Editorial Comment

	Vol. 226 No. 10
PERRY A. FISCHER, EDITOR

Vile photons. I told a lie in this column last March. I did it intentionally – well, sort of. In a column about hydrogen, I said: “Solar cells that are optimized for direct disassociation of water are making progress, but an area equal to about half the state of Nevada is needed to make a real impact.” I knew I hadn’t calculated anything, and intuitively, it seemed wrong. But I also knew that it was the kind of flip statement that I might be able to get away with in our culture. Hopefully, someone would questioned it, then I could use it as a segue, confess my mistake and then write a column about solar energy. Unfortunately, no one did.

The reality is that the state of Nevada comprises 110,000 sq. mi (285,000 sq km). Even with luxurious solar panel or mirror spacing and using present-day efficiencies, half that much area would be capable of generating over five times as much electricity as the entire US produces every day. To generate 5% of US electricity demand, all that is needed is a square about 22 miles on each side. Dividing this area into numerous smaller pieces would ensure that not too much land – even if it’s just desert – is used in any one place, and that solar plants would be sited closer to where the power is needed.

While still generally more expensive than most other electricity generating systems, efficiencies continue to improve, while prices continue to plummet. Sandia National Laboratories says it will take about 20 – 25 years for the price of solar power to be competitive with conventional electrical methods. If recent events are any measure, the optimists at Sandia might even be too conservative.

Speaking of Sandia, the Lab is now in final testing (over 27,000 hrs) of a new prototype solar collector. Each unit is comprised of a 37-ft-high array of parabolic mirrors that track the sun. The concentrated sunlight powers a Stirling engine (that’s sort of an ordinary, internal combustion, piston-driven engine, only it’s external “combustion”) that uses hydrogen as the working fluid. It’s almost twice as efficient as other solar technologies. This technology just became commercial. The success of the six-dish prototype project, now operating at the New Mexico test facilities, convinced Southern California Edison to back the construction of a 4,500-acre (7-sq. mi), 500 MW solar farm in Southern California. When completed in 2008, it would be the world’s largest solar facility. This is enough power to run a quarter million homes. The 20-year agreement includes an option to expand the project to 850 MW. As this goes to press, another contract was signed with San Diego Gas & Electric to provide 300 to 900 MW over a 20-year period using the same Sterling technology.

The difference between peak and base electricity demand is a huge and growing problem. Solar has a natural relationship with peak electricity consumption in areas with high cooling costs, such as the southern and southwestern US. Other renewable energy forms, such as wind and waves, bear no such relationship. If viewed from a peak-power perspective, this Stirling technology is arguably already cost-effective (~10 cents/kWh).

The recent passage of the US energy bill could be a boost to solar power, as it contains language that, although with vagaries and wiggle room, requires state utilities to set up “smart” meters on residential and commercial buildings, in order to charge different rates depending on the time of day.

Another new method, also using mirrors to concentrate sunlight, is producing hydrogen in a relatively less expensive process. It was developed by scientists from Israel, Sweden, Switzerland and France, and was funded by the European Union and the Swiss government. The research used the largest solar research facility in the world (1 MW), located at the Weitzman Institute in Israel.

The new method uses a well-known process to produce pure zinc from zinc oxide by heating it. The researchers found that adding a small amount of carbon (from coal or biomass) lowered the required temperature to 1,200°C (2,200°F) instead of 3,200°F – well within the solar oven’s ability. Production of pure zinc reached an average of about 50 kg per hour during tests. Much larger amounts would simply be a matter of scale. Once pure zinc is obtained, it can be stored or transported as needed. The final step involves heating the zinc with water to a temperature of 350°C (662°F). This produces zinc oxide, with which the process can be repeated, and hydrogen gas as a byproduct. The researchers said the process is very efficient and relatively self-sustaining.

A more fundamental discovery comes from a team of researchers at the US DOE’s National Renewable Energy Laboratory (NREL). At present, photovoltaic solar cells convert, at most, one incoming photon of light into one electron of electricity, and the rest is lost as heat. The team found that tiny nanocrystals produce as many as three electrons from one high energy photon of sunlight. Theoretically, solar cells based on these nanocrystals could convert more than 65% of the sun’s energy into electricity, more than doubling the present day efficiency of solar cells.

The usual anti-solar drivel is that solar power presently only provides about 0.01% (or whatever the small amount); therefore, it couldn’t possibly replace coal and oil. First, it’s the growth rate and the rate of technological progress that are important, and both of these are very good. Second, it isn’t necessary to replace fossil fuels, merely supplement them. Projections in the 50 – 100 year range always arrive at very large, even scary numbers for total energy demand. How we can get the needed supply for this century and beyond is not known, but solar power will likely play a significant role.

Because solar resources are unequally distributed among nations, you will still have winners and losers, but despite the .01% figure, it wouldn’t surprise me if it comprised 5%, even 10% of world power supply within 50 years – an unheard of, even blasphemous, idea in some circles.

The mere mention of the words solar energy evokes ridicule and scorn in some folks. Why, is still a bit of a mystery to me, but one that I’ve grown used to. I surmise that the underlying reason is mixed up in culture and politics. This reaction can, I believe, ultimately be blamed on photons – those tiny little quantum particles that make up light. I now realize that photons are vile evil-doers, hell-bent on sending all of us to an early heaven, usurping our strength, our long-cherished traditions, indeed, our very way of life. After all, they cause skin cancer, don’t they?  

To find out why photons are evil, you’ll have to read my Exploration column.