Let me tell you one of my pet peeves: space solar power. Okay, the stupidest thing ever. If anyone should like space solar power, it should be me. I got a rocket company and a solar company. I should be really on it, ya know. But it's like, super obviously, not going to work because, ya know, if you have solar panels - first of all, it has to be better than having solar panels on Earth, so then you say, okay, solar panel is on-orbit, you get twice the solar energy - assuming that it is out of Earth's shadow - but you've gotta do a double conversion. You've gotta convert it from photon to electron to photon, back to electron. You've got to make this double conversion, so, okay, what's your conversion efficiency? Hmm. All in, you're going to have a real hard time even getting to 50%. [The solar cells are better.] It does not matter, put that cell on Earth then. See, that's the point I'm making. Take any given solar cell, is it better to have it on Earth, or is it better to have it on orbit? What do you get from being in orbit? You get twice as much sun - best case - but you've got to do a conversion. You've got to convert it the energy to photons - well, you have incoming photons that go to electrons, but you - you've gotta do two conversions that you don't have to do on Earth, which is you've got to turn those electrons into photons and turn those photons back into electrons on the ground, and that double conversion is going to get you back to where you started, basically. So why are you bothering sending them to bloody space. "I wish I could just stab that bloody thing through the heart." BTW - electron to photon converters are not free and nor is sending stuff to space. Then it obviously super doesn't work. Case closed. You'd think. You'd think case closed, but no. I guarantee it's gunna come up another ten times. I mean, for the love of God.
He's ignoring one constraint: land area. You need to put those panels somewhere. This approach let you perform the concentration somewhere you aren't renting real estate. For an extremely dense island nation like Japan this actually makes a lot of sense.
Now, this doesn't refute the issues Musk is bringing up here, but he isn't taking consideration of this factor at all.
The difference in solar energy is also not a factor of two, but more like a factor of six (deeply inaccurate there, but that's the general idea).
Factor of two would be day and night. In space, it's day all the time, while on Earth it's night half the time, on average.
However, you also have sun angle. You're not getting much energy when the sun is near the horizon. Even if your panels track the sun, there's a limit to how close to the horizon they can track before they start shadowing each other. Atmospheric attenuation also becomes extremely strong: note how you can comfortably stare at a sunset.
Atmospheric attenuation is a big factor even when the sun is overhead. Even when it's straight above, you're still losing something like 30% (again highly inaccurate, just the general idea).
And then there's weather. On cloudy days, you don't put out much. How much this affects you greatly depends on where you put your panels, obviously, but it can be a big factor.
Then you have a meta factor from the fact that these other factors vary over time. If you took a constant 2x or 6x loss on your power generation, it would be one thing. But instead, you're generating a lot of power at some times, and none at other times, and those times don't necessarily line up with demand in a nice way. So now you have to efficiently store the power when you generate it, or have lots of additional capacity to make up the shortfall at night that does nothing productive during the day.
Now, I wouldn't be surprised if Musk's overall point is correct. Flinging massive solar panels into space ain't cheap, and the money you spend on rockets could buy you a lot of solar panels in various deserts, plus high-voltage transmission lines, plus storage facilities, plus.... But it's considerably more complex than "twice the solar energy".
Another point that strengths your arguments is that they are going to use mirrors to concentrate light on the panels, and reflective film is much lighter and cheaper than the solar panels.
It means that it's possible to occupy 5x-10x more area in the space with the same amount of solar batteries as on Earth. Yes, the harvest per square meter may be smaller, due to smaller efficiency of mirror->solar panel transition, but the cost/watt may be much smaller.
For instance, taking stuff to space is super mega expensive.
It is so expensive that I would argue it would be a lot cheaper to put solar panels into the ocean.
And since I've brought up ocean - the ocean has immense energy and if you don't have land because you are in the middle of ocean, perhaps it would be better to pursue ocean power.
Exactly, there's like a million other energy sources to exhaust before putting solar panels in space. The idea is so bad It's not worthwhile even bashing it.
Is this actually easier for an island nation than, say, floating solar panels in the surrounding waters? I assume Japan must see some benefit to space, but I'm having trouble working out just what it is.
