MISO Energy Storage Study Phase 1 Report - Utility Wind ...

THE MISO PLANNING ENVIRONMENT
reserves in the day ahead and real time markets in addition to bidding resources for energy
dispatch. In MISO day ahead and real time energy markets, prices are cleared at the intersection
of supply and demand based on the marginal cost for the last generation unit required. In the
same way, ASM’s clear prices at a zonal or system wide level based on reliability and
contingency requirements in each zone. By making ancillary services subject to market forces,
MISO encourages market participants to provide adequate services to ensure reliability in a cost
effective manner. Operations planning timeframes dictate the resources needed (see Figure 2-2).
The following ancillary services are observed in MISO:
• Regulation: automated second by second system balancing
• Frequency Regulation: maintains the power system frequency within a predetermined
range. This service requires the unit to be very flexible at short notice. Ranges from
inertial response that may be 1-2 seconds following a frequency disturbance, to primary
frequency response (5-10 seconds) and regulation (10 seconds to several minutes).
Mostly implemented by automated generator control (AGC).
• VAR (Volts-Amp-Reactive): maintains the electrical transmission system power factor
at a level close to 1.0, reducing losses.
• Contingency: energy supply available at short notice to meet unexpected system changes
• Spinning reserve: provides contingency generation that can be switched into use
immediately in order to respond to a system outage or sudden power loss. Spinning
reserves are designated synchronous if they are in sync with the transmission system (and
can be called upon more quickly) or non-synchronous. Sufficient reserves are required to
counter an “N-1” contingency meaning the largest expected unit outage from a system
failure. Supplemental spinning reserves are 10-minute start – meaning that they can be
dispatched in 10 minutes.
• Ramping: provides rapid ramping power (up ramp and down ramp) when demand
increases or decreases at a high rate (minutes to hours). Ramping is also referred to as
load following (see Figure 2-2). It is typically used during the shoulder hours either side
of the peak daily load. The MISO tariff does not fully recognize ramping resource value
although a separate MISO study group is analyzing the issue.
Ancillary services are an important component in estimating the benefits that energy storage
provides. Because energy storage can be switched on and off quickly, it is an attractive resource
for contingency and regulation. Where storage technology is less flexible, (e.g. when a pumped
storage system changes from pumping mode to storage mode it may take several minutes to
respond), then ancillary benefits are lower. For storage technologies such as batteries that only
have short-term power, the current cost is hard to justify without including ancillary benefits.
One ancillary service that energy storage could potentially provide in MISO is ramping. A
separate MISO study is reviewing the existing ramp resource Tariff treatment and this initiative
is explained in more detail in Chapter 4. RPS mandated variable generation and coal plant
retirement because of EPA regulation increase the ramping requirements on natural gas fired
generation. The result is that CC and CT units will be cycled more frequently than they were
designed to be. As a result, there is good potential benefit in using energy storage for ramp
services to reduce this cycling.
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