The Oil Drum v/JoulesBurn ser på EEstor i Who Killed the Electric Gas Tank?
A few months from now, or perhaps 5-10 years from now, we will know whether or not EEStor can make good on its promise to sell a electrical storage device capable of propelling a reasonably-sized automobile down a freeway for a couple hundred miles before needing a recharge. There are some indications that they are making progress and that this could happen, but there are many reasons to remain skeptical.
Har ikke fordøyd helt ennå (og må sove), men ble minnet på The limits of energy storage technology (Kurt Zenz House i Bulletin of the Atomic Scientists) som gir en veldig god, kort og konsis oversikt over situasjonen:
1 kilogram of crude oil contains nearly 50 mega-joules of chemical potential energy, which is enough to lift 1 metric ton to a height of around 5,000 meters. Furthermore, crude oil happens to be liquid at Earth's surface conditions, making it easy to store, transport, and convert.
The energy densities of natural gas and coal, around 55 mega-joules per kilogram and 20-35 mega-joules per kilogram respectively, are similar to those of crude oil. [...] Biofuels such as ethanol and biosynthetic diesel can have volume and mass energy densities equal to that of fossil carbon, but since they're regularly harvested, their areal energy densities are substantially lower.
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Today's lead acid batteries can store about 0.1 mega-joules per kilogram, or about 500 times less than crude oil. Those batteries, of course, could be improved, but any battery based on the standard lead-oxide/sulfuric acid chemistry is limited by foundational thermodynamics to less than 0.7 mega-joules per kilogram.
Due to the theoretical limits of lead-acid batteries, there has been serious work on other approaches such as lithium-ion batteries, which usually involve the oxidation and reduction of carbon and a transition metal such as cobalt. These batteries have already improved upon the energy density of lead-acid batteries by a factor of about 6 to around 0.5 mega-joules per kilogram--a great improvement. But as currently designed, they have a theoretical energy density limit of about 2 mega-joules per kilogram. And if research regarding the substitution of silicon for carbon in the anodes is realized in a practical way, then the theoretical limit on lithium-ion batteries might break 3 mega-joules per kilogram. Therefore, the maximum theoretical potential of advanced lithium-ion batteries that haven't been demonstrated to work yet is still only about 6 percent of crude oil!
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And given other required materials such as electrolytes, separators, current collectors, and packaging, we're unlikely to improve the energy density by more than about a factor of 2 within about 20 years. This means hydrocarbons--including both fossil carbon and biofuels--are still a factor of 10 better than the physical upper bound, and they're likely to be 25 times better than lithium batteries will ever be.
What about storing energy in electric fields (i.e., capacitors) or magnetic fields (i.e., superconductors)? While the best capacitors today store 20 times less energy than an equal mass of lithium-ion batteries, one company, EEstor, claims a new capacitor capable of 1 mega-joule per kilogram. Whether or not this claim proves valid, it's within about a factor of 2 of the physical limit based on the bandgap of the dielectric material. Electromagnets of high-temperature superconductors could in theory reach about 4 mega-joules per liter similar to our theoretical batteries given a reasonable density; existing magnetic energy storage systems top out around 0.01 mega-joules per kilogram, about equal to existing capacitors. Here again, both the realized technology and its ultimate physical potential are far behind the energy density of common hydrocarbon fuels.
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There is one more energy-storage approach that theoretically beats hydrocarbons. Energy density comparable to lithium-ion batteries has been demonstrated with flywheels, and a theoretical device composed solely of toroidal carbon nanotubes could reach 100 mega-joules per kilogram. But the fabrication and safety challenges inherent in such a device render it unlikely that even a small fraction of this potential will ever be realized.
The bottom line is that nature has given us hydrocarbons in the form of fossil carbon and biomass, and their energy-mass and energy-volume densities are superior to the thermodynamic limits of nearly all conceivable alternatives. Thus, it's quite likely that hydrocarbons of one form or another will be humanity's primary energy storage medium for quite a long time.
Ja, der har vi løsningen, dere: noen fantasillioner roterende nano-karbon-kringler i en liten eske. Så enkelt er det!
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