What power generation method is the best to sustain a hovering city?
The Technology
We're in the year 2250 on an Earth-like planet. All the space on the earth's surface has been used up by the population of 15 billion, so we're moving into the air. Cities, along with all the farming and other capabilities they need to thrive, are being built on hovering platforms.
The Situation
The construction project is almost complete. Wiring, services, roads, buildings, all have been put into place. There's just one thing left to go in: something on the end of the wires to squirt power juice down them. And nobody can decide what to use.
Supplies
This hovering city will come over another major city once approximately every six months. The city has batteries: total capacity 4GAh. At this point, cables and pipes are dropped, and supplies and power can be sent up to the city. After 24 hours, it disconnects again and moves on.
The Question
What power source is the best to plug into the end of the wires? It has to satisfy the following conditions:
- Sustain a city the size of London (7 million people) for 6 months at a time without refuelling.
- Can supply the city with a deficit of 4GAh over the six months; the deficit will be made up by the batteries.
- BONUS: Can keep the city hovering indefinitely.
I have tagged this hard-science because I am looking for a numerical comparison of power sources, since that is the only way I see to qualify a "best" power source to avoid this being too subjective.
1 answer
This is a supplement to @SF.'s answer just because.
Atmospheric electricity can be used to provide you some power, and technically could be done even without a space elevator.
In 'fine weather', the potential, aka 'voltage', increases with altitude at about 30 volts per foot (100 V/m), when climbing against the gradient of the electric field.[3] This electric field gradient continues up into the atmosphere to a point where the voltage reaches its maximum, in the neighborhood of 300,000 volts. This occurs at approximately 30"“50 km above the Earth's surface.
You could also put some capacitors and stuff to capture the lightning strikes that would be attracted by this giant structure too for a quick power boost.
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