How Japan Plans to Build an Orbital Solar Farm
spectrum.ieee.org
spectrum.ieee.org
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.
Now, this doesn't refute the issues Musk is bringing up here, but he isn't taking consideration of this factor at all.
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.
[1] http://en.wikipedia.org/wiki/Geography_of_Japan#Composition_...
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".
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.
- Japan has proven to be pretty good at building more land
- Japan has lots of ocean area to float panels on
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.
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.
http://en.wikipedia.org/wiki/Solar_variation
http://science.nasa.gov/science-news/science-at-nasa/2013/08...
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.
Sounds like a plan that could destroy a civilization in the long term.
The Earth will occasionally put such a satellite into shadow, but remember that the Earth is tilted, and so is the equator.
Getting up to GEO is hella expensive.
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.
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.
That beam is WAY more powerful than the sun per unit area. If not, we'd just use the sun.
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.
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.
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.
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.
Imagine the hideous health implications if a city block got cooked.
Also, it's pretty easy to keep the beam away from populated areas.
Of course, if it's only as intense as sunlight, you would wonder why they are bothering building a rectenna and an SPS. . .
They'd need a gundam squadron to protect it too.
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.
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.
1. How much mass are they putting into orbit?
2. How much is it costing them to put that into orbit?
3. How much energy will that generate?
4. How long will the solar cells last?