Science

Paradox about renewable energy: Solar panels and their toxic waste

Cradle-to-grave solar panels are actually not as "green" as we are led to believe.

Cradle-to-grave solar panels are actually not as “green” as we are led to believe.

Paradox about renewable energy: Solar panels and their toxic waste 1

Credit: Monash University

Around the world, there is a massive push to reduce our reliance on fossil fuels for various reasons – chief among them the preservation of our home planet. Among the various strategies being developed, one tends to receive the most attention – renewable technologies, like solar panels.

Touted as being completely sustainable, such claims often gloss over – or worse, ignore – the very real damage caused through the production and use of this technology. Just like wind turbines, solar panels may have a darker side to their existence than most truly appreciate.

That’s not to say that solar PV panels should be abandoned outright, but that a more honest, and realistic, conversation be had about them.

To give you some idea of the scale of the problem, you can peruse some interesting data provided here. To give you the gist of it, this study, conducted by environmental journalists who favor nuclear power found that solar panels (over their lifetime) create somewhere in the region of 300 times more toxic waste per unit of energy than nuclear power plants.

If we were to assume that PV panels and nuclear power plants were to each produce the same amount of energy over the next 25 years that nuclear produced in 2016, the difference in waste produced would be significant. If we took the waste and stacked it on a football field, nuclear waste would reach about the height of the Leaning Tower of Pisa. Solar waste, on the other hand, would equate to about the height of two Mt. Everests.

Of course, the nature of the waste generated between the two is very different, but the quantity of the latter cannot be ignored. At present, the most likely final location for this waste is in landfills – not ideal to say the least.

But how? To find out let’s track the life of a solar panel from cradle to grave.

What materials are used to make solar panels?

Like anything produced, solar panels require raw resources to build them. In the case of solar panels, this includes various materials, but are mostly made of a special kind of silicon.

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Source: IRENA/Flickr

As we explained in a previous article on the anatomy of solar panels, this is one of the most abundant materials on Earth. In most cases, the raw source of silicon (in the form of silicon dioxide, aka silica) is a mineral called quartz.

Getting your hands on this usually involves mining which attracts all the health and safety issues that that activity entails. Silica, similar to asbestos, also has some potential health problems associated with inhaling small particles of silica called silicosis. Just like asbestosis, this is a debilitating and usually fatal lung disease.

However, since mining is a common practice for sourcing many raw materials, this issue is not unique to the production of solar panels – but an important one.

Once the silica is extracted, it needs to be refined into a purer form, such as metallurgical-grade silicon. It is important to note that this material is used for many types of electrical components, but is a major constituent of solar panel production.

Production of this grade of silicon takes place in giant furnaces, which consume a lot of energy to keep them running. In most cases, the energy is provided through the combustion of fossil fuels either directly or from power stations supplying electricity to the grid.

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Example of a metallurgical-grade silicon facility, Polokwane, South Africa. Source: ferroglobe

This is especially the case for countries that are still heavily reliant on fossil fuels for generating power. While this energy investment is often “paid back” over the lifetime of the solar panel, the length of time this takes is directly dependent on a measurement called the carbon-intensity value.

This metric is a measure of the kilograms of CO2 emitted by kilowatt-hour of electricity. This value varies per country, with places like China having double that of, say, the United States. If panels were made in China and installed in China, the payback is relatively quick, if, however, the panels are made in China, then shipped to the U.S., the payback is considerably longer (even without factoring in the transportation emissions). If PV panels are made using low-carbon electricity, the payback is obviously a lot faster.

The production process of metallurgical-grade silicon itself also generates a lot of noxious gases, like sulfur dioxide and nitrous oxides, as well as, of course, carbon dioxide. While emitted at relatively low levels, large-scale production of solar panels can produce a significant amount of these gases (e.g. acid rain, etc).

But, this is only the start of the process for minting a new panel. This metallurgical-grade silicon also needs to be further processed. The metallurgical-grade silicon is also combined with hydrochloric acid to create trichlorosilane, which is the principal precursor to ultrapure silicon in the semiconductor industry.

It is also reacted with hydrogen to produce intermediary forms of silicon called polysilicon and silicon tetrachloride, at a ratio of about 1:3. The latter happens to be highly toxic.

