Now here is a smart idea, producing solar energy when the sun doesn’t shine, and getting hydrogen (which can be put in fuel cells) and de-salted water at the same time..

Harnessing the Sun When It Doesn’t Shine

By Jeremy Miller

Daniel G. Nocera, the Henry Dreyfus Professor of Energy at the Massachusetts Institute of Technology, thinks the key to our energy future may be found in the cells of plants.

He is working on an “artificial photosynthesis” system that uses sunlight to generate hydrogen gas that, in turn, can be used to power a hydrogen cell.

The design, which approximates the energy-generating chemical reactions that happen naturally in plants, he says, helps overcome what is cited as the most nagging problem of solar energy: the inability to generate electricity when the sun is not shining.

Mr. Nocera recently agreed to answer some questions for Green Inc. on his research. Excerpts from that e-mail exchange follow.

You have said that the sun provides enough energy in one hour to meet our energy needs for an entire year. How do we effectively harness that immense quantity of energy?

We can’t do it solely with established technologies, though it is mind-numbing when we consider how much existing technology remains on the shelf. We need to do it with new discovery. We need centralized solar, also known as concentrated solar, as well as indirect, or distributed solar. These two paths involve different technologies, but my fellow scientists are ready to set out on both courses. The change of heart in America towards science is certainly a big step in the right direction.

So you think that plants -– namely the way they convert sunlight to chemical energy through photosynthesis -– hold the key to our energy future?

That’s what I work on because I believe it is so. Our system uses sunlight to split water to oxygen and hydrogen. This is, indeed, how nature, through photosynthesis, stores solar energy.

I want you to realize that we need only a third of the amount of water in an Olympic-sized swimming pool to produce enough hydrogen and oxygen per second, globally, to meet the world’s energy needs by mid-century. And it is carbon-neutral.

Critics of solar energy point often to the fact that solar panels can’t provide energy when the sun isn’t shining. How do your designs compensate for this problem?

When the sun is shining, we take some of the output from the PV system and feed it to a water-splitting electrolyzer to produce hydrogen and oxygen. Then we store the oxygen and hydrogen, either as a gas or by fixing it with carbon. Then, when the sun goes down, we can recombine the oxygen and hydrogen in a fuel cell in order to get the energy back out.

We are now working on a new design where the PV and the electrolyzer are combined. The recent discovery of the new catalyst enables this possibility.

How do your designs overcome the usual knocks on hydrogen, namely the difficulties in generation and storage?

Hydrogen has both a storage and distribution problem. But the storage is especially problematic when it needs to be transported on a moving vehicle. Storing it in a stationary vessel is much less of a challenge, which is all that is necessary for our personalized energy design. Also, with our design, you don’t need to transport it, since you make and use it locally.

I have read that water desalinization is a sort of secondary benefit that emerges from this technology? How so?

The new catalyst works in seawater, making oxygen only and no chlorine. This, too, is a unique feature of the catalyst. Thus, you could imagine the technique also being used to provide distributed clean water.

You say that a key to wide-scale deployment of solar is that the materials used are cheap and readily available, and that they function at room temperature and standard atmospheric pressure. Just how readily available are these catalytic materials? Are there environmental costs –- like mining and manufacturing -– that need to be taken into account?

The materials we are looking at are some of the most abundant on Earth, though not in the same league as iron. Nevertheless cobalt and phosphate are readily available. Also the catalytic active site is a molecule, so you don’t need much of it. We can coat surfaces with less than 10 nanometers –- or, less than one-ten thousandth the width of a human hair -– of cobalt phosphate, and the catalyst is good to go.

By the looks of your designs, the home would become a sort of miniature solar power plant. What are the advantages and/or disadvantages to this type of decentralized power generation?

I only see advantages. The individual is in control of his own energy production. You can’t have a greater energy security. It is carbon neutral. And all people would be empowered — from the smallest village in the underdeveloped world, to the rural areas of the developed world. Of course, producing energy in a city this way does not seem as feasible to me. That is why you need both centralized (e.g., concentrated solar power delivered from a grid), and decentralized power.

The decentralized scenario, in my opinion, is the best way to tackle the global energy problem. As I say, “One person at a time, times a billion.” Instead of making one large system where significant scale-up is needed, here you scale instead to the individual. Then you can meet scale with manufacturing. This is the way our society historically does business.

So why don’t we have it now?

The biggest drawback is that it is too expensive. But this is why you need new science and engineering. I know that my colleagues from around the world can make this happen.

Any cost estimates for one of your home solar-hydrogen systems?

Not yet. I am working on designing the most cost-effective system. We have made significant strides in cost reduction in just six months since the discovery.

You have said that a sustainable energy future is achievable with “the right investments in science and the right policy.” In February, the federal government announced nearly $100 billion in stimulus funds for clean energy. Where, in your mind, should this money be going? Where shouldn’t it?

Much of the money should be going to vehicles that can move new discoveries more efficiently to the marketplace. I think that is where the Department of Energy’s Advanced Research Projects Agency[3], or ARPA-E, is on the right track.

But as I mentioned above, it is equally important to fuel the discovery machinery of science. We need the basic research. The stimulus package has been generous on this front. I have to say, I have incredible optimism right now. We as a society have finally set off on a path to meeting the energy challenge in a sustainable way.