What are CdTe solar panels?

Most solar panels today - and virtually all that are sold for residential use - are made with silicon solar cells.

Hundreds of millions of polycrystalline and monocrystalline silicon solar panels are manufactured annually. The economies of scale of this global manufacturing make it difficult for new technologies to break into the market, but one that has carved out a sizable market share is cadmium telluride.

Also referred to as CadTel or CdTe for the atomic symbols for cadmium and tellurium, this is a thin film solar technology. The potential benefits include lower cost, better efficiency in hot conditions, and resistance to certain types of degradation.

CdTe isn’t new - it’s been around for 50 years, but has played second fiddle to silicon-based solar. While growing in popularity, CdTe panels aren’t really available for the home market except in very limited cases. Still, increasing manufacturing volumes and human rights concerns about polysilicon made with forced labor in China could mean that CdTe solar could start showing up on homes in coming years. And because of the flexible nature of thin film solar, it might not look like conventional solar panels either.

What is cadmium telluride solar?

Cadmium telluride solar cells are made from a layer of cadmium sulfide (CdS) and a layer of cadmium telluride. In contrast to silicon cells that are made from ingots of crystalline silicon, CdTe solar is made using vapor deposition.

Basically, this means that the CdS and CdTe layers are sprayed or evaporated onto a supporting material. With silicon panels that supporting material must be rigid or slightly flexible because silicon cells can’t bend very much without cracking.

CdTe, on the other hand, is flexible and can be deposited on a wide variety of materials, such as glass, plastic films, and even textiles. This means a wider range of products are possible with CdTe solar, such as building integrated photovoltaics (BIPV).

What are CdTe solar panels made from?

The silicon used in conventional panels is the same element you find in beach sand, but CdTe panels might raise some concerns about what they’re made from.

Cadmium is a silvery-colored heavy metal that is toxic and a known carcinogen. The FDA has set the maximum limit of cadmium in bottled water at 0.005 mg/L - that’s 5 thousandths of a gram in a liter, so very little exposure to cadmium is acceptable.

On the plus side, the cadmium used in solar panels is sourced from the waste byproduct of zinc and copper mining. This means that CdTe panels don’t increase the amount of cadmium that’s produced globally.

Telluride, in addition to being a famous ski resort in Colorado, is the name of the mineral form of tellurium, which is an element with atomic number 52. It’s a silver-white metalloid that is mildly toxic. Telluride is extremely rare - its rarity is comparable to platinum - which is one of the limiting factors in making CdTe solar more common.

The sulphur in the CdS layer is a cheap and widely available element.

The most common CdTe product on the market is a conventional-looking solar panel made by First Solar. Like most solar panels, the majority of the weight is from the glass and aluminum frame.

It’s worth noting that the layer of CdTe is very thin: between 2 and 8 micrometers, which is about 50 times thinner than the thickness of a human hair. The CdS layer is even thinner. In contrast to a conventional silicon cell that you can hold in your hand, there is very little material needed to create the photovoltaic layer of a CdTe solar panel. This is fortunate because of the high cost of tellurium, but it also means there’s less cadmium to be concerned about.

Is cadmium telluride hazardous?

Because tellurium is mildly toxic and cadmium is highly toxic, you might have some safety concerns about CdTe technology. As it turns out, cadmium telluride is much less of a health concern than either element alone. In fact, the European Chemicals Agency does not consider CdTe to be harmful if ingested.

How is this possible? Let’s start with a comparison with sodium and chlorine. Elemental sodium is a metal that explodes when placed in contact with water. Elemental chlorine is a gas that is highly toxic. (It’s why you should never mix bleach with ammonia.)

However, if you combine sodium and chlorine, you get a delicious compound that you can sprinkle on your french fries. It’s known as table salt and has the chemical symbol of NaCl.

I don’t know if CdTe is delicious or not and I’m not inclined to try. The point here is that in same way NaCl is no longer dangerous compared to its constituent elements, CdTe is much less of a concern than either cadmium or tellurium alone.

Here’s an excerpt from a paper published by the Fraunhofer Centre in Germany:

CdTe has low acute inhalation, oral, and aquatic toxicity, and is negative in the Ames mutagenicity test. Based on notification of these results to the European Chemicals Agency (ECHA), CdTe is no longer classified as harmful if ingested nor harmful in contact with skin, and the toxicity classification to aquatic life has been reduced. Therefore, compound CdTe clearly cannot be classified by regulations of metallic Cadmium or other Cadmium compounds but has to be classified individually.

