Energy storage, whether in the form of fossil fuels or chemical batteries is a major element in the design of any power production system. Batteries, unlike fossil fuels, can be recharged with new energy. They must, however, store the energy chemically and there is a limit as to how quickly they can release the stored energy and regain it.
Now new technologies are being developed that may revolutionise energy storage, able to release huge amounts of energy over a very short time, and able to be recharged swiftly.
The key properties to consider with energy storage, is the total amount of energy that can be stored, and the maximum power that can be released.
Associated with the storage of energy is also the ability to "reclaim" energy - with regenerative braking for example. Reclaimed energy can then be given out again - potentially dramatically improving the metrics.
The main advantage of fossil fuels is their energy density. The amount of power than can be released is determined by the technology used to ignite the fuel. Larger amounts of fuel can be ignited to create larger explosions.
A capacitor's charge increases in proportion to its plate area and also inversely proportional to the plate separation. Since there is a limit to the insulation properties of the film used to separate the plates, large charges can only be stored by large capacitors.
An ultracapacitor uses advanced materials that both reduce the mass of the plates, and reduce the separation distance between them. This results in orders of magnitude increases in the amount of charge able to be stored when compared with a conventional capacitor.
As these advances continue to the molecular level, the possibility of huge increases in energy densities exist.
Since ultracapacitors can be recharged very quickly, the possibility of the 2 second fillup at an energy station is very real. Furthermore, since they can be recharged easily, they will be able to maximise reclaimed energy from breaking very efficiently.
A hydrid car engine might have a small diesel running at a constant 500rpm, trickle charging an ultracapacitor energy source supplying an electric motor - makes sense to me anyhow.
New technology flywheels currently being tested in laboratories promise huge increases in energy density.
Flywheels have been used for sometime in both the power industry and also in various urban transport schemes.
This seems a pretty whacky idea, but just last year a car powered by compressed air was demonstrated. The inventor is Guy Negre who used to design formula one cars.
Interestingly, the reclaimed energy from braking in urban transport results in a longer range in urban driving than on a motorway.
The big problem though is sufficient energy density, limiting the range of the car to around 100 miles.
Negre seems constrained by his determination to provide a completely air powered vehicle, while a hybrid design with a clean low-powered diesel to top-up the compressed air would seem a better bet for now.
After conducting some research I've come up with these figures with regard to energy density.
| Energy Source | Energy Density (KJ/kg) | Power Density |
| Diesel | 50,000 | N/A |
| Petrol | 47,200 | N/A |
| Flywheel | 64,800 | ?? |
| Lead Acid Battery | 79.2 | ?? |
| Mag. hydride Battery | 8,270 | ?? |
| Zinc Aluminium Air Battery | 720 | ?? |
| Super Power Accumulators | 72 | ?? |
| Ultracapacitor | 216 | ?? |
| Compressed Air | ?? | ?? |
As you can see, there is still a bit more research to be done determine the power density for each of the technologies.
But the new high tech flywheels look pretty good, I hadn't realised that energy density was so good. One source indicated that:
A flywheel the size of a coffee pot could store 50Kwh of energy, and release it at a rate of 10Kw, for domestic energy consumption.
In my search for data I was reminded of Richard Feynman's frustration that science cannot even settle on a single unit of energy. The use of Watts, Joules and Calories is a huge source of confusion in what could otherwise be a unifying theme.