High High Concentrating Concentrating Photovoltaics: Photovoltaics:

Past, Present, and FuturePast, Present, and Future

By: Shawn LambBy: Shawn LambASU – Dept. of PhysicsASU – Dept. of Physics

The Promise of The Promise of ConcentratorsConcentrators• Concentrator = any system that uses Concentrator = any system that uses

concentrating sunlight to harness energy. concentrating sunlight to harness energy. We will focus on Concentrating Photovoltaic We will focus on Concentrating Photovoltaic Systems (CPV)Systems (CPV)

• Since 1970’s concentrators have been Since 1970’s concentrators have been developed and researched.developed and researched.

• From 1975 to 1992 the total of research From 1975 to 1992 the total of research funds for concentrator technology funds for concentrator technology exceeds $40M worldwide.exceeds $40M worldwide.

• Today only a handful of companies Today only a handful of companies pursue research in concentrators.pursue research in concentrators.

Concentrating Concentrating PhotovoltaicsPhotovoltaics

• Of all types of Solar concentrating Of all types of Solar concentrating systems, CPV will have the most systems, CPV will have the most immediate impact on energy production.immediate impact on energy production.

• Uses optics to concentrate incident Uses optics to concentrate incident sunlight onto small PV cell.sunlight onto small PV cell.

• Concentrations from 2 to 1000+ suns.Concentrations from 2 to 1000+ suns.

• Must track the sun precisely (<0.1 Must track the sun precisely (<0.1 degree)degree)

• Cheaper because system uses less PV Cheaper because system uses less PV material (Silicon, AlGaAs, GaSb, etc.)material (Silicon, AlGaAs, GaSb, etc.)

Technology of CPVTechnology of CPV• Lightweight, cheap, plastic Fresnel lenses Lightweight, cheap, plastic Fresnel lenses

are used to concentrate light.are used to concentrate light.

• Light must be dispersed over cell not Light must be dispersed over cell not focused onto one spot.focused onto one spot.

• Cells mounted into receiver with built in Cells mounted into receiver with built in heat-sink to dissipate heat.heat-sink to dissipate heat.

• Ephemeris or autoguider used to track the Ephemeris or autoguider used to track the sun so that solar rays are incident to panels.sun so that solar rays are incident to panels.

• Exotic materials used for PV cell. Exotic materials used for PV cell. Economically viable since less material is Economically viable since less material is used.used.

Why Concentrate?Why Concentrate?

• Efficiency increases with concentration. Efficiency increases with concentration. Record set at 35% efficiency by NREL Record set at 35% efficiency by NREL using a multi-junction GaInNAs substrateusing a multi-junction GaInNAs substrate

• More common materials used in structure More common materials used in structure (such as metal, plastic, glass, steel, etc.)(such as metal, plastic, glass, steel, etc.)

• Cheaper overall:Cheaper overall:– Currently Flat Plate PV ~ $0.39 / kWhrCurrently Flat Plate PV ~ $0.39 / kWhr– CPV ~ $0.13 / kWhr (over the lifetime of CPV ~ $0.13 / kWhr (over the lifetime of

the project)the project)

Applications of CPVApplications of CPV• 3rd world water pumping for drinking or 3rd world water pumping for drinking or

agricultureagriculture• Grid-connected power farms (medium to Grid-connected power farms (medium to

large scale)large scale)• Off-grid homes (ex/ mountain homes)Off-grid homes (ex/ mountain homes)• Hydrogen production: store energyHydrogen production: store energy• Backup generators: reliability beyond Backup generators: reliability beyond

the grid (large battery banks)the grid (large battery banks)• Disaster relief units: after hurricane, Disaster relief units: after hurricane,

floodflood• Remote hospitals & refugee camps (tent Remote hospitals & refugee camps (tent

cities in desert)cities in desert)

Flat Plate vs. CPVFlat Plate vs. CPV

• Flat-Plate industry is well establishedFlat-Plate industry is well established

• Well developed production lines have Well developed production lines have brought overall costs down for F.P.brought overall costs down for F.P.

