Hurricane Ike has given us a massive object lesson on the importance of implementing the late Rick Smalley’s vision of the Store-Gen Grid (SGG; graphic courtesy Wade Adams at Rice’s Smalley Institute) – a highly distributed network of granular electric production and storage. One of the elements of the SGG concept is a household storage unit for about 100 kW-hrs of dispatch energy.
Well, we ain’t there yet. Of all the standard infrastructure services, only two seem to be reliable in a pinch: cell phones and natural gas. The electric grid is plainly extremely fragile. This is a major opportunity for nanotechnology. With a major power outage in the energy capital of the world, this topic ought to get *lot* more traction, and fast. So get your thinking caps on. According to the Houston Chronicle, nearly 3 million people lost power due to the storm. So I reckon there are about 3 million ready customers for the next big thing in distributed power. I’m one of them!
Now, when considering storage technologies, energy density *really* matters! Among practical materials, nothing is even comes close to gasoline or diesel fuel. Just before the storm, my wife was wise enough to ignore my objections and bought a neat little Honda 2kW generator. I got ten gallons of gas on Friday, and used about five gallons over a 36 hour period. This was just enough to keep the refrigerator going, charge cell phones, and run a lamp, two fans and a small TV set. This enabled us to essentially camp-out in our house. Forget about air conditioning, running the washer/dryer or taking a hot shower (the darned water heater has an electric starter).
Here are some representative (volumetric) storage energy densities (from Wikipedia):
|
Technology or Material |
Energy Density ( MJ / liter ) |
|
Capacitor Ultracapacitor |
~ 0.050 |
|
Lead acid battery |
~ 0.15 |
|
Flywheel |
~ 0.50 |
|
Lithium ion battery |
~ 1.50 |
|
Hydrogen Fuel Cell |
~ 1.62 |
|
Li Ion w/ nanowires |
~ 2.60 |
|
Ethanol |
~ 24.0 |
|
Gasoline |
~ 34.6 |
Let’s look at the Lead-Acid Battery (LAB) as an example, since it’s still the workhorse for storing electric energy. My five gallons of gas would equate to 4,383 liters of lead-acid batteries (LABs) (3.8*5*34.6/0.15). My total investment for generation and storage was $1020 ($1000 generator, $20 gas). How much does 4.3 cubic meters of LABs cost again? - about $20-$50/liter? And how much does it weigh? I can (and did) carry (lug) the generator and the five gallons of gas myself at the same time.
Overall, electrical storage energy density is worse than chemical storage a good factor of ten or more. An order of magnitude (or two) is nothing to sneeze at! It is plain that without sufficient oil/gasoline/diesel, we are in a world of hurt for the foreseeable future.
Each of the technologies listed above employs, or can be improved with, nanotechnology or nanostructured materials. Let’s do a little math and get a handle on the nano-scale challenge involved here. If gasoline has an energy density of, say, 35 MJ/l, it equivalently contains about 3.5 x 10-17 Joules per cubic nanometer. Modeling this as a parallel plate capacitor in vacuum with a 1 nm gap, you get the target energy density with a voltage difference of about 2.8 Volts. If you use a decent dielectric like TiO2 (k = 40ε0) instead of vacuum, you only need 0.44 V. About 1 V/nm is a pretty stiff electric field, but not larger than those considered routine for ultra-thin gates in the semiconductor industry. This all seems pretty doable; making the nanowire connections to the outside world will be the tricky part; it’s probably a job for carbon nanotubes or maybe graphene. Rick would have liked that.
I hope somebody out there gets to work on this pronto! Even at $100 / liter, it would be a useful technology. When you get the cost down to about $10 / liter, you’ll be a bona fide hero, and a very wealthy one at that.






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