This has come up before and never gotten a ton of mainstream attention, but I saw it again and thought I’d address it.
WHAT IS IT?
Breaking news: the Sun is really freaking bright. Like you cannot believe. In ideal conditions, the Sun is shining roughly 1050 watts on each and every square meter of ground. Given that the average American household uses an average of 1250 watts of power, this means that theoretically, an area the size of a pool table could generate all the energy a home needs. In reality, that’s not true. Here’s why.
1) We’re not pointing directly at the sun.
If you live between the latitudes of 23.5ºN and 23.5ºS, the Sun is directly overhead exactly twice a year. If you live outside those latitudes (the entire United States and Europe), the Sun is never overhead. That means that the Sun is shining on your piece of land at an oblique angle, and that means that each piece of ground gets a little less sunlight. If you could somehow point your solar panels directly at the Sun all day, pivoting to follow it, you’d get the maximum amount of light possible, but that still wouldn’t be the full 1050W because:
2) Sometimes it’s not sunny.
This is groundbreaking stuff, I know. Solar cells respond to roughly the same wavelengths of light as the human eye, weighted toward the long-wavelength end of the spectrum. That means, basically, that if you can’t see the sun, neither can they. IR light penetrates cloud cover better than visible light does, but that’s only a fraction of what solar panels absorb and it contains less energy than visible light. No matter where you are, it’s cloudy SOME of the time, so solar panels will be less effective. And even if you’re in a place like Arizona, where it’s almost never cloudy,
3) Sometimes it’s dark.
I’m so glad you have a resource like me to teach you about cutting-edge concepts like clouds and nighttime. This is a pretty obvious problem with solar, but not really taken as seriously in the public mind as I think it should be. Storing energy is really inefficient, so most power plants ramp production up and down to match demand. They burn more coal or natural gas or uranium when people need energy. Peak demand in the US is in the early evening, right when the Sun is going down. And solar panels don’t work at night. Best-case scenario for a solar panel is that it works exactly half the year.
SOLAR PANELS…IN SPACE!
The idea behind space-based solar power is that you put solar panels in space, where it’s never cloudy, never dark, and you can always point the solar panels directly at the Sun and get the maximum amount of power. In fact, you get a bonus; the atmosphere filters out about 30% of the Sun’s radiation, including over 90% of UV rays, which are the most energetic. Solar panels in space that could absorb UV — terrestrial panels don’t absorb UV because there really isn’t much on the surface to absorb — could gather WAY more energy than those same panels on Earth. The problem is how you get the power back to Earth.
That’s the idea behind wireless power. A Japanese company called Mitsubishi Heavy Industries (MHI) recently announced that they were able to send power through the air using microwave frequencies of electromagnetic radiation. The idea is that you shine a beam of microwaves a long distance, and something called a “rectenna” picks it up at the other end and turns it back into electricity. Pretty simple in concept.
Side note: some of the more aggressively annoying nerdy types among you might be thinking something along the lines of “but Nikola Tesla demonstrated wireless power transmission a hundred years ago! This is old hat!” First of all, Tesla’s system used something called resonant inductive coupling, which is terrible at long distance. It relies on the alignment of two oscillating electric coils and the magnetic interaction between them, which weakens astoundingly quickly the farther apart the components are. Some current cell phones use a 110-volt wall outlet to charge your phone from a distance of about a quarter of an inch (sitting on the charging mat). Tesla’s system managed to power a lightbulb at a distance of a hundred feet, but he needed 20,000,000 volts to do it. Needless to say, that won’t work from space. Tesla insisted that he had a viable method of long-distance power transmission, but he never built it and the Wikipedia section on his idea uses literally 42 footnotes to explain why it wouldn’t have worked. Go ahead and read it for yourself if you want.
Back to MHI. Their accomplishment is no small feat, I’ll admit. They say they’ve managed to send 10,000W of power across a distance of over 500 yards. That’s pretty impressive. Inhabitat says that that’s enough energy “to power your kitchen stove for an hour or more,” which is both incorrect and a comprehensive and fundamental misunderstanding of how energy works. In reality, 10kW is a lot of power. It’s enough to run your broiler, coffee maker, toaster, microwave, and all four burners on your electric stove at the same time. No mean feat.
