Energy Density

Climate change is an issue that is already affecting millions of people around the world. Global temperatures are rising, and greenhouse gasses emitted by human activity are the number one cause. Ok, now that that band-aid has been ripped off, let’s talk about solutions to this predicament.

One of the many factors that contribute to climate change is the generation of electricity. There are many different ways to generate electricity. Common ways include burning coal, oil, and gas; harnessing wind, sunlight, geothermal heat, and water movement; and splitting atoms in the form of nuclear fission.

Some of these methods, such as wind and solar, are called Renewable Energy sources. This means that the energy from the source is not depleted as it is used. For example, harnessing wind energy does not deplete the wind; there will always be more available. This can be a good thing, because not only will we never stop needing electricity, but as our global population grows, our demand will grow with it, and we need energy sources that we will not run out of.

Non-renewable sources then are called Fuels, as fuel is defined as a “substance consumed to provide energy through combustion, or through chemical or nuclear reaction.” Much like a battery, fuels already contain the energy within them, and it’s up to us to get it out. Coal, oil, natural gas, and uranium (the example we’ll use for nuclear power) are all examples of fuels. They are all burned (or fissioned, in uranium’s case) to release energy. But how much energy does each actually contain? Wood burned for energy is shown as a reference. Units are in MegaJoule per kilogram of fuel.

Wood————–     ~18 MJ/kg
Coal————–       ~30 MJ/kg
Diesel————       ~35 MJ/kg
Nat. Gas———-      ~38 MJ/kg
Gasoline———-      ~46 MJ/kg
Hydrogen———   ~130 MJ/kg
Uranium—  ~80,000,000 MJ/kg

To give some perspective to this, if each fuel type’s energy density was equal to seconds, most of these are obviously under one minute, hydrogen is just over 2 minutes, and uranium is equal to over 152 YEARS! [Compare fuel prices of each here]

Why is this important to know? Because we need to understand our energy before we can just go replacing a bunch of it. If we were to tear down a bunch of coal plants and replace them with windmills, how would that affect our electricity availability? Well, assuming we built the same capacity as we tore down, and had the same generation and transmission efficiency, we should have the same amount of energy produced. Unfortunately, that only counts while the wind is blowing. With fuel-less sources like wind and solar, you can’t just produce energy whenever you need it. For this reason, we almost always build natural gas plants to “back up” renewables (which means that if we tear down a[n emissions-free] nuclear plant to be replaced with renewables [plus nat. gas], emissions go up).

Now, the plus side to this is that coal emits a lot of greenhouse gasses which contribute to global warming, as well as toxic pollutants which contribute to about 7 million deaths per year. Replacing these, even if it were with natural gas alone, would still reduce our emissions (as well as be more fuel efficient, as nat. gas has a higher energy density). Doing this is not enough, however. Gas, whether operating alone or with renewables, still emits greenhouse gasses and does very little to reduce our impact on the climate. Wind and solar consistently perform at under 40% capacity factor, which means that when you install wind and solar, you’re getting your power from nat. gas at least 60% of the time. This does not help.

What this all comes down to is this: while renewables are a good concept, and are making improvements all the time, they are not reliable enough on their own to power the grid. They can be great for powering your house, or at least reducing your bill, but a hospital certainly couldn’t rely on them, and rising global temperatures means that the weather will become increasingly unstable, effectively hindering weather-based energy sources. Sources like geothermal and hydroelectric are a great way to decarbonize local grids, but these are both extremely geographically limited, and to my knowledge are pretty much taken advantage of everywhere we’re able to use them.

“But what about batteries?!” Good question. Batteries are similar to fuels in that they store energy. Energy is released from a battery using chemical reactions instead of combustion or fission. Batteries, like many renewables, can be great for personal use, but they cannot store enough energy to power a grid for a significant amount of time. They are making improvements on battery designs and efficiency all the time, but again, they’re just not as energy dense as most fuels.

With uranium being as energy-dense and abundant as it is, there really is no good argument for us not to use it as our primary source of power. It takes about 10 grams of uranium to produce as much power as one ton of coal. With so little fuel needed, there will be very little waste generated, no pollutants because we’re not burning anything, fuel costs will stay low, and the capacity factor for nuclear is around 90%. Really, I’d say this one is a no-brainer.