Thin-film solar panels: What you need to know

Have you ever encountered "flexible solar panels" or "stick-on solar panels"? Both fit under the broader umbrella of thin-film solar panels, a type of solar panel technology known for being lightweight while still producing renewable solar energy.

Compared to traditional solar panel cells holding most of the market share, thin-film solar panels include electricity-producing layers that are hundreds of times thinner than typical silicon cells. We'll cover the varieties, major manufacturers, and typical uses of thin-film solar panels.

Thin-film modules use one of the following four technologies: cadmium telluride (CdTe), amorphous silicon (a-Si), copper indium gallium selenide (CIGS), and organic photovoltaic cells (OPV).

Comparison of the four main types of thin-film solar panels

Like conventional solar panels, amorphous silicon (a-Si) solar panels primarily consist of silicon, but have different construction. Instead of using solid silicon wafers (like in mono- or polycrystalline solar panels), manufacturers make amorphous panels by depositing non-crystalline silicon (C-Si) on a glass, plastic, or metal substrate. 

One silicon layer on an amorphous solar panel can be as thin as one micrometer: thinner than a single human hair! Amorphous solar panels are the second most popular thin-film option after CdTe. Amorphous panels are much better than their counterparts in toxicity and durability but less efficient. They're great for small load requirements such as solar portable chargers and other consumer electronics. 

Advantages and disadvantages of amorphous silicon solar panels

Amorphous silicon solar panels have many advantages over their solar panel counterparts. Companies don't need to use many toxic materials to build amorphous silicon (a-Si) panels, which is not always true with other panels. Additionally, they require much less silicon than conventional solar panels. Amorphous solar panels are also flexible and durable, making them less susceptible to cracks than traditional panels constructed from solid silicon wafers. Smaller solar applications like portable chargers and RV setups also often use this technology.

There are also some disadvantages to amorphous solar panel technology, with the primary challenge being its efficiency. Amorphous solar cells are typically less than half as efficient as conventional silicon solar cells. Most amorphous solar panels hover around 7% conversion efficiency, while monocrystalline or polycrystalline solar panel arrays can have efficiencies of over 20%.

Cadmium telluride (CdTe) solar panels are the most popular type of thin-film technology. These panels comprise several thin layers: one main renewable energy-producing layer made from the compound cadmium telluride and surrounding layers for electricity conduction and collection. One of the most well-known manufacturers of CdTe panels is First Solar, an American company headquartered in Tempe, Arizona. The most widely used thin-film solar technology, CdTe panels, holds roughly 50% of the market share for thin-film solar panels.

Advantages and disadvantages of cadmium telluride solar panels

One of the most exciting benefits of CdTe panels is their ability to absorb sunlight close to an ideal wavelength or shorter wavelengths than are possible with traditional silicon solar cells. Shorter wavelengths mean higher energy absorption, which is easier to convert to electricity. Cadmium telluride panels are low-cost to manufacture and install compared to other thin-film solar panels.

One of the biggest concerns with CdTe panels is pollution. Cadmium is one of the most potent toxic heavy metals, so cadmium telluride, the compound used in these panels, also has toxic properties. Importantly, CdTe panels are not harmful to humans or the environment as they generate electricity on rooftops, and companies take proper health precautions when handling the materials during the manufacturing process. However, the safe disposal of old CdTe panels continues to be a concern. 

Like amorphous panels, cadmium telluride panels come at lower efficiencies than other solar panels. Sitting around 10-11%, CdTe panels are above the efficiencies of amorphous panels but still don't come close to the average efficiencies of standard silicon panels.

Copper indium gallium selenide (CIGS) solar modules have a compound called copper gallium indium diselenide sandwiched between conductive layers. This thin-film material goes on top of different types of base layers, such as glass, plastic, steel, and aluminum. The result is a powerful semiconductor. 

Some CIGS panels use a flexible backing, and the thin layers enable full-panel flexibility. Laboratory CIGS cells have reached efficiency highs of 22.4%. However, these performance metrics are not yet possible at scale. The primary manufacturer of CIGS cells was Solyndra (which went bankrupt in 2011). Today, the leader is Solar Frontier. MiaSolé also manufactures CIGS panels in the U.S. and China.

Advantages and disadvantages of CIGS solar panels

Unlike most other thin-film solar power technologies, CIGS solar panels offer competitive efficiencies to traditional silicon panels. With efficiencies exceeding 20% in laboratory tests, there may be a place for high-efficiency CIGS panels in the global solar panel market.

Like CdTe panels, many CIGS cells also use the toxic chemical cadmium. However, CIGS technologies use a lower percentage of cadmium and are therefore more environmentally-friendly than other thin-film cells. Even better, some models exchange the use of cadmium for zinc.

The biggest disadvantage of CIGS panels is they remain costly to produce, so they have a hard time competing against the more economical silicon or CdTe panels.

