To build about a billion O'Neil Cylinders, which is about the number you'd need for a full Dyson Swarm around our Sun, would consume (IIRC) 1% of Mercury's mass.

Lets assume the Dyson swarm would be built at 1 AU or 149,597,870,700 m ~= 150e9 m from the Sun.

Lets assume energy converting photovoltaics will be made of non-crystalline materials with a high light absorption coefficient allowing solar cell thickness of ~100 nm = 100e-9 m.

Sphere surface is 4pir^2, in our case 43.14150e9^2 = 3e23 m2 * 100e-9 m = 3e16 m3 is the total volume occupied by a Dyson swarm tech.

For comparison the volume of matter that Earth contains is 1e21 m3, which is 1e21/3e16 ~= 1e5 = 100,000 times larger than what is required for a Dyson swarm.

Which begs the question, how do you obtain sufficient energy to go scouting for material beyond the solar system in order to construct something that encircles the sun…

You figure out how to put a fusion reactor on a spaceship without melting the whole thing into a blob of metal and use a particle accelerator as a super high isp engine.

Sci-fi but mostly in the ’not melting down’ part.

Could you elaborate this? Is the melting because you suddenly have lot of energy and no way for cooling?

Yeah you need to work very hard to lose heat without losing mass in space. Basically you can only radiate it away, which is slow; there are ways of concentrating heat in one spot so it is radiated more efficiently, but that’s where you get to the melting part.

Consuming Mercury would give you a 2x car sheet metal thick full dyson sphere made of iron.

Earth, Mars and Venus each have about 10x the iron of Mercury. The asteroid belt is inconsequential.

If you consume all the iron core planets, you have about 5 cubic centimeter of iron to play with for each square centimeter of dyson sphere area.

There's a lot of unknowns for the gas giants, particularly what % of them contains iron, but Jupiter /might/ have as much as 100x earth heavy elements (including iron), but these would be at its core, and its not totally clear how you would extract them.

I think the key question is what sort of stresses you expect the sphere to be under, and thereby what materials and tensile strengths are required. It would not surprise me if the stress is basically nil (in theory you could orbit a sphere made of iron dust?) or totally infeasible for iron.

I don’t think proportion of mass is relevant here. An apple peel is maybe 3% of the mass of an apple, and a Dyson sphere would be a proportionally much thinner “skin” around a star than an apple peel.