Currently the "balanced" ratio for Solar is 21 Accumulators for 25 Solar Panels, although rated for 60kw, Solar Panels only actually get on average 42kw during a normal day cycle.
In theory, halving the Solar output from 60kw to 30kw on average would generate 21kw, meaning it would now take 50 Solar Panels to charge 21 Accumulators, effectively doubling the area required for Panels, making Solar still viable but less efficient in the long run.
I think that strikes a good balance from some quick dirty math.
People will still eventually switch over to Nuclear, I've not played with a single person that hasn't torn down their Solar fields to put down Reactors so I don't think it's anything to worry about, people will still go through and experience your mod for what it is :)
Also don't forget your Solar Walls, having a wall that outputs 5kw and a Panel output 6kw when it's 3x bigger doesn't make a lot of sense to be honest, again just my opinion :)