Thin Film Based Solar PV Power Plant - Pros and Cons - India Renewable Energy Consulting – Solar, Biomass, Wind, Cleantech
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Since they were first developed in the 50s, there have been no major changes to the basic crystalline silicon solar cell.
But significant improvements are now taking place with several competing innovations vying for the first position; in fact, crystalline silicon cells are now being referred to as “first generation” PV.

It is suitable, then, at this point in time, to round up the differences between crystalline and thin-film cells:

All of the thin-film technologies have the advantage of requiring much less semiconductor material. It can be less than 1 percent of silicone used in crystalline cells. And they can be manufactured using high-speed techniques such as roll-to-roll printing. Their disadvantage is their lower efficiency. Even so, many new manufacturers in each three types are coming online every month.

Between crystalline and thin-film modules, some differences are more apparent than others. Single-crystal PV modules have distinct, dark-colored cells that are either rectangular or octagonal in shape; multicrystalline modules have some sparkle to the cells, and are usually rectangular. In each, the electrical connections are evident as a regular pattern of parallel, silver lines called traces.

Thin-film is a broad term, since it refers to a variety of module compositions, including amorphous silicon (a-Si), cadmium telluride (CdTe), and copper indium gallium diselenide (CIGS). One of the main advantages to amorphous silicon is that it can be directly deposited on glass or even plastic, allowing it to be manufactured in long, continuous rolls, or incorporated onto a flexible substrate, such as laminates, shingles, and roofing tiles, even backpacks.
The appearance of amorphous silicon also tends to be more uniform, and because of this uniform color, thin-film products appeal to those concerned with aesthetics—architects, designers, and end users—for streamlined building-integrated applications.

The main difference between the two types is in sunlight-to-electricity conversion efficiencies and power densities.

Crystalline modules require less space than thin-film modules for the same amount of power—thin-film is less efficient in the conversion of sunlight to electricity.

Single- and multicrystalline modules have typical conversion efficiencies between 12% and 17%. But thin-film technologies can have half that, ranging from 6% to 8%. Thin-film modules take up about twice as much space to generate an equivalent amount of energy compared to crystalline modules.

Let’s take a look at how this difference influences PV system sizing. For a utility-interactive PV system, a typical crystalline module would be 170 to 220 W (STC), with efficiency between 12% and 17%, measuring approximately 3 by 5 feet.

An amorphous thin-film module might deliver between 60 and 70 W (STC) with efficiency between 6% and 8%, and measure about 3 by 3 feet.

Besides power density, there are 2 key differences in performance between crystalline and thin-film technologies.

The first is impact of cell temperature on power production. All PV modules experience a reduction in power with increasing cell temperature. For example, at 100°F, our sample crystalline module will produce approximately 6% less power than its STC rating. This effect is less pronounced for thin-film PV technologies—our example a-Si thin-film module would produce only 2% less power. While you can reduce cell temperature by allowing adequate air flow around any module, PV cells sitting out in the sun will still get hot—so thin-film a-Si modules are a better choice for warm climates like India, especially if there’s plenty of room for the larger arrays (which is what India relatively lacks in).

The second is initial module power stabilization.
Amorphous silicon modules take 6 to 12 months to reach their stable, rated output, whereas crystalline modules stabilize right away. So a-Si modules will show 20% to 25% higher-than-rated production at first. While that sounds like a bonus, this initial additional output must be considered in system design (for selecting wire sizes, charge controllers, and inverters).

For example, if the final design indicates a 15 A circuit, the initial extra output might require accommodating 20 A. After this stabilization, thin-film modules degrade at similar rates to crystalline, about 0.5% to 1.0% per year.

Some thin-film technologies provide better shade tolerance and low-light performance than crystalline modules.

Thin-films may also show higher power production in cloudy weather and diffuse light.

Other thin-film modules (without bypass diodes on every cell) have better shade tolerance than crystalline modules due to cell shape.
Click here for original article by Erika Weliczko

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