Solar Voltaic Energy. Outline Overview of Solar Power How Photo-voltaic (PV) Cells Work How Solar PV Cells are Made Solar PV –Applications –Efficiencies

Solar Voltaic Energy

Outline

• Overview of Solar Power• How Photo-voltaic (PV) Cells Work• How Solar PV Cells are Made• Solar PV

– Applications– Efficiencies– Economics– Facts & Trends– Research

Solar Power Overview

http://en.wikipedia.org/wiki/Image:The_Sun_w920607.jpg

PV Solar Radiation

http://en.wikipedia.org/wiki/Solar_cells

Photon Energy

Light & the Photovoltaic Effect

• Certain semiconductor materials absorb certain wavelengths – The shorter the wavelength the greater the energy– Ultraviolet light has more energy than infrared light

• Crystalline silicon – Utilizes all the visible spectrum plus some infrared

radiation• Heat vs. electrical energy

– Light frequencies that is too high or too low for the semiconductor to absorb turn into heat energy instead of electrical energy

How PV Cells Work

Florida Solar Energy Center

Cross Section of PV Cell


How Solar Cells are Made

Solar Cell Construction

• Materials– Crystalline Silicon– Gallium Arsenide (more expensive)

• Grown into large single-crystal ingots

• Sawed into thin wafers

• 2 wafers are bonded together (p-n junction)

• Wafers grouped into panels or arrays

http://en.wikipedia.org/wiki/Solar_panel

Creating Silicon Wafers

Growing Silicon Ingots

http://en.wikipedia.org/wiki/Czochralski_process

Czochralski Process

Drawing a Silicon Ingot

http://www.answers.com/topic/silicon

Silicon Ingots & Wafers

http://www.sumcosi.com/english/products/products2.html

Creating PV Cells

Computer Chips on Wafer

http://d0server1.fnal.gov/projects/silicon/www/svxwafer.jpeg

Silicon Solar Cell

http://en.wikipedia.org/wiki/Image:Solar_cell.png


PV Cells have efficiencies approaching 21.5%

Solar Modules and Arrays

Solar PV Systems• Cells are the building block of PV systems

– Typically generate 1.5 - 3 watts of power• Modules or panels are made up of multiple cells• Arrays are made up of multiple modules

– A typical array costs about $5 – $6/watt• Still need lots of other components to make this work• Typical systems cost about $8/watt



PV Modules have efficiencies approaching 17%


Solar Panel


Solar panel by BP Solar at a German autobahn bridge





Solar PV Applications

Spacecraft

Hubble Telescope

Mars Rover

International Space Station

Recreational Use (Sailboat)

Remote Areas (Mexico)


A solar panel in Marla, Cirque de Mafate, Réunion

Residential

http://www.californiasolarco.com/photos_html/grid_tied/rootop_system/nevada-city-2-4.html

Commercial

http://www.c-a-b.org.uk/projects/tech1.htm

Solar Centre at Baglan Energy Park in South Wales

Solar PV Efficiency

Solar Cell Efficiencies

• Typical module efficiencies ~12%– Screen printed multi-crystalline solar cells

• Efficiency range is 6-30%– 6% for amorphous silicon-based PV cells– 20% for best commercial cells– 30% for multi-junction research cells

• Typical power of 120W / m2 – Mar/Sep equinox in full sun at equator


Solar Panel Efficiency

• ~1 kW/m2 reaches the ground (sunny day)

• ~20% efficiency 200W/m2 electricity

• Daylight & weather in northern latitudes– 100 W/m2 in winter; 250 W/m2 in summer– Or 20 to 50 W/m2 from solar cells

• Value of electricity generated at $0.08/kWh– $0.10 / m2 / day OR $83,000 km2 / day


Solar PV Facts & Trends

DC Peak Power

Location Description MW·h/year

6.3 MW Mühlhausen, BDR 57,600 solar modules 6,750 MWh

5 MW Bürstadt, BDR 30,000 BP solar mods 4,200 MWh

5 MW Espenhain, BDR 33,500 Shell solar mods 5,000 MWh

4.59 MW Springerville, AZ 34,980 BP solar mods 7,750 MWh

4 MW Geiseltalsee, BDR 25,000 BP solar modules 3,400 MWh

4 MW Gottelborn, BDR 50,000 solar modules 8,200 MWh

4 MW Hemau, BDR 32,740 solar modules 3,900 MWh

3.9 MW Rancho Seco, CA, n.a. n.a.

3.3 MW Dingolfing, BDR Solara, Sharp & Kyocera 3,050 M·h

3.3 MW Serre, Italy 60,000 solar modules n.a.

World Largest PV Solar Plants


World Solar Power Production

Country

PV Capacity

Cumulative Installed in 2004

Off-grid PV [kW] Grid-connected [kW] Total [kW] Total [kW] Grid-tied [kW]

