There is a potential for utilizing a combination of combined heat and power (CHP) plants together with large scale heat pumps in district heating systems to balance intermittent renewable power production. The thought is to use a combination of both power production and consumption to balance both surplus and deficit in the electric power market. Much research has presented different modelling and simulations of such systems. This particular study present lessons and empirics from operating such a system. The DH system in Stockholm is large with over 12 TWh of heat demand annually. Since the 1970s the system has been operated with both CHPs and heat pumps. About 660 MW of heat pumps and 300 MW of electric boilers are currently operational in this system. Both the district heating and district cooling systems are equipped with storage. Besides constituting an empirical example, the paper contributes with input to future modelling of this kind of system. (C) 2017 Elsevier Ltd. All rights reserved.