Harvesting solar power in space and sending it back to Earth
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Elon Musk (http://shitelonsays.com/transcript/elon-musk-panel-bta-2012-...)
Doable? Sure. But you have to make a lot of panels before it pays off.
Not quite. When compared to stationary panels (which beat trackers economically, so they should be the baseline), space-based power harvests π (yes, pi) times as much sunlight due to lack of cosine loss, plus there's the bonus of reduced reflective loss. Atmospheric and weather loss is avoided entirely. I would estimate 4-5x the energy.
The big advantage of space-based solar imo is the ability to create giant collection areas defined by minutely pressurized helium structures. A giant parabolic mirror on Earth needs to fight gravity, winds, and the Earth's rotation (tracking). Similar concept: https://tec.grc.nasa.gov/past-projects/solar-concentrators/a...
Launch a 30,000 m^2 concentrating collector in a single launch? It's only 12 MW, but it's constant (unlike ground-based solar at ~18% capacity factor), and it's deliverable anywhere in the world, or even to other satellites. What if microsatellites could summon extra power by POSTing an ephemeris to an endpoint? Is there a market there?
It's an interesting niche tech, but spaceflight is just so expensive that I doubt it'll ever be viable.
If you use them with solar panels, then your panel will heat up and its efficiency will drop. Maybe lifetime as well. If you use a thermoelectric generator, you then have wearing mechanical low efficiency systems on board.
In both cases you need to reject heat, which is hard in space.
They also require precise pointing.
There's also the problem of beaming the power to earth. If you're in low orbit, there would have to be lots of receiving stations and the power would be intermittent unless you had a big constellation. And all the problems with inclination and the spinning earth... If you're in geostationary orbit, your sending and receiving antennas would need to grow huge.
What about beaming between satellites? You'd need a laser for that. Maybe they're becoming quite small and efficient with modern semiconductor technology developed for military uses. Still the receiving end might have low efficiency.
At that point the balance of system probably shifts to thin film PV. There would need to be a lot of advancement in that area before such a project becomes practical.
>What about beaming between satellites? You'd need a laser for that.
I was picturing a microwave rectenna, actually.
Harvest the energy in space. Microwave it to the wing-surface receivers of ultra-light high-altitude gliders which use the energy to stay aloft.
Use the gliders as a platform from which to deliver rockets.
And then oil prices went back to normal.
The real conceptual competitor at the time -- in fact, it's still the real competitor -- is plain old fission.
(Of course Earth-based nuclear power doesn't have the entire mantle of the sun as radiation shielding. So there's that…)
Geothermal is in part latent residual heat of formation, which is arguably either kinetic or gravitational energy again. Some is _also_ the result of radioactive decay, though I don't have the precise breakdown.
I suppose there might be some ways of tapping planetary or stellar magnetic fields, which aren't directly caused by nuclear power.
Similarly energy systems based on collapsed stars (white dwarves, neutron stars, black holes) would not be directly driven by nuclear processes.
But yes, your point generally stands: most available energy on Earth is largely ultimately derived from nuclear reactions.
>Some is _also_ the result of radioactive decay, though I don't have the precise breakdown.
Neither do I, but here's my logic: if there were no nuclear power in the center of Earth, Lord Kelvin tells us it would solidify in only ~40 million years[1]. The Earth being 100 times older, the amount of residual heat left today must be insignificant.
Stellar magnetic fields come from the convective mantle, which is nuclear powered. Not sure about planetary magnetic fields, but the above analysis suggests nuclear as well. Collapsed stars will be heated by gravitational potential, but we don't see a lot of those 'round these parts.
[1] https://en.wikipedia.org/wiki/William_Thomson,_1st_Baron_Kel...
The Big Bang (background microwave radiation) and Dark Energy would also come to mind as non-nuclear energy systems.
Not of much practical use to us on Earth, however.
If a single solar sattelite [multiple for redundancy, in reality] can replace a large proportion continent's energy infrastructure, it starts to sound a lot more attractive.
1. http://en.wikipedia.org/wiki/Transformer#Energy_losses
2. http://en.wikipedia.org/wiki/Electric_power_transmission#Los...
Woah there. Exactly how much power would each of these hypothetical satellites provide?
And while I don't have time right now for a complete rebuttal to Musk's criticisms I will point out that he's being somewhat of a hypocrite here. He's complaining about photon to electron to photon to electron conversion, but consider what might be his ideal: ground based solar power and electric cars. The only reasonable way to make that work is through photon to electron to battery to electron to battery to electron systems, which are every bit as ridiculous and ineffecient as what he is complaining about.
photon to electron in space to photon' to electron on ground ≃ photon to electron on ground
photon to electron (on ground) to battery (filling station) to electron to battery (car) to electron to kinematics VS raw oil (limited on this very planet) to petrol to kinematics
Also not considering resistance loss and petrol transportation. A little bit more complicated :)
Basically, you can't exceed the power per steradian of the sun with mirrors. So you would have to fill a large portion of the receiving end's sky to transmit any real power. Which means the mirrors would have to be really close (like they are in heliostats) or if they're far away, they would have to be really huge.
