[cvbncvbncgbc]

Elon Musk's opinion the concept( not this one in particular though ).

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.

[anateus]

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.

[JanezStupar]

I think that he doesn't rule them out either.

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.

[darkmighty]

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.

[itazula]

I have never met a man so ignorant that I couldn't learn something from him. -- Galileo Galilei

[chc]

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.

[pokstad]

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?

[mkaziz]

Makes them susceptible to enemy navies, IMO.

[gojomo]

Salt water is very corrosive.

[darkmighty]

There's very degrading ionizing radiation in space.

[oska]

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.

[1] http://en.wikipedia.org/wiki/Geography_of_Japan#Composition_...

[ericd]

Interesting point, they don't have large deserts to drop them in like we do in the western US.

[mikeash]

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".

[krasin]

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.

[bane]

2 counter-arguments

- Japan has proven to be pretty good at building more land

- Japan has lots of ocean area to float panels on

[austinz]

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.

[Tloewald]

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.

[austinz]

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%.

[1] http://www.sandia.gov/~jytsao/Solar%20FAQs.pdf

[2] http://en.wikipedia.org/wiki/World_energy_consumption

[Tloewald]

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.

http://en.wikipedia.org/wiki/Solar_variation

http://science.nasa.gov/science-news/science-at-nasa/2013/08...

[austinz]

0.02%, if you are building a hypothetical network of power plants with the same total surface area as the state of Maryland in orbit.

[deegles]

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.

[api]

Is he factoring in energy storage costs? That's the real problem. Gathering solar energy is easy, storing gigawatt-hours of it at night is not.

[itazula]

Nah, they'd be charging all of those Teslas.

[chadgeidel]

Ignorant question - what about a solar concentrator - like a mirror - instead of an array of "traditional" solar panels?

[ajuc]

I don't know for power genreation, but it would make awesome weapon.

[w1ntermute]

Sounds like the Memento Mori (from Mobile Suit Gundam 00): http://gundam.wikia.com/wiki/Memento_Mori

[jkdearden]

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.

[JanezStupar]

I remember reading about such a device being planned to "send power" to remote US army outposts e.g. near front lines.

[fuzzythinker]

Idea in "Die Another Day", hard to secure it to not be used as weapon.

[Panoramix]

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.

[gkop]

Why not use the solar electricity to mine bitcoin from space?

[mdelias]

Jeff Garzik Announces Partnership to Launch Bitcoin Satellites into Space http://www.coindesk.com/jeff-garzik-announces-partnership-la...

[cvbncvbncgbc]

So instead of improving the algorithms that support our virtual currency, we brute force the problem with sending stuff to space(!).

Sounds like a plan that could destroy a civilization in the long term.

[itazula]

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.

[nickhalfasleep]

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.

[cvbncvbncgbc]

In what orbit, that doesn't require propulsion, do you get constant line of sight?

[danielweber]

They nearly always call for geosynchronous orbit, because they want to always be over the rectenna on the ground.

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.

[mikeash]

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.

[oh_sigh]

L1

reference: http://en.wikipedia.org/wiki/Lagrangian_point#L1

[tectonic]

That's pretty amazing, thank you for posting this.

[danmaz74]

Having a stable source of energy at all time is even more important than the conversion efficiency. Case not closed.