Technology Components and Systems Applications

Technology Components and Systems Applications
Photovoltaics Technology Components and Systems Applications Clemson Summer School 4.6. – Dr. Karl Molter FH Trier

Dr. Karl Molter / FH Trier / molter@fh-trier.de
Content Solar Cell Physics Solar Cell Technologies PV Systems and Components PV Integration into buildings Clemson Summer School 2007 Dr. Karl Molter / FH Trier /

Introduction Photovoltaics, or PV for short, is a solar power technology that uses solar cells or solar photovoltaic arrays to convert light from the sun into electricity. Photovoltaics is also the field of study relating to this technology and there are many research institutes devoted to work on photovoltaics. The manufacture of photovoltaic cells has expanded in recent years, and major photovoltaic companies include BP Solar, Mitsubishi Electric, Sanyo, SolarWorld, Sharp Solar, and Suntech. Total nominal 'peak power' of installed solar PV arrays was around 5,300 MW as of the end of 2005 and most of this consisted of grid-connected applications. Such installations may be ground-mounted (and sometimes integrated with farming and grazing) or building integrated. Financial incentives, such as preferential feed-in tariffs for solar-generated electricity, have supported solar PV installations in many countries including Germany, Japan, and the United States. Clemson Summer School 2007 Dr. Karl Molter / FH Trier /

1. Solar Cell Physics Solar Cell and Photoelectric Effect The p/n-Junction Solar Cell Characteristics Clemson Summer School 2007 Dr. Karl Molter / FH Trier /

History 1839: Discovery of the photoelectric effect by Bequerel 1873: Discovery of the photoelectric effect of Selen (change of electrical resistance) 1954: First Silicon Solar Cell as a result of the upcoming semiconductor technology ( = 5 %) Clemson Summer School 2007 Dr. Karl Molter / FH Trier /

Solar Cell and Photoelectric Effect
Light absorption h effective separation of the charges - + Generation of „free“ charges Result: wearless generation of electrical Power by light absorption Clemson Summer School 2007 Dr. Karl Molter / FH Trier /

energy-states in solids: Band-Pattern
Atom Molecule/Solid • • • • • energy-states Clemson Summer School 2007 Dr. Karl Molter / FH Trier /

energy-states in solids: Insulator
electron-energy conduction-band bandgap EG (> 5 eV) Fermi- level EF valence-band Clemson Summer School 2007 Dr. Karl Molter / FH Trier /

Terms: Fermilevel EF: limit between occupied and non occupied energy-states at T = 0 K (absolute zero) valence-band: completely occupied energy-band just be- low the Ferminiveau at T = 0 K, the electrons are „fixed“ (tightly bound) inside the atomic structure conduction-band: energy-band just above the valence-band, the electrons can move „freely“ bandgap EG: distance between valance-band and conduction band Clemson Summer School 2007 Dr. Karl Molter / FH Trier /

energy-states in solids : metal / conductor
electron-energy Fermi- level EF conduction-band Clemson Summer School 2007 Dr. Karl Molter / FH Trier /

energy-states in solids: semiconductor
electron-energy conduction-band Fermi- level EF bandgap EG ( 0,5 – 2 eV) valence-band Clemson Summer School 2007 Dr. Karl Molter / FH Trier /

Electron-Energy At T=0 (absolute zero of temperature) the electrons occupy the lowest possible energy-states. They can now gain energy in two ways: Thermal Energy: kT (k = Boltzmanns Constant, 1.381x10-23 J/K, T = absolute temperature in Kelvin) Light quantum absorption: h (h = Plancks Constant, h = 6.626x10-34 Js,  = frequency of the light quantum in s-1). If the energy absorbed by the electron exceeds that of the bandgap, they can leave the valence-band and enter the conduction-band: Clemson Summer School 2007 Dr. Karl Molter / FH Trier /

energy-states in solids: energy absorption and emission
electron-energy conduction-band + - h Generation + - h Recombination x EF valence-band Clemson Summer School 2007 Dr. Karl Molter / FH Trier /

energy-states in semiconductors physical properties:
thermal viewpoint: The larger the bandgap the lower is the conductivity. Increasing temperature reduces the electrical resistance (NTC, negative temperature coefficient resistor) optical viewpoint: the larger the bandgap the lower is the absorption of light quantums. Increasing light irradiation decreases the electrical resistance (Photoresistor) Clemson Summer School 2007 Dr. Karl Molter / FH Trier /

doping of semiconductors
In order to avoid recombination of photo-induced charges and to „extract“ their energy to an electric-device we need a kind of internal barrier. This can be achieved by doping of semiconductors: IIIB IVB VB „Doping“ means in this case the replacement of original atoms of the semiconductor-material (e.g. Si) by different ones (with slightly different electron configuration). Semiconductors like Silicon have four covalent electrons, doping is done e.g. with Boron or Phosphorus: B 5 Si 14 P 15 Clemson Summer School 2007 Dr. Karl Molter / FH Trier /