What about the ecological effect on plant/plankton life in the ocean blocked by these floating panels? Assuming the cost of producing solar panels eventually comes down and we can cover large areas of the ocean, won't it take a toll?
About 72% of land in Japan is classified as 'mountainous' [1]. Some of this land is used for steeply terraced agriculture or forestry plantations but a lot is left unused. My guess, based on fairly extensive travel in Japan, is that there would be a lot of mountainous land with a good solar aspect situated fairly close to the major conurbations that could be used for solar panel farms.
It's not a given that rectification/conversion losses are necessarily greater than, less than, or equal to the gain in base output. A lot of whether that is true depends on how much solid state power electronics improve over the coming decades.
In terms of the cost of putting materials into space, isn't that the exact problem SpaceX is trying to solve? Right now, it would be economic folly to build one of these things. In decades or centuries, when we have moon colonies and/or asteroid mining and can do all the large-scale fabrication in situ, SSP could very well be significantly cheaper than other forms of power generation.
Assuming you wave a magic wand and get rid of the technical and cost issues, you then run into thermal pollution. You're collecting heat from space and beaming it to Earth and then inefficiently converting it to electricity.
According to [1], the surface of Earth receives 89,300 terawatts of power from the Sun on average. According to the stats at [2], world power consumption in 2008 was ~17 TW. So even if we could somehow build the tens of thousands of these power plants necessary to completely supply the Earth's power needs, and assuming that none of the consumed power ended up being radiated back into space, we would only be affecting the Earth's energy budget by 0.02%.
So with a magic wand and an incredible amount of money we'll only make the problem slightly worse.
And it's not clear how slightly -- climate change is being caused by accumulation of greenhouse gases during a period of reduced solar output (cyclical fluctuation of 0.1%). BTW 0.02% seems like a lot more when compared to the sun's cyclical variation of 0.1% (which has measurable effects) and suspected historical variations of perhaps 3% that caused ice ages.
I could see a space solar power station being used to transfer power to ships traveling to the Moon or Mars. Using a laser (or whatever) for energy transfer would be much more efficient in space.
It actually makes for pretty good power plants, usually they're called some variant of 'solar power towers'. The plants use a bunch of adjustable mirrors that focus sunlight in order to heat water and make it into steam that powers a turbine. There are also ones that use molten salts as a heating element, but that technology is a lot newer.
Maybe I'm missing something but in space you can have power night and day if you are using mirrors, and you don't have the atmosphere. Solar power in space is 1300W/m^2, whereas average solar power on Earth is about 200W/m^2, including atmosphere, day-night, latitude, etc. So that's a reasonable difference.
It probably doesn't offset the costs of such a project, but damn if I'm starved for some 50's style Massive Engineering projects. Instead all of the brightest minds are focused on optimizing other peoples mouse clicks.
Such a thing could be used to power a Lunar base and for sure boost research in power beaming.
His "doesn't work" is equivalent to saying "not profitable." But what if that energy is spent within a country whose economy can produce profitable services and products for export, making up for the cost to acquire that energy? Having a non-nuclear source of energy not dependent on other countries might be worth it.
In it's favor, a solar power satellite can get light nearly 100% of the time, while on the ground you are luck to average 50% with rotation and weather.
Just to put some numbers on it, GEO doesn't intersect the Sun-Earth line most of the time. The Earth's shadow touches GEO for a couple of weeks around the equinoxes, resulting in up to 70 minutes of shadow per day in that period. The rest of the time, they're in sun 100% of the time. So, as low as a 95% duty cycle at the worst point in the year, and 100% for most of the year.
Another ignorant question ... so you have a massively powerful microwave beam pointed at a certain spot of your nation. What happens when it misses? Passes over the inhabited land that's infinitesimal fractions of a degree away from the target?
From 36000 miles, a few miles is a rounding error. Must take some huge tolerances to keep the beam pointed in the right place.
Is this even dangerous, or am I off base? I know they're nervous about nuclear since Fukishima, but unless I'm mistaken there's similar risks with this option.