But the whole point of writing this is to tell you not to get too excited about the prospect of solar panels in space. Here’s why:
1) Distance
The reason Japan is looking into this so heavily is that they shut down all their environmentally-friendly nuclear reactors following the Fukushima disaster and have had to compensate with fossil fuels. Japan’s not very big or especially sunny, so it’d be tough for them to use solar panels on the ground. But in order to use space-based solar power, the satellite(s) would have to be within sight of Japan at all times, and that means geosynchronous orbit. Geosynchronous orbit is when a satellite is orbiting the Earth at the same rate that the Earth is spinning, so it stays fixed over a single spot on the Earth. It also requires that the satellite be roughly 26,000 miles away.
If you shone a standard laser pointer at that distance, the beam would be about 60 miles wide when it got to the Earth. Obviously we can’t build an array of rectennas 60 miles wide in Japan, because we might as well just build a solar panel array that size and not bother with the space part. Let’s assume, then, that we managed to engineer some kind of super-focused laser that could be focused to a rectenna array only a hundred yards across. That still doesn’t solve our problem because we haven’t thought about:
2) Safety
A microwave is a dangerous thing. The microwave oven in your kitchen emits EMR at a frequency of 2.45GHz. That’s a very specific frequency chosen because it interacts with water, which is how it heats your food. The beams from the satellites wouldn’t be the same frequency, but we’re still talking about a LOT of power. And that power will be beaming through the air.
Now, the beams will at least be in a predictable location, since the satellites are geosynchronous, but that airspace is going to have to be so restricted that it’ll make the White House look like a public airstrip. It will be a beam of energy of comic-book-death-ray proportions, and getting in the way of it will be instantly and comprehensively fatal. How much energy? We’ll see in a second. The point is that this is incredibly dangerous and will have to be treated as such. On to the final problem.
3) Scale
Imagine we’ve fixed the distance issue, we can focus the beams to an area small enough to build a sensor under, and we’ve instated military-grade protection to keep anyone from getting in the beams. Now we have to think about the other end. Let’s be wildly optimistic and assume that we’re replacing the entirety of Japan’s nuclear energy with space-based solar. According to this article, that’s about 45 gigawatts of energy. The most efficient wireless transmission yet accomplished was by NASA, which managed about 80%. That means that in order to get 45GW on the ground, the satellites will have to beam 56GW. So how much real estate in solar panels are we talking? The maximum efficiency of a solar cell, theoretically, is 86.8%, though no one has built one that does better than 43%. We’ll use the ideal number. That means we need that in order to supply the energy beams with 56GW of energy, we’ll need to capture 65GW from the Sun.
In space, since there’s no pesky atmosphere, the Sun shines about 1400W per square meter. But 65GW is a lot. In order to absorb all that, we’ll need a solar array with a total surface area of 46 square kilometers.
That’s a problem. That’s an area half the size of Manhattan. It’s the solar panel equivalent of thirteen thousand International Space Stations, and that took four separate launches to get all its panels. To build a solar panel array that size would take almost sixty thousand launches, and that’s not even counting the extra difficulty of getting them to geosynchronous orbit. It takes 15 times as much energy to get to geosynchronous orbit as to get to the ISS, so additional costs come into play.
Let’s do some math. Imagine we can build and launch one Delta IV Heavy rocket, the only one capable of such a task, every day. We can’t. We’ve only launched eight in the last eleven years.
Now imagine that the total cost of building and launching all these rockets is negligible. It’s not. It’s 20 trillion dollars.
Even if those two enormous deal-breakers weren’t issues (they are), it would take a hundred and forty-two years to get this entire solar array into space. And that’s with perfect conditions. That’s assuming that all the current technology problems are gone. That’s not a best-case scenario, it’s so far beyond a best-case scenario that it’s entering the realm of science fiction.
LET’S TALK DEATH RAYS
I mentioned that the beams of energy coming from the satellites will be preposterously dangerous. Let’s see how bad they really are.