N - Doping crystal view conduction-band valence-band EF - P+ majority carriers donator level energy-band view Si - - P+ n-conducting Silicon Clemson Summer School 2007 Dr. Karl Molter / FH Trier /

P - Doping conduction band valence-band EF B- majority carriers acceptor level + energy-band view crystal Si + B- + p-conducting Silicon Clemson Summer School 2007 Dr. Karl Molter / FH Trier /

p/n-junction without light
Band pattern view depletion-zone p – type region EF B- + n – type region - P+ - Diffusion + internal electrical field + - Ed Ud + - Clemson Summer School 2007 Dr. Karl Molter / FH Trier /

irradiated p/n-junction
band pattern view (absorption p-zone) E = h depletion-zone photocurrent - Ud - - - - - P+ P+ P+ P+ P+ EF B- B- B- B- B- + + + + + + Ed + - p–type region n–type region Internal electrical field Clemson Summer School 2007 Dr. Karl Molter / FH Trier /

p/n–junction without irradiation (semiconductor diode) crystal view
+ - - + p-silicon - + electrical field E + - diffusion n-silicon depletion zone Clemson Summer School 2007 Dr. Karl Molter / FH Trier /

p/n–junction with irradiation crystal view
- + p-silicon - + drift + - - + electrical field E + - diffusion n-silicon depletion zone Clemson Summer School 2007 Dr. Karl Molter / FH Trier /

Charge carrier separation within p/n–junction
diffusion: from zones of high carrier concentration to zones of low carrier concentration (following a gradient of electrochemical potential) drift: driven by an electrostatic field established across the device Clemson Summer School 2007 Dr. Karl Molter / FH Trier /

The real Silicon Solar-cell
Front-contact - + hn Antireflection- coating n-region p-region ~0,2µm ~300µm Backside contact depletion zone Clemson Summer School 2007 Dr. Karl Molter / FH Trier /

Equivalent circuit of a solar cell
USG RS ISG current source IPH ID UD RP RL UL IL IPH: photocurrent of the solar-cell ID /UD: current and voltage of the internal p-n diode RP: shunt resistor due to inhomogeneity of the surface and loss-current at the solar-cell edges RS: serial resistor due to resistance of the silicon-bulk and contact material ISG/USG: Solar-cell current and voltage RL/IL/UL: Load-Resistance, current and voltage ISG = IL, USG = UL Clemson Summer School 2007 Dr. Karl Molter / FH Trier /

Solar-Cell characteristics
UD diode- characteristic ID RL=0 RL=  U0 simplified circuit ID ID ISG RL UD=USG UMPP MPP IMPP MPP = Maximum Power Point ISG / PSG USG solar-cell characteristics Load resistance ISG = I0 = IK Power Clemson Summer School 2007 Dr. Karl Molter / FH Trier /

Solar-cell characteristics
Short-current ISC, I0 or IK: mostly proportional to irradiation Increases by 0,07% per Kelvin Open-voltage U0, UOC or VOC: This is the voltage along the internal diode Increases rapidly with initial irradiation Typical for Silicon: 0,5...0,9V decreases by 0,4% per Kelvin Clemson Summer School 2007 Dr. Karl Molter / FH Trier /

Solar cell characteristics
Power (MPP, Maximum Power Point) UMPP » (0, ,9) UOC IMPP » (0, ,95) ISC Power decreases by 0,4% per Kelvin The nominal power of a cell is measured at international defined test conditions (G0 = 1000 W/m2, Tcell = 25°C, AM 1,5) in WP (Watt peak). Clemson Summer School 2007 Dr. Karl Molter / FH Trier /

Solar cell characteristics
The fillfactor (FF) of a solar-cell is the relation of electrical power generated (PMPP) and the product of short current IK and open-circuit voltage U0 FF = PMPP / U0  IK The solar-cell efficiency  is the relation of the electrical power generated (PMPP) and the light irradiance (AGG,g) impinging on the solar-cell :  = PMPP / AGG,g Clemson Summer School 2007 Dr. Karl Molter / FH Trier /

