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Harvesting solar power in space and sending it back to Earth

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Re: Harvesting solar power in space and sending it back to Earth

#41

Post by schiffern »

kokotko wrote: post #7

"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…

>solar panel is on-orbit, you get twice the solar energy - assuming that it is out of Earth's shadow

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.

Re: Harvesting solar power in space and sending it back to Earth

#43

Post by Gravityloss »

willyt wrote: post #40
kokotko wrote: post #7

"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…

Why would you put solar panels up there? Why couldn't you just focus the energy into a beam and point it towards earth like space based mirrors for one of these solar power stations[0] where sunlight is focused on a 'boiler' which generates steam for a conventional turbine. I've no idea if the physics works out but i'd be interested to hear from someone who does. [0] http://en.m.wikipedia.org/wiki/PS20_solar_power_to…

Quite unintuitively, you can't really focus light from the sun to a long distance, since the sun is not a point source.

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.

Re: Harvesting solar power in space and sending it back to Earth

#44

Post by Gravityloss »

schiffern wrote: post #41
kokotko wrote: post #7

"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…

>solar panel is on-orbit, you get twice the solar energy - assuming that it is out of Earth's shadow 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 estima…

Concentrators have problems.

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.

Re: Harvesting solar power in space and sending it back to Earth

#45

Post by dredmorbius »

jacques_chester wrote: post #29
abecedarius wrote: post #3

Earlier quoted context omitted.

Powersats as basis for space colonies never added up for me -- couldn't the funders find work crews willing to live closer to spam-in-a-can style for higher wages, with overall much lower cost? 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…

I reckon I might have read that book too. Certainly the art rings some bells.

I think Heppenheimer's book re-used much of the O'Neill art.

Re: Harvesting solar power in space and sending it back to Earth

#46

Post by dredmorbius »

Cost would be absolutely prohibitive.

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.

Re: Harvesting solar power in space and sending it back to Earth

#47

Post by tripzilch »

willyt wrote: post #40
kokotko wrote: post #7

"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…

Why would you put solar panels up there? Why couldn't you just focus the energy into a beam and point it towards earth like space based mirrors for one of these solar power stations[0] where sunlight is focused on a 'boiler' which generates steam for a conventional turbine. I've no idea if the physics works out but i'd be interested to hear from someone who does. [0] http://en.m.wikipedia.org/wiki/PS20_solar_power_to…

well, first thing that comes to mind is, with that anyone that builds a device that focuses a large amount of solar energy into a tight beam aimed at the Earth, I'll have a hard time believing that's going to be used for some benevolent energy-harvesting purpose.

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?

Re: Harvesting solar power in space and sending it back to Earth

#48

Post by tehwalrus »

I'm reminded of Henry Tam's book "Kuan's Wonderland,"[1] where [SPOILERS] the government blocks out the sun with a disk in space, and then sells you the energy via a subscription. If you don't have one, you freeze to death.

[1] http://www.amazon.co.uk/Kuans-Wonderland-ebook/dp/B008144G9I...

Re: Harvesting solar power in space and sending it back to Earth

#49

Post by jacques_chester »

dredmorbius wrote: post #45
jacques_chester wrote: post #29

Earlier quoted context omitted.

I reckon I might have read that book too. Certainly the art rings some bells.

I think Heppenheimer's book re-used much of the O'Neill art.

Some of it is distinct.
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