Space power? June 12, 2009

Posted by Maury Markowitz in solar power satellites Tags: solar power satellites

A few weeks back the science interwebs were alight with the news that Pacific Gas & Electric, California’s largest power supplier, had inked a deal to buy solar power beamed down from space. The fact that the post was on the NEXT100 blog, not an official PG&E press release, didn’t stop anyone from blogrolling it to the other end of the Earth in moments. Nor did the fact that the company, Solaren Corp, didn’t even have a web page seem to trigger any concern. If you googled it up, you could only find this company from Armenia, and even today you have to poke about a bit to find this page, which is entirely content-free and may not even be the same company (it’s listed in Washington).

Space power, eh? Ain’t gonna happen. Let me show you why…

Building a solar panel on Earth is pretty easy, but you only get sunlight during the day, and there’s weather to consider too. Poking about on the net, I found that we get a little under 2000 hours of “bright direct sunlight” a year here in Toronto. Since there’s 8544 hours in a year, that means we get useful sunlight about 1/4 of the time.

And even then we don’t get all of the power we could; in Earth orbit, with no atmosphere to filter the sunlight, there’s about 1,366 Watts of solar energy for every square meter, but by the time it gets down here, we get about 1,000 W/m2.

The high frontier

Ok, so put those solar panels in space. Five times as much power, right there – four times the sunlight because there’s no night or clouds, and another boost because of the greater power of that light due to the lack of the atmosphere.

Of course you have to get the power down to the planet, but we know how to do that. There’s a system called a “rectenna” that beams the power down as microwaves, and it’s pretty efficient, upward of 90%. This will be attenuated somewhat by the atmosphere, so maybe the overall effect is on the order of 85%. Now put the satellite in a geostationary orbit (GEO) so it sits above your target market, like California, and beam the power down to the grid.

So we’re looking at getting maybe four times as much power as the same panel on Earth, and it’s almost 24 hours a day (there’s the odd eclipse). That’s a lot more useful than day-only power like a panel here on Earth. So what’s not to like?

Show me da money!

Uhhh, how about the $12,000 a pound shipping costs? Here, follow along as I do a little math…

A really good solar cell for space applications is the ZTJ cell from emcore. It’s about 30% efficient, which is way higher than a traditional cell like you see on a rooftop, which might get you about 12% if you’re lucky. At 30%, you’re looking at getting around around 400 W/m2 of the 1,366 available. The Next100 press release stated they were looking at 200 MW, so that’s 500,000 m2 of cells. How much do they weight? emcore has them at 84 mg/cm2. That’s 5 billion cm2 we have to cover, so that’s 420 billion mg, or about 925,000 pounds.

At $12,000 a pound that’s $11 billion just for the launch cost of the cells.

Ok, you know, $11 billion isn’t all that much in the grand scheme of things. OPG is planning on spending over $20 billion CAD on the Darlington B expansion, for instance. But the difference is the power it’s going to produce. Solar cells are generally rated for about 20 years, so we’re looking at 200 MW being generated 24/7 for 20 years. That’s about 35 billion kWh in total. How much is a kWh? Well for baseload, here in Ontario you’re looking at about 4 cents and in California it peaks out at about 6 cents. Let’s split the difference and call it 5 cents.

So over 20 years we get $1.75 billion worth of electricity. Anyone else see the problem?

Now there are ways you can improve on this, slightly. Solaren’s patent shows a system that uses concentration, which boosts you into the 40% efficiency range and lets you replace the solar cells with mirrors. Those mirrors can be based on lightweight inflatable structures, so the launch mass goes down. But solar cells aren’t really that heavy in the first place, so the savings aren’t huge – they’re nowhere near the 100 times reduction you’re going to need to make the numbers work out. And then there’s the small problem that every attempt to make a lightweight space mirror has failed miserably.

Basically if you just set up those exact same panels on Earth you get some amount of power, let’s call it 1 solaren. Now if you set them up in space you get 5 solarens. The difference is 4 solarens. Unless the shipping costs are less than the price you get paid for those 4 solarens, just set it up here on Earth and use the money you save to buy four more of them. And the simple fact of the matter is that electricity is cheap, rockets are not.

Fugetaboutit!

I need to point out that there’s nowhere near this many high-efficiency solar cells in the world, and no way to make them fast enough either. emcore’s the only company that’s actually signed deals for concentrated PV, and their production is only a few hundred kW a year. A 850 kW plant was going to take 15 months to supply. 200 MW represents decades of worldwide production, and there’s no sign that either emcore or Spectolab has any sort of deal with Solaren.

And forget about actually launching this stuff up there. The entire worldwide capacity to GTO is about 70 launches a year, with an average of about 5 tons of payload. Most of these are used by the military, and they’re not going to sell them to you. To get this stuff up there, you’ll need to buy the spare capacity of the entire world for several years.

And they say they’ll be operational in 2016? Hmmm.

And did I say 20 years of power? Good luck with that. There’s this looming problem called the Kessler Syndrome that we’re right on the leading edge of running into. Basically all the junk that we’ve been putting up there for the last forty years is still floating around, bumping into things. We’ve already lost two satellites in GEO, and they were way smaller .

Sweet mother Earth

I don’t know what to think of the Solaren story. The company really exists, at least there’s a phone number and people who answer it. They really did file a patent, but anyone can do that. But the plan is so grandiose, and so near-term, that there’s just no way I can see this being remotely possible. If they said they wanted to launch a 2 kW testbed in 2016 that’s one thing, but a 200 MW production system?

Hear that beeping? That’s my BS detector going off.