This doesn’t mean that there aren’t any environmental concerns about CdTe. When disposed of in a landfill under acidic conditions, CdTe can leach into the environment.

This underscores the need for solar panel recycling. In contrast to silicon cells that are made with relatively low cost raw materials, the tellurium in CdTe cells is rare and expensive. Because of that, there’s a strong incentive to recycle CdTe panels. In fact, First Solar (the largest manufacturer of CdTe solar panels) already offers recycling in four countries.

What are the pros and cons of cadmium telluride solar?

According to the Department of Energy, the main advantages of CdTe solar cells are higher efficiency and lower cost manufacturing.

First Solar, the largest manufacturer of CdTe solar, also claims that their panels have better high temperature performance and does not experience light induced degradation, which can cause silicon solar panels to lose efficiency over time.

Environmental impact is also a benefit, despite potential concerns about cadmium. Not only does CdTe make use of cadmium that would otherwise have to be disposed of, but the manufacturing is less energy intensive. According to First Solar, their solar panels have a carbon footprint that is 2.5 times lower than monocrystalline solar panels.

Finally, CdTe solar manufacturing is dominated by First Solar, an American company. The manufacturing process does not use polysilicon from China, a raw material that is currently banned for import from the Uyghur region of China because of concerns about forced labor and child labor.

While there is some polysilicon manufacturing in Europe, North America, and other regions of China, the Uyghur region is a major manufacturing center. Because of this ban, the price of silicon-based solar panels has slightly risen recently and some companies have experienced supply chain issues. In addition, the challenges of accurately tracing and labeling the origin of polysilicon means there’s uncertainty whether any Chinese-sourced polysilicon was truly made without forced labor. First Solar’s US-based supply chain and manufacturing avoids this serious issue.

The main downside to CdTe right now is limited manufacturing. First Solar’s production is sold out through 2025, and they have manufacturing contracts that extend as far as 2029. They are currently expanding their manufacturing in Alabama, Ohio, and India with the hope of meeting that demand.

First Solar company overview

First Solar is the largest solar panel manufacturer in the United States. According to the company, they are the only solar manufacturer among the world’s ten largest that is headquartered in the US and not manufacturing in China.

Their latest product is the Series 7 solar panel. It has an efficiency of 19.3%, a very low annual degradation rate of 0.3%, and comes with a lengthy 30 year performance warranty.

That efficiency trails the best silicon solar panels such as REC and SunPower, which exceed 22%. However, I don’t have pricing information, so its possible that First Solar’s products are more cost effective.. Whether due to price or other advantages, the utility market has been won over: according to an interview in PV Magazine, 90% of utility-scale solar projects last year were CdTe.

First Solar previously sold its products for the residential market, but stopped doing so and currently only sells into the utility and commercial markets. Unfortunately, it might be awhile until you can purchase these panels for your home. However, with their factory production ramping up in Alabama and Ohio, we might see that change in the next few years.

Other manufacturers of CdTe solar

The solar manufacturing industry is dominated by giants, and it’s hard to break into it: you need a lot of capital to start a solar panel factory.

One startup company, Toledo Solar, gave CdTe manufacturing a go. According to Crunchbase they’ve received a total of $17.4 million in investment and have between 1 and 10 employees. A recent company press release states that they are now looking to be acquired and strongly hinted that First Solar would be a great candidate to buy them.

There’s also the Canadian company Elemex that has a product called Solstex. It’s a building facade panel that incorporates thin film CdTe. This means that the exterior wall of a building can look completely normal but generate electricity.

It sounds great, but Elemex highlights only one project that has used Solstex - the EllisDon office building in London, Ontario. Similar to silicon-based solar shingles for the home market, it seems that CdTe-based BIPV products haven’t expanded beyond niche markets.

Bottom line: CdTe is a popular product in the utility market that we might see on homes one day

Cadmium telluride solar technology isn’t new: it’s been around for 50 years. It’s made major inroads into the utility-scale market, but despite its advantages, it’s still second to silicon-based solar by manufacturing volume. Because of the huge scale of investment into silicon-based solar, this might not ever change. However, with ongoing investment and new manufacturing capacity from First Solar, it’s possible that homeowners will be installing CdTe in the coming years.