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Photovoltaics Bob Parkins, Energy Services Mgr, Western Area Power


Topics to be Covered: Solar Energy Fundamentals PV System components, types and configurations Basic performance and economics Case studies BP 0802


World Energy Outlook - Sustained Growth Surprise Geoth. Solar Biomass Wind Nuclear Hydro Gas Oil & NGL Coal Trad Bio. 0 500 1000 1500 1860 1880 1900 1920 1940 1960 1980 2000 2020 2040 2060 exajoules Copyright- Shell International Limited


Earth at Night "Our ignorance is not so vast as our failure to use what we know.” M. King Hubbert

Market Growth Expectations: 

Market Growth Expectations Market growth in excess of 30% p.a., led by grid-connected market Grid-tied Large Scale Power Off-Grid-Rural Off-Grid Industrial Source: Strategies Unlimited, April 2000 1 GW Rooftops (Japan, Germany) Remote Habitational Telecommunications Corporate Image Non-subsidized Residential Rooftops Commercial Building Facades (TF) PV Integrate Products Small Solar Farms


Grid-Tied System: Commercial


Grid –Tied: Residential


Definitions: Photovoltaic (or PV) systems convert light energy into electricity. The term "photo" is a stem from the Greek "phos," which means “light”. "Volt" is named for Alessandro Volta (1745-1827), a pioneer in the study of electricity. "Photo-voltaics," then, could literally mean "light-electricity." BP 0802


Definitions: Photoelectric - The ejection of electrons from a substance by incident electromagnetic radiation, especially by visible light. First observed in 1838 and explained by Albert Einstein (Noble Prize). BP 0802


Components: The PV cell is the basic unit in a PV system. An individual PV cell typically produces between 1 and 2 watts. Silicon cells typically produce about 1/2 volt, regardless of the size. BP 0802


Connecting cells together forms larger units called modules. Connecting modules together forms arrays. Connecting arrays together forms larger systems. BP 0802




Components: Cells, Modules or arrays, by themselves, do not constitute a PV system. Also needed are the balance of system (BOS): Structures on which to mount and orient them to the sun (e.g. ground or roof mounted, tracking) Conversion from Direct Current (DC) to Alternating Current (AC), together with switches, wiring and protective devices. Storage, like batteries, where appropriate. BP 0802


Rack Mounted PV


PV Configurations DC Systems PV DC Load Remote, Direct Use Example Load: Fan, Pump BP 0802


Water Pumping


DC Systems PV Battery DC Load Remote with Storage Charge Controller BP 0802


DC-AC Systems PV Battery Inverter DC to AC DC Load AC Load Off-Grid Charge Controller BP 0802


Mt. Evans Observatory


AC Systems Version 1 PV AC Load Inverter DC to AC Grid Grid Tied – Net Meter (Bidirectional) BP 0802 Net Meter DS DS: Disconnect Switch


AC Systems Version 2 PV AC Load Meter Inverter DC to AC Grid Grid Tied – Dual Meter BP 0802 Meter DS DS: Disconnect Switch


AC Systems Version 3 PV AC Load Meter Grid Grid Tied with Battery Backup BP 0802 Meter DS Power Center* Critical AC Load * Power Center: Inverter + Charge Controller + Battery


Hybrid Systems PV Battery Inverter DC to AC DC Load AC Load Off-Grid Charge Controller BP 0802 AC Generator Battery Charger AC to DC Manual Transfer Switch

System Types - Flat Plate Collectors: 

System Types - Flat Plate Collectors Solar cells are typically placed on a substrate, like sheet glass, and sealed from the environment with an encapsulant and a transparent cover. BP 0802



Concentrator Advantages: 

Concentrator Advantages Require less area. Use much fewer PV cells. Use relatively inexpensive materials (plastic lenses and metal housings). BP 0802

Flat-plate collector advantages:: 

Flat-plate collector advantages: They do not require complex tracking systems to follow the sun. They can use less expensive cells as the operating temperatures are less. Hence, They are simpler to design and fabricate and use all the sunlight that strikes them. BP 0802

Other Types of Concentrators:: 

Other Types of Concentrators: Thermal Concentrating Solar Thermal Power Parabolic Troughs Power Towers Dish Sterling All use tracking mirrors to focus and amplify sunlight to produce electricity through a conventional thermal cycle. Commonly used in large central generation. BP 0802


Parabolic Troughs Troughs move to follow sun Recirculating fluid heats to 300-400°C (570-750°F) Creates high-pressure steam that drives a turbine NREL Long parabolic troughs focus sunlight on tube containing a working fluid Parabolic trough with tube of working fluid at focus


Energizes a heat-transfer fluid. California’s Solar Two heats molten salt to 565°C (1050 °F). Heat exchangers create high-pressure steam. Hot salt can be stored for dispatchable power. Power Towers Thousands of sun-tracking mirrors (“heliostats”) focus sunlight on a central tower NREL


