Active power - is the real component of the apparent power at fundamental frequency, expressed in watts or multiples thereof such as kilowatts (kW) or megawatts (MW) - Article 2(20) of the Network Code on requirements for grid connection of generators (NC RfG).
Active power reserve means the active power which is available for maintaining the frequency.
According to the Network Code on System Operation each Transmission System Operator (TSO) is required to communicate the available level of active power reserves to other TSOs upon request.
Documentation
Network Code on requirements for grid connection of generators (NC RfG), Article 2(20)
Network Code on System Operation, Article 108, 109
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