> Is this even dangerous, or am I off base? I know they're nervous about nuclear since Fukishima, but unless I'm mistaken there's similar risks with this option.
No, not true. Don't confuse ionizing radiation as from Fukushima, with non-ionizing radiation, as from microwaves. They're very different. Microwave radiation isn't nearly as dangerous -- it can't break cellular bonds like ionizing radiation can, it can only heat things up.
A microwave power system would have to pass strict safety tests, to make sure the microwave radiation level at the surface (near occupied areas) is well below that from the other big electromagnetic emitter -- the sun. That should be an easy standard to meet.
The danger isn't from "overflow" radiation when the microwave beam is on target. The danger is when the microwave is off-target by a couple hundred feet (teensy fractions of a degree, considering the distances involved) and suddenly your concentrated 1GW beam is pointing at an apartment building.
That beam is WAY more powerful than the sun per unit area. If not, we'd just use the sun.
> suddenly your concentrated 1GW beam is pointing at an apartment building.
Wait ... have you calculated the antenna size required to produce a beam able to pick out an apartment building, at microwave wavelengths, from orbital heights? Consider the distances and the available microwave frequencies, and you'll see that you cannot get a beam narrow enough to resolve an apartment building from orbital heights, with any reasonable dish size.
Remember that, at sufficient distances, all antennas become cosine emitters with no ability to concentrate their energy in a specific location. This is true for lasers, x-ray emitters and it's certainly true for microwave emitters.
My point is that a practical system such as we're discussing must have a large receiving array to accommodate the beam size at ground level. It's not going to be anything resembling a death ray.
"That beam is WAY more powerful than the sun per unit area. If not, we'd just use the sun."
A common misconception, but untrue.
What matters isn't power per area but cost per kilowatt-hour. To collect solar power on Earth you need a lot of expensive components (photovoltaic cells), plus you probably need to track the sun, and even so you'll have huge losses due to night-time, weather, winter sun angle, and so on. In comparison, a rectenna array is just a bunch of little bent pieces of wire. It's almost trivially inexpensive to build, and in some cases it can live side by side with other land uses. Even if the power density is only a few hundred watts m^2 (compared to over a kilowatt/m^2 from the sun at peak power) that power can be converted with upwards of 80% efficiency (compared to much less than 50% efficiency) and the full amount of that power is available 24/7 through every season. The hypothetical 1kw/m^2 at noon on a summer's day actually rounds out to only a tiny fraction of that over the entire year. Meanwhile, a rectenna converting 100 W/m^2 of RF power can end up producing the same average power as a solar installation, except that power is always available and the cost of the ground component is a teeny, tiny fraction of the ground solar installation.
That still leaves the cost of the space component, of course, which is decidedly non-trivial. But a big advantage is that the space component can have a very, very long service life and can also serve various markets (especially remote regions where power delivery is difficult) which can provide the up-front high-profit business to pay off its cost.
> That beam is WAY more powerful than the sun per unit area. If not, we'd just use the sun.
Not necessarily. Rectennas can get ~80% conversion efficiency, PV panels you can actually get in bulk are closer to 30. So you can have a beam about as strong as the sun and get ~triple the power out the other end by using microwaves instead of light.
When you express what SPS is doing as "making solar 3 times more land-efficient" it looks kind of crazy. Maybe dump the billions of dollars that would be needed for launching just one of these into squeezing another percentage point out of all new solar cells.
I can't believe nobody has mentioned this yet: exactly this was one of the standard disasters in SimCity 2000, where "microwave" was one of the power plant types.
Microwave tech was awesome and cost effective until the first time the satellite got out of alignment and burned half the city down. I've been terrified of the idea ever since: you just can't make a weapon like that fail safe, and if you do manage, then your throughput is too low to make it worth it.
What you possibly could do is to not have a single emitter but loads of them for each collector. So that a single satellite getting out of alignment would be harmless. Many emitters would need to get out of alignment pushing the beam in the same direction for it to be harmful.
