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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
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
U.S. Primary Energy Flow by Source and Sector, 2009
(Quadrillion Btu)
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
• 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)?
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
• 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)?
Flat Plate PV
Flat Plate PV
Portland Habilitation Center PV System860kW 7-inverter system by Dynalectric Oregon
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.concentrix-solar.de/
http://www.amonix.com/content/company
Concentrating PV
Fresnel lenses
Concentrating PV
http://www.solfocus.com/en/
Concentrating PV
Cassegrain-like compound optics
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
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)?
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
(%)
Annual insolation at
optimal tilt & azimuth
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 (%)
Annual insolation at
optimal tilt & azimuth
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
• 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)?
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
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
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
• 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)?
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
• 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)?
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)
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