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SolarTown Learning

Solar Panels: Thin Film or Crystalline

Category: Solar Panels

Which Should You Choose?

Today, there are numerous solar photovoltaic products offered from vendors large and small, with the selection growing every month. To the average consumer, a home solar panel may appear the same as any other, but becoming a discerning solar buyer will help you choose the most appropriate solar system for your home. With a little knowledge about how solar technology works and what forms it takes in consumer products, you'll have no problem choosing the most efficient and aesthetically-pleasing home solar energy system to suit your needs.

How Solar Cells Work

First we wanted to give you a quick primer on how solar cells work. If you don't want to know the science behind solar cells, then skip to the next section. But the technology is interesting if you like photons and silicon.

 A solar module consists of solar or photovoltaic cells-often 36 in total in a four row by 9 column configuration-that are made up of thinly sliced (1 mm thick) wafers of semiconductor material, most commonly silicon. Each cell, which will vary in size depending on the watt/amp rating of the panel, is made up of two wafers, one negatively charged, the other positively charged.

Sunlight consists of packages of energy called photons. As the photons hit the solar cell, a portion of the sun's energy is absorbed by the semiconductor material. When this energy is absorbed, photons cause silicon to vibrate which disassociates electrons from the silicon molecules as electrical current. This energy is then captured by miniscule fingers of electrical contacts and turned into DC energy by the systems in a solar array.

The rate at which solar energy is absorbed by a solar cell, called the absorption coefficient, will depend on two main factors: the type of material used to make the solar cell and the wavelength or energy of the light reaching the solar cell. Some materials are much more efficient at absorbing solar energy, which we discuss in more detail below.

Types of Photovoltaic Cells

In general, the most popular solar photovoltaic cell types fall into two categories: crystal cell (with mono- and polycrystalline being the most popular) and thin film.

Crystal Cell Photovoltaics

Crystal cell technology for a residential solar pv system is generally manufactured using silicon (Si) and includes single-crystalline, multicrystalline, and amorphous solar cells. Each technology is produced using slightly different methods and will result in varying degrees of efficiencies.  And each technology is suited for different kinds of of applications.

On both mono- and polycrystalline panels, there is usually a layer of toughened glass (3 mm thick approximately) applied over the silicon wafers to provide protection against hail, temperature fluctuations, and extreme weather, yet it's thin enough to still let the light through. In fact, the glass is often textured to fracture the light spectrum, which allows optimal wavelengths of light to be readily absorbed. It is also often finished with an anti-reflective coating, since silicon (which is made of sand) is a highly-reflective material.

Monocrystalline Photovoltaic Cells

Single-crystalline photovoltaic cells have been the most popular technology, currently capturing about 42% of the market. Known also as monocrystalline or single crystal silicon solar cells, these are cut from a single crystal of silicon usually made from one large man-made ingot. These large crystals are somewhat fragile and difficult to handle, making them prone to breakage, resulting in what appears to be a higher production cost than other PV options.

Yet despite the cost and fragility of monocrystalline photovoltaics, the single piece of silicon crystal means PV panels such as these are much more efficient than other options, achieving approximately 16-18 percent efficiency. As one piece, there is lower resistance within the solar cell, making it efficient even in low-light conditions. Some modules, like the Sanyo HIT Double Bifacial Solar Modules, collect solar energy on both sides of the panel, boosting their efficiency even more.

Polycrystalline Solar Technology

Polycrystalline solar cells-known by other names such as multicrystalline-are cheaper to manufacture than monocrystalline cells because they are produced from many small blocks of silicon. They are now the most popular solar technology on the market, garnering about 45% of the market. The blocks are made by pouring liquid silicon into molds which are then sliced into plates. These cells are easier to handle and work with, resulting in fewer losses to breakage.

Polycrystalline comes with a significant downside, however. By connecting together many independent silicon cells, polycrystalline panels function less efficiently than the single-cell model in monocrystalline cells-approximately 12-14 percent efficiency.

Thin Film Solar Photovoltaics

Thin film PV, a relatively new technology, is currently making inroads into the solar panel market. Thin film technology currently garners a little over 5% of the market, but its market share is increasing rapidly. It owes its newfound popularity to the ease with which it is made, especially on a mass scale. The cost of thin film is much less expensive than either monocrystalline or polycrystalline, and thin film technology may not last as long:  25 years for thin film versus up to 40 years for monocrystalline or polycrystalline. But there are those who say that thin film is more aesthetically pleasing than PV modules.

Thin film solar cells, which are also known as polycrystalline thin film or amorphous thin film silicon cells, are made by applying layers of semiconductor a few micrometers thick (1/100 the thickness of a human hair) to a medium such as flexible metal or plastic. In thin film, the semiconductor material is generally copper indium diselenide or cadmium telluride, although they can also be produced using thin film silicon.

The biggest boon to using thin film solar technology is the lower cost and flexible installation options. The strength of a thin film solar cell depends by and large on the durability and flexibility of the surface onto which it is applied.

Additionally, because the liquid semiconductor material can be applied to almost any surface, the applications are numerous. Not only does this offer many benefits in terms of how many surfaces can be used to collect energy, it also allows for better integration of the technology into existing structures. They are being integrated into everything from solar shingles to roof tiles, skylights and windows to building facades. The attractive integration of solar into virtually any structure will prove in future to offer an enormous boost to the solar industry.

Most thin film PV will function between 6-8 percent efficiency, which is still much lower than the 16 to 18 percent efficiency enjoyed by many monocrystalline solar cells. With lower efficiency, thin film solar technology requires that you install a larger array to produce the same amount of energy from a monocrystalline or polycrystalline alternative.

Every roof is different and some roofs are not visible to the street and others are very visible. Some roofs are small and efficiency of the panels weighs heavily in the homeowner's calculation. And some roofs are very large, and the efficiency of the panel may not be as important. Every homeowner has different preferences. Knowing the kinds of technologies that are available and the different products available will help the homeowner make an informed decision.