it‟s good to live near a starresources.solmetric.com/get/photovoltaic energy production.pdf ·...

It‟s Good to Live Near a Star

An Introduction to Photovoltaic Energy Production

SolmetricSebastopol, CA

Mission: Improve the effectiveness of solar systems and

those who install them by providing high quality, easy-to-use,

accurate tools with embedded technical know-how.

http://www.solmetric.com

http://www.solmetric.com/

Topics

• Where is PV in the US energy mix?

• How does PV work?

• What do PV systems look like?

• What is my solar resource?

• How is PV array performance measured?

• What are the trends in the PV industry?

• Where are the jobs in PV (and RE generally)?

http://www.eia.doe.gov/energy_in_brief/renewable_energy.cfm

http://www.eia.doe.gov/energy_in_brief/renewable_energy.cfm

U.S. Primary Energy Flow by Source and Sector, 2009

(Quadrillion Btu)

http://www.eia.doe.gov/emeu/aer/pecss_diagram.html

http://www.eia.doe.gov/emeu/aer/pecss_diagram.html

Annual US Installed Grid-Connected PV Capacity2000-2009

Utility

Non-Residential

Residential

Installed PV capacity worldwideas of 2009

As of July 2010, Germany

accounted for nearly 50% of

the total cumulative PV

installations in the world.

Germany

Spain

Japan

US

Italy

China

Australia

ROE

ROW

India

European Photonics Industry Consortium, Report

on Photovoltaics: PV Market Overview 2009.

Topics








Grid-tie PV system

PV modules

To the house To the grid

Typically 72-96

solar cells per

PV module

From Cells to Arrays

Cell

Module

Panel

Array

How Solar Cells Work

• Charge generation by photons

• Charge separation by built-in electric field at the junction

•Charge collection at the contacts

+

Basic mechanisms of a solar cell:

Photon

Solar cell

I-V curve of a solar cell

Equivalent circuit I-V Curve

(+0.6v)

Curr

ent

Voltage

Isc

Voc

Curr

ent

Voltage

Imp

Vmp

Maximum Power Point

I-V “building block”

Area = Imp x Vmp

Units are watts (W)

Max Power Point Imp, Vmp

Curr

ent

Voltage

Imp

Vmp

I-V and P-V Curves

Max Power

Max Power Point

I-V

P-V

Pow

er

Pmax

In x Vn

Cells in Series & Parallel

I

V

I-V

building

blocks

Series

Parallel

Total (net) I-V curve

Effect of partial shadingInverter must identify and track the right peak

Cu

rre

nt

Voltage

Isc

Voc

Po

we

r

Max Power(until the shade pattern changes!)

PV array performance factors

•Local climate

•Array-inverter matching

•Array tilt and orientation

•String layout

•Shade

•Soiling

•Array temperature

Topics








Flat Plate PV

Portland Habilitation Center PV System860kW 7-inverter system by Dynalectric Oregon

Combiner Boxes860kW System at Portland Habilitation Center, by Dynalectric Oregon

Combiner Box860kW System at Portland Habilitation Center, by Dynalectric Oregon

Concentrating PV

(CPV)

Concentrating PV

High Gain Solar

http://www.skyline-solar.com/index.htm

Concentrating PV




Concentrating PV

http://www.morgansolar.com/

http://www.morgansolar.com/

Concentrating PV

http://www.concentrix-solar.de/

http://www.amonix.com/content/company

Concentrating PV

Fresnel lenses

http://www.amonix.com/content/company

http://www.emcore.com/

Concentrating PV

http://www.emcore.com/

Concentrating PV

http://www.solfocus.com/en/

Concentrating PV

Cassegrain-like compound optics

http://www.solfocus.com/en/

Multi-junction solar cellsUsed in CPV to boost efficiency

Solar Thermal

(not PV, but still cool!)

PS-10 & PS-20 Solar Thermal “Power

Towers” near Seville, Spain

Solar thermal „power towers‟

Solar thermal „power towers‟

Trough Concentrators

http://www.stirlingenergy.com/

Dish Stirling engines

http://www.stirlingenergy.com/

Topics








Solar Resource

no access

reducedaccess

maximumaccess

•Climate

•Array orientation

•Shade

Annual Sun Paths

Energy = 12 kWh

Assume an average irradiance of 1 kW/m2 for 6 hours

Insolation = 1 kW/m2 x 6 hr = 6 kWh/m2

Insolation: Solar energy per unit area - kWh/m2

Area = 2 m2

Annual insolation at

optimal tilt & azimuth

Annual energy

available to PV

system

Loss due to sub-

optimal tilt &

azimuth

TOF (%)

TOF: Tilt & Orientation Factor Insolation at actual tilt & azimuth

as % of insolation at optimal tilt & azimuth

Tilt & Orientation Factor (TOF)

Annual Insolation vs Array OrientationExample: Honolulu International Airport, HI

http://www.solmetric.com/annualinsolation-us.html




Annual energy

available to PV

system

Loss due to sub-

optimal tilt/azimuth

Loss due to

shading

TOF (%)

Solar Access

(%)



Solar Access: Insolation with shade

as % of insolation without shade

Impact of Trees Located SE and SW of an ArrayTwo strings of 12 BP-120‟s driving an SMA-2500

