Handbook of Energy Storage for Transmission or ... - W2agz.com

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The value of storage in mitigating the effects of wind turbulence is therefore defined by
the value of spilled energy, set by the power purchase contract or wholesale market prices
in effect at the time.
As for dispatchability, storage can absorb wind energy produced during off-peak periods
(rather than deliver it to the grid) and later discharge this energy during on-peak periods.
The value of this service is determined by the turnaround efficiency of the BESS and the
contract or market prices for on-peak and off-peak periods.
Control/Dispatch Strategy
To mitigate the effects of power fluctuations from windplants, the VRB would charge
and discharge in response to real-time load measurements at the point of utility
interconnection. During power surges the VRB would charge, and during sags it would
discharge, damping the power fluctuations and allowing the windplant to operate at full
power. The VRB could be dispatched by the grid operator or energy supplier during peak
periods.
The stability function would be invoked as necessary during the turbulent wind
conditions. Dispatching would be invoked during the system peaks, on a daily basis over
several weeks per year.
The energy to perform both of these functions would be allocated in the control system.
Through simple energy accounting, the energy margins to charge and discharge during
power fluctuations would never be compromised by the peaking function.
Prospects for Success
The VRB meets the cycle life and storage capacity requirements for this application. One
study [Norris, 2002] estimated that the energy discharged by a 1.5 MW / 1.5 MWh flow
battery to stabilize a 20 MW windplant would be only 28 MWh per year, equivalent to 19
complete charge-discharge cycles 3 , well within the capability of the VRB. The energy
storage specifications (MWh) of the VRB would be optimized to meet specific project
objectives.
Again, it will be important to validate VRB reliability in the field. For the VRB to
qualify as “firm capacity”, for example, it may be necessary to prove a level of reliability
equivalent to other generating sources.
3 An additional 150 MWh were used to provide load shifting, totaling 119 equivalent cycles per year.
However, the optimal load shifting operation for the VRB may be different based upon stack life and
capital cost. In this application, windplant stability provides significantly more revenue than load shifting,
so the cycling requirements are primarily determined from the stability application.
Vanadium Redox Battery 26