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Load as a Resource

Spinning Reserve From Responsive Load

Responsive load is the most underutilized reliability resource available to the power system today. It is currently not used at all to provide spinning reserve. Historically there were good reasons for this, but recent technological advances in communications and controls have provided new capabilities and eliminated many of the old obstacles.

CERTS researchers at Oak Ridge National Laboratory are working with industry to demonstrate the enormous potential for provision of spinning reserves through advanced load control technologies. Air conditioning represents an especially promising end-use resource for providing spinning reserve because air conditioning is highly correlated with electric system peak demands and provision of spinning reserve is compatible with control of air conditioning through conventional demand response or load management programs.

The electric power system is unique in that it must match aggregate production and consumption instantaneously and continuously. The continuous random minute-to-minute fluctuations in load and uncontrolled generation are compensated for with regulating reserves. Frequency deviations are compensated for with frequency-responsive reserves, and the daily cycling of load through load following and generator dispatch. Sudden failures of generation and transmission are compensated for with three reserves: 10-minute spinning reserve, 10-minute non-synchronized reserve, and 30-minute operating reserve.

Figure 1. The electric power system is unique in that it must match aggregate production and consumption instantaneously and continuously. The continuous random minute-to-minute fluctuations in load and uncontrolled generation are compensated for with regulating reserves. Frequency deviations are compensated for with frequency-responsive reserves, and the daily cycling of load through load following and generator dispatch. Sudden failures of generation and transmission are compensated for with three reserves: 10-minute spinning reserve, 10-minute non-synchronized reserve, and 30-minute operating reserve.

Spinning reserve is called frequently, but for very short periods of time. Recent data from NYISO indicates spinning reserve was called 239 times in 2002 for periods of time rarely exceeding 10 minutes in duration.

Figure 2. Spinning reserve is called frequently, but for very short periods of time. Recent data from NYISO indicates spinning reserve was called 239 times in 2002 for periods of time rarely exceeding 10 minutes in duration.

The inherent thermal inertia associated with many end-uses, in this case air conditioning, means that these end-uses are especially well-suited to provision of spin because these end uses can be interrupted for brief periods need for spin, generally without consumers perceiving any diminution in the end use services they receive.

Figure 3. The inherent thermal inertia associated with many end-uses, in this case air conditioning, means that these end-uses are especially well-suited to provision of spin because these end uses can be interrupted for brief periods need for spin, generally without consumers perceiving any diminution in the end use services they receive.

Emerging smart thermostats are well-suited for enabling provision of spinning reserve through control of air conditioning units.

Figure 4. Emerging smart thermostats are well-suited for enabling provision of spinning reserve through control of air conditioning units.

The performance of these end-uses can, in fact, exceed the performance of an equivalent amount of generation providing spin since load can be dropped instantaneously (generation must ramp up more slowly to avoid damaging equipment). In addition, from a statistical point of view, the large numbers of end use devices means they ought to be inherently more reliable when called to provide spin than generation.

Contact:

Brendan Kirby
Oak Ridge National Laboratory
(865) 576-1768

http://certs.lbl.gov