Solar-cell characteristics (cSi)
P = 0,88W, (0,18) P = 1,05W, (0,26) P = 0,98W, (0,29) Clemson Summer School 2007 Dr. Karl Molter / FH Trier /

Solar-cell characteristics
Clemson Summer School 2007 Dr. Karl Molter / FH Trier /

2. Solar-cell Technologies
Materials Technologies Market shares and development Clemson Summer School 2007 Dr. Karl Molter / FH Trier /

Materials Si Silicon (Si) Ge Germanium (Ge) Ga As
Definition of semiconductor: This is a matter of electron configuration Si 14 Silicon (Si) Extract of periodic table: Ge 32 Germanium (Ge) IIB IIIB IVB VB VIB IB Ga 31 As 33 Gallium-Arsenide (GaAs) Al 13 Sb 51 Aluminium-Antimon (AlSb) P 15 In 49 Indium-Phosphorus (InP) Copper, Indium, Gallium, Selenide (CIS) Cu 29 Se 34 In 49 Ga 31 Cd 48 Te 52 Cadmium-Telluride (CdTe) Clemson Summer School 2007 Dr. Karl Molter / FH Trier /

Efficiency of different solar cells (Theory / Laboratory)

Arguments for different technologies
Potentially high efficiency Availability of material Low material price Potentially low manufacturing costs Stability of characteristics for many years Environment friendly and non toxic Materials and manufacturing process Clemson Summer School 2007 Dr. Karl Molter / FH Trier /

Evaluation of mono-crystalline Silicon:
Mass production efficiency between % (>23% in laboratory) A lot of raw material needed Raw silicon costs are strongly varying in time Well known production process, but consumes much energy, optimization by EFG and band-Technology Very good long term stability material almost pollution free Second place in market shares Clemson Summer School 2007 Dr. Karl Molter / FH Trier /

Evaluation of multi-crystalline Silicon:
Mass production efficiency between % A lot of raw material needed Raw silicon costs are strongly varying in time Well known production process, consumes less energy than mono-Si very good long term stability material almost pollution free First place in market shares Clemson Summer School 2007 Dr. Karl Molter / FH Trier /

Evaluation of amorphous Silicon (a-Si):
Mass production efficiency only 6 – 8% Thin-Film Technology (<1µm), only few raw material needed Well known production process, consumes far less energy than crystalline Silicon large area modules can be manufactured in one step long term stability only for efficiency between 4 – 6% material almost pollution free Clemson Summer School 2007 Dr. Karl Molter / FH Trier /

Evaluation of Copper, Indium, Diselenide (CIS)
Mass production efficiency 11 – 14% Thin-Film Technology (<1µm), only few raw material needed large area modules can be manufactured in one step good long term stability raw material not pollution free (Se, small quantity of Cd) Clemson Summer School 2007 Dr. Karl Molter / FH Trier /

Evaluation of GaAs, CdTe and others
Mass production efficiency up to 18% some raw materials are rather rare raw material very expensive some production processes not suited for mass production long term stability not well known raw material not pollution free (esp. As, Cd) Clemson Summer School 2007 Dr. Karl Molter / FH Trier /

Production process 1. Silicon Wafer-technology (mono- or multi-crystalline) Most purely silicon % SiO2 + 2C = Si + 2CO melting / crystallization Occurence: Siliconoxide (SiO2) = sand Tile-production Mechanical cutting: Thickness about 300µm Minimum Thickness: about 100µm Plate-production typical Wafer-size: 10 x 10 cm2 Link to Producers of Silicon Wafers cleaning Quality-control Wafer Clemson Summer School 2007 Dr. Karl Molter / FH Trier /

Production- Process mono- or multi-crystalline Silicon crystal growth process Clemson Summer School 2007 Dr. Karl Molter / FH Trier /

Production - Process Silicon Band-Growth Process
EFG: Edge-defined Film-fed Growth Less energy-consumptively than crystal-growth process Thickness: about 100µm Only few Silicon waste, since no cutting necessary Clemson Summer School 2007 Dr. Karl Molter / FH Trier /

Production Process Thin-Film-Process (CIS, CdTe, a:Si, ... )
semiconductor materials are evaporated on large areas Thickness: about 1µm Flexible devices possible less energy-consumptive than c-Silicon-process only few raw material needed Typical production sizes: 1 x 1 m2 CIS Module Clemson Summer School 2007 Dr. Karl Molter / FH Trier /

