We present the design and evaluation of a capacitor-driven efficient renewable energy management and sharing system, called REMS system, that is designed to replace battery-based energy storage units. We first identify potential applications and requirements of the REMS system. Then we describe the design of REMS system which aims at minimizing the energy leaked away and providing accurate and fine-grained energy sharing between embedded devices. We extensively evaluate our system under different real-world settings. Results indicate that our charging and discharging control can effectively minimize the energy leaked away. Moreover, the energy sharing design can efficiently share renewable energy among multiple devices and significantly extend the lifetime of a system.