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ISO Rules for Intermittent Generation. By Todd Ryan The RenewElec Workshop Oct 21 st 2010. Why rules for Intermittent Generation ?. Renewable generation is different than traditional generation in its variability and limited ability to be dispatched

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Iso rules for intermittent generation

ISO Rules for Intermittent Generation

By Todd Ryan

The RenewElec Workshop

Oct 21st 2010

Why rules for intermittent generation
Why rules for Intermittent Generation?

  • Renewable generation is different than traditional generation in its variability and limited ability to be dispatched

    • This creates issues in the operation and reliability of the markets

    • Rules need to be created to correct theses issues without unnecessarily discriminating against or towards a given technology

  • Making rules for intermittent generation allows the market to:

    • Accurately model resources to ensure reliable operation, dispatch, and pricing

    • Level the playing field when market rules unduly discriminate against types of technologies

Intermittent specific rules
Intermittent Specific Rules

  • ISOs must first define an asset category:

    • Examples: Intermittent Generation, Intermittent Power, Variable Energy Resources

  • Intermittent-specific rules exist in all areas of of the rules governing the operation of the markets

    • Interconnection

    • Energy Market

    • Ancillary Services Market

    • Capacity Market

Interconnection forecasting telemetry
Interconnection: Forecasting & Telemetry

  • Difference:

    • Intermittent generation is inherently variable

    • Scheduling intermittent generation solely based on economics would lead to non-optimal scheduling

  • Rule change:

    • Forecasting: Required to directly or indirectly subscribe to a forecasting service

    • Telemetry: Required to have sufficient metrological telemetry to provide to the forecasting service

Interconnect lvrt
Interconnect: LVRT

  • Difference:

    • Wind turbine’s dynamic response different than traditional generation’s response to line voltage drops

    • Can lead to cascading reliability issues when unregulated

  • Rules:

    • Wind plants need to stay online for 9 cycles during a line voltage fault

    • Must maintain a power factor between 0.95 leading and lagging

Energy market scheduling
Energy Market: Scheduling

  • Difference:

    • intermittent generation can are less ‘schedulable’ than traditional generation

  • Rule:

    • Intermittent resources can only be economically scheduled up to their forecasted value

    • This should limit them amount of time when out-of-merit generation is needed

Energy market dispatch
Energy Market: Dispatch

  • Difference:

    • Intermittent generation can only be dispatched down

    • Not often viewed as desirable because of wasted renewable and economic energy

  • Rules:

    • Not often dispatched; sometimes defined as ‘undispatchable’.

    • One common reason to be dispatched down is a transmission constraint (a.k.a., “bottled”)

Energy market settlements
Energy Market: Settlements

  • Difference:

    • Intermittent generation is not as in control of its output than traditional generation

    • Less likely to be able to game the energy market and more likely to be undeservedly hit by over-production/under-production charges

  • Rules

    • Some ISOs have excluded intermittent generation from their excessive/deficient energy charges

Ancillary services
Ancillary Services

  • Difference:

    • Ancillary services can only be scheduled on a dispatchable resource

    • Intermittent generation is not viewed as dispatchable

  • Rules

    • Currently ISO’s do not allow Intermittent resources to provide any of the ancillary services

  • Could intermittent resources?

    • Given more accurate persistence forecasting

    • Given a 5-minute energy and ancillary services markets

Capacity market offer amount
Capacity Market: Offer Amount

  • Difference:

    • Intermittent generation does not have control of the of the delivery of capacity on peak days

    • The choice of how much to offer into the capacity market becomes more of a gamble for both the provider and consumer

  • Rules:

    • Some ISO’s limit the amount of capacity an intermittent generation provider can offer to a small fraction of their nameplate value

Capacity market da requirement
Capacity Market: DA Requirement

  • Difference:

    • Traditional generation must offer their auctioned capacity into the Day-Ahead market

    • This guarantees the price certainty the Capacity market aims to provide

    • Renewable generation is forced to be scheduled to their forecast – can conflict with a capacity obligation

  • Rules:

    • Intermittent generation is excluded from the DA offer requirement

Capacity market penalties
Capacity Market: Penalties

  • No Difference: Undelivered capacity leads to penalties and potential loss of injection rights

    • Can be a severe disincentive for intermittent generation to participate in the capacity market

  • In areas that don’t limit the offer amount of intermittent generation, this penalty does so in practice


  • Technology-specific rules are only used when absolutely necessary

  • Rules based on asset-class are more common

  • Renewable generation is often grouped in as intermittent generation

  • Rules specific to intermittent generation exist in all aspects of the markets

  • Intermittent specific rules will need to be reassessed as renewable penetration increases



Todd Ryan

Doctoral Student

Engineering and Public Policy

Carnegie Mellon University

[email protected]