Definition: The megavolt-ampere reactive hour (MVARh) is a unit of measurement for reactive energy in electrical systems. It represents the amount of reactive power (in megavolt-amperes reactive, MVAR) consumed or supplied over a period of one hour.

History/origin: The concept of VARh (volt-ampere reactive hour) arose from the need to quantify reactive power, which is an important component of AC electrical systems. MVARh is simply a scaled-up version of VARh, using the 'mega' prefix to represent a million VARh. It's part of the larger framework of electrical power measurements developed alongside AC power systems.

Current use: MVARh is used by utility companies and large industrial consumers to measure and bill for reactive power consumption. Maintaining an appropriate reactive power balance is crucial for efficient grid operation, and MVARh meters help track and manage this.