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

35

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

47

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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