Australia 48,640 6,760 52,300 6,670 780Austria 2,687 16,493 19,180 2,347 1,833Canada 13,372 512 13,884 2,054 107France 18,300 8,000 26,300 5,228 4,183Germany 26,000 768,000 794,000 363,000 360,000Italy 12,000 18,700 30,700 4,700 4,400Japan 84,245 1,047,746 1,131,991 272,368 267,016Korea 5,359 4,533 9,892 3,454 3,106Mexico 18,172 10 18,182 1,041 0Netherlands 4,769 44,310 49,079 3,162 3,071Norway 6,813 75 6,888 273 0Spain 14,000 23,000 37,000 10,000 8,460Switzerland 3,100 20,000 23,100 2,100 2,000United Kingdom 776 7,386 8,164 2,261 2,197United States 189,600 175,600 365,200 90,000 62,000


Solar Cell Production Volume

http://sharp-world.com/solar/generation/images/graph_2004.gif

Sharp Corporation

Solar PV Cell Research

Solar PV Components• Inverter

– Converts DC power from solar array to AC for use in your home

• Wiring– Connects the system

components• Batteries

– Used to store solar-produced electricity for nighttime or emergency use

– Mainly used for remote sites that aren’t tied into the electrical grid

• Charge controller– Prevents batteries from

being over charged

• Disconnect switches– Allows power from a PV

system to be turned off

• Electrical meter– Measures electrical

production and use– Often runs backward if

system is attached to the electrical grid

Total system cost = ~$8.00 / watt

BATTERY

Stand Alone Solar PV System

Grid Connected Solar PV System

Connecting PV to the Grid

Net Metering

• When your system produces more electricity than your home uses– electricity flows backward out to the grid

• Meter runs backward and you get credit for the electricity you sell to the utility



Siting & Designing Solar PV

Solar PV Dependencies• Location, Location, Location !• Latitude

– Lower latitudes better than higher latitudes• Weather

– Clear sunny skies better than cloudy skies– Temperature not important

• Direction solar arrays face– South preferred, east and west acceptable

• Absence of shade– Trees, Flatirons, etc.

Solar PV Design – Key Factors

• Location– How much solar radiation does the system

receive?

• DC rating– How big is the system

Solar PV Design – Module

• Module Efficiency– How efficiently does the solar system convert

solar radiation into DC power– Best retail systems approaching 17%– Holy Grail of solar PV research

• DC to AC derate factor– How efficient is the system converting DC to

AC power

Solar PV Array Design

• Array Flat Panel– Remains in a constant fixed position

• Array tilt (equal to latitude best)– Increase solar radiation by 10-20%

compared to 0% tilt– Sunnier locations benefit more

• Array azimuth (180° best)– Directly south

Solar PV Array Tracking

• Array 1-axis tracking– Tracks sun across the sky during each day– Stays at a constant tilt– Increase solar radiation by 25-30% compared to no

tracking– Sunnier locations benefit more

• Array 2-axis tracking– Tracks sun across the sky during each day– Adjusts tilt – more in winter, less in summer– Increase solar radiation by 33-38% – Sunnier locations benefit more

PV Design Website

• National Renewable Energy Lab

• PVWATTS• http://rredc.nrel.gov/solar/calculators/PVWATTS/version2/

• Examples– Portland (97229)– Phoenix (85034)– Boulder (80309)

Solar PV Economics

Solar PV Energy Payback

• Expected lifetime of 40 years

• Payback of 1-30 years– Typically < 5 years

• Solar cells 6-30× energy required to make them


Cost Analysis

• US retail module price = ~$5.00 / W (2005)• Installations costs = ~$3.50 / W (2005)• Cost for a 4 kW system = ~$17,000 (2006)

– Without subsidies– Typical payback period is ~24 years

• Honda 4 kW system = ~$12,500 (2007)• With subsidies

– Payback is ~12 years


Economic Example 1/3

• 4000 watt system @ 40o fixed tilt

• $32,000 initial cost

• 4000 watt (4 kW) system is about 23.5 m2

– Assume 5.5 kWh / m2/day

• 23.5 x 5.5 = 129.25 DC kWh/day – hitting the solar modules


• Module Efficiency = 17%– 129.25 kWh/day x 0.17 = 21.97 DC kWh/day

• Derate factor – 77%– Takes into account inefficiencies in the DC/AC

conversion and internal module components– 21.97 DC kWh/day x 0.77 = 16.92 AC kWh/day

• Output = ~17 kWh / day


• Pay $32,000, save $555/year– 16.92 kWh/day x $0.09/kWh x 365 days/year

• 1.7% return

• Over 20 years @ 6%– Cost of Energy = $0.452/kWh– Compared to $0.09/kWh from Xcel– EXPENSIVE!