Organic photovoltaic (OPV) cells produce electricity using conductive organic polymers or small organic molecules. In a cell using organic photovoltaic material, several layers of thin organic vapor or solution are deposited and held between two electrodes to carry an electrical current.

Advantages and disadvantages of organic PV cells

OPV cells are most popular in the growing building-integrated photovoltaic (BIPV) market. Because you can use different types of absorbers in organic cell technology, OPV devices come in various colors and can even be transparent. This aesthetic advantage makes OPV a popular option for unique BIPV applications. The materials companies need to build organic solar cells are abundant, leading to low manufacturing costs and market prices.

Unfortunately, like other thin-film PV options, organic photovoltaic cells currently operate at relatively low efficiencies. OPV cells typically have efficiency ratings of about 11%, but scaling PV module production up while keeping efficiencies high is a problem. Much of the research currently surrounding OPVs focuses on boosting efficiency. OPV technology also has a shorter lifespan than traditional panels and other thin-film options. Cell degradation that doesn't occur in inorganic modules is an ongoing struggle for organically-based photovoltaic products.

These are the current leading manufacturers of thin-film PV:

First Solar

The top thin-film manufacturer, First Solar, dominates the CdTe technology space. To date, First Solar has only served the commercial market, offering low-cost installations at the mass scale for businesses, institutions, and solar power plants. Holding the world record for CdTe cell efficiency at 18.7%, this manufacturing behemoth offers an impressive 25-year warranty. First Solar thin film is also known for its gorgeous aesthetic designs, such as its frameless, glass-on-glass model that boasts increased panel output due to its hyper-reflective glass coating.

SoloPower

The San Jose solar firm SoloPower is known for versatility and ultra-lightweight design, making it an ideal candidate for building-integrated photovoltaics (where the panel integrates into a building's envelope, often along vertical surfaces). SoloPower is one of the world leaders in CIGS manufacturing.

Sharp

Sharp Solar is a global leader in thin-film solar, having been in business for over 50 years, and is the top manufacturer of a-Si technology. The Japanese firm is known for being one of the first innovators in solar cell development and has contributed to research and development for cell and module efficiency improvements of PV technology since 1959.

Solar Frontier

Solar Frontier, the world's top manufacturer of CIGS thin-film, also hails from Japan. This manufacturing giant is partially responsible for the strong forecasted growth for CIGS PV installations worldwide. If thin-film solar continues to scale in the commercial sector and penetrate the residential market, CIGS will be the technology to achieve it. Sharp Solar has stated that they can produce a 30% efficiency CIGS cell – a feat that would revolutionize the concept of thin-film solar.

When comparing thin-film panels to the standard monocrystalline and polycrystalline solar panels more commonly used in the residential market, a few factors clearly distinguish one from another: carbon offset, efficiency, roof space, and installation cost.

Carbon offset

Regarding carbon offset, thin-film solar panels will have a significant edge over traditional panels. The silicon required for standard panels is much more significant than for thin-film panels, which means that the emissions needed to create a thin-film cell and panel are much lower than for mono or polycrystalline panels. 

However, the moderate amounts of cadmium, a known carcinogen, in thin-film solar panels may negate this "environmental benefit". If this is a significant concern, you may want to choose CIGS thin-film panels, which have very little cadmium. You also could looking for community solar installations with CdTe technology to ensure the panel plant isn’t directly near your house or yard.

Efficiency

Efficiency has been the ultimate deciding factor preventing thin-film panels from gaining a foothold in the residential PV market. Whereas today's standard silicon PV panels will have somewhere in the range of 15-22% efficiency, thin-film panels will likely hold a median closer to 11-13%, which can significantly impact your system's physical size and electricity output. 

Roof space

Because of the underwhelming efficiency, your available roof space will impact your thin-film solar installations. A standard panel installation can significantly cut your electricity bills even if you have limited roof space, but thin-film solar needs to be installed on larger roofs to accommodate the increased amount of space necessary for the system.

Installation cost

Finally, the installation cost will differ significantly between thin-film and typical solar because thin-film panels are easy to install and require much less labor. As long as you work with a company that provides a mounting solution for thin film, reduced labor costs are a hard selling point for a thin-film installation over standard PV panels.

Thin-film solar panels are primarily used in commercial- and utility-scale installations like solar panel farms, solar for corporations, and solar for schools and universities. The "economies of scale" concept applies to thin-film panel technology because the lightweight, versatile panels are easy to install. The larger the installation, the more cost-effective it becomes, as reduced installation costs offset the panel output losses due to lower efficiencies.

There is still an opportunity for thin-film in the residential sector: Larger houses with adequate roof space can benefit from an economies-of-scale installation and the aesthetic benefits of the frameless, glass-on-glass thin-film models commonly offered by the leading manufacturers. If aesthetics are a strong priority for your PV installation, thin-film solar may be the most cost-effective way to get your desired look.

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