Monday, April 17, 2006

SPV-Nuc smackdown

Photovoltaic electrical power generation is not increased by filtering for multiple wavelengths so as to "yield many times the output current of the most sophisticated cells now available". If you look back to your solid state and semiconductor physics you'll remember that holes (electrons) in the n dopant are kicked loose by photons and attracted towards the p dopant causing current. But the energy required to kick loose the electron(s) is a quantum or multiple thereof.

Photons in the lower wavelengths simply don't have the energy (the photoelectric effect is what Einstein got his Nobel prize for), and most wavelengths in the upper bands are not the right frequency. The action requires a specific frequency or multiple thereof. Anything else doesn't qualify. So you can DQ anything below (about) yellow - which means yellow, orange, red and lower (near-IR and IR).

Wavelengths in the green, blue, violet and soft UV are next, and they do the job of sufficiently energizing electrons to allow them to migrate from n to p. Wavelengths shorter and harder than that, the mid- to hard- UV, are blocked by atmospheric absorption so don't even reach the cells. Thus your input is limited to the range of green to soft UV in the mid-500 nanometers to just shorter than 400 nm.

But keep in mind that the wavelengths have to be a multiple of the quantum required. Not just any old photon will do, there has to be a je ne sais quoi between the photon (doing the courting) and the electron (being receptive). If the photon doesn't have the juice then the electron isn't gonna dance.*

Solar photovoltaic cannot and never will approach the power densities that nuclear can produce. In fact it will never even get close. SPV produces a few electron-volts (eV) per event, or a few volts per unit, and nuclear produces a few MeV per event, with a much higher event density, and a few megawatts per plant.

Furthermore, the best efficiencies achieved by the most exotic solar photovoltaic semiconductors are on the order of <20%, and the affordable substrates are about 10% efficient. It would require tens (if not hundreds) of square miles of PV to produce the electrical power that comes out of a nuc reactor. That land then becomes essentially useless for anything else. And the production required to make the cells would be staggering (include the dopants, steel, etc.)

Yes, more energy density can be produced by solar concentrated into thermal driving steam turbines, but these are still only millionths of the capability of nuclear. And neither photovoltaic nor thermal are worth much in the high northern or southern latitudes.

Nuclear waste is a real problem, but it can be dealt with well engineered solution, e.g. Yucca Mountain. (Storing rods in onsite ponds is not a safe or long term solution, btw.)

Nuclear power can be engineered well to be reliable and safe. Many countries do it, and most do it well. Burning petroleum to push millions of people back and forth in single-user vehicles with hundreds of horsepower per person is so ridiculous that words cannot describe. That petroleum they throw away into the atmosphere is too valuable as raw material for production of plastics, or as fuel for vehicles that truly need portable fuel (ships, planes and trucks).

Increasing energy efficiency - especially in building materials and buildings - is a valuable and necessary step, but only part of the solution in that they reduce the demand for new energy manufacturing plants. Bringing new energy plants to society is just as necessary as population grows and energy needs expand.

The reality is that the world has large energy needs in both existing societies (Western world) and emerging markets (China, India). Burning petroleum will heavily increase atmospheric CO2 (and CO and methane) loading and will accelerate global climate change in a manner that is orders of magnitude more damaging and dangerous to the planet (both civilization and nature) than the problem of nuclear waste disposal.

To close, I am deeply aware that the battle lines of this argument are drawn, and that most people on the "green" side are comparable to religious zealots in their commitment to solar and against nuclear. It is unfortunate that they cannot be realistic about both the challenges and the solutions. As we see, there are some (Patrick Moore, Stewart Brand, James Lovelock) who can see the alternatives and make a decision based on realistic alternatives, but there is simply no arguing with those for whom sheer belief is the only illuminating factor.