ABC project”
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SAM How To
The inputs for SAM are divided into “input pages”. These appear
at tabs along the side of the program window.
Input
Pages
Clicking on one of
these will open a
window where you will
put the assumptions for
your model
Format note:
All values
shown in SAM
in blue with
light shading
are calculated
values based
on other inputs
in the model.
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SAM How To Case
Pages When modeling a tenKsolar RAIS Array,
you will need to model two separate
arrays and then combine the output.
One array will be for the set of modules
with reflectors. The other array will be for
the front row modules without reflectors.
The only difference between the two is
how reflection (under the shading page) is
handled.
We will use the multiple simulations
feature in SAM to combine the output of
the two.
As it is very easy to duplicate cases in
SAM, it is best to first create a case with
the base assumptions.
Reflector Modules Output
Total System Output
Front Row Modules Output
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Key SAM input pages
In modeling the output for a tenKsolar RAIS Wave array, the
input pages listed below are pages you will need to work with:
Climate
Annual Performance
Array
Shading
Module
Inverter
Other input pages that model economic parameters will be
addressed in future guides.
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SAM Input Page: Climate
This is where you
get climate files for
all over the world
Process to add them
to the project is
described on the
next page.
Select the
climate
you wish
to model
here.
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Climate: How to Add Climate Files
1. Click on link indicated to open the website that provides additional climate files. Save the weather file from DOE website to your PC
2. Indicate to SAM the directory where the files are located on your PC
3. Hit the “refresh list” button to populate drop down climate list
4. Select Climate file from drop down list
5. Then hit “add to project” button to copy file to program
Now you can run SAM for the new location.
5.
1.
2.
3. 4.
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SAM input page: Annual System
Performance Type in the assumptions as listed below.
15 16
Compare conventional solar to the RAIS architecture: In a conventional solar string of 1,000 Cells the limiting current cell is the lowest 1 in a 1000 cells or 3.29 sigma In a RAIS PV module, with Cell Optimizing architecture, the limiting current cell is lowest 1 in 2.14 cells or 0.72 sigma
RAIS™ Architecture Dramatically Reduces
Impact of Cell Variability on Degradation Rate
1000 cell Solar String
RAIS architecture
4.6 times lower rate for RAIS compared to conventional string
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SAM input page: Array
The Array input page
is a complex input
page.
For a tenKsolar RAIS
Wave we are
concerned with
1. Array Sizing
2. System Derates
3. Tracking and
Orientation.
All other
assumptions will be
left as default.
1. 2.
3.
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SAM input page: Array
Array Sizing
This is where you input
the configuration of
your array based on
the layout of your array.
As all tenKsolar
modules are connected
in parallel, the modules
per string is always 1.
The strings in parallel is
the number of modules
in the array.
The number of
inverters is per the
layout.
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SAM input page: Array
Input the System
Derates as indicated.
Back ground on the
assumptions are
explained on the
next slide.
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Explanation for System Derates
• Mismatch – as each module is
connected in parallel there are no
mismatch losses
• Diodes & Connections – there are
no diodes on a RAIS Wave module
• DC Wiring – We have measured this
value to be at this level (see Note 1)
• Soiling – we have performed
experiments to validate this
assumption (See note 2)
• Sun Tracking – system dependent
• Nameplate – to account for the
effect of the fresnel losses during
early morning and late afternoon
efficiency,
• AC Wiring – we have measured this
value to be at this level (see Note 1)
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Note 1:
DC-AC Conversion Efficiency
All Modules Report DC Power
Revenue Grade AC Meter Monitored Daily (At Supply Entrance of Building)
All Losses Including: Nameplate, Inverter, Mismatch, Diodes, DC Loss, AC Loss
Measured Data is 93.3% Efficiency with inverter
Accounting for Inverter Efficiency 97.6
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Note 2 - Soiling
While tenKsolar RAIS PV module is the most tolerant PV module to soiling, it is
important to account for site conditions. This can vary according to the level of
dirt, snow, bird droppings, etc on the system. Estimates have ranged from 1% -
5% depending on the site conditions.
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SAM input page: Array
Input the
assumptions for
tracking and
orientation as shown.
As the tilt of the
module in the RAIS
wave is always
45°the tilt is always
set as shown.
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SHADING
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Shading
Two main components
• Direct Beam • Geometric Analysis Completed Off-Line
• Position of Sun by Azimuth and altitude,
System Config, Reflectivity,
• Output is Text File with Entries of Reflection
Gain by position of sun
– By azimuth – position E-W relative to
due south
– By altitude – elevation of sun relative
to horizon
• Values Range from >1 (Summer) to <1
(Winter)
• Import Directly into SAM
• Examples / Explanations follow
• Diffuse • Use Sky Diffuse Option to Allow for Diffuse
Reflection Gain (Diffuse)
• View Analysis and Measurements Made to
Determine Value
azimuth a
l
t
i
t
u
d
e
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June 21 @ Solar Noon
Minneapolis (45 degrees N Latitude)
Sun is high altitude (64 degrees) and
at zero azimuth
Two components of solar energy
1. Direct on solar module
2. Reflected (80% efficient)
Components are additive
Reflector Gain Value 1.56
SAM integrates average power value
over hour
-20 0 20
1.002109 1.002109 1.002109
1.465058 1.47254 1.465058
1.573813 1.585384 1.573813
1.500212 1.465536 1.500212
90
80
70
60
Reflector Gain Table
Azimuth By
Altitude Beam
Shading Factors
Example
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SAM input page: Shading
Shading input page is
another complex input
page.
Modeling a tenKsolar
RAIS Wave array with
reflectors requires input
to two sections
1. Azimuth by
Altitude Reflection
Shading Factors.
