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I'm Going To Disney World

Well, actually, I'm going to a resort at Disney World to attend a workshop on Space Solar Power. It should be like old home week, though I haven't been involved in the field for fifteen years or so.

We'll see what the interweb situation is up there before I make any promises about blogging for the next couple days.



Brock wrote:

Rand, in a recent interview with WaPo Elon Musk had this to say about SPS:

WaPo: Should not NASA be funding research to make Space Solar Power possible in this time of energy crisis as they did in the 1970ís?

Elon Musk: No, I donít believe in space solar power. It will never be competitive with ground solar power. The cost of converting the electron energy to photon energy and then back again on the ground overwhelms the 2X increase in solar incidence. And thatís before you consider the cost of transporting the solar panels and converters to orbit!

I'd be interested in knowing if anyone at your conference has a specific rebuttal to that.


Godzilla wrote:

Having read on the subject in the past I share Elon's opinion. The fact he owns a solar power startup means he knows the economics better than most people. He is no fool theory-wise either: the man has bachelor degrees in Economics and Physics.

The main possibilities I see for this technology are: long-distance power beaming to enable a worldwide power grid, application in military surface navy vessels for power generation or augmentation (I have not done the math to see if receiver area is sensible or not for this one, I still think nuclear power makes more sense for the navy regardless), possibly power beaming for in-space propulsion (no atmosphere means no attenuation).

I also remember reading about some Japanese proposal to use power beaming satellites for powering handheld devices. But I believe this required a low-orbit satellite network.

Big D wrote:

IMNSHO, a good nuke beats both, hands-down.

kert wrote:

his math is faulty. first, solar flux is higher than a mere 2x outside the atmosphere, and second, geostationary SPS would have continuous sunlight, i.e. at least another 2X advantage over anything terrestrial, for average output.
other than that, hes right.

Karl Hallowell wrote:

his math is faulty. first, solar flux is higher than a mere 2x outside the atmosphere, and second, geostationary SPS would have continuous sunlight, i.e. at least another 2X advantage over anything terrestrial, for average output.
other than that, hes right.

No, kert, he's about right. A tracking system on the ground is almost 40% as efficient as a continuous lit SPS in orbit. That's because the atmosphere only absorbs about 25% of solar influx, that is, at sea level solar influx is around 1kW per square meter while it is roughly 1.3 kW per square meter in space.

Carl Pham wrote:

geostationary SPS would have continuous sunlight

Um, how? What happens when it's night time at the point over which the SPS is stationary (say Los Angeles)? Or are you saying the Earth's shadow doesn't reach out at least 22,000 miles? Hard to see how we get lunar eclipses, then.

If you put the SPS where the Sun does shine all the time, how do you beam it down to Earth without turning it off from time to time or having some kind of mad racetrack of receiving stations all along the ground path?

Besides, let's be realistic. It's not low solar flux that impedes the use of solar power here on Earth. It's much more the fact that the capital investment (solar panels, batteries, fancy charging system) is enormous. Even factoring in free power, the payback period for the very expensive power-collection machinery is too long to compete with other sources of power.

And that does not even take into account the problem with transportable energy, i.e. energy to run automobiles, airplanes, and ships. It's so far impossible to get energy storage densities (kW/kg) for electrical energy that are even close to realistic needs. Battery technology just sucks. Given that we spend something like 25% of our energy budget on transportation, this is a serious limitation.

Furthermore, our big headaches are largely with transportation energy, not the energy we need for big fixed-location operations like electric power generation, home heating, or industrial power. We've got lots of realistic options for that stuff, from nukes to passive solar to cogeneration or massive coal plants that sequester all the CO2 (or whatever bugs you about burning coal).

Even if Musk overrates the expense, I'm still seeing SPS as a solution in search of a problem.

kein schwein wrote:

Tintenfische sind in Wahrheit furchtsame Geschoepfe.

Anonymous wrote:

Carl, lunar eclipses are brief, and quite rare.

Google geostationary solar power satellites, and you'll see things like

"Sunlight would not be blocked, except for a period of about an hour each night within a few weeks of the equinoxes."


" In geostationary orbit, an SPS would be illuminated over 99% of the time. The SPS would be in Earth's shadow on only a few days at the spring and fall equinoxes; and even then for a maximum of 75 minutes late at night when power demands are at their lowest."

MG wrote:

Perhaps, rather than arguing about time-integrated solar flux comparisons, we could discuss what the burdened cost of electrical delivery is to geographically remote locations?

That seems to be a more fruitful direction.

Leland wrote:

I'm with MG. The issue isn't how to bring massive solar power capability to NYC. How about getting sustaining solar power capabilities in remote areas, developing the capability to provide excess, and then moving it into replace urban generation sources.

Though, it is still hard to beat Big D's nuke.

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This page contains a single entry by Rand Simberg published on October 1, 2008 12:38 PM.

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