Do solar panels contain cadmium or other heavy metals?

Solar panels produce clean energy. But are the panels themselves non-toxic?

Everyone knows that solar panels turn sunlight into electricity, and they do that without any pollution. But that doesn’t mean that making the panels themselves isn’t pollution-free.

If you’re a homeowner who is thinking about installing solar panels, you might be wondering: what exactly is inside that sheet of glass? Maybe you’re worried because solar panels will go on top of your roof where rainfall hits the panels and washes off, or they’ll go in your backyard, where your kids or other people might be hanging out.

If there’s anything toxic inside - especially heavy metals like cadmium, lead, or mercury - could toxins leach out and poison your home?

The answer is no. The type of solar panels that are by far the most common on homes are made of crystalline silicon (c-Si). Silicon is the same element in sand, and is non-toxic. c-Si cells are currently 95% of the market.

The rest of a solar panel is made of the aluminum frame, a glass cover, a couple layers called the encapsulant and backsheet which are made of various plastics, and the wiring. None of these have any toxicity concerns, with the possible exception of a very small amount of lead used in the wiring solder.

However, the amount of lead we’re talking about is comparable to what can be found in any electronics in your home – like your TV, computer, or DVR. Unless you plan to eat your solar panels (not recommended!) none of this poses any health risk to a homeowner with solar panels on their home.

In addition, solar panels are designed to withstand a lot of abuse. This includes high winds, heavy snow loads, and hail impacts. This means that even if there were hazardous materials inside, a solar panel is built sturdy enough to hold up to the elements for more than two decades. You can read our article on solar panels and hail damage to learn more about strength testing.

Thin-film solar panels and toxicity

Even though the common type of solar panel is non-toxic, there is a type of solar cell that can contain toxic materials: thin-film solar cells.

Conventional solar cells are made by cutting wafers from a block of silicon. Thin-film cells, in contrast, are made by depositing chemical layers on a substrate such as glass or plastic. Often the substrate is flexible, which is why these cells are called thin-film.

There are different materials used to make thin-film cells, each with differing toxicities.

Cadmium telluride

Cadmium telluride (CdTe) is the most common type of thin-film solar cell in production.

First Solar, a US-based manufacturer, makes attractive PV modules that can be used in home applications. Normally, thin-film cells have quite a bit lower efficiency than c-Si cells, but the latest products from First Solar have a 14% efficiency, which is pretty close to polycrystalline cells.

First Solar also claims that their product is more environmentally friendly than c-Si cells because of the lower energy inputs required in manufacturing.

However, cadmium telluride has toxicity concerns. It’s harmful if swallowed, and is very toxic to aquatic life.

Copper indium gallium selenide (CIGS)

CIGS is another mainstream thin-film technology. The company Solyndra, now bankrupt, was one of the few companies that attempted to bring CIGS cells into mainstream use. Solar Frontier, a Japanese company, is a current producer of CIGS solar cells. MiaSolé, a company based in California but owned by a Chinese parent, also manufactures CIGS cells.

None of elements used in this type of cell are heavy metals. However, individual elements used in CIGS, such as indium, do have known toxicities.

But that doesn’t mean that the CIGS molecule has the same health risks. However, there is currently no published toxicity or health data for copper gallium indium selenide.

Amorphous silicon

Amorphous silicon cells, like c-Si cells, are made of non-toxic silicon but differ in the chemical form that the silicon takes. To get briefly technical, crystalline silicon cells are made of silicon in an ordered crystal lattice, while amorphous silicon takes on a loose, disordered arrangement.

Because of this difference, amorphous silicon can be deposited onto flexible substrates to make solar cells.

The non-toxic nature of amorphous silicon and low energy required during manufacturing are major benefits, but so far it remains a niche product.

Portable solar panels and thin-film

One of the product categories that you might expect to find widespread use of thin-film cells is for portable power charging devices, but even this is still dominated by c-Si. This is because it’s possible to make crystalline silicon semi-flexible by reducing its thickness.

This type of semi-flexible solar cell is extremely popular for mobile applications such as camping and motorhomes, and small charging devices for smartphones and laptops.

Most flexible and portable solar panels that you’ll find on the market are made of flexible c-Si cells, and not thin-film.

Thin-film solar cells: a health concern?

The most toxic of the thin-film technologies is CdTe, which contains cadmium. It’s also the one in most widespread use. If you’re thinking of going with a CdTe panel, such as those available from First Solar, should you be concerned?

According to a study by Virginia Tech, no. According to the study:

The CdTe compound is less leachable and less toxic than elemental Cd. The risks to the environment arising from broken solar panels during adverse events are considered by reviewing experimental results, theoretical worst-case modeling, and observational data from historical events. In each case considered, the potential negative health and safety impacts of utility-scale photovoltaic installations are low. The need for end-of-life management of solar panels is highlighted in the context of recycling to recover valuable and environmentally sensitive materials. Based upon the potential environmental health and safety impacts of CdTe photovoltaic installations across their life cycle, it is concluded they pose little to no risk under normal operating conditions and foreseeable accidents such as fire, breakage, and extreme weather events like tornadoes and hurricanes.

In other words, cadmium telluride is less of a hazard than metallic cadmium, and even in exceptional cases like a fire, the risks are relatively low.

This doesn’t mean that there is zero risk, which is why the authors highlight the need for recycling at the end of the product’s life.

Cadmium in your home now

Do you have a battery-powered tool, like a drill or dustbuster? There’s a good chance that it has a nickel-cadmium battery. But there’s little risk to you, because it’s safely packaged inside a durable housing. When the product has reached the end of its life, you can take the battery to a Home Depot or Lowe’s and recycle it.

With proper lifecycle handling, there’s no reason that CdTe solar panels can’t be considered just as safe as these other common consumer products.

Further reading

Even if you are one of the few people who choose thin-film panels for their home, the environmental benefits vastly outweigh the minimal toxic risks of a technology like CdTe.

Mercury is one of the most common heavy metal pollutants - it’s the reason why pregnant women are advised to limit their intake. The reason for that mercury pollution? 42% of it is from coal-fired power plants. This means that by choosing solar energy, you’re actually helping to reduce heavy metal pollution in the environment.

If you want to learn more about the environmental benefits of solar panels, including conventional c-Si cells, read our article on the topic.

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