CUTTING EDGE SUN

Harnessing the Sun When it Doesn’t Shine
Jeremy Miller, May 27, 2009 (AP via NY Times)

SUMMARY
Daniel G. Nocera, the Henry Dreyfus Professor of Energy at the Massachusetts Institute of Technology (MIT), is one of the leading scientists in the pursuit of capturing solar energy through artificial photosynthesis.

Plants use carbon dioxide (CO2), the main greenhouse gas involved in climate change, and sunlight to make chemical energy.

Dr. Nocera (click to enlarge)

The sun provides enough energy in one hour to meet U.S. energy needs for a year.

The Nocera-MIT team’s artificial photosynthesis system uses solar cells to generate electricity and uses some of the electricity to simulate what plants do by splitting water in the presence of a catalyst into hydrogen (H2) and oxygen (O2). Stored, the H2 and O2 represent potential chemical energy in the form of a hydrogen fuel cell available to generate electricity in the absence of sunlight and active solar panels.

Right now the process is bulky and inefficient but Dr. Nocera believes that by 2050 the process could be efficient enough to require no more than a third of the water in an Olympic-sized swimming pool to produce enough hydrogen and oxygen per second, globally, to meet the world’s energy needs, emissions-free.

Nocera’s key breakthrough, some 6 months ago, was finding materials, cobalt and phosphate, to act as catalysts that are earth-abundant and cheap. Mere molecules of the catalyts are required. Surfaces coated with less than 10 nanometers (less than 1/10,000th the width of a human hair) of cobalt phosphate can, in the presence of sunlight, separate water into oxygen and hydrogen.

Artificial photosynthesis. (click to enlarge)

Nocera sees many advantages to his system’s distributed generation. It is domestic energy that represents no possibility of compromised security and would empower system owners from poor villages to rural landowners and suburban homeowners.

While Nocera’s system is designed to generate energy for individual users, he also advocates the development of concentrating solar power plant (CSPP) utility-scale systems for grid-delivered energy to large urban populations.

Distributed and Central solar energy generation are separate technologies but Nocera firmly believes science is up to the challenge of advancing both.

His next step is making the artificial photosynthesis system cost effective.

click to enlarge

COMMENTARY
The promise of hydrogen has always been 20 years away because of the expense of storage and distribution, especially for vehicles. Artificial photosynthesis is stationary so that, at the individual user-scale, there is no need for distribution and there is no storage problem.

Rooftop solar systems large enough to generate excess electricity when there is sun can make use of the hydrogen fuel cell concept as cost-effective storage if the catalyst – the most expensive part of the storage component of the system – is made from abundant and therefore cheap materials. The catalyst is a water-splitting electrolyzer that splits water into hydrogen and oxygen. They can be stored as gases or fixed with carbon.

Schematic. (click to enlarge)

Despite the fact that, according to Nocera, there is already a “mind-numbing” amount of undeveloped New Energy technology, bringing the costs of artificial photosynthesis down will require still newer breakthroughs. Nocera is confident science and engineering are up to the task. He welcomes the Obama-led turn toward science, thinks the bulk of the multibillion dollar stimulus fund money earmarked for New Energy is being well-directed by the Department of Energy’s Advanced Research Projects Agency (ARPA-E) and wants a complimentary program to take new breakthroughs – like an artificial photosynthesis system – from experiment to the marketplace.

Bonus: Nocera's breakthrough catalyst transforms seawater, making hydrogen and oxygen but not chlorine. This unique feature suggests it may also be used someday as a distributed source of clean desalinated water.

The chemistry. (click to enlarge)

QUOTES
- Nocera: “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.”
- Nocera: “…[I]t 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…”