<p>Delay Tolerant networks (DTNs) are an initiative to broaden the coverage area of existing network technologies. It should make it possible for senders and receivers to communicate without requiring continuous network access. In DTN, we have a finite amount of node energy. To conserve energy, each node must communicate with other nodes while operating in low power mode for the majority of the time. However, doing so degrades system performance and is not always feasible. This study discusses the deep detail about the DTN energyefficient strategies. In this paper we divided DTN energyefficient strategies into two broad categories: energy-aware routing and energy-saving schemes &amp;other strategies. Energy-aware routing protocols category is further divided into newly developed routing protocols and existing routing protocols improve energy using add-on strategies<b>.</b> The main objective of this study is to compare all category protocols in different areas such as performance, methodology used for energy conservation, strategies used for relay selection and simulation parameters used by different protocols. We also take into account the comparison of add-on strategies, which have the potential to improve the energy consumption in DTN. This paper also empirically analyses the existing routing protocols such as Epidemic, Spray and Wait (SNW), Prophet, Encounter Based Routing (EBR) using different parameters, such as number of nodes, buffer size, etc., to analyse energy consumption in terms of overhead. We have employed THE ONE simulator for experimental setup. The EBR protocol outperformed the other protocols, as it employs direct contact single copy forwarding with no replication.</p>