| This paper considers energy harvesting sensor nodes monitoring multiple {\em fixed} targets. The goal is to monitor these targets for the longest time period. A key challenge, however, is that sensor nodes have varying energy harvesting rates, meaning the coverage lifetime of targets is limited by sensor nodes with low energy. to this end, we consider energy sharing between sensor nodes. We model the problem as a Mixed Integer Linear Program (MILP). Advantageously, our MILP models non-linear energy conversion rates. We also outline a heuristic for large-scale networks. Our results show energy sharing and non-linear energy conversion rates prolong coverage lifetime. Lastly, our heuristic achieves 90% of the optimal coverage lifetime. |