Dyson sphere construction

Question

Often in science fiction, writers attribute the enormous energy capability of an advanced civilization to Dyson spheres. I've never heard of a detailed schematic of how the energy from the star is utilized. My question is "What is the most energy absorbant form of a Dyson sphere?" Would lining the inside with solar panels be the best option? What about a water heat transfer? Also, what would the most cost-efficient way of transporting this energy be? Long wires? Microwave electricity (Look it up. It's awesome.)?

Answer 1

Nothing will be 100% efficient.

It will certainly be solar panels, if the end product is electricity. Using carrier multiplication and radiative recombination the maximum theoretical conversion from sunlight to electricity is 86%.

At least we can do better than nature. Plants, through photosynthesis, max out at 11% for our solar spectrum.

Depending on the output energy type, other technologies might be used to cut out the photoelectric effect middle-man. But 86% is pretty good and it might just be simpler to use the gathered electricity to generate the other energy types.

Answer 2

Yes, I think our best option to capture the sun energy will be solar panels.

In his book "The High Frontier: Human Colonies in Space," Gerard K. O'Neill mentions some alternatives like mirrors combined with different gases; but our current solar technologies have become a lot more efficient and cheaper during these years.

Also don't forget that solar panels are a lot more efficient in space, because the almost continue exposure to sun and inexistant clouds or atmosphere.

As for the transmission of energy, we could use microwaves or laser rays, both of them transfer the energy in highly efficient ways.

Don't think that the idea of building a Dyson's sphere is too far away in the future, how hard could it be to build several small satellites exclusively to collect solar energy? Also if we already have space stations in our time, what could we do in the future with asteroid mining or moon mining?

I even think that we will start building satellites to collect sun energy and with time also space stations (eventually space cities) and this complexes will evolve in huge orbital hives that eventually will become our fabled Dyson sphere.

Answer 3

All of the energy of the sun is contained within the Sphere. If the wall was too good an insulator the insides would eventually cook. You could use the temperature difference between the inside and outside to generate power.

In addition, unless you enjoy constant sunlight, you would need something to provide shadows for 50% of the time. Either mirrors to direct the sunlight to a solar furnace or solar cells to collect it directly could be used. Assuming that's 50% of the suns output gathered at any one time... that would be quite a lot of energy.

I would think it getting too hot (too much energy) within the sphere would be the greatest problem.

Answer 4

I have to disagree with majority on the solar panels. It is almost impossible (not quite since we are assuming superscience anyway) to build a solar panel that absorbs the entire spectrum output by the star efficiently. Solar panels also do not absorb the energy of the solar wind and are in fact damaged by it which would require significant energy to be spent on maintenance. You also need to consider the energy needed for manufacture and technology that requires precise patterns of specific materials can't be that efficient if the scale is large enough you need to worry about material supplies.

Instead build an inner shell that receives the energy that the star puts out and is heated to thousand degrees or so. The material or structure is not sensitive, but higher the temperature your alloy or ceramic can sustain, higher the efficiency. And the structure should be robust enough not to need constant maintenance and conduct heat relatively well.

Then build an outer shell radiator that probably also needs decent thermal conductivity and reasonable robustness (should be able to survive impacts from micrometeors left over from construction).

Then put insulation (mostly vacuum and some reflective surface) and a heat engine in between the two shells. The heat engine will maintain a stable and high temperature differential and generate energy from it.

You also need a system to stop the sphere from colliding with the star. I think a system of light sails you can spread over the inner surface to use the light pressure to move the sphere would be sufficient. The energy loss is minimal since the reflected photons will simply go heat the surface of the star or some other part of the sphere. And this requires no propellant. Besides you need some system to shut down sections of the sphere for repairs anyway.