Do renewables actually reduce greenhouse gas emissions?

To generate power, fossil fuels must be burned; when they are burned, they emit greenhouse gases (and other forms of pollution) that alter the chemical composition of the atmosphere and impact the climate. Solar and wind, by contrast, emit nothing whatsoever as they generate power. This is one of the major reasons that politicians champion them as a “green” sources of energy.

 

But when all is said and done, does the deployment of renewables like solar and wind actually reduce the amount of greenhouse gases in the atmosphere from what it would have been otherwise?

 

The answer is not as obvious as you might think.

 

To examine this question thoroughly, I’m going to play devil’s advocate (renewables fans, please bear with me.) I’ll use a three-pronged approach: (1) Lifecycle Analysis, (2) Energy Debt, and (3) what I’ve decided to call the “Renewables Catch-22”.

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1. Lifecycle Analysis

 

The first thing I want to to know is: from cradle to grave, do renewables actually emit fewer greenhouse gas emissions than other sources of energy?

 

Long before they ever begin to generate electricity, solar panels are mass-produced in factories that use tremendous amounts of water and fossil fuels. Furthermore, constructing a mega-solar farm is hardly a “green” operation: it requires bulldozers and all manner of diesel-powered equipment to clear off dozens of acres of land. Similarly, wind turbines must be manufactured then shipped across long distances to get to site.

 

In other words, the amount of carbon dioxide emitted by these energy sources over their lifecycle is definitely not zero.

 

Even so, when you look across the entire lifecycle, renewables (and nuclear) are dramatically cleaner from the standpoint of greenhouse gas emissions. The numbers vary, depending on the type of fossil fuel and the exact technology being used. But solar, wind, and nuclear all emit anywhere between one-tenth and one-fiftieth as much greenhouse gas per unit energy compared to fossil fuels. That’s huge.

 

Don’t believe me? The World Nuclear Administration (p. 7), the National Renewable Energy Laboratory (p. 2), the Energy Information Administration (p. 17), and the World Energy Council (p. 4) have all produced studies to this effect.

 

Consider also that unlike fossil fuels, renewables have plenty of room to reduce lifecycle emissions even further -- if the factories used to manufacture them and the vehicles to transport them were run off more renewably-generated electricity.

 

Okay, so it looks like renewables win this time. But does that mean renewables are off the hook? Do renewables actually reduce greenhouse gas emissions?

 

....I’m afraid we can’t conclude that just yet. There are still a couple of more tests that renewables need to pass before we can say this is true.

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2. Energy Debt

 

The next question I have is the following: do renewables generate enough clean energy to offset the amount of energy it took to make them?

 

At first, this might seem like a silly question. Fossil fuels obviously generate way more energy than we put into them; otherwise, the world wouldn’t turn. But the answer isn’t so clear-cut for renewables because the global industry is relatively new, they currently produce such a small portion of total electricity (particularly solar), and their deployment isn’t driven purely by market forces.

 

If it turns out that it takes more energy to produce renewables than they are capable of generating themselves, the whole argument in their favor becomes invalid.

 

Focusing only on wind energy for a moment, I found that a wind turbine pays back its “energy debt” within a few months. Wind turbines last for years, so this is no big deal.

 

The answer for solar, however, is a bit more complex.

 

When I was in university, I used to do research on solar cells. One day I came into the lab, and everyone was excited because Stanford had just published a new paper called “Energy Balance of the Global Photovoltaic (PV) Industry – Is the PV Industry a Net Electricity Producer?”.

 

I started to read the paper. I was a bit surprised once I figured out what it was saying. The gist was that the solar industry was a net consumer of electricity as late as 2010, and that it would take several more years for the industry to pay back the “energy debt” of its early development.

 

(For context: solar panels were invented in the 1950s, but their development didn’t really pick up until the early 2000s. The panels are built to last 20-30 years [http://energyinformative.org/lifespan-solar-panels/], and the other components in the system last between five and ten years.)

 

Although people in my lab were excited by how soon solar had become a net electricity producer, I interpreted the news differently. All this time, we had been pushing solar as “green” energy, and it had actually been consuming more electricity than it could produce! I felt duped.

