Problem To provide an electricity supply system that efficiently utilizes electricity. In particular, the invention relates to MHC fusion complexes that contain a MHC molecule with a peptide-binding groove and a presenting peptide covalently linked to the MHC protein. An auxiliary layer is formed over the control gate layer so as to expose a protruding portion of the control gate layer. Thus, the hot water supply operation may be continuously performed, without a defrosting operation, and hot water supply performance and heating performance may be improved.