An effective approach for energy conservation in wireless sensor networks is scheduling sleep intervals for extraneous nodes, while the remaining nodes stay active to provide continuous service. Depending on different types of applications, the network lifetime may be much more critical than covering the entire monitored area at every data reporting round. This paper presents a competition based distributed scheme called FCS to address the fractional coverage problem in wireless sensor networks with tiny, lowcost sensors. Through localized, energy-aware competition, the proposed scheme achieves the desired fractional coverage with a minimum number of active sensors. By taking account of both residual battery energy and recent reporting latency, an enhanced version of FCS which uses a novel competition metric to constrain the maximum reporting latency throughout the network is also proposed. These two schemes also contain the desirable property that it can be extended easily to handle the more general k-coverage problem.