The intermittent nature of generation is one of many reasons why "System Reliability Impact" needs to be considered. The N+1 and N+1+1 criteria should identify potential common mode failures. Mitigation can include things that improve distribution system integrity under stress or injection of power into the system at critical locations. The mitigation power storage could be at the generation point, but as long as the system model is satisfied, there is no reason why that is the only location acceptable.
Bath County Pumped Storage Station (
This station was built to take off peak power from conventional and nuclear plants and time shift it to peaking power.
[ul]
[li]maximum generation capacity of 3,003 MW[/li]
[li]an average of 2,772 MW,[/li]
[li]total storage capacity of 24,000 MWh (11.5 hours drawdown time)[/li]
[/ul]
I could not find the time to reverse power flow (pumping to generating), but it is known to be quite fast. Likely limited by the ability of the dynamic breaking system to absorb the generating system inertia.
PJM seems to treat the ability of a battery to smooth the power supply curve out as one of the aspects of the ancillary services market. The ability to respond serious system disturbances by making a fast start in respond to major loss of generation is another aspect of the ancillary market.
This paper "Technical Analysis of Pumped Storage and Integration with Wind Power in the Pacific Northwest, USACE Hydro Design Center Aug 2009 discusses some of the interactions between pumped hydro storage and integration of wind energy generation into a power system.
This is an interesting article describing the implementation of 100% Stator Ground Fault (SGF) protection (ANSI # 64S) at the Bath Pumped Hydro Station.
(I think this might be of interest due to the considerable amount of discussion related to generator protection that has occurred on this forum. ANSI 64S is relatively expensive but for a high value asset it becomes cheep insurance.)
My comments here are from the standpoint of professional engineer who is a power customer. It is not part of a field of engineering where I am likely to practice. In other-words I am a spectator to the technically challenging subject of integrating renuables into the North American Grid.
Fred