Does not work.
This is something I've wondered about. It seems like one should be able to make a counterexample by focusing an enormous area on a tiny one. Is it just because due to "fuzzy focus," the concentrated focus volume unavoidably grows as the mirror size grows?
And even if it is intended to, what will be the accuracy of this beam? what's to say some orbital junk won't crash into it and "oops" scribble a nice kilometres-wide Lissajous figure of scorched Earth onto our planet, like a hit and run graffiti tag?
Even if, according to WP, NASA is "a distinctly civilian (rather than military) orientation encouraging peaceful applications in space science", the US government has proven itself rather incapable of keeping itself in check, so the odds of it going to turn into "hey we could also turn it into a gigantic solar death ray space weapon", somewhere, at some point given its life cycle, seem pretty high to me?
That said, perhaps people don't consider it feasible, as in, "not in MY world". Sounds dystopian sci-fi and so on.
Mr. Musk is just ranting. He's used conversion efficiency as his whole argument. The only argument worth having is total cost of ownership, which relates to payback time.
Btw, great quote.
Someone make a stupid mistake on the ground, and your ship crash, and then BOOOM, a 20km wide hole shows up in your space center.
Of course I guess it that for those countries it would still be easier to put the panels somewhere else and build out the connection infrastructure than to put it in space.
That feels overly simplistic. What are the actual losses?
Why?
Because if you pick a frequency that, like a microwave oven, heats up water, then you are wasting energy. The atmosphere is well stocked with water at varying, often unpredictable levels. Wasting beam energy on heating up passing water molecules is kinda pointless, so the frequencies chosen pass through without interacting.
So no. A beam going off axis will not set your city on fire.
In terms of the actual concept, the original book to read is Gerard O'Neill's 1976 The High Frontier. O'Neill proposed to boostrap orbital colonies at L4 and L5. These colonies would build and maintain orbital solar stations.
I think that realistically, that window has passed. If solar power stations were built now, it'd all be done remotely. That's a pity, because as romantic engineering visions go, O'Neill colonies were amazing: http://en.wikipedia.org/wiki/File:Spacecolony4.jpeg
But I loved the space colony vision even so, and it was sad feeling it slip away over the decades. You can read Heppenheimer's book online: http://www.nss.org/settlement/ColoniesInSpace/ (I remember it as better than O'Neill's, though of course O'Neill gets much more credit for the ideas.)
It doesn't have to be absorbable by water to interact with biological matter.
The studies use 2.45Ghz, which is also used in most microwave ovens.
The actual offsetting design element is that energy is received over a large area -- 10km^2 -- so that at any one point the radiation that a human or other living creature would receive would be below the safe threshold.
Goddamit I hate being so confidently wrong.
https://en.wikipedia.org/wiki/List_of_common_misconceptions#...
From Hacker News a couple weeks back.
The one benefit to space-based solar with some form of power beam (likely microwave based, look up Heppenheimer's book it's now online) is reliability. Solar presently only works when the Sun shines -- that's during daylight, and not under cloudy conditions.
Orbital solar would be 24/7/365, with the exception of a couple of brief outages each year at high noon on the equinox when your powersat was eclipsed by the Earth itself. Feed-ins from another location could glide you through this, or a reserve biomass-fed plant, or ... The point being it's an utterly predictable downtime.
The alternative is to build out a (vastly cheaper) ground-based solar infrastructure ... and find some viable way of storing energy for a period of time (possibly up to a couple of weeks). A hard problem, but ultimately less hard, I suspect, than trying to orbit megatons of material.
http://physics.ucsd.edu/do-the-math/2012/03/space-based-sola...
Honestly, reading through his stuff is almost depressing. But as long as he sticks to the physics stuff, it's pretty hard to argue - all the math and sources are there.
The planned proposal claims that they can use some nifty beamforming to get good microwave transmission. It appears that the proposed technology will reduce the weight to diameter size of the transmitter, but Do The Math's calculations should still more or less be in the right magnitude.
[1] http://www.amazon.co.uk/Kuans-Wonderland-ebook/dp/B008144G9I...
[1] Based on energy consumption figures from http://en.wikipedia.org/wiki/World_energy_consumption
I'm just commenting on what they wrote and I see nothing about a farm of satellites in the article. Perhaps the original source is more clear about it. Or maybe this technology doesn't scale down well and that's the reason they're writing about one powerful satellite?
11,800 tonnes in GEO for 500 MW. At Proton-M prices, that's $295/watt for the launch. Not great…