Clean energy is growing fast — but it's not yet winning the race against fossil fuels

Fossil fuels have long provided the vast, vast majority of the world's energy. But in recent years, cleaner sources like wind and solar have been growing at an astonishingly rapid clip. And that's led a lot of people to wonder when we might hit a tipping point: When will clean energy start growing faster than fossil fuels?

This week, Bloomberg stirred a lot of excitement by declaring that we've already hit the tipping point: "Fossil Fuels Just Lost the Race Against Renewables."

Unfortunately, that headline isn't quite right. Clean energy isn't winning the race against fossil fuels just yet. And it's worth exploring why in more detail, to better understand just how massive a task it will be to decarbonize the world's energy supply and avoid significant global warming.

This chart, showing clean energy winning, omits a few things...

Bloomberg's key piece of evidence is a chart from Bloomberg New Energy Finance showing that countries around the world added more electric generating capacity from hydropower, nuclear, solar, wind, biomass, and geothermal in 2013 than they did from oil, gas, and coal:

(Bloomberg New Energy Finance)

That is a neat milestone. But it doesn't prove that clean energy is growing faster than dirty energy. There are a two big things this chart omits:

1) Electricity is not the same as energy. The first thing to note is that the chart above only shows electricity capacity additions. Remember, "electricity" is not the same thing as "energy." We use electricity to power our homes and appliances. But most of the world's cars and planes don't run on electricity; they run on oil. A lot of buildings don't use electricity for heat; they burn gas. Those non-electricity energy sources aren't counted above.

If we're worried about global warming, we have to consider that bigger picture. Electricity and heat were only responsible for about 42 percent of global CO2 emissions from fuel combustion in 2012. For clean energy to truly win the race, it will have to make inroads in other sectors as well, particularly transportation.

2) 1 GW of solar is not equal to 1 GW of coal. The second criticism of the chart above is that it only shows electricity capacity additions. "Capacity" is defined as the maximum output a power plant can produce under specific conditions. It is not same as how much electricity a power plant will actually generate in its lifetime.

Here's a way to illustrate the difference: coal plants can burn coal pretty much around the clock. So, over the long run, a coal plant will typically produce between 50 to 80 percent of its maximum output. Solar photovoltaic panels, by contrast, only work when the sun is shining. In the long run, they might produce just 20 percent of their maximum output. These percentages are known as "capacity factors."

This is important to keep in mind. Imagine that the world installed 2 gigawatts' worth of solar panels and a 1-gigawatt coal plant. If you only looked at a chart of capacity additions, you'd assume solar is absolutely crushing coal. But that's not necessarily true! When you take capacity factors into account, the coal plant is likely producing more total electricity.

For now, fossil fuels are still keeping pace with renewables

So let's look at a better chart that shows the world's energy consumption from different sources. This way we're looking at all primary energy — not just electricity but also cars and airplanes and heating and so on. We're also not being misled by looking solely at capacity; we're looking at actual use.

As it happens, BP offers this data in its Statistical Review of World Energy 2014. And the chart below looks more daunting for clean energy:

All told, fossil fuels made up 87 percent of the world's primary energy consumption in 2013. By contrast, low-carbon sources — including nuclear, hydropower, wind, solar, and biomass — made up just 13 percent.

That ratio hasn't changed since 1999, as the University of Colorado's Roger Pielke Jr. has pointed out. In other words, the world's energy supply hasn't gotten any cleaner for 14 years.

Yes, clean energy sources have been rising over that time. That little yellow sliver showing renewable energy is growing at rapid clip (that includes solar and wind, but it also includes biomass energy and biofuels/ethanol for vehicles, both of which often come in for criticism). Hydropower is also expanding. Nuclear power, by contrast, is stagnating.

But coal, natural gas, and oil have more than kept pace with the growth of clean energy. An illustrative example: In 2013, non-hydro renewable energy consumption grew by 38.5 million TOE (tons of oil equivalent). But coal consumption grew by 103 million TOE — more than twice as much. If this is a race, fossil fuels are holding their own.

There's reason to be optimistic about clean energy — but the challenge is daunting

Solar panels in a row at sunrise. (Photo by Frank Bienewald/LightRocket via Getty Images)

I don't mean to be totally pessimistic about renewables. That Bloomberg chart does offer some genuinely good news about clean electricity — namely, that the world is building more and more power plants fueled by solar, wind, and hydro, while the pace of fossil-fuel plant additions is slowing down.

What's more, there are lots of encouraging clean-energy trends out there. The cost of wind and solar has been dropping dramatically all over the world. The price of batteries for electric cars has been plummeting much faster than expected (which is crucial, because building cars that run on clean electricity instead of gasoline will be an important part of greening the energy supply). Meanwhile, China has been cracking down on dirty coal plants in a quest to mop up air pollution.

Given these trends, it's quite likely that, at some point soon, clean energy will grow faster than fossil fuels globally. Maybe we're already approaching the inflection point. Maybe we'll hit it in 2020. It's hard to predict exactly. But when that happens, the fraction of energy we get from low-carbon sources will start expanding. The fraction of energy from fossil fuels will start shrinking.

Still, if the world wants to avoid drastic global warming, then it's not enough to have some progress in clean energy here or there. There will need to be a truly seismic shift — the proportion of energy we get from carbon-free sources would have to rise from 13 percent to something like 90 percent this century, maybe more.

We're not yet close to that pace. Here's a glimpse at how dramatically our energy system would have to change to get there.

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(Thanks to Robert Wilson for first pointing out/critiquing the Bloomberg story, which is being circulated far and wide this week.)

Further reading:

• Important reminder: "energy" and "electricity" are not the same thing
• These 5 charts show why clean energy isn't yet catching up to fossil fuels
• Carbon intensity has to fall 6% each year if we want to stop global warming. We're at 1%.

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