For more scrupulous manufacturers, the waste products can be recycled to recover the silicon for future production, but in most cases, it is simply thrown away. If silicon tetrachloride is exposed to water, this usually results in the release of hydrochloric acid, which is obviously not great for the environment.

While countries like the U.S., UK, and European Union nations have very strict environmental standards, most production of polysilicon now occurs in the Far East, where regulations are less stringent.

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Source: DiyanaDimitrova/iStock

In fact, a 2008 Washington Post investigation showed that one Chinese polysilicon facility simply dumped its waste tetrachloride into the neighboring fields instead of investing in the equipment needed to recycle and reuse it. This, understandably, lead to an international outcry, and the Chinese government set standards requiring at least 98.5 percent of this waste be recycled.

However, it is unclear how well this is actually policed.

What are the environmental impacts of solar panel production?

But wait, we’re not finished yet.

Unfortunately, the production of polysilicon is still not the end of the story.

In order to be useful for the purpose of making a solar panel, some more preparation is needed. First, polysilicon needs to be formed into brick-like ingots and then sliced into thin wafers. The silicon wafers are then “doped” with substances like gallium, cadmium, arsenic, antimony, bismuth, lithium, etc., in order to create the solar-cell components which are vital for producing the photovoltaic effect. Most of these are, in their own right, potentially very hazardous to the environment.

This process also requires the use of phosphoryl chloride, which also happens to also be very toxic and highly corrosive.

Not only that, but most of these steps also require the use of more hazardous chemicals – foremost among them hydrofluoric acid. This is one of the most powerful acids in the world and is highly dangerous if not handled properly, as some horror stories from (yes you guessed it) China highlight.

Work is currently apace to replace hydrofluoric acid with sodium hydroxide, but this chemical has its own inherent issues, too. However, it is far easier to handle and treat should accidents occur.

But, that’s still not the full extent of potential environmental damage from solar PV production.

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Source: DmitriMaruta/iStock

PV panel manufacture also consumes a lot of water, too. Water is used for various parts of the process including cooling, chemical processing, and air pollution suppression. To give you a rough idea of how much water is used, utility-scale projects in the 230- to the 550-megawatt range can consume up to 1.5 billion liters of water for dust control during construction. They may also use another 26 million liters annually for panel washing during operation.

However, it is important to note that the amount of water used to help cool thermoelectric fossil fuel and nuclear power plants is usually considerably higher than this, by comparison.

Are solar panels hazardous to the environment throughout their lifetime?

After all that processing during manufacture, surely the environmental impact of solar panels is now finished? After all, the production of many physical goods has at least some environmental impact.

Think again.

While the actual process of converting sunlight into electricity can be considered “green”, there are some other problems with solar panel arrays that are not usually considered.

For example, large-scale solar PV arrays need space – a lot of it. If not cited on brownfield sites or in deserts, this may require the clearance of perfectly useful land (or indeed the use of water bodies such as reservoirs) to make room for the panels. This can directly impact local ecosystems in the short term but could also have longer-term effects on the habitats of native plants and animals.

Large-scale land clearance in preparation for a PV installation often results in soil compaction and an alteration of natural drainage channels. With little to no significant vegetation allowed to grow around the panels (as this would obviously cast shadows over the panels), this can result in a significant increase in soil erosion and surface runoff. Much like deforestation, this can be disastrous for local ecosystems over the long run.

As we touched on above, some operational solar PV power installations can also require the need for large amounts of water. This is often used for cleaning or cooling purposes, depending on the system in question (solar collectors or “regular”). If large enough volumes of groundwater or surface water are consumed in this fashion, and can, and will, directly impact the wider environment around the PV installation.

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A floating solar farm on Tengeh Reservoir. Source: Sembcorp

While most of these issues are not really relevant to domestic-scale installations, they are significant enough to be taken seriously.

For solar thermal solar panels, there are other potential environmental hazards. Some systems can require some pretty hazardous fluids that are used to transfer heat from the panel. Domestic-scale solar water heating systems, on the other hand, typically use a low-toxicity antifreeze like propylene glycol.

With the best will in the world, the pipework, pumps, and other ancillary equipment used to contain these liquids cannot last forever and are prone to rupture over time.

