Why hospitals use generators when there is no power outage?

So during heat waves some hospitals either elect to or are asked by local utilities to “sell back” electricity to the grid.  This serves several purposes.  First it allows a major 24/7 consumer of electricity to mitigate its draw during high use times. This can help the utility companies to prevent brown outs and maintain quality of service.  It also allows the hospital to test their generators under load in an environmentally stressful situation.

Hospitals do this in a planned manner and it is done with no interruption of power to the facility.  Some hospitals use the power directly from the generator and some provide the electricity to the grid.  If the generators have any problems the hospital staff returns the systems to normal operations.