It depends on what you mean by fossil fuels. With solar and wind you absolutely need gas peaker plants to come online quickly and provide power during downtime

It depends on what you mean by fossil fuels. With solar and wind you absolutely need gas peaker plants to come online quickly and provide power during downtime so that’s not going away anytime soon. Batteries may offer some replacement but we’re not there yet. Pumped hydro is probably the best bet if governments can work out the issues with it and start getting it right.