Energy harvesting is becoming an important enabling technology for sustainable sensor networks. However, the uncertainty and non-uniformity of harvestable energy and the unbalanced workload will often result in the node failures of solar-powered sensor networks. In order to decrease the energy depletion and improve the performance, we introduce an ultra-capacitor-based energy sharing system and design an energy sharing scheme based on it to optimize the network throughput. Different from most of the existing approaches which are focusing on energy management on single node, our design considers energy as a shared resource which makes it be used more efficiently, especially in the case with limited energy. Theoretical analysis and simulation results indicate the energy sharing system as well as the energy sharing schemes can effectively improve the network performance.