Field of Science

Powering the planet with solar energy

Nathan S. Lewis, Professor of Chemistry at Caltech, writes about our energy problem in Powering the Planet, Engineering & Science No. 2, 2007.

If you think there is no problem with CO2 and global warming, then do carry on. Otherwise, how to deal with that and get enough energy at the same time?

After much meandering about other sources of energy that won't solve the problem (which admittedly is highly interesting) he gets down to business:
Willie Sutton was a famous bank robber, and when they finally caught him someone asked, “Why do you rob banks, Mr. Sutton?” He said, “Because that’s where the money is.” I believe in that, too.
One hundred twenty thousand terawatts of solar power hits the earth, so Willie Sutton would say go to the sun because that’s where the energy is. It is the only natural energy resource that can keep up with human consumption. Everything else will run up against the stops, soon. In fact, more solar energy hits the earth in one hour than all the energy the world consumes in a year.
Solar is the only way to go. In fact, a very, very small area of the Earth's surface is needed to generate all the energy we need:

Top: The nation’s entire energy needs could be met by tiling a 400 × 400 kilometer parcel of land in the sunny Midwest with solar panels.
Bottom: Six such squares, appropriately sited, could power the world.

Sounds promising, no? Problem is that electricity is difficult to store.
I believe that the best way to store massive quantities of electricity is to convert it into chemical fuel. Th e best technology for that purpose that we have now uses a solar thermal system that collects and concentrates solar energy to electrolyze water. You get H2 for fuel, which you can distribute through pipelines and store in tanks. And then you can pump it out of the tank whenever you like and run it through a fuel cell, which converts it back into electricity and water. The problem is, the existing technology is not scalable. The setup in the photo above makes about a kilogram of hydrogen—the energy equivalent of about a gallon of gasoline—every day. And we would have to build one of these every second, for 50 straight years, just to hold the CO2 concentrations to 550 ppmv. We need to find a better way to make fuel from sunlight directly so that we can bring energy to whoever wants it whenever they want it—day or night, summer or winter. My lab and other labs at Caltech are working on that, too.
Sigh. No respite. Give up? Here's his word on that:
I haven’t talked much about economics, but I will say that it’s easy to prove, thinking 100 years out, on a risk-adjusted net-present-value basis, that the earth is simply not worth saving. It’s a fully depreciated, four-billion-year-old asset. Unless you have policy incentives that refl ect the true cost of doing this experiment, the economically efficient thing to do is just what we are doing now. On the other hand, with the appropriate policy incentives, the financial opportunities are commensurate with 50 Exxon Mobils on the supply side, and, in devising ways to lower our energy consumption from triple to double by 2050, 50 more Exxon Mobils on the demand side. Th is is both the challenge and the opportunity.
&nbs; &nbs; &nbs; &nbs; &nbs; &nbs; I leave it to you to decide whether this is something that we cannot afford to do, or something at which we simply cannot afford to fail. Remember, we get to do this experiment exactly once. And that time, like it or not, is now.
"The Earth is simply not worth saving." So much for risk-adjusted net-present-value calculations.


  1. The PDF does not seem to want to load (I sometimes get glitchy internet access at work) so I can't check the article, but... what about nuclear? Sure, it's not a permanent solution, but it ought to get us through the next hundred years even with pessimistic estimates; and unlike carbon-based energy sources, it won't make the planet unlivable if we do foolishly keep using it until it runs out.

  2. Lewis does talk about nuclear power. Here's what he says:

    So let’s look at carbon-neutral energy sources. We could go nuclear, which is the only proven technology that we have that could scale to these numbers. We have about 400 nuclear power plants in the world today. To get the 10 terawatts we need to stay on the “business-as-usual” curve, we’d need 10,000 of our current one-gigawatt reactors, and that means we’d have to build one every other day somewhere in the world for the next 50 straight years. I’ve been giving this talk in one version or another for five years—we should have already built on the order of 1,000 new reactors, or double what’s ever been built, just to stay on track. So we’re really behind.

    Th ere isn’t enough terrestrial uranium on the planet to build them as once-through reactors. We could get enough uranium from seawater, if we processed the equivalent of 3,000 Niagara Falls 24/7 to do the extraction. Which means that the only credible nuclear-energy source today involves plutonium. That’s never talked about by the politicians, but it’s a fact. Forgive my facetiousness, but on some level we should be thanking North Korea and Iran for doing their part to mitigate global warming. We’d need about 10,000 fast-breeder reactors and, by the way, their commissioned lifetime is only 50 years. Th at means that after we choose this route, we’re building one of them every other day, or more rapidly, forever.


    I can email you or anyone else the PDF...

  3. Interesting. I don't really buy comments of the form "There isn't enough X on the planet.." because people have been saying we will run out of oil for how many decades now? Obviously we will run out at some point, but estimates of the global amount of discoverable resources consistently tend to run wildly low.

    This calculation about the number of nuclear reactors required to maintain a "business as usual" curve is worrisome though. Although, I would still argue that aggressively moving to nuclear is way better than doing nothing at all...

    Non-renewable resources don't just suddenly dry up one day -- rather, as they become more scarce, they become more expensive. In fact, if the carbon emissions issue were not a factor, I would argue that there would be nothing at all wrong with continuing on our present course. A gradual monotonic increase in the price of oil is arguably the least painful way to both recalibrate our concept of "business as usual", as well as incentivize the development of alternative energy sources. If there is a viable way of continuing "business as usual", you damn well better believe corporations are going to figure out how to find it when the price of oil starts to become impractical (and if they don't, other people will and will drive the old guard out of business -- yay capitalism!). And if there is no viable way of continuing "business as usual", and we need to lower our standards of living, doing it through a gradual increase in cost is probably less painful than legislating a lower standard of living all at once.

    It's just that pesky "impending climate disaster" that torpedoes this whole plan... I have no doubt that capitalism's insatiable ability for short-term/local optimization will rapidly uncover the most cost-effective alternative energy source as soon as oil is no longer cost-effective. But of course capitalism falls down hard when it comes to long-term planning and/or global optimization... By the time there is a profit incentive to switch away from oil, the damage will already be done.

    If we could get people on nuclear, though, even if Lewis's bleak predictions come true, we could at the very least get things on a track where corporations would have a powerful incentive to discover the next best thing, without melting the icecaps on the way there.


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