Installing an electrical subpanel can be tough.
If the service panel does not have room for new circuit breakers and you cannot use tandem breakers, a subpanel may be the answer. A subpanel connects to the main service panel with a thick three-wire cable. The feeder breaker in the main panel acts as the main disconnect for the subpanel. Before installing one, consult with an inspector to make sure you do not overload your overall system.