Sunday, March 7, 2010

Wait, what?

I'm seeing stuff in the news about some research done by MIT (usually a pretty good bunch) which claims to use some combination of voodoo, a catalyst and some solar energy to crack water into hydrogen and oxygen. The numbers in their press release, as reported by Scientific American, are:
  • Energy input from a "five meters by six meters" photovoltaic array.
  • A time period of "less than four hours".
  • A total amount of stored hydrogen/oxygen fuel of "enough energy for the average American home", which he quotes as "30 kilowatt-hours". (Holy shit, the average American home uses 30 kWh/day?!)
OK, let's do the maths.
  • 5m x 6m = 30m^2 photovoltaic array, at the peak commercially available efficiency of 20%, at peak solar power density of roughly 1kW/m^2, that's 6kW of solar panels.
  • 6kW over four hours gives 24kWh of electrical energy from the sunlight.
He claims to generate enough hydrogen/oxygen fuel to generate 30kWh, with an input of 24kWh of electricity. Now, even assuming that the electrolysis process is 100% efficient, one of two things MUST be true:
  1. The 'catalyst' that he's developed is consumed in the process and it costs more than 6kWh to produce the amount he's quoting, OR
  2. The second law of thermodynamics "doesn't apply because this is chemistry not physics." If anyone uses this argument I will personally punch them in the nipples.
My initial reaction to this claim was "thou shalt not suffer a witch to live", but instead I'm going to err on the side of assuming the reporting article is wrong and it actually says "enough energy for the average American home in conjunction with changes to make the home more efficient" or something, which could easily mean that they're generating 10-15kWh of fuel from the 24kWh of solar energy, which is an attainable target if you accept the existence of a fancy new catalyst.

Still, however impossible the initial claims, efficient storage of solar energy in the form of hydrogen is one piece of the puzzle for long-term renewable small-scale solar baseline power. I'll be keeping my eye on this one.