Total nostalgia anecdote here, but Sim City 2000 had that as a disaster. I believe it was a constant risk whenever you built orbital-solar-to-microwave plants.
Is it? Most (old) ovens used to be rated at 1KW, but they certainly weren't 1 square meter, more like half a square foot. You can fit quite a few half-square "feet" in a square meter (roughly 3*6 -- so 1kw/sqm would be about 1/18 of a microwave oven?).
The trick is you don't let the microwave beam get very strong. If you keep it at a fraction of solar power (say, a few hundred watts per m^2) then it won't be that dangerous. And yet because it's RF energy instead of solar energy and consistently at the same power 24/7 it's much, much easier to build the ground based infrastructure to collect and use the power.
Also, it's pretty easy to keep the beam away from populated areas.
In fact, the beam wouldn’t even be intense enough to heat your coffee. In the center of the beam in a commercial SPS system, the power density would be 1 kilowatt per square meter, which is about equal to the intensity of sunlight
Of course, if it's only as intense as sunlight, you would wonder why they are bothering building a rectenna and an SPS. . .
Seems simple to prevent: Keep an active signal loop between receiver and satellite. If something goes wrong, shut off the satellite. Worst case a couple of seconds, which with microwaves isn't long enough to do substantial damage (I suspect).
Most of the debris is in low orbits. So no direct problem.
But if you build it in low earth orbit and fly it out on its own power in a slow spiral, then it's going to be a big problem. Flying with chemical rockets only up to LEO and electric propulsion from there on saves mass hugely.
Best to assemble moderate pieces and fly them higher after completion.
It wouldn't cast an umbral shadow at all. It would cast a incredibly faint penumbral shadow.
Look at it this way, at the sizes that are commonly talked about for these, at the orbital heights being talked about, the occlusion of the sun would be on the order of a very minor sun spot, and only for very brief periods of time.
It seems like the article discusses the challenges of building large structures in space.
Maybe the large-scale building techniques developed for this application would be useful for building large space stations. Space would be a lot cheaper if our spacecraft didn't have to use huge amounts of fuel to get out of earth's gravity well, which logically implies production [1] and refueling facilities in space using resources that don't have to be brought from Earth.
Which will probably be bigger structures than the ISS, which means the technology to build large structures in space is something which will be useful for reasons beyond solar power.
[1] At first, the spacecraft itself will probably be built on earth, and fuel will be the only thing produced in space.
I don't think there are many power plants on Earth that function unattended and maintenance-free for very long. It will be nice if transport to space will be commonplace enough 25 years from now that sending a regular rotation of maintenance techs will be feasible.
http://youtu.be/J_af0ow1__E?t=43m12s
Let me tell you one of my pet peeves: space solar power. Okay, the stupidest thing ever. If anyone should like space solar power, it should be me. I got a rocket company and a solar company. I should be really on it, ya know. But it's like, super obviously, not going to work because, ya know, if you have solar panels - first of all, it has to be better than having solar panels on Earth, so then you say, okay, solar panel is on-orbit, you get twice the solar energy - assuming that it is out of Earth's shadow - but you've gotta do a double conversion. You've gotta convert it from photon to electron to photon, back to electron. You've got to make this double conversion, so, okay, what's your conversion efficiency? Hmm. All in, you're going to have a real hard time even getting to 50%. [The solar cells are better.] It does not matter, put that cell on Earth then. See, that's the point I'm making. Take any given solar cell, is it better to have it on Earth, or is it better to have it on orbit? What do you get from being in orbit? You get twice as much sun - best case - but you've got to do a conversion. You've got to convert it the energy to photons - well, you have incoming photons that go to electrons, but you - you've gotta do two conversions that you don't have to do on Earth, which is you've got to turn those electrons into photons and turn those photons back into electrons on the ground, and that double conversion is going to get you back to where you started, basically. So why are you bothering sending them to bloody space. "I wish I could just stab that bloody thing through the heart." BTW - electron to photon converters are not free and nor is sending stuff to space. Then it obviously super doesn't work. Case closed. You'd think. You'd think case closed, but no. I guarantee it's gunna come up another ten times. I mean, for the love of God.