LOL! That's not how electricity works. Maybe think of it a little like investing in rain (once lots of renewables are on the grid). You need water so you invest to make it rain but sometimes it floods. So you also give away water for free or even pay people to take water to reduce the flood if there's too much.
If you use electricity when there is too much wind or solar on the grid it can be free or even have a negative price. Market forces
This is completely independent of any 'ROI'. The cost of building the wind or solar is recovered because the other ~90% of the time the cost is higher. Fortunately for EV owners is pretty easy to charge in that 10% window
And... that's not really 'math' so much as just informing you of something that occurs. Much like I'm trying to inform you that not just the top 1% are buying Model 3s. People making $40k/yr DO own model 3s and the cost of electricity DOES go negative sometimes. Those are just 'facts' like a TDI runs on diesel.