> steam based thermodynamic cycles

Technical question: my understanding is that the frequency of an electrical grid is literally related to the RPM of turbines providing power, and that over/under frequency are related to supply and demand.

https://www.brighthubengineering.com/power-plants/45640-grid...

If we hypothetically had a grid that was 100% solar, presumably there'd no longer be any spinning turbines. At that point, would the grid frequency be completely synthetic? How would supply/demand impact the frequency in that case?

Edit: partially answered here ("smart inverters):

https://www.energy.gov/eere/solar/solar-integration-inverter...