Solar PV Policy

CO Amend. 37 Solar Provision

• $4.50 rebate/watt up to 10 kW

• Combination rebate/REC for larger systems– REC = “Renewable Energy Credits”

• Funded by a $0.63/month surcharge on all Xcel customer bills

• $20 million/year program for 10 years

CO Amend. 37 Solar Provision

• On-site solar requirement– 2007 – 2010: 0.06% of a retail electricity sales – 2011 – 2014: 0.12% of a retail electricity sales– 2015 – On: 0.2% of a retail electricity sales– Focus on Xcel

• 44,000 kW of on-site solar by 2015• 1500 to 2000 new on-site solar installations

– Depending on average size– $352 million in PV solar installation sales– $200 million in rebates

Federal Tax Credit

• 30% tax credit – Max of $2,000 for residential installations– No maximum for businesses

CO Cost Analysis

• 4,000 watt system• $32,000 initial cost• $18,000 Amendment 37 rebate

– 4000 x $4.50

• $2,000 Federal Tax Credit– ($32,000 - $18,000) x 0.30 = $4,200– However, maximum of $2,000

• After rebate/tax credit cost– $32,000 - $18,000 - $2,000 = $12,000

Return on Investment

• For $12,000 you can save $555/year– 4.6% return

• Over 20 years @ 6%– Cost of Energy = $0.169/kWh– Compared to $0.09/kWh from Xcel– Still EXPENSIVE! – $$$

Solar PV Cell Research

Emerging PV Techologies

• Cells made from gallium arsenide– molecular beam epitaxy– 35% efficiencies have been achieved

• Non-silicon panels using carbon nanotubes– Quantum dots embedded in special plastics– May achieve 30% efficiencies in time

• Polymer (organic plastics) solar cells – Suffer rapid degradation to date


Thin Film Solar Cells

• Use less than 1% of silicon required for wafers

• Silicon vapor deposited on a glass substrate

• Amorphous crystalline structure– Many small crystals vs. one large crystal



Flexible PV Cells

http://www.princeton.edu/~chm333/2002/spring/SolarCells/potential%20images/flexible_pv_cell.jpg

http://en.wikipedia.org/wiki/Image:Nrel_best_research_pv_cell_efficiencies.png

Benefits/Costs of Solar PV

• Reduces pollution

• Stabilizes electricity costs

• Lessens dependence on fossil fuels

• Increases self-reliance

• Can size for small, on-site installations

• Not grid dependent

• Currently expensive $$$$$

Solar Thermal Energy

Solar Thermal Collectors

• Focus the sun to create to create heat– Boil water– Heat liquid metals

• Use heated fluid to turn a turbine

• Generate electricity

Solar Thermal Dish Collector

http://www.eia.doe.gov/cneaf/solar.renewables/page/solarthermal/solarthermal.html

Solar Thermal Dish Schematic

Solar Power Towers

http://solstice.crest.org/renewables/re-kiosk/solar/solar-thermal/case-studies/central-receiver.shtml

Solar Trough Scheme

http://solarbridge.org/pedestrians.html

Parabolic Trough Cross-Section

http://www.irishsolar.com/howdoes/how_does_1.htm

Solar Thermal Collector Trends

Year

Number ofCollector Shipments

(Thousand Square Feet)

Companies Totalb Imports Exports

1995 36 7,666 2,037 530

1996 28 7,616 1,930 454

1997 29 8,138 2,102 379

1998 28 7,756 2,206 360

1999 29 8,583 2,352 537

2000 26 8,354 2,201 496

2001 26 11,189 3,502 840

2002 27 11,663 3,068 659

2003 26 11,444 2,986 518

2004 P 24 14,114 3,723 813

http://www.eia.doe.gov/cneaf/solar.renewables/page/solarthermal/solarthermal.html

Next week:

Geothermal Energy

Documents

Solar Voltaic Energy. Outline Overview of Solar Power How Photo-voltaic (PV) Cells Work How Solar PV Cells are Made Solar PV –Applications –Efficiencies