Silicon Microwires: A Powerful Lesson in Technology Strategy
As the world’s supplies of conventional energy sources run lower and the problems of greenhouse gas emissions have become better known, the business opportunities for alternative energy sources have skyrocketed.
The challenge with many of those opportunities, however, is that they often have significant environmental costs of their own that must be dealt with. As a well-known example, nuclear power, however clean it might be able to operate provided all safeguards are considered, still leaves a mass of nuclear waste to dispose of in the long term. As another example, the battery systems of hybrid cars may present toxic disposal problems at end of their lives — and become a costly accumulation as adoption rates for these kind of vehicles increase.
Though these examples are fairly obvious, one of the surprises to many who begin to investigate the full lifecycle issues with many so-called “green” or “low carbon footprint” technologies is how dirty some of those really are, especially as compared to the amount of energy they can provide.
As one recent study looking at alternative energy in the U.K. recently noted, if you consider full lifecycle carbon footprint implications (including all emissions from initial manufacturing and/or harvesting of raw materials all the way to eventual waste disposal), direction combustion of grass (for bioreactor energy) contributed almost 80 grams CO2 per kWh of energy eventually delivered. On the other end of the spectrum, Nuclear Energy produced only around 5 grams CO2 per kWh of energy.
Perhaps those numbers aren’t a surprise, but one that certainly will be to me is that current Photovoltaic Cell technology is actually fairly high in carbon footprint, with some 58 grams of CO2 produced per kWh of energy for installations based in the U.K. (The reference to the U.K. location is because total energy produced by solar cells is a function of how much sunlight is available for the cells to receive.) Comparatively, then, using a so-called “clean” solar cell produces almost 75% of the CO2 that burning grass in biomass reactors would produce.
Why are the Photovoltaic numbers so high? Because it takes a great deal of energy to produce solar cells in the first place. Once produced, the carbon emissions are lower, but the carbon footprint is already established and the damage is done.
To improve on this, many companies and research facilities have investigated the making of ultra thin film Photocell technology, which of course lowers both costs and overall carbon footprint. According to the Department of Energy, conventional single-crystal silicon cells produce approximately 10 X the energy required to produce them. Multicrystalline silicon can produce between 12 X and 16 X the energy required to produce them, depending on whether or not they are in a ribbon form.
Those are mportant steps forward, but perhaps one of the most exciting of recent strategic innovations in this field is the one recently announced by graduate student Michael Kelzenberg and other materials scientists at CalTech in the February 14th issue of Nature Materials. (See also the related Scientific American article about the same work.) Their system reforms silicon into vertical “microwires” of crystalline structures (shown in the attached picture here). These microwires, which also include embedded nanoparticles of aluminum oxide to reflect more light inside (and therefore increase the efficiency of the systems), capture as much as 85% of the available solar spectrum while requiring only around 1% of the silicon conventional wafers would need.
This is of course only an early result and will take some time before moving from the lab to production reality. It is, however, an example of how asking the right strategic question of precisely the right group of people can make the biggest possible business impact. We look forward to hearing how this breakthrough innovation develops over the next few years. It will likely make a major difference in all of our lives — and make this part of “Green Technology” even greener than ever before.