AC

Pow

er

Outp

ut

(W)

Time of Day

Solar

Noon

TSRF: Total Solar Resource FractionInsolation with actual shade, tilt & azimuth

as % of insolation with optimal tilt & orientation and no shade

TOF (%)

Solar Access

(%)

Loss due to sub-

optimal tilt/azimuth

Loss due to

shading

Annual energy

available to solar

system

TSRF (%)



TSRF = Solar Access x TOF

The original SunEye 110

Shade analysis tools from Solmetric

The new SunEye 210

http://www.solmetric.com/buy210.html



Topics








Performance Verification Tools

Inverter readout compared with system model

I-V curve measurements compared with

PV model

DC measurements compared with

PV model

Verification: Measurements compared with a standard

Basic Comprehensive

I

V

Copyright Solmetric 2009

Benefits of I-V Curve MeasurementCompared with DMM & Clampmeter Testing

Cu

rre

nt

Voltage

Isc(Clamp meter)

Voc(Multi-meter)

• Full I-V curve More diagnostic value

• Automated Fast & less chance of record keeping mistakes

Copyright Solmetric 2009

Series and Shunt LossesContributors to reduced fill factor

Cu

rre

nt

Voltage

Imp

Vmp

Isc Max Power PointImp, Vmp

Voc

Shunt

loss

Series

loss

Useful indicators: • Imp / Isc ( shunt loss)

•Vmp / Voc ( series loss)

I-V measurement methods

Load can be:•Electronic•Resistive

•Capacitive

I sense

V sense

Cu

rre

nt

Voltage

Load requirements:

• Voltage & current range

• Power dissipation

• „Sweep‟ dynamics, esp sweep rate,

which must be slower to accurately

test high-efficiency modules

PV modelsFor predicting PV array performance

• Sandia National Labs PV Array Model

– Most comprehensive (30+ parameters)

– ~400 modules modeled, more will flow starting ~ mid-2011

• 5-Parameter Model

– Developed at U. Wisconsin, used by CEC for NSHP program

– ~1,700 PV modules modeled at this time

• Simple Datasheet Model

– Translates Pmax (STC) to actual irradiance & temperature

– User enters data sheet parameters

These 3 methods are available in the Solar Advisor Model (SAM) from NREL and are

embedded in the Solmetric PV Analyzer.

Solmetric PV AnalyzerPVA-600

http://www.solmetric.com/pva600.html

http://www.solmetric.com/pva600.html

Testing individual PV strings860kW System at Portland Habilitation Center, by Dynalectric Oregon

Max Power measurement (example)Ratio of measured to predicted (target)

I-V & P-V curves (example)Red dots are the model predictions

•Shaded area is the inverter‟s MPPT voltage range

•Model set to „array as sensor‟ mode

Example measurement results

Field-aged thin film string

Array-as-sensor mode

0

1

2

3

4

5

6

7

8

0 50 100 150 200 250 300 350 400

Voltage - V

Cu

rren

t -

A

String 4B14

String 4B15

Troubleshooting ExampleAbnormal (red) and typical (blue) I-V curves of adjacent strings

I-V curve of the failed module

Irradiance changed between measurements

Effect of shade on PV arrays

+

PV Module with Bypass DiodesExample: 72-cell module

Partial shadingInverter must identify and track the right peak

Cu

rre

nt

Voltage

Isc

Voc

Po

we

r

Max Power(until the shade pattern changes!)

Partial shading Business card on 1 cell in a string of 15, 48-cell modules

Shadow of leafless tree branchSingle module with 72 cells and 3 bypass diodes

Partially shaded residential arraySingle string, along lower edge of roof

Shade 2 cells in the same cell stringSingle module with 72 cells and 3 bypass diodes

Shade 2 cells in adjacent cell stringsSingle module with 72 cells and 3 bypass diodes

Topics








Trends in the PV industry

• Public policy remains the main driver for expansion

• Coming (and going) of state-level incentive programs & the ITC

• Increased (for now) federal funding for R&D in PV, RE generally

• Shift to production-based incentives and feed-in tarrifs

• Many more PV manufacturers, lower $$$/Watt. Commodity pricing.

Trends in the PV industry

• More financing options (from city, county, installer, PPA)

• Vertical integration (cells + modules + system design + construction)

• Increasing numbers of utility projects

• Tough to get huge utility projects approved

• Faster approval for 1-20MW „substation‟ projects

Topics








Jobs in PV (and RE generally)

• RE is one of the few industries now growing rapidly

• “Are there green jobs? Maybe not, but the green sector has jobs!”

• They are in traditional disciplines

• Hiring is taking place in all of the disciplines

• New roles in energy auditing, consulting, retrofit, policy, advocacy

• Lots of PV and RE start-ups, from components to systems

• Many applicants for every job

• Field experience or specialized training are an advantage

• Do informational interviews and job shadowing

• Choose a job and field that you are passionate about

• Do internships to get experience and build a relationship with a potential employer

Jobs in PV (and RE generally)

it‟s good to live near a starresources.solmetric.com/get/photovoltaic energy production.pdf ·...

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