I don’t assume that, and I won’t argue for an entirely free market. I also agree with your observation that accumulation happens, however we might have different views on how long that actually takes. Atm the shift to renewables is disrupting the accumulation we already have in the energy sector, because it requires very little capital to build your own little solar powerplant compared to a fossil or nuclear powerplant (or large hydro, btw.). Same thing for battery storage units. So with renewables, there’s more potential for competition.

That might change again in the future through continued accumulation and shitty policies, but my point is: as long as we don’t have either monopolies or cartels and thusly competition in the market still exists, even large corporations can’t simply dictate prices to increase their margins.

They can’t, if you have a functioning market economy. There should be competition and renewables, due to their more decentralized nature even incite competition.