Power beaming
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Moving energy from one place to another through "empty space" (or air) is called "beaming". Beaming enough energy to run a machine (such as a vehicle) is called power beaming.
Ideally, a working system would also be able to transmit this energy in a way that would not cause harm to living organisms.
There are only 3 known ways to move (transmit) energy from one place to another:
- Fuel or batteries requires periodic refueling operations, or requires that all the energy ever required be transported with the machine.
- The power grid requires wires or some other solid connection from one place to another.
- Beaming does not require either.
Efficiency issues
Taking the theoretical example of transferring 50 MJ of energy from one place to another (see space elevator and space elevator economics): The base cost of payload transfer, given the current power grid rate of about US$0.11/KWh [1] (http://www.ornl.gov/info/press_releases/get_press_release.cfm?ReleaseNumber=mr20021220-00) = about US$0.03/MJ, is around US$1.74/kg. Factoring for transmission losses, assuming current laser efficiencies of 2%, solar cell efficiencies of 30%, and atmospheric losses of about 20%, this works out to about 0.5% overall efficiency, or $350/kg.
The most efficient power beaming system today is a laser beaming system with photovoltaic panels on the climber optimized to the wavelength of the laser. With the best (and most expensive) current usable technology, efficiency is around 0.5%. If climbers are to be disposable, the most expensive photoelectric panels may not be an option.
Losses due to atmospheric spreading can be reduced by the use of adaptive optics, or power beaming from outside the atmosphere, and losses due to absorption can be reduced by a properly chosen laser wavelength, although laser power beaming from the ground does not work though clouds.
Although laser and photovoltaic technologies have been rapidly advancing, it is unknown what transmission efficiency improvement is possible. Further optimization of photovoltaics, for example, typically rely on enhancing the absorption of particular wavelengths, which may not match up with the wavelengths of more efficient lasers. The most efficient lasers - laser diode arrays, which can surpass 50% efficiency - currently have poor coherence, and could not be used, leaving as available options standard chemical lasers with efficiencies of a few percent or less. Only the advent of high-coherence diode laser arrays or a similar technology would allow for notably improved power usage efficiency, as laser efficiency comprises most of the energy loss, and there is only a limited amount of improvement possible in photovoltaic panels.