Geothermal steam turbines cost more to build and operate, but may operate (mainly) at times when solar and wind don't. Hydro turbines are much cheaper to maintain than steam turbines, although dams are expensive to build. Both compete with turbines driven by NG, likewise operated mostly when the much cheaper solar and wind are not producing enough. As storage is built out, demand for geo and NG declines. Their marginal cost grows as the fraction of time they spend idle increases, because their turbine maintenance cost is not strongly dependent on actual usage.