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PV Design Basics Aaron Liggett Applications Engineer Jan. 27, 2017 San Diego, CA
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Transcript of PV Design Basics - aeesolar.com · Typical Grid Tied Solar System Top Down Process • Modules •...

PV Design Basics

Aaron Liggett

Applications Engineer

Jan. 27, 2017

San Diego, CA

PV Design Basics

The fundamentals of PV design; session will provide a basic understanding of photovoltaic (PV) design.

Whats to come:

Common practices

String sizing

Design considerations

Safety

Typical Grid Tied Solar System

Top Down Process

Modules

DC cabling

Racking

Inverter

Monitoring

Interconnection

Note: When grid power is lost the PV system will disconnect.

Why Sizing and Design is Important

Do not want to exceed 100% yearly offset

Visually appealing

Compensate for customers needs/requests

Comply with NEC and HOA requirements

Safety

System Design Process

Customers usage:

Yearly energy usage can be found on utility bill.

Things to Consider:

Inefficiencies in home

Old appliances

Lack of insulation

System Design Process

Total usage for the year is 10,298kWh

Project address:

123 Main St.

Anytown, CA 95661

Information needed for analysis:

Azimuth

Tilt angle

Shade

Customer requests

System size that will fit on roof Remember FSB!!

Ground mount

PVWatts

Now that we know the household usage proceed to PVWatts

Input site information

Module type

Array type

System losses

Tilt

Azimuth http://tools.solmetric.com/Tools/RoofAzimuthTool

http://pvwatts.nrel.gov/http://tools.solmetric.com/Tools/RoofAzimuthTool

PVWatts

1kW of solar will produce roughly 1,260kWh per year

Take this value and divide it by the total household usage

10,298kWh/1,260kWh8kW solar array needed

But what can actually fit on the roof?..

Roof Sizing

ALWAYS account for Fire Setbacks (FSB)

Roof AccessResidential with Single Ridge

(IFC 605.11.3.2.2)

Single ridge needs two 3 pathways on array faces along edge of load bearing exterior wall.

After FSBs we can

only fit 18 modules

Note: FSB vary depending on structure;

please reference the IFC and consult your

local AHJ.

Verifying Structure

Lag screw length required

Plywood decking, skip sheathing

Life of roof

Snow load

No fire damage or broken/damaged rafters

Confirm structure is adequate

Can reference span tables

Typ. Array will add 3-5 psf to roof

www.solarabcs.org/permitting

http://www.solarabcs.org/permitting

Racking Selection

UL 2703 for Bonding

NEC Article 250 and 690 Part V

Follow Panel manufacture spec. for mounting

Type of roofing

Comp, Tile, Standing seam etc.,

Design tools actcouncil.org Source for wind and

snow loads

SnapNrack Configurator

Dont forget to add extra

attachments for conduit routing!

http://windspeed.atcouncil.org/http://snapnrack.com/configurator/

Characteristics of Solar Modules

PV module voltage has an inverse relationship with temperature, which means that at lower temperatures, PV modules voltage raises and at higher temperatures, PV modules voltage falls from its nameplate rating.

Temperature Effects

String Sizing Max. Voltage

REC280TP

Module Voc 39.2V

Temp Coef. Voc -0.31%o All found on module data

sheet

Lowest record temp. -3C

o SolarABC interactive map

Note: Residential system are not to exceed 600 VDC per NEC 690.7 (c)

+ 25

Required Information Formula

http://www.solarabcs.org/about/publications/reports/expedited-permit/map/index.html

String Sizing Max. Voltage

+ 25

Convert temp coefficient from %/C to V/C

39.2*-0.31%= -0.122 V/C

Input all information

39.2 + 3 25 0.122 939.2 + 28 0.122 9

39.2 + 3.416 942.62 9

= 383.6 < 600V

Calculations

String Sizing Min. Voltage

REC280TP

Module Vmp 31.9V

Temp Coef. Vmp -0.39%o All found on module data

sheet

Location high temp. 28C

o SolarABC

o Use rise adder for cell temp

Note: Be sure that Min string voltage is above inverter Min operating voltage.

+ ( + ) 25

Required Information Formula

http://www.solarabcs.org/about/publications/reports/expedited-permit/map/index.html

String Sizing Min. Voltage

+ ( + ) 25

Max temp 28C+25C= 53C

o Use Vmp coefficient -0.39%/C or -0.124

Input all information

31.9 + 53 25 0.124 931.9 + 28 0.124 9

31.9 3.472 928.43 9

= 255.8 > inverter startup voltage

More Calculations

Selecting an Inverter

Inverter Data

DC input information 5.04kW DC 383.6V Max 255.8V Min 1:1 DC/AC ratio

AC information is provided 30A OCP for 240V NEC 690.8(B)(1)

BOS placement

Dont place inverters in direct sunlight w/o shade covers

Confirm with AHJ and utility for special requirements

Verify if Rapid Shutdown is required NEC 690.12

Working spaces NEC Table 110.26(A)(1)

Considerations

Interconnection

Breaker tie-in

o 120% rule

NEC 2014 705.12(D)(2)

Install breaker opposite to main breaker.

o 100% rule

Supply side connection

o Requires service-rated disco

Min. 60 amp rating

o Equipment must have AIC rating sufficient for the max. available fault current

o IPC, double-lugged panels

Interconnection Methods

System Conclusion

(2) strings of (9) REC280TP modules o Min 255.8 VDC Max 383.6 VDC

o PV STC DC size 5.04kW

(1) Fronius Primo 5.0-1o DC/AC ratio 1:1

o OCP- 30A breaker

Offset

o 5.04kW*1260kWh=6,350kWh/yr

o 61.7%

Final Design

Module Level Electronics

Microinverters SolarEdge String

Cost $$$ $$ $

Rapid Shutdown o

Shade mitigation -

Module level monitoring -

Variable string lengths oo

Max DC Voltage 60 350 600

Strings with varing tilt and azimuth -

o Requires more equipment

oo Variable string lengths possible with multiple MPPTs

Safety

Always comply with OSHA regulations

Only a qualified person should perform electrical work

Green Job Hazards

o Fall

o Electrical shock

o Heat/cold stress

Always wear proper PPE

Hazardous materials on site

o Asbestos

Vermiculite

Siding

Green Job Hazards

https://www.osha.gov/dep/greenjobs/solar.html

https://www.osha.gov/dep/greenjobs/solar.html

Resources and References

NABCEP

o Reference Guide

Imagine Solar

Solar Living Institute

USGBC

National Electric Code (NEC)

o CEC

IFC

IBC

AEE Catalog

UL

Learn More References

http://www.nabcep.org/http://www.nabcep.org/resourceshttp://imaginesolar.com/https://www.solarliving.org/http://www.usgbc.org/https://standardscatalog.ul.com/

Office: (916) 559-8823Mobile: (916) 806-4896

[email protected]

Aaron Liggett

Questions?

mailto:[email protected]

Lumber Grade Stamp

String Sizing Max. Voltage Using NEC Table 690.7

Module Voc: 39.2

Max low temp: -3C

39.2*1.12=43.9VDC/module

43.9*9(string length)= 395VDC