In electric grid power generators, curtailment is the deliberate reduction in output below what could have been produced, in order to balance energy supply and demand or due to transmission constraints. The definition is not strict, and several types of curtailment exist. "Economic dispatch" (low market price) is the most common. Curtailment is a loss of potentially useful energy, and may impact Power Purchase Agreements. However, utilizing all available energy may require costly methods such as building new power lines or storage, becoming more expensive than letting surplus power go unused.