We’ll put the rectenna arrays on the sites of their existing power plants, of which there were 54. Assuming even distribution, each station will be getting 800MW of microwave energy beamed on to the sensor array. I’ve decided, totally arbitrarily, that the arrays will be a hundred yards wide. That means that the concentration of energy on these rectenna arrays will be…
2829 watts per square inch.
I’ll give you some perspective. In 1977, a woman tried to remove a casserole from a microwave oven. The device said it was finished cooking, but was in fact still on. She had her hands and forearms in the microwave for a total of about 5 seconds, whereupon she experienced extreme burning sensations and a feeling of “needles” in her arms. She suffered permanent nerve and skin damage as a result. That was a 600W microwave, spread over an area of about a square foot (the inside of the microwave) for a concentration of about 4 watts per square inch.
Now, absorption levels vary by wavelength, so that case study isn’t a perfect example, but suffice it to say that 2829 watts per square inch will FUCK YOU RIGHT UP. Let’s imagine you fell over the fence on to the array. You would die. You would probably catch fire. Imagine putting a piece of steak in the microwave for half an hour, and that’s what would happen to you in five seconds. Your whole body and clothes would burn away and you would be left as a pile of ash on someone’s fancy rectenna array. It’ll kill birds, too. A bird flying 30 mph will take about six seconds to cross a beam that wide, so it’ll be burnt to a cinder long before it gets through.
Planes are a different story. An airplane moving at 500 mph will cross a beam that size in less than half a second, so exposure time is way down. And aluminum reflects microwave radiation, as long as it’s smooth, so it’s possible that none of it would get into the passenger cabin. Honestly, I don’t know what would happen. I don’t know how much energy the skin of the plane would absorb, or if the paint matters, or if the windshield would stop any of it. It’s worth noting that a geosynchronous satellite has to be located over the Equator, and Japan is not on the Equator, so the beam would be coming in at an angle. If it shone through the windows, would it cook people inside a plane? Would it melt upholstery? Would it pop rubber tires? I don’t know, and a lot less research has been done on the effects of microwave radiation on airplane tires than its effects on biological tissue. You’d probably want to avoid it though.
CONCLUSION
We don’t know how to shine a microwave beam far enough to get it from a satellite to the Earth. Even if we did, it would create a death ray that would fry anything that got in its way. Even if we could protect people from the death ray, the number of solar satellites we’d need to replace Japan’s nuclear power plants is so prohibitively large that it would take us centuries to implement. This cannot be done on a scale that makes it useful for generating power for whole countries. It is simply not possible. Sorry.
Unreasonably Dangerous Onion Rings 
What if there was multiple solar panales, one that’s geosynchronous, some large panels at lagranian points, and the rest as relays. The death ray can beam to an high altitude weather balloons that hold a rectna and converts to electricity. This way we can keep the beams more narrow, and avoid some of the issues. I don’t know what’s the best way to bring electricity down. Either using cables or batteries, but I feel someone else cleaver can think of a way.
The geosynchronous part is important. In order to regulate power output to meet demand, the power needs to be on all the time, and that’s the only way to do that. There may be a better way to arrange the solar panels, but the fact remains that it is the stuff of fantasy to put that much hardware in space, no matter where it goes. You need thousands and thousands of solar panels to generate meaningful amounts of energy, and it is simply impossible to send them all into orbit.
What size shadow would that array cast?
Probably none. If they’re far enough apart, light will sort of diffract between them and they won’t actually cast a big shadow. Planes don’t cast a shadow for the same reason, although in this case we’re talking about roughly 20,000 planes at once. Plus there’s the distance. The moon, for perspective, is 2100 miles across and 240,000 miles away, for a ratio of about 1:114. If we put our 13,000 ISS’s in a 114×114 grid with 700 feet of space in between them (ludicrously impossible to keep them from colliding that close together but whatever), the grid would be about 22 miles wide at a distance of 26,000 miles, making it barely a tenth the diameter of the moon in the sky. It’s only going to be between us and the Sun twice a year, like a solar eclipse, and even then you probably wouldn’t be able to see it even if you wanted to. And the farther apart the arrays are (to avoid disrupting each other’s orbits), the more light gets through between them.
great and helpful blog to everyone.. thanks a lot for sharing