Are solar panels environmentally friendly?

While growing rapidly, renewable energy still constitutes a minority of the energy usage in the United States. Because of that, people are still learning how it works and whether it’s really better than fossil fuel energy sources.

It’s easy on the internet to find articles suggesting that not only are wind and solar energy not environmentally friendly, but that they’re worse for the environment than fossil fuels. For example, Donald Trump claimed that the noise from wind turbines cause cancer (it doesn’t).

The bottom line is: yes, solar panels are environmentally friendly. In the worst case, solar panels have an energy payback time of 4.1 years, and will generate 8 to 12 times as much energy in their lifetime than was needed to mine the raw materials, manufacture, and install them. Recycling solar panels is still new, but more companies are doing it. And solar panel manufacturing releases fewer heavy metals than burning coal.

So why does some information persist that solar panels are worse for the environment than fossil fuels? It’s worth taking a look at where the data is coming from.

Fossil fuel lobbyists

Much of the disinformation about renewable energy can be traced back to the fossil fuel lobby, who stand the most to lose from the continuing transition to cleaner sources of energy.

For example, the Institute for Energy Research is a think tank currently lead by Robert Bradley, a former director at Enron. They claim that solar power will be the cause of a coming environmental crisis because there is no plan for recycling solar panels, and that solar panel manufacturing releases nitrogen trifluoride (NF3), a potent greenhouse gas.

While semiconductor manufacturing for computer chips, tv screens, computer monitors, and solar panels does release NF3, the global amount is tiny: the greenhouse gas equivalent of 0.06% of the emissions caused by CO2, according to a University of Edinburgh researcher. In addition, newer manufacturing facilities are more efficient and release much less NF3 than older facilities.

IER also makes the rather absurd suggestion that waste from nuclear power is less impactful than waste from solar panels. While it may be true that a decommissioned solar plant would produce a large volume of waste, which would you rather have in your backyard: Highly radioactive nuclear waste with a half life of 245,000 years? Or discarded solar panels consisting mainly of glass and aluminium?

So we know where some bad information is coming from. Let’s look at some facts next.

Energy payback period of solar panels

One way of understanding the environmental footprint of solar panels is to look at how long they take to generate the same amount of energy that was spent to manufacture and install them.

There are two numbers that are commonly used to measure this:

• Energy payback time (EPBT) describes how long it takes the solar panels to generate the same amount of energy that was used to mine the raw materials, manufacture the product, install it, and dispose of it at the end of its life.
• Energy return on investment tells you how much more energy the product will generate during its lifetime than was used to manufacture and install them.

There were some early studies that looked at the EPBT of solar panels, and ended up with payback periods for solar that were very long. But those studies used outdated data on manufacturing processes that have since become much more efficient.

So the next question is: where do you find good data?

Finding quality studies

If you spend some time searching Google Scholar, you will find many newer studies that support the case that the EPBT and EROI of solar is favorable. But the methodoloy of these studies vary: for example, some may not include the energy involved in mining the raw materials for solar panels.

Where the solar panels operate also affects the energy payback, because using solar panels in very sunny places will result in a shorter payback time than in regions with less sun.

Because of this, for the lay person who nonetheless wants to dig into the scientific literature, probably the best approach is to look for a well-researched meta-analysis.

A meta-analysis doesn’t collect original data, but instead reviews existing literature, aggregates their results, and tries to arrive at a common conclusion that is supported by the underlying studies.

A recent paper from the University of Toledo titled “Energy payback time (EPBT) and energy return on energy invested (EROI) of solar photovoltaic systems: A systematic review and meta-analysis” is one I read that seems to cover all the bases. The authors reviewed 232 papers on this topic and found 11 and 23 papers that passed their screening for EPBT and EROI analysis, respectively.

Energy payback time for solar panels

This study looked at different solar photovoltaic technologies including thin-film, polycrystalline and monocrystalline silicon, and calculated the energy payback time for each.

Thin-film technologies, which include several different chemistries, had the best payback period, ranging from 1.0 for cadmium telluride to 2.7 years for amorphous silicon. But thin-film isn’t widely used for homes, so we won’t focus on that.

Poly and mono silicon is the most popular type for residential solar arrays. Here’s their energy payback time:

• Polycrystalline silicon: average energy payback time of 3.1 years
• Monocrystalline silicon: average energy payback time of 4.1 years

So you can see that manufacturing monocrystalline silicon, which is a more pure silicon product, is more energy intensive than cheaper poly cells. However, mono panels are more efficient, so you do get a higher quality product in the end.

Energy return on investment for solar panels

Let’s look at EROI next, which measures how much more energy the product generates over its lifetime than was used to manufacture and install it.

EROI is expressed as a factor. For example, an EROI of 1 would mean it produced the same amount of energy in its lifetime as was used in its manufacturing lifecycle. An EROI of 2 would mean that it generated twice as much energy as was used, while an EROI of 0.5 means that twice as much energy was used to make the product than it generated during its life.

