His carbon footprint is zero, but there’s more going on here.
Superman is a hero in the DC universe. Honestly, if you don’t know who Superman is, it’s worth spending some time reading about him. He’s pretty iconic.
According to the comics, Superman gets his superpowers by absorbing energy from our sun. So, he’s a living and breathing solar cell. This is great. His powers don’t require a fossil fuel energy source, and he doesn’t even need to eat anything. From the get-go, his carbon footprint is zero.
But that’s not very exciting.
What’s more relevant for this study is to think about how much energy Superman could reasonably absorb, and if that’s enough energy to power his super-abilities. His super-abilities include a bunch of things that, to us mere mortals, are incredibly energy intensive: laser vision, x-ray vision, freeze breath, running, flying, and overall impressive athleticism. We’re going to tackle all of these powers individually.
How Much Energy can Superman Absorb?
Even for an undercover Kryptonian, Superman doesn’t look like a normal human. He’s a beefcake with a physique close to Dwayne “The Rock” Johnson whose surface area is around 2.5 square meters (27 square feet). To maximize his time in the sun, let’s assume that Superman absorbs sunlight both on the Earth’s surface (1,120 Watts per square meter) and directly from space (1,367 Watts per square meter). New York City, a good proxy for Metropolis, gets around 2,629 hours of sunlight per year, or just over 7 hours per day. Let’s say that Superman absorbs all of this sunlight, then tops that off by flying around in space for 6 hours each night. Of course, to optimize the amount of light absorbed he wouldn’t want anything to block the sun from reaching his skin.
The last thing we need to know is Superman’s efficiency converting sunlight to usable energy. At the time of this writing, the most efficient solar cell humans have ever created works at 40.7% efficiency. However, this is Superman, so we’ll also consider if he’s working at 100% efficiency.
Assuming Superman is working at the same efficiency as our best solar cells, he can absorb 16.55 kWh per day, or 403 kWh per adventure. If he’s a 100% efficient “super” solar cell, then he can absorb 40.67 kWh per day, or 990 kWh per adventure.
Is that enough energy to use his powers?
X-ray Vision
Modern x-ray scanners use around 1kW to operate. We know from the comics that Superman/Clark Kent uses this ability often. Let’s say he uses it twice per week as he searches Metropolis for injustices that he can right, and that each time he uses x-ray vision for around 5 seconds. This would mean that his x-ray visions require 0.0094 kWh per adventure, the lowest value for any of his superpowers.
With the same amount of energy, Superman could run a standard home coffee pot for around 42 seconds and get maybe a small sip of coffee.
Laser Vision
The comics and absolutely terrible recent movies show Superman using his laser eyes to blast through stuff like walls, doors, and occasionally whole buildings. Various real-life manufacturers use laser cutters all the time (for less destructive purposes). Using power numbers associated with those laser cutters, we can estimate that his laser blasts require around 0.047 kWh per adventure.
This is barely enough energy to brew 1 cup of coffee using a standard home coffee pot.
Running
To run “faster than a speeding bullet,” Superman would need to run at around 3,500 mph. From our analysis of the Flash, we know that Superman would burn 13.58 calories (energy) per second at this speed. Let’s also assume that he runs a good amount during one of his adventures, maybe 50 miles. Converting calories to units of electricity, this means he uses 0.81 kWh while running.
That’s enough energy to brew around 25 cups of coffee. There aren’t a lot of studies on this, but the best guesses are that if you drank all of this coffee at once you probably wouldn’t die, but you would start to hallucinate. Also, you’d have to pee pretty bad.
Freeze Breath
Superman’s freeze breath is an industrial flash freezer coming out of Clark Kent’s mouth. Superman seldom uses his freeze breath, but he will have to use it longer than his other abilities to make sure that the desired object freezes totally through. In real-life, this might take up to 10 hours to flash freeze a cow. Once again, he is Superman, so let’s say it only takes him an hour. That means he uses 3.5 kWh per adventure for his freeze breath.
You could brew around 100 cups of coffee with this much energy (probably iced coffee, because, you know, freeze breath). If you drank all this coffee at once, the caffeine would almost certainly kill you.
As a side note, air conditioning generally has a pretty horrendous carbon footprint. This is, in part, why homes in the southern US use more energy per square foot than houses in more moderate climates across the country.
Flying
Up until now, Superman’s powers haven’t put much of a dent into his energy budget (though we have brewed a lot of coffee). But now we have to dive deep into Superman lore/fandom. In the early comics, Superman couldn’t fly. He could jump huge distances. One might even say that he could leap tall buildings in a single bound. But I would guess that most of us think of flying when we think of Superman. So we’re going to assume he can fly.
To figure out how much energy Superman uses while flying, we’re going to look to a real-life analog. And because Superman fights for truth, justice, and the American way, we’re going to look at the most American flying animal in existence — the Bald Eagle.
According to several sources, bald eagles use about the same power to fly as 2-3 standard incandescent light bulbs (25-40.2 watts per kilogram). If Superman’s physique is similar to Dwayne “The Rock” Johnson, and his flight energy requirements are roughly the same as a bald eagle, then Superman uses around 702 kWh of energy while flying.
Ah ha! We’ve finally found out where Superman has to spend most of his energy! The energy he uses in flight is just barely under what Superman can absorb in between adventures assuming he’s 100% efficient at converting sunlight into usable energy. If Superman was only as efficient as our best solar cells, then he couldn’t fly around at all.
Also, assuming Superman is as into coffee as we are, then he could use his flight energy to make enough coffee to fill 30 bathtubs.
The Final Analysis
From a certain reading of our Superman analysis, we can easily reach the conclusion that using clean solar energy pretty much makes you a superhero. But we can do even better than this.
From our calculations, we know that Superman can absorb 990 kWh per adventure. We also know that Superman expends around 707 kWh per adventure using his superpowers. That leaves him with 283 kWh worth of energy in between adventures, or 11.63 kWh per day. If we convert this energy into food calories, it comes out to around 10,000 calories per day. That’s a lot of food. But let’s go back to our Dwayne “The Rock” Johnson comparison: Johnson eats around 5,000 calories per day just to maintain his impressive physique. If you take anything away from our Superman analysis, it should be that The Rock is basically just half a Superman.
But c’mon, we already knew that.