High Efficiency photovoltaic power plants: the III-V compound solar - PowerPoint PPT Presentation

High Efficiency photovoltaic power plants: the III-V compound solar cells G. Gabetta Hyperlink

Contents � CESI: who are we? � The photovoltaic conversion and the III-V compound semiconductors � Solar Cell Manufacturing: MOCVD � Solar Cell Manufacturing: Post growth � CPV solar cells � High efficiency CPV power plants

A Long Legacy in Offering Independent Advise and Unbiased Solutions to Clients in the Energy World • CESI was incorporated in 1956 as an independent Company • We like to be Partners to our Clients, to the point that some of the major European utilities and electromechanical companies are also Shareholders and among them : • ENEL • Terna • Prysmian • ABB

CESI: Today’s Capabilities for Our clients’ Tomorrow Plants and Testing • Milan Plants and Testing • Berlin Laboratories Laboratories • Mannheim • Seriate in 5 locations in Italy & Germany in 5 locations in Italy & Germany • Piacenza More than 800 Experienced More than 800 Experienced Professionals delivering around Professionals delivering around 100 M€ of Sales 100 M€ of Sales Extensive References Extensive References and a Commercial and a Commercial Network in 35 countries Network in 35 countries

Division Testing and Certification Solar solutions for Aerospace and terrestrial applications CESI is developing and manufacturing GaAs space solar cells since 1990 and it is presently one of the leading companies in the world. The solar cells are manufactured under an ISO 9001:2000 quality certification and are fully qualified under ESA ECSS. The production is focused on GaAs based materials; to date more than 100.000 solar cells were delivered for more than 60 satellites on 25 different countries. Current performance of the cells : 29% efficiency CESI based on the space experience is developing and manufacturing solar cells for terrestrial applications. Performance of the cells 36% efficiency at 1000 sun. Current manufacturing capacity 18MW/year.

CESI Heritage in III-V solar cells � CESI is one of the world’s pioneers in developing GaAs solar cells for both space and terrestrial applications (80 international publications). � 1975 - 1985: preliminary activities on CPV � 1982 - today: development of SJ and TJ solar cells for space � 1990 - today: production of CTJ 28% space solar cells � 2009: development of TJ solar cells on CESI reactor for terrestrial CPV application � 2010- today: qualification and production of CPV CCTJ 38% solar cells N° of Installed Cell surface N° of cells N° of (m 2 ) satellites power (kW) countries 62* 60 180 >100.000* 18 *(40 in orbit) * (40.000 TJ)

CESI Solar Cell Product Overview Name Type/technology Application Typical Protection Note Field Efficiency Diode CTJ29% InGaP/InGaAs/Ge Space 29% AM0 Si, external Qualification pending, LEO and GEO CTJ28% InGaP/InGaAs/Ge Space 28% AM0 Si, external Qualified, LEO CSJ GaAs/Ge Space 20% AM0 N/A, reverse P on N, with screen ENE S.A. CTJM InGaP/InGaAs/Ge Space 27% AM0 Monolithic Using Emcore wafers CCTJ 38% InGaP/InGaAs/Ge Terrestrial 38% AM1.5 Si, external Suns 800x, qualified � The production is driven and sustained by a continuous R&D effort to increase efficiency and reliability while decreasing the cost for space and terrestrial products.

Contents � CESI: who are we? � The photovoltaic conversion and the III-V compound semiconductors � Solar Cell Manufacturing: MOCVD � Solar Cell Manufacturing: Post growth � CPV solar cells � High efficiency CPV power plants

The Sun as energy source Key Facts* Mass: 1.9891 x 10 30 kg Mass Conversion rate: 4.3 x 10 9 kg/s × 10 26 W Luminosity: 3.827 × × × × 10 7 W/(sr × Radiance: 2,009 × × × × × m²) × × 10 9 years Age: 4.57 × × × Lifetime: 1.53 x 10 13 years Mean Radius: 0.696 x 10 6 km Distance from Earth: 1.496 x 10 8 km AM0 radiance: 1367 W/m 2 * NASA- sun fact sheet

The Solar Spectrum • The total solar energy absorbed by Earth's atmosphere, oceans and land masses is approximately 3.85 x 10 24 J/year. 1.36 kW/m 2 • In 2002, this was more energy 1.00 kW/m 2 in one hour than the world used in one year However: The solar energy is distributed and not always available!

