I'm not sure why you'd discuss this without mentioning the section of the linked article which addresses exactly this issue (maintaining a stable grid with 100%

I'm not sure why you'd discuss this without mentioning the section of the linked article which addresses exactly this issue (maintaining a stable grid with 100% renewables, and current levels of hydroelectric power): > Here, we do not model the reliability of an optimized future California grid but discuss a recent optimization study in which 100% WWS in the California grid was modeled for two years. Hart and Jacobson[30] used a stochastic optimization model of system operation combined with a deterministic renewable portfolio planning module to simulate the impact of a 100% WWS penetration for California every hour of 2005 and 2006. They assumed near-current hydroelectric and geothermal but increased geographically-dispersed time-dependent wind, solar PV, and CSP with 3-h storage. They constrained the system to a loss of load of no more than 1 day in 10 years and used both meteorological and load forecasts to reduce reserve requirements. They found that, under these conditions, 99.8% of delivered electricity could be produced carbon-free with WWS during 2005/2006 > The result of Hart and Jacobson[30] suggests that, for California, a large part of the intermittency problem of wind and solar can be addressed not only by combining the two, but also by using hydroelectric and CSP with 3-h storage to fill in gaps. The remaining differences between supply and demand can likely be addressed with the inclusion of demand-response management; energy efficiency measures, CSP with storage longer than 3 h, additional pumped hydroelectric storage, distributed or large-scale battery storage, compressed-air storage, flywheels, seasonal heat storage in soil, out-of-state WWS resources, the addition of flexible loads such as electric vehicles, vehicle-to-grid methods, and oversizing the number of WWS generators to simplify matching power demand with supply while using excess electricity for district heat or hydrogen production. If you want to refute this, you need to start with Hart and Jacobsen, and work from there.