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Storing the Sun

From ON Magazine, Issue No. 1, 2010

Daniel G. Nocera
Dr. Nocera, the Henry Dreyfus Professor of Energy and a professor of chemistry at Massachusetts Institute of Technology, has made a groundbreaking discovery in energy technology. Photograph by Len Rubenstein
Daniel Nocera Cracks the Code of Solar Energy

June 4, 2010—“Everybody talks about the weather, but nobody does anything about it.” This quote, widely attributed to Mark Twain, applies to the subject of solar energy as well. Everybody talks about it, but nobody has figured out how to store it. Nobody except Daniel G. Nocera, that is.

Last year, Dr. Nocera, the Henry Dreyfus Professor of Energy and a Professor of Chemistry at Massachusetts Institute of Technology, solved one of the great problems that has stood in the way of broader adoption of solar energy. The power of the sun, after all, is no good at night or on rainy, overcast days. What has been lacking to date is a way to store solar energy so that it can be used whenever it is needed.

Dr. Nocera’s lab figured out a way to use the sun to easily and cost-effectively split water into its component elements, hydrogen and oxygen, which can then be cheaply stored until combined on demand to create a hydrogen fuel that can generate electricity. This technology, married to a photovoltaic panel, a storage tank, and a fuel cell, would enable homeowners to power their homes—and their fuel-cell cars—on or off the grid.

News of Dr. Nocera’s discovery has raced around the globe at the speed of light, its potential impact on society and the environment inspiring astronomical levels of enthusiasm. One German researcher called it “probably the most important single discovery of the century,” and Time magazine named Dr. Nocera one of the 100 scientists “who most affect our world.” With the world now beating a path to his laboratory’s door, ON managed to sneak in to ask him a few questions.

The primary-use scenario for your invention seems to be homeowners with photovoltaic panels on their roofs. Businesses, with their plants and data centers, consume much more energy than households do—can they someday benefit from this technology as well?

Yes. We’re already at the benchmark where we can power an average home easily. To meet structures with much larger energy requirements, we would have to improve the technology by a factor of 10 per unit time—in other words, it would have to work 10 times more quickly. That’s assuming your goal is to be off the grid completely. It’s possible to use the technology for some of your power needs and still remain on the grid for the rest.

I’m particularly interested in applying this technology for poor people and the non-legacy world. A lot of developing nations don’t have a reliable energy infra­structure in place; my invention can help them to cost-effectively generate and distribute power using resources they already have—sun and water—along with some other reasonably inexpensive materials.

How about vehicles that travel long distances, such as trains and airplanes? Could this technology offset some of their energy use?

Again, right now this is ideal for the fuel-cell car. In January, Honda announced that it’s making a huge investment in home-refueling stations; this is now possible and practical because I can provide a cheaper way to make hydrogen. But for long-haul transport, liquid fuel—which can be made from biofuel—is still preferred. So that remains a research goal. Late last year, the U.S. Department of Energy announced it was awarding grants to develop hydrogen-based solar fuels, so we’re ahead of the curve already. We can take the hydrogen from water, but optimizing it for specific applications depends on lots of engineering issues.

Given the magnitude of the problem you’ve solved, the solution when described seems deceptively simple. How long did it take to get it right?

I like to describe it as a big lake, and you know you need to get to the other side, but you can’t cross it in one giant leap. So you lay down stepping stones that enable you to make gradual progress. For this project, the stepping stones represent 25 years of work. We explored multielectron reac­tions, coupling protons to electrons, but the real key was to study how plants use photosynthesis from the sun to split water into hydrogen and oxygen. This process be­came known in just the last four years, and we were able to study and learn from that. We didn’t try to rebuild the architecture of how plants do that, but we took the es­sence of those architectural elements and incorporated them into our design. It really provided a clear roadmap for our research, and it wasn’t long after we figured out how nature does it that we were able to do it.

And the research still goes on. As a scientist, I always want to know how things work and how to make them work better. So rather than resting on our discovery, we’ve been refining it and have developed a second catalyst that works as well or better than the first one. We just submitted a paper on it to a journal.

Storing Solar Power
Storing Solar Power— Solar panels work well when the sun is out, but not when it sets. In a major sci¬entific breakthrough, MIT’s Dan Nocera has figured out how to store solar power for on-demand use. Diagram by Casey Reed

The catalyst seems to be a critical part of your breakthrough. Can you explain what it is and why it was so innovative?

The catalyst is what splits the water molecules and allows the hydrogen ions to make hydrogen gas. Previous attempts to develop a suitable catalyst were unsuccessful either because the materials were too expensive or too much energy was required. Furthermore, they tend to break down over time. What we did was to develop a cobalt-based molecular catalyst that sits in a solution of cobalt and potassium phosphate, so it is able to regenerate itself as it breaks down.

That is absolutely the key to my discovery and the thing I’m proudest of. This is the first self-healing catalyst ever developed. And that’s an important property because that means it can work with dirty water, even waste water. Expensive electrolyzers require absolutely pure water or else they get cruddy and stop working; in developing nations, you can’t rely on the quality of the water supply, and you don’t want to impact their potable water sources.

Enabling materials to repair themselves versus trying to create something that is indestructible: Do you believe that is a useful model for other researchers studying sustainable solutions to consider?

Definitely. I think that if you begin to look beyond sheer indestructibility, it can open up new avenues for research. And I think that’s particularly important when the technology in question won’t necessarily be deployed in carefully controlled environments. If you can’t eliminate constraints, you have to be able to work around them.

Are there risks to storing hydrogen and oxygen on one’s own property?

What we would do is to store the materials in underground storage tanks. Certainly there’s a potential risk in any form of energy, but it’s really no different than methane, which we use all the time. But scaling the technology from a lab application to actual household and neighborhood implementation will require the expertise of companies that specialize in using this kind of material safely.

What other obstacles—scientific, economic, political, social, regulatory, or other—stand in the way of widescale adoption of this technology?

As with any new technology, there are a few. I want to serve the poor, and while my discovery is cost-effective in and of itself, it relies on photovoltaic panels for the front end and a fuel cell in which to mix the hydrogen and oxygen, and these materials need to be cost-effective as well. I’m in the process of trying to forge partnerships with companies and organizations to make this happen.

Scientifically, there are still some refinements we need to do to ensure that it is super robust and maintenance free. These things are going to be in remote areas around the world, so it needs to be something you can set up and leave alone for years, and it will continue to work reliably. From a regulatory standpoint, there aren’t a lot of federal standards having to do with fuels; generally, they fall under the purview of local fire codes. But I’ll need partners to help suss that out.

What’s most exciting and promising, though, is the social acceptance my invention has received. People are very enthusiastic about this, and that proves that it satisfies a very real need. As a scientist, you can’t ask for anything more than that.

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