• F.P. doesn’t need to track: uses diffuse, F.P. doesn’t need to track: uses diffuse, non-incident sunlightnon-incident sunlight

• Small flat-plate structures are easily Small flat-plate structures are easily transported and installedtransported and installed

• CPV has better future prospects but a bad CPV has better future prospects but a bad (un-warranted) reputation(un-warranted) reputation

Weaknesses of CPVWeaknesses of CPV

• Not well established market (yet)Not well established market (yet)

• Must track the sun accurately (only Must track the sun accurately (only incident rays used)incident rays used)

• PV material tends to overheat (thus PV material tends to overheat (thus reducing the efficiency gained by reducing the efficiency gained by concentrating)concentrating)

• Needs cooling: passive or active Needs cooling: passive or active (water flow over surface or Peltier (water flow over surface or Peltier cooling)cooling)

• PV substrate has a shortened lifetime PV substrate has a shortened lifetime (typically ~ 5 years) (typically ~ 5 years)

Players in the GamePlayers in the Game• Amonix (Torrence, CA) – large scale grid-tied Amonix (Torrence, CA) – large scale grid-tied

power applications. High concentration power applications. High concentration Fresnel LensesFresnel Lenses

• ENTECH (Keller, TX) – Space applications ENTECH (Keller, TX) – Space applications • BP Solar (Linthicum, MD) – PV solar appsBP Solar (Linthicum, MD) – PV solar apps

• Sunpower (Sunnyvale, CA) – R&DSunpower (Sunnyvale, CA) – R&D

• NREL (Golden, CO) – R&D NREL (Golden, CO) – R&D

• Sandia Labs (Albuquerque, NM) – R&D, Grid Sandia Labs (Albuquerque, NM) – R&D, Grid stabilitystability

• National Center for Photovoltaics (DOE) – National Center for Photovoltaics (DOE) – R&DR&D

• Energy Efficient and Renewable Energy Energy Efficient and Renewable Energy (DOE) (DOE)

Future Objectives for CPV Future Objectives for CPV R&DR&D

• More efficient, large-scale production More efficient, large-scale production is needed to stay cost competitive is needed to stay cost competitive with flat plate PVwith flat plate PV

• Tracking systems must be improved Tracking systems must be improved and made cheaper (currently ~ $20K)and made cheaper (currently ~ $20K)

• Cooling systems must be integrated Cooling systems must be integrated into the modules themselvesinto the modules themselves

• Optics: anti-reflection using thin films or Optics: anti-reflection using thin films or water flowwater flow

• Higher efficiency substrate made cheaplyHigher efficiency substrate made cheaply

Tracking the SunTracking the Sun• Cheaper, more accurate tracking systems Cheaper, more accurate tracking systems

are needed for CPV technology.are needed for CPV technology.• Autoguiding techniques, borrowed from Autoguiding techniques, borrowed from

astronomy, using a CCD or CMOS imager astronomy, using a CCD or CMOS imager can be developed into a closed-loop can be developed into a closed-loop tracker for < $100 (relatively disposable). tracker for < $100 (relatively disposable).

• Decentralizing the CPV modules into Decentralizing the CPV modules into several independent tracking systems several independent tracking systems working coherently could drastically working coherently could drastically reduce downtime for the system.reduce downtime for the system.

• An ephemeris can be used for times when An ephemeris can be used for times when the autoguider cannot find the sun the autoguider cannot find the sun (cloudy day).(cloudy day).

Cooling / Anti-reflectionCooling / Anti-reflection

• Energy is lost by reflection of solar rays off Energy is lost by reflection of solar rays off of glazing layer (glass) also by decreased of glazing layer (glass) also by decreased efficiency due to substrate heatingefficiency due to substrate heating

• Thin films have been used but are very Thin films have been used but are very expensive. It has been shown that a thin expensive. It has been shown that a thin dynamic layer of water flowing over the dynamic layer of water flowing over the surface of the PV panels will reduce surface of the PV panels will reduce reflection as well as cool the systemreflection as well as cool the system

• Passive cooling includes designing modules Passive cooling includes designing modules to draw heat away from substrate (heat to draw heat away from substrate (heat sink)sink)

EconomicsEconomics• Currently medium sized, silicon CPV Currently medium sized, silicon CPV

generators produce electrical energy generators produce electrical energy (fed to grid) at $0.21 / kWhr (fed to grid) at $0.21 / kWhr

