2-1. Solar Energy The direct conversion of sunlight to electricity

1953, Bell Labs: Darryl Chapin- Calvin Fuller-Gerald Pearson Efficiency =6%

Physics of Photovoltaic Generation

n-type semiconductor p-type semiconductor Physics of Photovoltaic Generation Depletion Zone

Typical output of a module (~30 cells) is ≈ 15 V, with 1.5~3 A current One cell ≈ 0.5 V, with 1.5~3 A current (Max 1.5 W)

In order to achieve more PV power: Ns numbers of PV modules are serried as a PV Panel N p numbers of PV strings are paralleled as a PV Array

Electric Model of Photovoltaic Cell

PV Analytical model Cell short circuit current Diode reverse saturation current Cell series resistance Environment temperature Power density Thermal coefficient of short circuit current Thermal coefficient of open circuit voltage

PV Analytical model

I-V Characteristics of PV Array

P-I Characteristics of PV Array

I-V & P-I Characteristics of PV Array for Different Environmental Temperature

Silicon Crystalline Technology  Currently makes up 86% of PV market  Very stable with module efficiencies 10-16% Mono crystalline PV Cells Made using single cylindrical crystal of Si Operating efficiency up to 15% Multi Crystalline PV Cells Made from block of melted and re-crystallized silicon Cell efficiency ~12% Accounts for 90% of crystalline Si market

Thin Film Technology  Silicon deposited in a continuous on a base material such as glass, metal or polymers  Thin-film crystalline solar cell consists of layers about 10μm thick compared with μm layers for crystalline silicon cells PROS Low cost substrate and fabrication process CONS Not very stable

Amorphous Silicon PV Cells  The most advanced of thin film technologies  Operating efficiency ~6%  Makes up about 13% of PV market PROS Established manufacturing technologies available CONS Loss in efficiency

Poly Crystalline PV Cells Copper Indium Di-selinide  High efficiency levels PROS 18% laboratory efficiency >11% module efficiency CONS Undeveloped manufacturing process Non – Silicon Based Technology

Poly Crystalline PV Cells Cadmium Telluride ( CdTe) PROS 16% laboratory efficiency 6-9% module efficiency CONS Undeveloped manufacturing process Non – Silicon Based Technology

Environmental Aspects  CO 2 emission during fabrication process  Acidification  Disposal problems of hazardous semiconductor material In spite of all these environmental concerns, Solar Photovoltaic is one of the cleanest form of energy

Payback Time Energy Payback Time: EPBT is the time necessary for a photovoltaic panel to generate the energy equivalent to that used to produce it. A ratio of total energy used to manufacture a PV module to average daily energy of a PV system. At present the Energy payback time for PV systems is in the range 8 to 11 years, compared with typical system lifetimes of around 30 years.

PV Water Pumping: PV powered pumping systems are excellent,simple,reliable – life 20 yrs Commercial Lighting: PV powered lighting systems are reliable and low cost alternative. Security, billboard sign, area, and outdoor lighting are all viable applications for PV Consumer electronics: Solar powered watches, calculators, and cameras are all everyday applications for PV technologies.

PV Telecommunications Residential Power: A residence located more than a mile from the electric grid can install a PV system more inexpensively than extending the electric grid (Over 500,000 homes worldwide use PV power as their only source of electricity)

PV

30% increase in global manufacturing of solar cells every year

Expected Future of Solar Electrical Capacities

Efficiency and Disadvantages Efficiency is far lass than the 77% of solar spectrum with usable wavelengths. 43% of photon energy is used to warm the crystal. Efficiency drops as temperature increases (from 24% at 0°C to 14% at 100°C.) Light is reflected off the front face and internal electrical resistance are other factors. Overall, the efficiency is about 10-14%.

Efficiency and Disadvantages Cost of electricity from coal-burning plants is anywhere 8-20 cents/kWh, while photovoltaic power generation is anywhere $0.50-1/kWh. Does not reflect the true costs of burning coal and its emissions to the nonpolluting method of the latter. Main problem is balancing efficiency against cost. Crystalline silicon-more efficient, more expensive to manufacture Amorphous silicon-half as efficient, less expensive to produce.