CONCENTRACION FOTOVOLTAICA - 2009 03 12 CPV Webinar

POLITÉCNICA

Webinar in Photovoltaic ConcentrationMarch 12, 2009

Webinar in Photovoltaic ConcentrationWebinar in Photovoltaic ConcentrationMarch 12, 2009March 12, 2009

High concentration photovoltaics: potentials and challenges

J.C. Miñano, P. Benítez

LPI-LLC, USAUniversidad Politécnica de Madrid, Spain

Webinar in Photovoltaic ConcentrationWebinar in Photovoltaic ConcentrationMarch 12, 2009March 12, 20092/42

1. Why high concentration photovoltaics (HCPV)?

2. Concentrator optics fundamentals

3. Advanced HCPV optics

4. Comparing HCPV systems

5. HCPV versus 2-axis tracked flat-plates

6. Summary

Outline

FhG-ISE

monolithic multijunction tandem III-V solar cells in concentration

Why high concentration photovoltaics (HCPV)?Record cell efficiencies

• From ~30% to 40% during the last decade• III-V cells are very expensive (~$50,000/m2-$200,000/m2) • HCPV purpose is to decrease cell cost by reducing its area

FPPV=Flat panel PVHCPV=High Concentration Photovoltaics

(High) concentration factor(High) concentration factor

Solar cell

Area A

sunlight

electricity

Area A

What is HCPV?

solar radiation

cell cost other costs+

efficiency×

energy=

1. Concentration to decrease cell cost2. Efficiency=(optical efficiency) x (cell efficiency)3. optics, tracker Tolerance4. only direct radiation is useful for concentration (90-65%)

Why high concentration photovoltaics (HCPV)?

6. Summary

Outline

Classic imaging PV concentrators

Example: Flat Fresnel lens

Rays tilted at the acceptance angle α: rays focus approximately on the edge of the cell

(degs)

0.5 1 1.5

T(θ) (%)

Geometrical and chromaticaberrations

Formal definition of acceptance angle α: Angle at which transmission drops to 90% of maximum

Ideal lens

Real lens

For a given optical design concept:

sin α ≈

constant × cell side

Such “constant” strongly depends on the optical design concept

Modifying the geometrical concentration

α’ α

Some examples of CPV systems based on flat

Fresnel lens

Illumination non-homogeneity in imaging concentrators

Fresnel lens

Therefore, imaging concentrators have to compromise uniformity and

pointing tolerance

Sun image on the cell

Perfect aiming Misspointing

Sun angular diameter= 0.53º (r=±0.27º)

Classic non-imaging secondary optical elements (SOE)

Prism homogenizer

Classic non-imaging secondary optical elements (SOE)

CPC-type non- imaging

concentrator(reduces cell area)

Compare cost and efficiency!

Other imaging concentrator designs

Cassegrian two-mirrorsParabolic mirror

Other imaging concentrator designs

Cassegrian two-mirrorsParabolic mirror

6. Summary

Outline

1. Higher Efficiency

2. Higher Tolerance

3. Higher Concentration?

Why advanced HCPV optics?

• To be achieved without increasing the number of optical elements.

• Each optical surface must perform as many functions (concentration, homogenization, etc.) as possible.

• The highest Tolerance for a given Concentration will maximize Efficiency at system level.

Symptomatology:

1. Optics surfaces require high accuracy

2. Assembling is expensive because fine adjustments become

compulsory.

3. Efficiency decreases significantly from single unit to array.

Optical mismatch

4. Efficiency increases significantly when the cells are bigger.

5. The electricity production waves in moderate windy

conditions

6. The efficiency decrease due to dirt accumulation is more

severe than in flat modules

Do you need more tolerance?

