» From the first spark to future fireworks
» How do Photovoltaics generate Power?
» PV materials
» Further down the road

From the first spark to future fireworks

Since the photoelectric effect was first discovered in 1839 photovoltaic technologies have been growing and improving with great leaps and bounds. And the future looks as bright as the sun.

The advancement in technology has been much more rapid in the past decade where new photovoltaic technologies that show promise for further energy efficiency gains and cost reductions are starting to emerge.

Today, efficiencies have climbed to greater than 30%, with the promise of 40% on the way. New thin film technologies with low production costs promise competitive markets with costs matching that of monthly electric bills.

How do Photovoltaics generate Power?

The PV process converts sunlight directly into electricity. The sun emits photons (light), which generate electricity when they strike a photovoltaic cell.

Solar cells are made of silicon, a special type of melted sand, consisting of two or more thin layers of semi conducting material, usually silicon. The layers are given opposite charges - one positive, one negative.

When sunlight strikes the solar cell, electrons are knocked loose and move toward the treated front surface of the solar cell. The result is an electron imbalance between the front and back of the cell and causes electricity to flow - the greater the intensity of light, the greater the flow of electricity.

PV materials

Cadmium telluride (CdTe)

CdTe is an extremely efficient light-absorbing material for thin-film solar cells. It is much easier to deposit and more suitable for mass production as compared to other thin-film materials. Apart from amorphous silicon, CdTe is the only technology that can be delivered on a large scale.

Copper Indium Selenide (CIS)

CIS is the component highly relevant for thin film solar cell application simply because of their high optical absorption coefficients. It also has highly versatile optical and electrical characteristics that can be manipulated and tuned for a particular need in any given device.

Copper Indium Gallium Diselenide (CIGS)

CIGS is a variation of CIS. CIGS are multi-layered thin-film composites and unlike conventional silicon based solar cell it is best described by a more complex heterojunction model. Gallium is used to increase the optical bandgap of the CIGS layer as compared to CIS. Thus the result is an increase in the open-circuit voltage. Indium, another component used in the technology, can easily be recycled from decommissioned PV modules. Selenium provides better uniformity across the layer and so the number of recombination sites in the film are reduced which benefits the quantum efficiency and thus the conversion efficiency.

Gallium arsenide (GaAs) multijunction

GaAs multijunction devices are the most efficient solar cells to date. These cells consist of multiple thin films produced using molecular beam epitaxy. They use 20 to 30 different semiconductors layered in series. Each type of semiconductor will have a characteristic band gap energy which causes it to absorb light most efficiently at a certain color, or more precisely, to absorb electromagnetic radiation over a portion of the spectrum. The semiconductors are carefully chosen to absorb nearly the entire solar spectrum, thus generating electricity from as much of the solar energy as possible.

Further down the road

NanoMarkets, an industry analyst firm, believes that PV technology will offer a major long-term opportunity to those who can look beyond short-term supply constraints and focus on the unique advantages of thin-film/organic PV that can be exploited. These advantages include weight, flexibility and low-cost production methods.

PV and environmental experts emphasise that the role of renewable energy, including solar water heating, especially in electrically heated buildings will gain importance in the coming years. Building integrated photovoltaics (BIPV) have the most potential as they are economic as an alternative to expensive cladding. Analysis indicates that BIPV will approach cost-effectiveness sometime after 2020.

In India, both crystalline silicon technology and thin-film solar panels have found takers. India is also evaluating emerging technologies, including nanotechnology and concentrator photovoltaic cells, to bring down the cost of solar equipment.