Solar power's efficiency is advancing at a steady rate, and with improvement such as concentrated cells and novel materials the question is not so much if solar can be cheaper than coal power someday, but rather when. However, when this scenario does eventually arise, solar faces some remaining challenges, the most significant of which is the intermittent nature of the power source.
In short, without something to store solar power efficiently, it’s infeasible as a primary electric power source.
Batteries and ultracapacitors are frequently discussed as possible means of solar power storage, but they are very expensive. Other novel storage methods have also been explored, but they seem uncertain prospects at best. Some scientists point out that there is already a system that takes solar power and stores it -- photosynthesis in plants.
When it comes to imitating nature's hydrogen producing system (remember, sugar is only the secondary product of photosynthesis, driven by the production of the primary product -- hydrogen ions -- from using sunlight's energy to split water), many scientists have tried. However, the electrocatalysts needed to split water into hydrogen and oxygen are typically even more pricey than batteries. However, one MIT professor has discovered a possible alternative using cheap materials that he says may help keep the dream of solar power (and solar storage) alive.
Daniel Nocera PhD, a professor of chemistry at MIT, devised a catalyst system using strips of cobalt, nickel, and phosphate, all relatively inexpensive chemical compounds. By eschewing expensive catalysts like platinum, the cost of the system is kept low. So why didn't others think of this efficient system? Well, he says that it is commonly known that cobalt dissolves relatively easy in water, making it typically a poor electrode material, and typically earning it a quick dismissal. To remedy this, Professor Nocera chose a somewhat creative approach, instead adding dissolved cobalt directly to the solvent and relying on a thin cobalt film which formed on the electrode.
The success of the result surprised even its creator. He describes, "Here's the luck. There was no reason for us to expect that just plain cobalt with phosphate, versus cobalt being tied up in one of our complexes, would work this well. I couldn't have predicted it. The stuff that was falling out of the compounds turned out to be what we needed."
Now he is looking to improve upon his lucky break. He states, "Now we want to understand it. I want to know why the hell cobalt in this thin film is so active. I may be able to improve it or use a different metal that's better."
However, he also wants to move towards a production system. He states, confidently, "We were really interested in the basic science. Can we make a catalyst that works efficiently under the conditions of photosynthesis? The answer now is yes, we can do that. Now we've really got to get to the technology of designing a cell. "
Some are skeptical about Professor Nocera's big claims. They say that his system is cheap and promising in some respects, but that he is overstating its potential for commercial scale hydrogen production. By an important metric, the peak efficiency current density (the higher this number, the faster the rate of hydrolysis), his best reported result of 10 milliamps per square centimeter is only a hundredth of the current commercial electrolyzer rate of 1000 milliamps per square centimeter.
Even one of his teachers is taking issue to Professor Nocera's alleged hyperbole; Thomas Meyer, who has been a mentor to Nocera, states, "The claim that this is the answer for artificial photosynthesis is crazy. [This] could prove technologically important [as a] research finding, [but] there's no guarantee that it can be scaled up or even made practical."
John Turner, a research fellow at the National Renewable Energy Laboratory in Golden, CO, adds, "At least what he's published so far would never work for a commercial electrolyzer, where the current density is 800 times to 2,000 times greater."
While some say he is wasting his time and should refocus on batteries, Professor Nocera continues his research and his big talk. He's teaming up with Professor Michael Grätzel of the École Polytechnique Fédérale in Lausanne, Switzerland to make a full solar cell and catalyst system which produces hydrogen. Professor Grätzel invented a unique dye that gives off electrons when exposed to sunlight. Professor Nocera hopes to merge the two inventions to create an artificial, fuel-generating leaf, what he sees as the future of electric power generation.
One thing's for sure -- Professor Nocera's work and rhetoric will likely continue to draw rebukes from colleagues, but it’s hard to argue the temptation of emulating nature's most successful energy fixing design and storing power by a simple equation -- "sun + water = fuel".