Harvesting ambient energy has enabled the development of energy harvesting wireless sensor networks (EHWSNs). Solar is the most effective environmental energy source with high power density feature that makes it suitable for many WSNs applications. In these networks, the uncertainty in harvesting rate due to dynamic weather conditions drives the development of EH adaptive medium access control protocol (MAC) protocols. From the literature, most of the available protocols for Solar EH-WSNs (SEH-WSNs) have limited consideration in achieving Energy Neutral Operation (ENO). By applying ENO, nodes can use any surplus harvested energy to maximize performance. Therefore, this paper proposes a new ENO based adaptive duty cycle MAC protocol, called ENCOD-MAC, that supports the node to operate as close to the ENO condition as possible. Moreover, it incorporates additional harvested energy and considers battery level to adjust its duty cycle, thus improving network performance. Its performance has been evaluated using real harvesting rates in GreenCastalia. The simulation results show that the proposed MAC reduces the packet delay by up to 16 when compared to QPPD-MAC in the network. © 2022 IEEE.