• Currently Fossil / Nuclear / Hydro costs Currently Fossil / Nuclear / Hydro costs about $0.08 / kWhr (will only increase)about $0.08 / kWhr (will only increase)

• Gallum Arsenide has near future Gallum Arsenide has near future prospects of ~$0.07 / kWhrprospects of ~$0.07 / kWhr

• Future projections show silicon CPV Future projections show silicon CPV systems at <$0.09 / kWhrsystems at <$0.09 / kWhr

• By 2020 CPV is predicted at ~$0.06 / By 2020 CPV is predicted at ~$0.06 / kWhrkWhr

Grid Connected Power Grid Connected Power FarmsFarms• Net metering - credit for powerNet metering - credit for power

produced by PV (paid by power companies)produced by PV (paid by power companies)• Sell “green tags” to independent brokers Sell “green tags” to independent brokers

(label stating that electricity was produced (label stating that electricity was produced by renewable source).by renewable source).

• Federal / State subsidies for renewable Federal / State subsidies for renewable energy power farms, including PVenergy power farms, including PV

• Several test facilities: 480 kW Euclides Several test facilities: 480 kW Euclides Project in Canary Islands, Spain by BP Solar. Project in Canary Islands, Spain by BP Solar. Entech’s 300 kW project in Austin, TXEntech’s 300 kW project in Austin, TX

• Investors needed for future developmentInvestors needed for future development• ~20 year lifetime (if cells are maintained ~20 year lifetime (if cells are maintained

and or replaced)and or replaced)

Future of World CPV MarketFuture of World CPV Market• Medium to large sized solar farms for Medium to large sized solar farms for

rural power generationrural power generation

• Water pumping applications are most Water pumping applications are most likely as well as water pasteurizationlikely as well as water pasteurization

• Could be used as a form of revenue for Could be used as a form of revenue for isolated villages to sort of “link together” isolated villages to sort of “link together” separate PV power farms into a quasi-separate PV power farms into a quasi-stable gridstable grid

• Unlikely CPV will overtake flat-plate PV on Unlikely CPV will overtake flat-plate PV on world marketworld market

Disaster Relief / Humanitarian Disaster Relief / Humanitarian AideAide

• Used to power refugee camps and remote Used to power refugee camps and remote hospitals in places where fuel is not hospitals in places where fuel is not readily available.readily available.

• Portable power trailers could be brought Portable power trailers could be brought to the location upon demand and to the location upon demand and transported easily.transported easily.

• Hybrid CPV, Wind, Diesel Generator Hybrid CPV, Wind, Diesel Generator system most probable (need to split up system most probable (need to split up the electrical load).the electrical load).

• Would pay for itself (if maintained Would pay for itself (if maintained correctly) in a short amount of time.correctly) in a short amount of time.

ConclusionsConclusions

• Under-exploited renewable energy Under-exploited renewable energy resourceresource

• Needs maturity in public opinion / Needs maturity in public opinion / knowledge and industry production knowledge and industry production capabilitiescapabilities

• Future economics looks good, has Future economics looks good, has potential to overtake most forms of potential to overtake most forms of renewable electrical productionrenewable electrical production

• Technology: Tracking, cooling, anti-Technology: Tracking, cooling, anti-reflection can be improvedreflection can be improved

Further InformationFurther Information• The National Renewable Energy LabThe National Renewable Energy Lab::

www.nrel.govwww.nrel.gov• For information on how PV has helped in For information on how PV has helped in

disaster relief visitdisaster relief visit:: www.nrel.gov/surviving_disaster/www.nrel.gov/surviving_disaster/

• National Center for Photovoltaics:National Center for Photovoltaics: www.nrel.gov/ncpv/www.nrel.gov/ncpv/

• U.S. Dept. of Energy, Energy Efficient U.S. Dept. of Energy, Energy Efficient and Renewable Energy (EERE):and Renewable Energy (EERE): www.eere.energy.gov/solar/www.eere.energy.gov/solar/

• Sandia National Labs PV:Sandia National Labs PV: www.sandia.gov/Renewable_Energy/renewablwww.sandia.gov/Renewable_Energy/renewable.htme.htm