Technology -Trends Thin-Film Technology few raw material needed demand of flexible devices production of large area cells / modules in one step enhancement of cell efficiency Tandem-cell for better utilization of the solar spektrum Light Trapping, enhancement of the light absorption Transparent contacts bifacial cells Solar-concentrating photovoltaics Clemson Summer School 2007 Dr. Karl Molter / FH Trier /

Tandem-cell Pattern of a multi-spectral cell on the basis of the Chalkopyrite Cu(In,Ga)(S,Se)2 Clemson Summer School 2007 Dr. Karl Molter / FH Trier /

Thin Si-Wafer Clemson Summer School 2007 Dr. Karl Molter / FH Trier /

energy payback time (EPBT)
BOS: Balance of System = inverter, cable, transport, assembly … Clemson Summer School 2007 Dr. Karl Molter / FH Trier /

Market Shares of the main solar cell technologies Thin-Film
Si-Band-growth multi-crystalline Si mono-crystalline Si of the main solar cell technologies Clemson Summer School 2007 Dr. Karl Molter / FH Trier /

Solar-Cell Manufacturer

Worldwide installed PV-Power

In Germany installed PV-Power

PV-Module price experience curve: price per Wp against cumulative production with Research & Development end of 2004 without Research & Development cumulative production in MWp Clemson Summer School 2007 Dr. Karl Molter / FH Trier /

3. PV Systems and Components
PV System-Technology Solar Irradiation Energy yield and savings Clemson Summer School 2007 Dr. Karl Molter / FH Trier /

PV-Systems The basic photovoltaic or solar cell typically produces only a small amount of power. To produce more power, cells can be interconnected to form modules, which can in turn be connected into arrays to produce yet more power. Because of this modularity, PV systems can be designed to meet any electrical requirement, no matter how large or how small. Clemson Summer School 2007 Dr. Karl Molter / FH Trier /

PV Module A PV-Module usually is assembled by a certain amount of series-connected solar-cells typical open-.circuit Voltage using 36 cells: 36 * 0,7V = 25V Problem: due to series connection, the failure of one cell (defective or shadow) reduces the current through all cells! Clemson Summer School 2007 Dr. Karl Molter / FH Trier /

PV Module in order to avoid this kind of failure, cells or cell strings are bypassed by diodes which shortcut the defective or shaded cell(s) : Clemson Summer School 2007 Dr. Karl Molter / FH Trier /

Grid-connected PV-System
Solar- Generator protection- Diode inverter (virtual load) DC AC load utility- grid Grid The grid is involved as a temporary energy storage Clemson Summer School 2007 Dr. Karl Molter / FH Trier /

inverter concepts = ~ … central = ~ … module-integrated = ~ … string-inverter … = ~ multistring-inverter Grid Clemson Summer School 2007 Dr. Karl Molter / FH Trier /

PV – Solar Home System (SHS) with AC-Load
Generator Protection- Diode charge- regulator DC Accumulator (storage) inverter DC AC load Fuse Main difference to a grid connected System: - a local DC energy storage and DC/DC regulator is necessary - an additional DC/AC converter is necessary -> increase of Balance of System (BOS) costs Clemson Summer School 2007 Dr. Karl Molter / FH Trier /

Solar-generator: Dimensioning I
The solar-generator voltage and power has to be adopted to the load and storage (in case of a SHS) or the inverter (in case of a grid connected system) This is achieved by suitable series and parallel connection of PV-Modules SHS without inverter are mostly 12V or 24V and sometimes 48V DC-Systems. To compensate voltage loss at the charge-regulator / inverter and the cabling, the nominal voltage of the modules should always be slightly above the minimal required input voltage of the charge-regulator / inverter Clemson Summer School 2007 Dr. Karl Molter / FH Trier /

Solar-generator: Dimensioning II
The dimensioning of the solar generator depends also on the solar irradiation conditions of the location and the orientation of the module surface: Orientation of the module surface (Azimuth) : Northern Hemisphere to South, Southern Hemisphere to North (Deviations less than ± 30° reduce the energy gain less than 5% Guide: Inclination (tilt angle) ~ latitude of location more steeply: more energy gain during spring / autumn more flat: more energy gain in summer Sun-Tracker is expensive and complicated (moving parts) and increases the energy gain by only 10 to 15% Clemson Summer School 2007 Dr. Karl Molter / FH Trier /

