The studied micro-CHP unit converts concentrated solar energy into electricity and heat by coupling a 46.5 m² parabolic trough collector with an oil-free single-cylinder steam engine operating according to the Hirn cycle. Originalities of this system are two axis solar tracking and direct steam generation. The exhaust heat of the cycle is recovered to cover building's heat needs, while the electricity is either self-consumed or fed back into the electricity grid. Experimental studies have shown that it is impossible to achieve continuous operation of the facility without an additional heat source. Thus, we are studying solutions for integrating a backup heating system from dynamic thermal simulations performed with TRNSYS© software One of them consists in adding a 30 kW boiler to the primary circuit in order to ensure daily electricity production. However, this is restricted by the considered storage tank. A parametric study on the volume of the storage tank makes it possible to propose an optimal solution for heat recovery. The results indicate that a storage volume of 3 m 3 meets the needs of the building and limits the heat losses due to heat storage. In order to optimize the use of such a micro-CHP unit, a heat sharing between several buildings equipped with 3 m 3 storage seems therefore to be a coherent solution.