Make sense?

Going again to the Toledo study, here’s what the EROI for silicon solar panels looks like:

• Polycrystalline silicon: energy return on investment of 11.6
• Monocrystalline silicon: energy return on investment of 8.7

This means that polycrystalline panels will generate 11.6 times as much energy in its lifetime than was needed to manufacture and install them, while mono panels are a little worse with an EROI of 8.7.

Again, thin-film does the best: cadium telluride cells have an EROI of 34.2. But CdTe cells are still more expensive than silicon, not widely used in homes, and have the unfortunate problem of being made with cadmium, a toxic heavy metal.

Bottom line: solar panels definitely pay for themselves

The study looked at the full lifecycle operation of solar panels. This includes not just the energy required to make the panels, but also the electronics such as inverters, and the support hardware such as racking.

After looking all that, you can safely conclude that solar panels definitely are environmentally worth it and do pay back the energy that was needed to make them.

One last thing to keep in mind: the most recent data used in this study was from 2013. Given the rapid rate of change in the solar industry and constant improvements in manufacturing efficiency, you should expect that solar panels manufactured in 2019 will have a lower footprint than the figures from this study.

Comparing solar to non-renewable sources

How does this energy payback period compare to fossil fuels? I found one study via Oilprice.com, an publication for the oil and gas industry. It mentions that the EROI of oil drilling started at a high of 1200 way back in 1919. (Those were the days when you could stick a fork in the ground in Texas and expect oil to gush out.)

Since then, Earth’s easily reached oil resources have been extracted and oil exploration has required much more energy, to the point now where companies are mining oil sands and cooking rocks with steam to melt the oil out of them.

These days, the EROI of the oil industry is 11 - about the same as silicon photovoltaic panels.

Limitations of energy payback analysis

While energy payback analysis is one way of looking at environmental impacts, it has a very important limitation, which is that it ignores pollution.

If you look at the EROI of oil extraction and solar panels, you’ll see that they’re pretty similar. But that only tells you about the energy that was spent to extract them. It doesn’t tell you about the pollution caused by actually burning the fuels.

Solar panels are carbon-free

Once you’re done manufacturing and installing a solar panel, it generates pollution-free electricity for 25 to 30 years, maybe even more.

But when you extract oil or coal from the ground, you still have to burn it in a car or a power plant, and that process is definitely not carbon-free.

Not only is it not carbon free, but it produces dangerous pollution such as PM2.5, which causes asthma, and even pollution you might not expect, like radiation and heavy metals. This happens because radioactive elements and heavy metals are trapped in rocks, and burning coal releases that into the atmosphere. Coal burning is why your canned tuna contains mercury.

Recycling solar panels

One last major issue to consider with solar panels is recycling. Because the solar energy industry is still young, and solar panels last decades, the earliest installed solar panels are still operating in many cases.

But in the coming decades - as a former Enron executive at the Institute for Energy Research might warn you - solar panels will start to reach the end of their life and need to be disposed of.

What’s important to know about this issue is that the ability to recycle solar panels already exists. More than 80% of the mass of a solar panel consists of glass and aluminium, both of which can be handled by existing recycling streams.

The remaining materials consist of elements such as copper, silver and silicon wafers. There are companies that already are recycling these materials.

For example, First Solar is one of the largest solar panel manufacturers, and already has recycling facilities on three continents that will recover up to 90% of the materials in a solar panel. There are other companies emerging too, such as Recycle PV in California.

As the solar industry ages, you can be sure that more companies will emerge to handle the coming waste stream problem.

Conclusions

I’ve done my best to distill out the key results from a dense academic article, but if you’re inclined I’d encourage you to read the whole thing. To summarize the answer to the question posed in headline of this article:

• Solar panels are definitely an environmentally friendly energy source.
• The energy payback time for solar panels ranges from 3.1 to 4.1 years, depending on whether they are monocrystalline or polycrystalline silicon.
• The energy return on investment is between 8.7 and 11.6, depending on whether they are monocrystalline or polycrystalline silicon solar panels.
• Solar panels eventually become carbon negative because they replace fossil fuel sources from the grid.
• The majority of a solar panel consists of recyclable glass and aluminium.
• Facilities are available now that can recycle the remaining silicon and wiring that makes up a panel, and more will come online in the future.
• The most common type of solar panels are made of non-toxic silicon and may contain only a tiny amount of heavy metals (lead) that is used in soldering.

In other words, if you’ve chosen solar power for your home, you should feel good that you’re doing a positive thing for the environment.

References

• Energy payback time (EPBT) and energy return on energy invested (EROI) of solar photovoltaic systems: A systematic review and meta-analysis
• A New Long Term Assessment of Energy Return on Investment (EROI) for U.S. Oil and Gas Discovery and Production
• Institute for Energy Research (Sourcewatch)
• Nitrogen trifluoride global emissions estimated from updated atmospheric measurements
• End-of-Life Considerations for Solar Photovoltaics