Hot working fluid powers an engine mounted on the arm. Entire unit rotates to follow the sun. May be able to operate in fossil-fuel hybrid configurations. Dish Sterling Engine Banks of curved mirrors focus light on a receiver NREL


Solar Fundamentals: Sun’s Path Across the Sky - Altitude SS WS SS: Summer Solstice (June 22) WS: Winter Solstice (December 22) BP 0802 ALTITUDE AZIMUTH SOLAR NOON (True South)


E S Seasonal Path – Sunrise/Sunset Plan View N W Summer Winter Spring or Fall Winter Summer BP 0403


Seasonal Driver: The Earth’s TILT Tilt = 23.5 degrees SUMMER WINTER SPRING FALL N S N S N S N S BP 0403


Annual Variation of Sun’s Position at a given time June 22 Dec 22 BP 0802 + + + + + + + + + + + + Analemma Time =12:00 p.m.


Photographic record of Analemma


Boundless Energy The solar resource base of the continental United States is more than 1016 kWh/year. The U.S. receives more than 1000 times as much energy from the sun as it consumes for all purposes, including electrical, heating, and transportation.

Solar Fundamentals - Irradiance:: 

Solar Fundamentals - Irradiance: The amount of solar power striking a surface. Typically measured in watts per sq meter (W/m2) Clear sunny day = 1000 w/sq m on a surface facing the sun at a right angle. BP 0802


Irradiance - Effect of Seasons Time of Day Noon Sunrise Sunset Irradiance (W/m2) 1,000 Jul Dec BP 0802


Irradiance - Effect of Local Weather Clear & Sunny Clouds Fog Time of Day Noon Irradiance (W/m2) 1,000 BP 0802

PV Power Ratings - Standard Test Conditions STC:: 

PV Power Ratings - Standard Test Conditions STC: Maximum PV power (also called peak watts) output is rated at: 1000 w/m2 irradiance 25 deg. C (cell Temperature) Air Mass = 1.5 NREL's Solar Energy Research Facility (SERF) Note: Manufacturers rate their modules at STC.

PV Power Ratings - PVUSA Test Conditions PTC: : 

PV Power Ratings - PVUSA Test Conditions PTC: Maximum PV power output rated at: 1,000 W/m2 irradiance 20 deg. C ambient temperature 1.0 m/sec wind speed (calm) Note: More closely reflects actual operating performance of PV modules. BP 0802

Solar Fundamentals - Insolation: 

Solar Fundamentals - Insolation The amount of solar energy striking a surface. Energy = power x time; hence, insolation = irradiance x time. Typically measured in kwhrs per sq meter per day. BP 0802


Quiz: A kilowatt hour is equivalent to: 1. A Tibetan cherpa carrying a 90 lb pack from sea level to the top of Mt Everest. 2. The combined heat from 3,412 lighted kitchen matches. 3. The energy delivered by my 200 HP Dodge Intrepid for 13.5 seconds. 4. All of the above. BP 0403


Quiz: Answer: All of the above. Note: One kWh equals about 2.6 million foot pounds or 3,412 BTU. BP 0403


Insolation (kWhrs/m2/day) Power 1,000 Irradiance (W/m2) Time (hrs) Peak Sun Hrs A1 A2 (under curve) A1 = A2 Energy = Power x Time BP 0802 (box)


Calculating PV Generation Using Insolation Given: A PV module with a name plate rating of 100W. Insolation for a given day = 5 peak solar hrs. Energy produced = 100W x 5 hrs. = 500Whrs = 0.5 kWhrs BP 0403

True Or False: 

True Or False Eugene, Oregon (home of the Ducks) gets more insolation than Miami, Florida. BP 0802

Insolation kwh/sq m/day: 

Insolation kwh/sq m/day June 21 Dec 21 Kansas City, MI 6.1 3.0 Boston, MA 5.0 2.2 Denver, CO 6.7 4.4 Eugene, OR 6.1 1.7 Miami, FL 5.0 3.9 San Jose, CA 7.0 3.3 Tucson, AZ 7.1 5.0 BP 0802

Irradiance and Time: 

Irradiance and Time


Irradiance and Time

Maximizing the Solar Harvest: 

Maximizing the Solar Harvest Tilt and Orient Array Properly towards true South Prevent Shading Minimize Array Soiling And perhaps, adjust array for different seasons and track the sun E to W BP 0802


Array Tilt Angle Is the number of degrees that the array is tilted up from horizontal. BP 0802


Irradiance (w/m2) Time (Month) Jan Jul Dec Tilt = horizontal Tilt = vertical Tilt = Latitude Module Tilt Angle vs. Season BP 0802

