On Solar Silver Bullets
It's very common for people talking about peak oil, global warming, and so on to say that there's no silver bullet: we need to combine biofuels, solar, conservation, wind, nuclear, and others. I disagree. We may quite likely end up using a combination, but the put-downs appear to me to be unjustified: I think a solar silver bullet, in particular, will feasible within the next few decades. The main requirements for the version I'll present are (a) improved materials, which I expect to keep on coming from nanotech, and (b) drastically reduced manufacturing costs, which I expect from the slowly accelerating approach towards self-reproducing machinery that we've been experiencing for a couple of hundred years now.
The discussion: At the moment when I google for solar "no silver bullet" I get 20,800 hits; the top is the Rev. Donald Sensing at Winds of Change who summarizes a variety of sources, starting with MIT's Vladimir Bulovic saying
"If 2 percent of the continental United States were covered with photovoltaic systems with a net efficiency of 10 percent, we would be able to supply all the U.S. energy needs..."Sensing's response puts together more quotes:
So: who's for paving over Georgia [with solar cells]?...Indeed it's worse than that: rain happens, clouds happen, thunderstorms come and go. Two weeks ago my village was in the news when Colgate University's Seven Oaks Golf Course, which adjoins my back yard, was mostly a lake after over 8 inches of rain in a few days. Streets were impassable, the nearby golf-cart bridge from which all my children have played Pooh-sticks was visible only as a whitewater swirl, yet the village needed power.
...we still need power at night. Hence,
We need about 1.17 × 1012 kilograms, or 1.17 billion tonnes, of lead-acid batteries to store the energy.
The same Bulovic calculation is cited at an Instapundit article at TCSDaily, The Silver Bullet Fallacy, which suggests
If you covered all the rooftops, roads, parking lots, etc., with solar collectors, you'd get an area the size of Ohio, which might do the trick.That kind of thing -- looking at 40,000 - 50,000 square mile sizes -- is fun, but it's only fair to note that there is nothing magical about Bulovic's 10% figure, or even about photovoltaics as such: Stirling Energy Systems says that
The southwest region of the United States is ideally suited for this. In fact, a solar farm 100 miles by 100 miles could satisfy 100% of the America’s annual electrical needs.That's only 10,000 square miles. Who is Stirling Energy Systems? As of mid-2005, they reached a large scale development in that
Stirling Energy Systems (SES) recently announced a contract with San Diego Gas & Electric (SDG&E) to provide between 300 and 900 megawatts (MW) of solar power.Solar stirling? Worldchanging noted in August 2005 that
In the 80’s, Cummins tried another kind of solar Stirling- the free piston type...Ah...35% rather than 10%, that explains the smaller area. In general, the efficiency of a Stirling engine can approach (H-C)/H, the thermodynamic limit, where H is the Hot temperature (from absolute zero) and C is the Cold temperature. This approaches 100% as H gets enormously higher than C, and focused sunlight gets very hot -- as hot as the solar surface, at 5500°C. So I am expecting Stirling engines to get better and last longer. They still need good weather and big batteries, though -- or do they?
Free piston Stirling engines are now under development by NASA for use as isotope-heated space power generators, requiring life of many years. Their heat-electricity efficiency is in the 35% range.
Sample Silver Bullet: Let's imagine a Stirling engine within a half-transparent, half-reflective balloon -- in other words, the reflector is part of the balloon's inner surface and the engine's heat collector is at the focal point (halfway between the center and the surface). At any given moment, the engine is suspended from the top of the balloon, and it shifts that suspension point to make the balloon's reflective surface rotate through the day. The balloon might be made of the strong, transparent carbon nanotube sheets reported in Science in 2005, which I wanted for my giant parasol in November. It's a hydrogen balloon, and the Stirling engine's working fluid is hydrogen, so leakage from the engine itself is not a problem. (Can nanosheets hold in the hydrogen? I hereby expect that they can, reasonably well.) It's an unmanned balloon, about as intelligent as a Roomba, so the occasional burnout isn't a deal-breaker. The balloon controls its altitude by adjusting its volume; it may be able to compress by pulling in the transparent side, or we might have to connect it to a separate and fully-transparent balloon above it which compresses from very large to quite small. The balloon's working altitude is up above the cloud layer, usually in the stratosphere, so weather doesn't matter: it does not even need the strength to resist high wind.
Oh, you think it needs strength when it comes down? But it can be met by an airship, a ferry which takes water up and brings compressed hydrogen down. It gets loaded with water, and enough hydrogen to lift it up...the Stirling engine decomposes that water into more hydrogen and oxygen and compresses the hydrogen. (If you compress hydrogen to more than 16 times the pressure of the air around it, it sinks.)
Observe: No weather problems, no batteries, and instead of covering 50,000 or even 10,000 contiguous square miles, you have balloons miles over your head, obscuring your view of the sun about 1% of the time. (I'd say less, but remember that hydrogen generation from electricity is not 100% efficent, and we can expect other losses.) If that's unacceptable, we put the balloons out over the ocean. Does it sound nutty to you? Well, there's worse to come: sometimes I would put those stratospheric balloons close together, right in front of a hurricane, to cool tens of thousands of square miles of ocean. See? (If that's not nutty enough, read my giant parasol note; I was smiling as I wrote it, but I really do mean it just the same.)
Now, is this solar-stirling-balloon silver bullet a huge engineering project? Sure. But it doesn't have to start huge, though it will benefit from economies of scale. If you believe that Stirling engine development will continue down the familiar learning curve now that installation is getting common; if you believe that increasingly-robotic manufacturing will continue on the path it's been treading; if you believe that nanomaterials like those nanosheets will go on getting better...well, if you believe all that (and I do), then you can expect something loosely resembling this silver bullet to come along in the next couple of decades, unless something better comes along first. Personally I expect that something better -- something based on facts I don't know, and imaginings I wouldn't have imagined even if I knew the facts -- will most likely come along first.
I'm not denying the value of, say, Armed Liberal's 3% Solution response to the Sensing post. I've spent a lot on insulation, I drive a hybrid, I've been talking with the village Utilities Commission about geoexchange heating/cooling (they like the idea, but not the kind of system I want to use, or it would be in place now). Sure, that stuff matters right now, and there are no silver bullets right now. But I don't think that long-term thinking should be based on what's available now, and I guess I'm more Singularitarian than most.
If Bush believed as I do, by December 2001 we'd have seen the commencement of weekly White House Technology Prizes, totalling maybe $1,000,000 to split among a few honored innovators each week, with video downloadable (yes, even in 2001) on the web, with categories of inventions and ... oh, well. (And an oil tax, probably made revenue-neutral by setting it against the payroll tax.) Well, he doesn't. But I'm right. And remember that conservation will not help us against Al-Qaeda, but technology will, because technology will also reduce oil usage by China and all the rest, and therefore the prices of fungible oil worldwide.
Or then again, maybe not.
UPDATE: Yes, I switched in the middle from Bulovic's "all the energy needs" using 2% of the 3.7M square mile area of the US using 10%-efficiency, to Stirling Energy Systems' 10K square miles for all electrical energy with their apparently 35% efficient Stirling engines. If they're both right (and if Stirling was actually assuming 35% in that particular statement) then the energy usage of the US is 7,400 square miles' worth of solar input, while the electrical energy usage of the US is 3,500 square miles' worth of solar input; that seems reasonable enough, and doesn't change my overall prediction, but it was sloppy.