Solar Energy components Global solar exposure The total amount of solar energy falling on a horizontal surface. The daily global solar exposure is the total solar energy for a day: typical values for daily global solar exposure range from 1 to 35 MJ/m 2 Direct solar irradiance Direct solar irradiance is a measure of the rate of solar energy arriving at the Earth's surface from the Sun's direct beam, on a plane perpendicular to the beam. Global solar irradiance Global solar irradiance is a measure of the rate of total incoming solar energy (both direct and diffuse) on a horizontal plane at the Earth's surface.

Solar Direct Radiation at Normal Incidence (DNI) For Italy : www.solaritaly.enea.it/ Halthore R. N., et al. 1997. "Comparison of Model Estimated and Measured Direct-Normal Solar Irradiance," J. Geophys. Res. 102(D25): 29991-30002

The Photovoltaic conversion The built in potential of a p-n junction splits the electron-hole pairs generated by the absorbed photons in the semiconductor crystal Operating the diode in the fourth Positive ions � quadrant generates power Negative Ions Dark I-V (diode) I L Illuminated I-V (solar cell)

Photovoltaic conversion Applying a variable load between the Anode and the Cathode of the solar cell, the I-V characteristics can be measured. The figures of merit for the device can be defined as follows: Photons �� � ��� ����������������� ��������������� 0.6 ��� Collecting grid e - 0.5 �� 0.4 CURRENT (A) + + + + 0.3 Load N 0.2 P 0.1 �� 0 0.00 0.20 0.40 0.60 0.80 1.00 1.20 ��� VOLTAGE (V) η η η = V m x I m / P sole x Area η FF = Voc x Isc/ V m x I m η η = V m x I m / P sole x Area η η FF = Voc x Isc/ V m x I m Fill factor Conversion efficiency

Main solar cell types � The photovoltaic effect can be activated in all semiconducting materials. � Mainly for commercial reasons the semiconducting materials that have been used so far in the manufacture of solar cells are summarized in the following table. Terrestrial Application Plant Type Efficiency AM1.5 Cristalline and polycristalline Flat plate 12-16% Silicon Thin film: CI(G)S, CdTe, Flat plate 8-14% amorphous/microcristalline Si GaAs (CPV) Concentrating PV 38-40% Space Application PVA Type Efficiency AM0 Monocrystalline Si Flat plate (Honeycomb) 14-18% GaAs Flat plate 19%(SJ); 28%(TJ) (Honeycomb/mesh)

The III-V Compound semiconductors Triple junction high efficiency cells require different bandgap semiconductors whose lattice constant is compatible to the crystalline substrate (Germanium). ��� ����� �� Ge

Terrestrial III-V multijunction solar cells • Unmatched performances: record efficiencies above 41%, possibility to reach 50% efficiency. No other technology allows such performances. • The present overall production capability is worth of a theoretical CPV production capacity of about 0.5-0.8GW/year (@500x). • 6” Ge wafer technology already available for CPV • “Grid Parity” achievable in the medium term: projected 6c$/kWh by 2015. III-V compound technology showed a steady improvement in the last 30 years

The III-V compound semiconductors vs the Group IV semiconductors in photovoltaics Advantages InGaP � Better energy conversion. � Light gets absorbed in few micrometers below surface. � With respect to Silicon cells….: � Higher efficiency devices (28%* vs 18% of best performing Si) � Higher radiation resistance for space applications � Lower temperature degradation � Extremely efficient operation at very high photon densities Disadvantages � Higher cost � Extremely sophisticated fabrication technology * TJ cells

The III-V solar cells � Two basic structures: � Single junction solar cells: efficiencies 19-20% (AM0) Grid N + -GaAs � Triple junction solar cells: efficiencies 28- 30% AR AR Window: N + -AlInP (AM0) Emitter: N + -GaInP Junction 3 Base: P -GaInP BSF: P + -AlInGaP TD: P ++ -AlGaAs Tunnel diode TD: N ++ -InGaP III-V solar cells Window: N + -AlGaAs Grid Junction 2 manufacture use epitaxy, Emitter: N + -InGaAs P + -GaAs AR AR Base: P-InGaAs whereas Silicon cells use Window: P + -AlGaAs Buffer: P + -InGaAs diffusion furnaces Emitter: P + -GaAs TD: P ++ -AlGaAs Tunnel Diode Base: N-GaAs TD: N ++ -GaAs Window: N + -AlInP Buffer: N + -GaAs Emitter: N -InGaP Junction 1 Substrate: N -Ge Substrate: P -Ge Contact Back Contact

The triple junction cells The monolithic series Solar spectrum ������������������ ������������������ connection of three sub- _ cells is obtained by tunnel diodes Non usable InGaP InGaP part I InGaAs InGaAs Ge Ge Junction 3 Junction 2 + V Junction 1 The Tunnel diode operates in the ohmic portion of its I-V characteristics