This can result in the leak of such liquids into the environment, which is obviously not ideal for plants and animals. So far so good (well bad), but surely the environmental impact stops when the panels are retired?

Hold your horses.

What happens to old solar panels?

So far we’ve tracked the life of a solar panel from raw materials to its installation and use. But what happens to old solar panels when they reach the end of their useful lifespans?

Most solar panels tend to have a useable life of around 25 years, or so. Once their useful lifetime has elapsed, panels will need to be decommissioned, removed, and replaced with new panels (with the added impacts already discussed above).

But what happens to those used panels? Are they safe to just throw away? Can they be recycled?

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Source: David Clarke/Flickr

As we’ve seen, these pieces of tech are packed with some pretty toxic materials – especially older units. What’s more, the problem is set to grow over the coming years.

By around 2050, or so, organizations like the International Renewable Energy Agency (IRENA) predict that around 78 million metric tons of solar panels will likely have reached the end of their lives. Something will need to be done with all this waste.

While most electronics can be recycled relatively safely, the toxic contents of solar panels are going to become a real problem if no reliable method of safely decommissioning old panels is found. If not, most of these panels, as today, may simply end up in the landfill.

One of the problems compounding recycling efforts is that the solar cells tend to be encapsulated in plastic and sandwiched between glass and a backing sheet. While not technically challenging to disassemble, it takes time, and time means money for potential recycling firms.

Some methods for recycling do exist which are also supported by some regulatory frameworks requiring solar panels to be recycled, rather than just chucked away. However, existing methods are not the most environmentally friendly way of dealing with them.

For example, at a typical e-waste facility, solar panels are stripped of their aluminum frames and junction boxes to recover the metals within. However, the rest of the panel, as we’ve already highlighted, is encapsulated in layers of ethylene-vinyl acetate (EVA) plastic bonded to the glass, and is a lot harder to process.

For this reason, the rest of the panels (glass, polymers, and solar cells) are often simply shredded, although it is coated in silver electrodes and soldered using tin and lead. Since the bulk of this material’s mass is glass, it is often just treated as an impure form of crushed glass.

This waste glass can’t usually be recycled further as it often contains plastics, lead, cadmium, and antimony which, if they were to leach out of the waste, can be particularly deleterious to the environment.

Can solar PV panels be recycled?

Traditionally, as we’ve seen, only a small proportion of a solar panel can be recycled, but things are changing rapidly.

Paradox about renewable energy: Solar panels and their toxic waste 8

Source: Redwin Law/Flickr

One of the main problems with recycling solar panels is the low cost-benefit ratio of doing so. From some estimates, a typical 60-cell silicon panel can yield somewhere in the region of $3 worth of recovered aluminum, copper, and glass.

However, the cost of recycling the entire panel, in the U.S., costs somewhere in the region of between $12 and $25, including transportation costs. On the other hand, it costs less than $1 (depending on the state) to simply dump an old panel.

From a business perspective, there is no obvious financial benefit to recycle the panels, so why bother?

One reason is that the panels do contain some very valuable materials, like silver and silicon. If the price is right, extracting these can be worth investing the time to efficiently recycle old PV panels.

This is exactly what some companies, like Veolia, are doing. Based in France, this company has developed the world’s only commercial-scale silicon PV recycling plant. The company takes old panels, grinds them up, and then subjects the waste to a special optical technique to recover a low-purity form of silicon.

Veolia has initially developed a heat and ball mill process that was able to recapture more than 90 percent of the most valuable materials in each panel (including silver). However, the new optical technique is able to recover in excess of 95 percent of the most valuable constituent materials in PV panels.

Great news, but some organizations want to go even further. A research team led by the National Renewable Energy Laboratory is working on a way to recycle PV panels to extract the metals and minerals in a high purity form. This, they hope, will make PV panel recycling truly economically viable and as environmentally friendly as possible.

“What we call for is what we name a high-value, integrated recycling system,” study lead Garvin Heath explained in an interview with Grist. “High-value means we want to recover all the constituent materials that have value from these modules. Integrated refers to a recycling process that can go after all of these materials, and not have to cascade from one recycler to the next.”

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Source: LoveSilhouette/iStock

Another example comes from We Recycle Solar, which is based in California. They have developed a special technique to extract as much of the valuable materials from solar PV panels as possible.