Tolerance

Tolerance budget has to be shared among:

1. Sun’s angular extension ±0.27°2. Optical component manufacturing

(shape and roughness)3. Module assembling4. Array assembling5. Tracker structure stiffness6. Tracking accuracy

0.1°-0.5° present automotive industry standards

Advanced HCPV optics: Free-form designs

• Free-form: surfaces with no prescribed symmetry

• New degrees of freedom to the design: A single optical element can perform multiple functions

• The SMS 3D design method of Nonimaging Optics is the most advanced method to design free-forms

Free-form XR for HCPV (Boeing-LPI)

Homogenizing prism

Free-form lens

A. Plesniak et al. “Demostration of high performance concentrating photovoltaic module designs for utility scale power generation”, ICSC – 5, (Palm Desert, CA, USA, 2008)A. Cvetkovic, M. Hernández, P. Benítez, J. C. Miñano, J. Schwartz, A. Plesniak, R. Jones, D. Whelan, “The Free Form XR Photovoltaic Concentrator: a High Performance SMS3D Design”, Proc. SPIE Vol. 7043-12, 2008

Free-form mirror

Solar cell

Free-form lens

Secondary lens (R)

Solar cell

Primary lens (R)

RR free-form Kohler design for HCPV

A. Cvetkovic et al. “High Performance Köhler Concentrators with Uniform Irradiance on Solar Cell”, ICSC – 5, (Palm Desert, CA, USA, 2008)

RR free-form Kohler design for HCPV

A. Cvetkovic et al. “High Performance Köhler Concentrators with Uniform Irradiance on Solar Cell”, ICSC – 5, (Palm Desert, CA, USA, 2008)

Other free-form designs (for SSL)Free-form RXI Free-form RXI with Kohler

integration

6. Summary

Outline

What should be the criterion to compare CPV systems?

• Final merit function = cost of electricity

• It is difficult to evaluate before product is very mature

• Several parameters are usually selected as merit functions to compare

Some parameters for CPV systems comparison

1. Module electrical efficiency at nominal conditions

2. Concentration

3. Tolerance angle (in degs)

4. Nominal power per unit area of the module, Pmodule (in Wp /m2)

5. Nominal power per unit area of the cell, Pcell (in Wp /cm2)

6. Estimated yearly energy production in certain reference locations (in kWh/(m2 year))

7. Others: Mounting complexity, numbers of parts per unit area of the module, materials cost, weight, depth, thermal design, etc

Electrical efficiency η (%)

The efficiency-concentration-tolerance (ECT) space

Tolerance α (degs)

Concentration Cg

= 27%Cg =400xα

= ±0.5 degs

Example: Fresnel lens concentrator with

0.5 degs

Boundaries of the ECT space

Thermodynamic limits:• Electrical efficiency (for infinite junctions) limited to: η < 86%

• Concentration × Tolerance2 < n2 ≈

2.25 (n=refractive index of encapsulant)

Electrical efficiency η

Boundaries of the ECT space

Tolerance (degs)

Concentration

η < 86%

Concentration × Tolerance2 < n2 ≈

Tolerance > sun radius = 0.26ºη

Cg =400xα

= ±0.5 degs

Example: Fresnel lens concentrator with

Comparing CPV systems in the ECT space

= 27%Cg =400xα

= ±0.5º

= 27%Cg =1,000xα

= ±1.8º

Fresnel lens concentrator XR free-form concentrator

Electrical efficiency (%)

Tolerance (degs)

Concentration

1,000400

±0.5º

±2.8ºConcentration × Tolerance2 ≈

constant

±1.8º

Fresnel lens concentrator

XR free-form concentrator

Electrical efficiency (%)

Tolerance (degs)

Concentration

2,000400

±0.5º±1.3º

Concentration × Tolerance2 ≈

constant

±2.8º

Fresnel lens concentrator

XR free-form concentrator

A. Plesniak et al. “Demostration of high performance concentrating photovoltaic module designs for utility scale power generation”, ICSC – 5, (Palm Desert, CA, USA, 2008)

Target Target

Advanced XR HCPV

Target ≈

±2.0º 31% 1,200xTarget ≈

±2.8º 33% 600x

6. Summary

Outline

solar radiation

cell cost other costs+

efficiency×

energy=

HCPV versus 2-axis tracked flat-plates

• Solar radiation: Diffuse radiation can add 15-30% more for flat-plates.

