DC bus signaling (DBS) is frequently employed for coordinating the operation of Distributed Energy Resources (DERs) in DC micro and nanogrids, in a decentralized way. The V vs. I curve of Renewable Energy Sources (RESs), such as solar photovoltaic (PV), usually includes a droop, a Maximum Power Point Tracking (MPPT) and a current limiting segment/mode. However, the reference current for the interface (I) cannot be determined solely based on the DC bus voltage (V). Variations of the solar irradiance change the DC bus voltage values on the V vs. I curve where transitions from one mode to another occur. This is an issue for single-stage power interfaces that, without the intermediate DC bus of two-stage interfaces, cannot employ conventional search-type MPPT algorithms. This paper presents a novel control scheme in which a non-search-type MPPT algorithm that does not rely on measurements of the solar irradiance is employed. It allows a smooth transition for the reference current of the interface as the mode of operation, on the V vs. I curve, changes due to variations in the solar irradiance and DC bus voltage. The performance of the proposed scheme is demonstrated experimentally for a stand-alone DC nanogrid based on DBS for the PV source operating by itself and along with an energy storage unit. Load and solar irradiance variations are considered in the experiments.