One of the most obvious questions that come to mind before thinking of investing in a Solar Photovoltaic (PV) system is – What kind of Solar PV panel should I buy? And the answer to this question is, ‘It depends’ – mainly on factors such as intended application, user’s budget, space available, amount of sunlight, impact of environmental factors and shading, Return on Investment required, etc.
The intention of this article is to provide an overview of a few Solar cell technologies available, their efficiencies, relative costs and applications which I believe will help people make an informed decision before investing a Solar PV system.
However before delving any further it is important to understand what a solar PV panel is made up of. A solar panel is made up of a number of solar cells connected together which are manufactured from semiconductor materials. A solar cell is a device which generates electricity directly from visible light by means of the photovoltaic effect. At present, most solar cells are silicon-based, since this is the most mature technology.
Solar cells can be classified into
1. Wafer-based cells which are made of crystalline silicon that includes Monocrystalline and Polycrystalline silicon
2. Thin Film Solar cells that include Amorphous silicon, Cadmium Telluride (CdTe) and Copper Indium (Gallium) diSelenide (CIS or CIGS)
Monocrystalline silicon cells are manufactured from a single silicon crystal and are the purest form amongst all other types. This type of Silicon goes through several cycles of slow and energy intensive filtration and separation processes and thus is the most expensive type of silicon. These cells are usually created in a circular shape or ‘rounded corners’ to create high purity crystal structures.
Monocrystalline cell efficiency generally ranges between 16-20%
· Offer the highest Return on Investment
· Exhibit better performance in low light conditions as compared to polycrystalline silicon
· Higher efficiency rating than other technologies
· Higher production costs makes them more expensive than other types
· Their rounded edges shape leads to substantial wastage of original silicon
· The entire circuit can break down if the panels are in full shade or snowy conditions
Due to their higher efficiencies these are mostly used where space is a premium such as rooftops
Polycrystalline silicon cells are made from melting different silicon crystals together. The techniques for production of Polycrystalline silicon are less critical, and hence cheaper, than those required for Monocrystalline material. These cells have a square shape.
Polycrystalline cell efficiency generally ranges between 12-17%
· Lower costs with higher efficiencies have led Polycrystalline silicon to emerge as the premier material for solar panels
· Polycrystalline solar panels are fragile
· Widely used for commercial solar cell production
Thin film solar panels are made up of a much thinner level of photovoltaic material then monocrystalline or polycrystalline solar panels. While these thin module are much lower in price, they also have a lower module efficiency (roughly 1/2 of monocrystalline solar panels, but roughly comparable with polycrystalline solar panels).
The three common types of Thin Film Panels are
Amorphous silicon (a-Si) is the non-crystalline form of silicon. It is the most well-developed of the thin film technologies to-date.
Panel efficiency generally ranges between 7 to 9%.
· Lower manufacturing costs makes these cells very cost competitive
· These panels have a lower efficiency than monocrystalline and polycrystalline solar cells
· The expected lifetime of amorphous cells is shorter than the lifetime of crystalline cells
· Amorphous silicon can be produced in a variety of shapes and sizes which can be used in a variety of applications such as powering electronic calculators, solar wristwatches, garden lights, and to power car accessories
This photovoltaic technology uses Cadmium Telluride, a thin semiconductor layer designed to absorb and convert sunlight into electricity. Cadmium Telluride represents the second most utilized solar cell material in the world after silicon.
Cadmium Telluride solar panels currently achieve an efficiency of upto 16%
· Can be manufactured at lower costs than silicon based solar panels
· Cadmium is one of the top 6 deadliest and toxic materials known
· Tellurium is an extremely rare element
Copper indium gallium (di) selenide (CIGS) is a semiconductor material composed of Copper, Indium, Gallium, and Selenium. CIGS has the advantage of being able to be deposited on flexible substrate materials, producing highly flexible, lightweight solar panels
CIGS technology has achieved efficiency levels of 20% in the laboratory.
· Show better resistance to heat than silicon based solar panels
· CIGS panels are not as efficient as crystalline solar cells
· So far being able to produce solar panels at prices that can compete with polycrystalline or cadmium telluride panels has not been possible
· Solar Facts and Advice
· Applied Photovoltaics