• Efficiency for flat-plates use to be rated at 25ºC cell temperature while the efficiency is rated at 20ºC ambient temperature for concentrators.

• Efficiency vs temperature coefficients are different for Si and MJ cells

• Flat plate trackers don’t need accuracy

Concentration-tolerance-efficiency comparison is not possible because technologies are quite different.

solar radiation efficiency

other costs

Conventional silicon

High efficiency

silicon

HCPV for equal

output

High performance

HCPVGoal

Module efficiency at STC (%)

12.0 19.3 - - -

Average efficiency in operation (%)

10.6 17.5 22.4 27.0 30.0

Annual solar irradiation (kWh/(m2·year))

2580 2580 2012 2012 (78%)

2012 (78%)

Nominal annual DC electrical energy density (kWh/(m2·year))

274 451 451 543 (198%)

604 (220%)

(100%) (78%)

(164%) (164%)

Example: Seville (Spain)

(100%)

FhG-ISE

Record cell efficiencies

• The derivatives of efficiencies for MJ and Si cells vs time are significantly different.

• Si cells are more mature (less risk and less expected improvements)

• The same considerations affects to cell cost of both technologies

The most important advantages of HCPV vs flat-plates come from the comparison of recent time evolution of efficiencies

6. Summary

Outline

Summary

1. The potential of HCPV relies on the fast increase of MJ cells

efficiency

2. The near-term challenge is beating 2-axis tracking flat-panels

3. To succeed, HCPV needs high efficiency, sufficient high

concentration and as much tolerance as possible

4. The best Efficiency-Concentration-Tolerance is being achieved by

Advanced Optics.

5. Scaling-up HCPV will need the synergy with present high-

throughput low-cost industries (such as automotive or solid state

lighting)

LEGAL NOTICE

Devices shown in this presentation are protected by the following US and International Patents and Patents Pending:

Patents Issued

HIGH EFFICIENY NON-IMAGING US 6,639,733 October 28, 2003COMPACT FOLDED-OPTICS ILLUMINATION LENS US 6,896,381 May 24, 2005COMPACT FOLDED-OPTICS ILLUMINATION LENS US 7,152,985 December 26, 2006COMPACT FOLDED-OPTICS ILLUMINATION LENS US 7,181,378 February 20, 2007DEVICE FOR CONCENTRATING OR COLLIMATING RADIANT ENERGY US 7,160,522 January 9, 2007DISPOSITIVO CON LENTE DISCONTINUA DE REFLEXIÓN TOTAL INTERNA Y DIÓPTRICO ESFÉRICO PARA CONCENTRACIÓN O COLIMACIÓN DE ENERGÍA RADIANTE Spain ES P9902661 December 2, 1999 OPTICAL MANIFOLD FOR LIGHT-EMITTING DIODES US 7,380,962OPTICAL MANIFOLD FOR LIGHT-EMITTING DIODES US 7,286,296THREE-DIMENSIONAL SIMULTANEOUS MULTIPLE-SURFACE METHOD AND FREE-FORM ILLUMINATION- OPTICS DESIGNED THEREFROM US 7,460,985 December 2, 2008

Patents Pending

DEVICE FOR CONCENTRATING OR COLLIMATING RADIANT ENERGY - a continuation of US 7,160,522FREE-FORM LENTICULAR OPTICAL ELEMENTS AND THEIR APPLICATION TO CONDENSERS AND HEADLAMPS PCT/US2006/029464 July 28, 2006MULTI-JUNCTION SOLAR CELLS WITH A HOMOGENIZER SYSTEM AND COUPLED NON-IMAGING LIGHT CONCENTRATOR PCT/US07/63522 March 7, 2007OPTICAL CONCENTRATOR, ESPECIALLY FOR SOLAR PHOTOVOLTAICS PCT/US08/03439 Mar 14, 2008

CONCENTRACION FOTOVOLTAICA - 2009 03 12 CPV Webinar

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