2. Sky Diffuse
Shading Factors.
Both of these features
are disabled for SAM
Case for front row
modules
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Beam Radiation Shading Factors
To input the azimuth
by altitude beam
radiation shading
factors
1. Click the
“import” button
2. Select the
azimuth by
altitude beam
shading
(reflector) file
provided by
tenKsolar. The
values in the
table will update.
3. Be sure to check
the “enable”
check box
1.
2.
3.
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Sky Diffuse Shading
Enter the sky diffuse shading factor as
shown = 1.19
This applies only to the sub array with
reflector modules.
Be sure to check the “enable” check box
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Experiment – Cover Reflectors w/ Dark Cloth on Mixed Cloud Day – Compare Reflector Gains (North Over South Power)
Upper Line – Reflector Gain Drops to 1.19 Under Purely Diffuse Conditions
Lower Line – When Reflector Covered – 1.0 in Direct Sun, Drops to 0.89 (North vs. South Row Shading Effect)
Reflector Gain
Diffuse and Beam
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Front Row PV: 135o
Second Row PV - Top: 135o
Second Row PV – Bottom: 108o
Diffuse Sky Analysis - Assume Uniform Intensity
“Infinite Collimated Point Sources”
RAIS WAVE
Areas Shown Are Light Acceptance Angles Reflector Diffuse Net Gain: 40o / 180o * 0.8 = 17.8% (Measured = 19%)
Reflector Diffuse Total Gain: 40o / 103o *0.8 = 31.1% (Measured = 30%)
6’
32o 45o 45o
Reflector Top: 32o
Reflector Bottom: 48o
Diffuse Sky – View Factor Analysis
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Accounting for row edge effects
When estimating the increased output for reflectors in practice it
is important to account for the effect of reflection received by
edge panels.
For each edge reflector, you should reduce the effect of
production by 10%. As this is only a small percentage in an
overall system, this effect is reduced to only it’s contribution to
the overall system.
For example, in a 14 panel wide system, the effect would be
(12 * 1 + 2 * 0.90) / 14 = 98.6%.
This reflection adjustment factor can be applied in the system
derates to account for production effects
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SAM Input Page: Module
To input the
assumptions for a
RAIS PV module,
Select the “Module”
input page, and select
“Simple Efficiency”
from the module type
drop down.
The assumptions
shown here are based
on the inherent design
of the 180W RAIS PV
module and should be
input exactly as
shown.
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Demonstration of temperature Corrected Cell
Efficiency
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Front Row Module
Back Row Module
Demonstration of reflector energy gain
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Explanation of User Defined Mounting
Structure Variables
Concentrating PV Module
efficiency to calibrate
mounting structure variables
a – calibrated to match 40
degree C NOCT assumption
b – calculated from empirical
data
dT – calcualted from empirical
data
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Mounting structure variables definition &
typical values
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b =
Sum (-1.485 + -1.3852 + - 1.4925)/3
---------------------------------------------
Sum (29.211 + 31.06 + 30.426) /3
b= -0.048
Emprical derivation of ‘b’ – wind speed
variable
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2 C dT =
Empirical derivation of dT – temperature
delta between cell and back of module
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Measurement of NOCT
SAM input page: Inverter
Input the module
performance
assumptions as
indicated under the
“Single Point
Efficiency Inverter”
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Duplicating a Case
Once all the assumptions are
entered, it is time to duplicate the
case to create a separate sub
array for the front row modules.
Select “Case” from the SAM
program drop down menu
Select the “Duplicate Case” menu
option
Type “F2” to rename the case to
tenKsolar “Front Row”
Depending on which case you
modeled, you need to either
enable or disable the reflector
(shading) options accordingly
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Combining Arrays
To combine the output of
multiple sub arrays
1. Select the
simulation menu
2. Select “Multiple
systems” from the
drop down menu
3. Check the boxes for
both sub arrays and
check the enable this
simulation box
4. Check the
enable this
simulation box
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Combining Arrays
To combine the output of
multiple sub arrays
1. Select the
simulation menu
2. Select “Multiple
systems” from the
drop down menu
3. Check the boxes for
both sub arrays and
check the enable this
simulation box
4. Check the
enable this
simulation box
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Projecting output for a 40KW RAIS Wave
Array
To complete this exercise,
let’s setup the model for a
standard 40KW array.
In this configuration, you
will see there are 13 front
Row modules and 143
Interior Row modules.
Go to the appropriate
cases in SAM and enter
the correct number of
modules and inverters
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Input for Interior Row Sub Array
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Input for Front Row Sub Array
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A couple notes
SAM does not see the added peak rating for the interior rows
above 180. The additional power is calculated dynamically using
the reflector gain file.
Given the granularity of inverters at 5KW each, and the sub
arrays being divided into separate groups that are not in 5KW
increments, the inverter balancing in the model may appear to be
sub-optimal. If you are concerned with that level of detail,
contact tenKsolar to review how this can be adjusted more finely.
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Running SAM
Run SAM by
clicking the
green arrow
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SAM Results
Summary
results can
be found
here
SAM
provides a
wealth of
additional
results that
you can
explore!
Be sure to drag the divider bar
over to reveal the “combined”
system output
Be sure to view
the graphs for
the combined
system
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Modeling Conventional Solar Arrays in SAM
Modeling a conventional solar array in SAM is fairly
straightforward.
The simplest approach is to create a new case in SAM, and use
the default values.
Then go to the Array page and select “Specify array size” and
enter the desired array size for SAM to calculate.
If desired, select a specific module and inverter.
Then hit run.
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