Solar irradiation characteristics (northern hemisphere, ~ 50° latitude) tilt south-east south-west west east energy production with respect to optimal orientation Clemson Summer School 2007 Dr. Karl Molter / FH Trier /

Total solar irradiation

Solar Irradiation in Germany
Data from 2002 Irradiation on horizontal surface between 900 (North) and 1300 (South) kWh/m² per year Clemson Summer School 2007 Dr. Karl Molter / FH Trier /

Solar irradiation in the USA
Shown is the average radiation received on a horizontal surface across the continental United States in the month of June. Units are in kWh/m2 Clemson Summer School 2007 Dr. Karl Molter / FH Trier /

Solar Irradiation worlwide (kWh/m² a) on horizontal surface

Solar Irradiance worlwide Average : (W/m²) on horizontal surface Clemson Summer School 2007 Dr. Karl Molter / FH Trier /

Example: practical energy gain

Energy-Yield is dependent on: location / Climate middle-Europe: 700 – 900 kWh per kWp installed PV-Power Orientation (Tilt, Azimuth) ± 20° deviation  ± 5% Energy-loss PV-Technology determines area needed and efficiency eventually additional use (aesthetics, weather proof, SHS) pollution free electricity generation, CO2 reduction etc. Clemson Summer School 2007 Dr. Karl Molter / FH Trier /

Incentives for solar generated electricity (EEG, in Germany)
Grid connected system, electricity produced is totally feed into the grid The table shows the amount paid per kWh solar electricity produced: year 2004 2005 2006 2007 2008 Building integrated 57,4 ct 54,53 ct 51,80 ct 49,21 ct 46,75 ct More than 30 kW 54,6 ct 51,87 ct 49,28 ct 46,82 ct 44,48 ct More than 100 kW 54,0 ct 51,30 ct 48,74 ct 46,30 ct 43,99 ct Facade- bonus 5,00 5,00 ct Open-land systems 45,7 ct 43,42 ct 40,60 ct 37,96 ct 35,49 ct Clemson Summer School 2007 Dr. Karl Molter / FH Trier /

4. Building Integrated PV
PV as a multifunctional part of buildings Examples further informationen Clemson Summer School 2007 Dr. Karl Molter / FH Trier /

4.1 Weather Protection Rain and wind tightness storm resistant climate-change resistant durable Clemson Summer School 2007 Dr. Karl Molter / FH Trier /

Example: Utility Tower in Duisburg

Example: roof Clemson Summer School 2007 Dr. Karl Molter / FH Trier /

4.2 Thermal insulation In combination with usual heat-insulating materials In combination with heat insulating glass Clemson Summer School 2007 Dr. Karl Molter / FH Trier /

Example: special roof Clemson Summer School 2007 Dr. Karl Molter / FH Trier /

example: Swimming pool

4.3 Heating / Air conditioning
Combination of PV and thermal Energy-conversion (Air / Water) Optimization of PV Efficiency Clemson Summer School 2007 Dr. Karl Molter / FH Trier /

4.4 Shading Regulation by „Cell density“ use of semitransparent cells Clemson Summer School 2007 Dr. Karl Molter / FH Trier /

Example: Shading Clemson Summer School 2007 Dr. Karl Molter / FH Trier /

4.5 Sound absorption Clemson Summer School 2007 Dr. Karl Molter / FH Trier /

4.6 Electromagnetic Absorption
Faraday's cage principle Reduction of Electro smog inside of buildings Clemson Summer School 2007 Dr. Karl Molter / FH Trier /

4.7 Production of electrical energy

Example: PV-Roof and Front,

4.10 Design /Aesthetics PV facade and roof-elements are highly valuable building materials which may be adapted to many different Design-criteria Clemson Summer School 2007 Dr. Karl Molter / FH Trier /

Alwitra Solar-foil Clemson Summer School 2007 Dr. Karl Molter / FH Trier /

Solar-roof shingle Clemson Summer School 2007 Dr. Karl Molter / FH Trier /

Example: Sports-Center Tübingen

Example: Fire-brigade

Example: BP Showcase Clemson Summer School 2007 Dr. Karl Molter / FH Trier /

Information sources in the Internet (selected)
U.S. Department of Energy ( and links within these pages Wikipedia ( and links within this page Software: Valentin Energy Software: PVSOL, Meteonorm ( Clemson Summer School 2007 Dr. Karl Molter / FH Trier /

This Powerpoint Presentation can be downloaded from: Clemson Summer School 2007 Dr. Karl Molter / FH Trier /

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