ScholarGate
Get started
Process / pipelineElectrical EngineeringInteger programming, schedulingPipeline

Unit Commitment

Also known as: UC, Generator Commitment, Thermal Unit Scheduling

OriginatorCharles J. BaldwinYear1959Sources3Related methods8

Unit Commitment (UC) is the problem of deciding which power generation units should be switched on or off over a planning horizon (typically 24-168 hours) to minimize total operating cost while meeting demand and reserve requirements. Introduced by Baldwin et al. in 1959, UC is a fundamental scheduling problem in power system operations, combining combinatorial optimization (which units to commit) with continuous optimization (optimal power output). UC remains one of the most important and computationally challenging problems in power systems.

Key highlights

  • Captures true economic costs of generator ramping and cycling
  • Accounts for all relevant operational constraints (ramping, minimum uptime, minimum load)
  • Modern solvers can handle large systems efficiently using decomposition
  • Directly relevant to competitive electricity market design and pricing

Intuition

This section is available to Pro members. Upgrade to Pro

How it works

This section is available to Pro members. Upgrade to Pro

When to use it

UC is essential for all power systems planning generation over multiple hours. Used in day-ahead energy markets, maintenance scheduling, and long-term capacity planning. Critical when many fast-start generators (natural gas, batteries) enable flexible scheduling. Less critical for systems dominated by baseload (coal, nuclear) where commitment barely changes. Becomes harder with increasing renewable variability (requires frequent adjustments).

Strengths & limitations

Strengths
  • Captures true economic costs of generator ramping and cycling
  • Accounts for all relevant operational constraints (ramping, minimum uptime, minimum load)
  • Modern solvers can handle large systems efficiently using decomposition
  • Directly relevant to competitive electricity market design and pricing
Limitations
  • Mixed-integer nature makes the problem NP-hard; no polynomial-time algorithm for global optimality
  • Computational time grows exponentially with horizon length and number of units
  • Requires accurate, forward-looking estimates of demand and renewable generation
  • Large-scale UC with thousands of constraints and variables can take hours to solve

Common pitfalls

This section is available to Pro members. Upgrade to Pro

Applications

This section is available to Pro members. Upgrade to Pro

Frequently asked

How is Unit Commitment different from Economic Dispatch?

UC decides which units are on/off over multiple periods; Economic Dispatch (ED) finds optimal output for already-committed units in a single period. UC includes commitment costs; ED ignores them. UC typically solves hourly; ED runs every few minutes.

Why is UC an NP-hard problem?

UC includes binary variables (on/off for each unit each hour) that couple with continuous variables (power outputs) through nonlinear costs and constraints. The combinatorial space grows exponentially: 2^(units × hours).

How can I solve large UC problems in reasonable time?

Use decomposition: Lagrangian relaxation, Benders decomposition, or column generation. Modern solvers (CPLEX, Gurobi) with heuristics can find near-optimal solutions in hours. For real-time applications, use fast approximations or machine learning surrogates.

Can UC handle uncertainty in demand and renewables?

Deterministic UC uses point forecasts; stochastic UC (SCUC) models uncertainty as scenarios. Robust UC ensures feasibility over a range of outcomes. Stochastic variants are harder but essential with high renewable penetration.

Sources

  1. 1.
    Baldwin, C. J., Dale, K. M., & Dittrich, R. F. (1959). A study of the economic shutdown of generating units in daily dispatch. AIEE Transactions, 78(3), 272-282.
    https://ieeexplore.ieee.org/document/4066301
  2. 2.
    Padhy, N. P. (2004). Unit commitment in power systems. International Journal of Electrical Power & Energy Systems, 26(5), 363-375.
    https://scholar.google.com/scholar?q=Unit+commitment+in+power+systems+Padhy
  3. 3.
    Wood, A. J., Wollenberg, B. F., & Sheblé, G. B. (2013). Power Generation, Operation, and Control (3rd ed.). Wiley-Interscience.
    https://scholar.google.com/scholar?q=Power+Generation%2C+Operation%2C+and+Control+%283rd+ed.%29+Wood

You have read it. What now?

Ask about this methodSimilar methods

Cite this page

ScholarGate. (2026, June 3). Unit Commitment. ScholarGate. https://scholargate.app/electrical-engineering/unit-commitment

Unit Commitment | ScholarGate