Reduces solar panel production from 60 kW to 9 kW. (Note that this change dates back to when I played earlier, unpublished versions of this mod in 1.1. I haven't gotten to space yet, so if this makes early platforms unplayable I may change it.)

Solar is quite strong in space: https://wiki.factorio.com/Solar_panel

I was able to adapt my first ship to function in orbit of Fulgora via the usage of efficiency modules over speed modules plus a few extra panels, so reducing a panel to 20 or 30kW is probably playable enough. When reducing to 9kW, I think designing functional ships should still be possible, but due to the way the game calculates weight the extra size will make ships a lot heavier and thus slower. Yes, another area the game is horribly balanced (of course, contents of the cargo bay have no effect on space platform weight).

The other obvious effect is that making an early transition from coal power to solar power sounds totally unrealistic at only 9kW per panel. More realistic though.

Well, it's consistent with how train weight works, I suppose.

My first thought was to make a kind of Space Solar Panel with the original power density, which takes 5 times as many green circuits and uses low-density structure instead of steel and can only be deployed in 0 g, which is explained by having the graphics being a fold-out panel with 5 times more area. Problems being that I would have to 1) make graphics for this, and 2) make those graphics not be super annoying for how it would at least somewhat block things behind it. But, it would let me have it both ways.

As to balance with coal, I've played 1.1 games with these 9 kW solar panels before and have actually found it perfectly possible to transition off of coal with them, tho this may be easier for me just because I tend towards a more land-grabby play style. And when I do build lots of solar I like the aesthetic of sprawling fields consuming the landscape. It's the equal but opposite aesthetic of extremely power and energy dense nuclear plants. The problem then becomes not quickly transitioning to nuclear, but that's what the cores option is for.

space platform weight is mostly negligible
what slows down platforms the most is drag, something which that wiki page strangely omitted, nor is it mentioned anywhere in game (or at least i haven't been able to find it)
just try it out now, add 1x1 tiles to your ship one by one horizontally and watch its impact on speed, it's like tying parachutes to a bird