Due to the sustainable power supply and environment-friendly features, self-powered IoT devices have been increasingly employed in various fields such as providing observation data in remote areas, especially in rural areas or after disaster scenarios. However, in such areas, the self-powered IoT devices can not directly reach the IoT backbones because those locations generally are located in rural areas or lack electrical infrastructures. Therefore, the collected data of those self-powered IoT devices are transmitted to the sink through multi-hop routing. Generally, the sink is located at the marginal deployment area, which leads to that the devices located at the other sides have to transmit their data across the whole deployment area. The devices directly linked with the sink have to relay the collected data of all devices. Subsequently, the data overflow among self-powered IoT devices is caused. Motivated by this issue, this paper aims to design a UAV-assisted self-powered heterogeneous system to provide comprehensive monitoring data. In this system, we leverage the unmanned aerial vehicle (UAV) easy deployment merits to dispatch it collects data from self-powered IoT devices, periodically so as to alleviate the data overflow. Moreover, based on that in the data flow density area, the self-powered IoT devices are expected to have a more considerable capability, we also developed a placement upgrade strategy to upgrade the general homogeneous self-powered IoT system to the heterogeneous self-powered IoT system. Simulation results indicated the developed UAV-assisted self-powered heterogeneous system can achieve around $1.2\times$ the amount of data delivery to sink compared with the homogeneous self-powered IoT system.