Wireless Power Transfer (WPT) technologies aim at getting rid of cables used by consumer devices for energy provision. As long distance WPT is becoming mature, the health impact of WPT becomes increasingly important to consider. In this paper we look at how to maximize the wireless power transfer to remote devices, while maintaining a safe level of electromagnetic radiation (EMR) for humans that are in the vicinity of the energy transmitters. Classically, this problem can be described as a centralized optimization problem of finding the optimal set of safe power levels at locations of human presence. Instead, we advocate to formulate this problem as au agent based Distributed Constraint Optimization Problem (DCOP). As a solution to this problem we introduce CoCoA_WPT, a variant of the DCOP solver CoCoA. CoCoA_WPT provides a solution of similar quality to centralized solver even for a large scale network involving over a thousand nodes. Based on CoCoA_WPT, we propose a self-adaptive charging system: Transferring Energy Safely by Self-Adaptation (TESSA). TESSA keeps the charging network safe even when it is perturbed by environmental dynamics. We show that TESSA can reach on average up to 85% of the theoretical optimal maximum total transmitted power (calculated using centralized solution) while satisfying the EMR safety constraints.