Array Orientation: 

Array Orientation Use a compass to find magnetic South Adjust for magnetic declination which varies with geography to get true South. BP 0802

Magnetic Declination Map: 

Magnetic Declination Map


Extreme effects of Shading on c-Si Modules % of One Cell Shaded 0 25 50 75 100 3 Cells Shaded % Loss of Power 0 25 50 66 75 93 Bypass diodes reduce the effect of shading by allowing current to bypass shaded cells and modules. BP 0802


Shade Prevention Avoid shading from buildings, trees, and other obstacles Cut back vegetation as it grows Place array far enough off the ground to allow snow shedding Periodically wash arrays Consider using diodes BP 0802


Tilt Angle Adjustment Advantages Daily adjustments increases output by 15-20% Quarterly adjustments increase output by 5 % Disadvantages Adds complexity to the system Adds costs BP 0802


Solar Tracker Types Single Axis Double Axis Passive Active BP 0802


Single Axis Tracking BP 0802


Tracker Pluses and Minuses (+) produce power during peak times (-) add expense and complexity (-) wind > 25 mph can be a problem (-) avoid in remote locations BP 0802


PV Cell Types Selenium Silicon single crystalline (c-Si) polycrystalline (p-Si) Thin Film amorphous Silicon (a-Si) Copper Indium diSelenide (CIS) Cadmium Tellride (CdTel) Galium Arsenide (Ga-As) Multi-junction BP 0802


Single Crystalline Silicon Silicon - very abundant, although limited quantities of semiconductor grade feedstock Comprises great majority of manufactured modules Single crystals typically grown into ingots, then processed Mature and proven technology High efficiencies Relatively expensive Performance degrades in heat, reverse in cold BP 0802


Polycrystalline Silicon Requires less silicon feed stock Crystals typically cast - less waste Mature technology High efficiencies, although less than c-Si Less expensive to produce Performance similar to c-Si BP 0802


Building Integrated PV System


Penetrationless Mounting Techniques


Optional Penetrationless Sys – Ballasted Pans


Amorphous Silicon Non-crystalline form of silicon Absorbs solar radiation 40 times more efficiently than c-Si; hence, much thinner (several microns vs. 100+) Uses much less silicon in highly automated, fast production Less efficient, but cheaper BP 0802


Amorphous Silicon (cont.) Easily deposited on low cost substrates (polymers, thin metal) Performs well in heat and dim light Well adapted to consumer products and building integration (tinted glass) BP 0802


aSi Advantages can be deposited on low-cost substrates BP 0802




Integrated Building Shading


PV Shingles


Advanced Thin Films (CIS, CdTel, Ga-As) Similar characteristics as amorphous Use more exotic, less common material New technology - recently introduced Efficiencies between a-Si and c-Si Multi-junction cells yield much greater efficiencies concentrators: Ga-As space: GaInP2/Ga-As/Ge BP 0802


Advanced Thin Film (cont.) Potential to be inexpensive to produce Fast production rates and low costs could dominate world production in the future BP 0802


PV Module Efficiency Efficiency = Percentage of solar irradiation that is converted into usable energy (Direct Current – DC). Given: Irradiance = 1,000 W/m2 Module Efficiency = 10% Usable Energy = (0.10)(1,000 W/m2) = 100 W/m2 DC BP 0403


PV Module Performance Type c-Si p-Si a-Si CIS CdTel Ga-As Space systems Module Efficiency (%) 12 - 15 9 - 13 5 - 6.5 7.5 - 10 7 - 9 25 - 30 30+ BP 0802


Maximizing production or minimizing costs in a fixed area - which PV modules are best ($/W vs W/SF)?


Aesthetics - what works?






In Summary


The BIG Picture Why PV - The Benefits 1 Unlimited fuel supply FREE fuel (unless corporations charge for it and the Government taxes it!!!!!!!) Clean - no pollution or emissions Does not use water Silent Minimal visual impact BP 0802


The Benefits 2 Reduces peak demand, benefiting consumers and utilities High quality power - equals or exceeds grid Reliable - insurance against utility outages Generates at load (Distributed Generation) Dependable Low maintenance BP 0802


The Benefits 3 Power source where grid power is unavailable or expensive Hedge against fossil fuel price spikes Energy independence Short project lead time Easily expanded Little or no siting opposition Desired by the Public BP 0802


Some Parting Thoughts: Economic Tools and Issues Renewable Portfolio Standards System Benefit Charges Green Energy Programs/ Green Tags Net Metering Unobstructed Interconnection BP 0802


Economic Tools/Issues (cont) Tax/Financial Incentives (The American Way) Grants/Butdowns Tax Exemptions (property value) Income Tax Credits, one time Production Tax Credits, on-going Depreciation Loans Leasing BP 0802


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