 

As I was writing this blog, I searched for other studies that made this same kind of “energy debt” estimation from the beginning of time. The only one I could find was a December 2016 publication by a group from the Netherlands. They concluded that the solar industry will pay back its historical energy debt at the latest by 2018, but could have done so as early as 1997.

 

If these studies are accurate, it’s unclear whether up to this point solar has led to a net reduction in greenhouse gas emissions. Perhaps solar has actually increased them.

 

But even if this is the case right now, it won’t be for much longer. Solar is still a very nascent industry with lots of room to grow, and things are rapidly accelerating in the right direction.

 

For example, the Netherlands group also found that for every doubling in solar panels installed, the energy cost to make them decreases by 12-13% and the greenhouse gas emissions decrease by 17-24%. Several other studies have also shown that energy payback period for today’s solar panels is as low as 1-2 years and falling.

 

Then, looking past 2018-ish, can we finally conclude that renewables will lead to reduced greenhouse gas emissions?

 

Nope; not yet. You might be getting annoyed by now, but there is just one more point I want to discuss.

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3. The Renewables Catch-22

 

...My final point is an important one. It’s that renewables are unreliable. Yes, I know, you’ve heard this all before. But this really is a problem – or, if you’re an optimist, a challenge. The more prevalent renewables become, the greater the challenge.

 

Roughly speaking, with today’s technology, renewables generate power only 10-30% of the time. The rest of the time, either the wind isn’t blowing, or the sun went behind a cloud. Furthermore, we can’t always predict when, exactly, that power generation is going to occur.

 

So herein lies the ultimate catch-22: people demand power 24/7 and we want it exactly when we want it. That’s not going to change. So that means at least for now, renewables need to be backed up by another power source to make up the difference when renewable power isn’t available.

 

It turns out that natural gas plants are particularly adept at ramping up and ramping down, or “load following” renewable energy sources throughout the day. They do this far better than traditional “baseload” power sources, such as nuclear or coal power.

 

In theory, nuclear power, which is emissions-free, can load-follow, too. But it tends to be prohibitively expensive. Interestingly, some of the world’s leaders for renewable energy generation – Germany and California – are phasing out nuclear power, and don’t view it as a solution.

 

I want to emphasize that natural gas isn’t the worst thing. Net-net, deployment of natural gas often ends up being better for the climate than the alternatives. Sure, burning (and fracking for) natural gas emits greenhouse gases. But the quantity emitted is much, much lower than it is for coal, and the pollution is considerably less harmful to human health.

 

My point here is simply that, for the time being, more renewables inevitably means more natural gas. A lifecycle analysis of renewables combined with natural gas is much, much higher than it is for renewables alone. Perhaps that should be taken into consideration more often when determining the cleanliness of renewables.

 

Given this fact, whether or not in the end, deployment of renewables does in fact reduce greenhouse gas emissions depends on what the renewables and natural gas are replacing. If they’re replacing coal, then the answer is still yes. If they’re replacing nuclear power, then the answer is no.

 

You might also be wondering, what about batteries? Batteries could potentially solve the unreliability problem by reducing the dependence of renewables on other sources of power. Of course, we’d need to factor the energy costs of batteries into the lifecycle and energy debt calculations for renewables, which could get a bit tricky. But yes, it’s one possible solution.

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Conclusion

 

Finally, I think I’m ready to answer the original question. My answer is on the whole, yes, renewables actually do (or at least, they will) slow climate change – but not in every case.

 

Why? In the years to come, the vast majority of growth in energy demand will occur in developing countries. Until now, the developing world has had little choice but to rely upon coal. The increasingly viable option to deploy renewables combined with natural gas as an alternative to coal will make an enormous difference in greenhouse gas emissions and other forms of pollution that would have been emitted otherwise.

 

On the other hand, renewables may not be the best choice for developed countries, where energy demand is stagnant. Here they may actually increase emissions, especially if they are used to replace nuclear power.

 

So there you have it: renewables are indeed becoming a powerful tool for the world – it’s no myth. But they should be viewed critically and deployed thoughtfully. Otherwise, there’s just no point.