Since its founding five years ago, the company has recycled thousands of panels from homes, businesses, and solar farms. Like other recycling companies, they first remove the aluminum frame, and wiring, etc.

They then shred the rest of the panel and subject it to special chemical processing, electrolysis, and additional processes. This treatment allows the company to separate out the metals, silicon, and glass for future shipments to downstream processors.

This process heavily reduces the amount of non-salvageable material from used solar panels, significantly reducing the need for landfills.

Another company, Echo Environmental, follows the same initial processing of used solar panels. But, unlike other companies, they then subject the remaining parts of the panels to a series of milling processes.

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Source: Gerard O’Laoi/LinkedIn

This separates out a clean portion of the glass, which can then be sold for use in fiberglass insulation or reflective paint. The rest of the panel (silicon, etc.), is then mixed with other shredded circuits and shipped for smelting.

Yet another company, Australia-based Lotus Energy, has developed a method of recycling almost 100 percent of old solar panels. What’s more, the process uses no chemicals.

The process is able to yield high-grade aluminum, high-grade silica dust, copper, PVC, and silver. The silica cells can also be salvaged for reuse by some manufacturers.

Can old solar panels be repurposed or resold?

Another angle of attack to deal with the mounting PV panel waste problem is finding a way to repurpose, rather than recycle or dump, old panels. Since old panels are likely more valuable as they are, rather than as their constituent parts, this could be a very promising endeavor.

For example, retired panels from rooftops or solar farms could, conceivably, be repurposed for use powering e-bikes. Other initiatives include recertifying and reselling old, but perfectly functional, PV panels.

This practice would have to come with a caveat, however. Much like the reseller market for sending used mobile phones to developing countries, some countries have very poor or non-existent e-waste regulations. This could mean that old solar panels are later dumped anyway – except under less strict environmental restrictions.

That would just be exporting the problem, not dealing with it.

Another compounding problem with reselling old panels is, once again, financial. Newer panels have dropped considerably in price over the years, seriously eating into the potential profits of the secondhand PV panel market.

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Source: Jimmy_Joe/Flickr

According to the U.S. Energy Information Administration, the average cost of PV modules shipped in 2019 (the most recent year for which data is available) was 41 cents per watt of electricity generated at peak performance. A decade earlier, the average was $2.79 per peak watt.

But, the newest panels on the market are more efficient than ones built over a decade ago. If the price is not that much more for a new panel, and its efficiency is significantly higher, consumers are more likely to fork out a little bit more to get more bang for their buck. After all, one of the most important factors with any investment is its payback period.

Yet another issue is the financial incentives that tend to come with buying and installing new panels. Oftentimes, government tax incentives exist that help with the cost of installing the technology. In the U.S., for example, it is currently the federal government’s policy to reduce the cost of a new PV installation by as much as 26 percent.

But this policy does not normally extend to older, secondhand panels.

What can be done to deal with the coming solar PV waste problem?

While reports of the impending solar waste “crisis” are alarming, strategies are already being developed to deal with it. From ways to recycle 100 percent of old panels to the potential for reusing or repurposing old panels, the only real problem will be one of imagination and will.

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A graphene-enabled solar panel in Crete, Greece. Source: Graphene Flagship

The best method would be to repurpose and install older panels as the environmental cost has already been spent for these units. If incentives can be extended to old panels, or other benefits from installing new panels (warranties, certification, etc) only then will a healthy market for them be possible.

Until then, governments will likely continue to churn out legislation mandating the need to fully recycle old panels, rather than dump them in a landfill. So long as recycling can be made profitable, this will help significantly reduce the environmental cost of extracting and processing raw materials.

There are some other avenues to explore, like graphene-based silicon panels, organic solar panels, or thin-film panels, but these will only introduce their own unique cradle-to-grave issues. Whatever the case, it will be exciting to see what innovative ways to deal with older solar panels will be.

Published by Christopher McFadden.

Source: interestingengineering.com

Nguồn: https://interestingengineering.com/renewable-energy-paradox-solar-panels-and-their-toxic-waste
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Navy Phan is an editor at Justbartanews. She edits nature, space, mystery, and interesting facts on Science. She hopes she can bring more interesting and useful information to all Justbartanews's readers.

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