SUMMARY
Over the past several years, wireless sensor network has attracted many researchers as well as general users; because of its various applications such as commercial and military applications. The sensor nodes are basic unit of a sensor network that is energized by low powered devices. In un-tethered wireless sensor nodes the power supply is a crucial system component. The energy supplying is made in two aspects, first store the energy and distribute it as per the requirement, else refill the consumed energy by scavenging from external power source like solar energy, Temperature gradients, Vibrations, Pressure variations, flow of air and liquid. If some nodes deplete their energy quickly, that node will not sense and that region is called blank region. This could be avoided by reducing the energy consumption of each sensor node to improve the lifetime of the wireless sensor networks. Therefore, the usage of energy of each sensor nodes must be optimized to maximize the network life. This survey paper is concentrated on the energy consumption for typical sensor node component and then discussed the directions to conserve energy in wireless sensor networks. This paper also gives the classifications of the energy conservation schemes, which are later discussed in detail. Special focus is given over the areas in the literature such as data aggregation along with load balancing techniques. Finally, the paper is concluded with insights for researchers about energy conservation in wireless sensor networks