Renewable surplus power is increasing due to the increasing penetration of these intermittent resources. In practice, electric grid operators either curtail the surplus energy resulting from renewable-based generations or utilize energy storage resources to absorb it. In this paper, we propose a framework for utilizing water pumps and tanks in water supply networks to absorb the surplus electrical energy resulting from renewablebased electricity generation resources in the electrical grid. We model water supply networks analytically, and propose a twostep procedure that utilizes the water tanks in the water supply network to harvest the surplus energy from an electrical grid. In each step, the water network operator needs to solve an optimization problem that is non-convex. To compute optimal pump schedules and water flows, we develop a second-order cone relaxation and an approximation technique that enable us to transform the proposed problems into mixed-integer secondorder cone programs. We then provide the conditions under which the proposed relaxation is exact, and present an algorithm for constructing an exact solution to the original problem from a solution to the relaxed problem. We demonstrate the effectiveness of the proposed framework via numerical simulations.Index Terms-Water-energy nexus, energy harvesting, optimal water flow, water networks, second-order cone relaxation.
arXiv:1808.05046v1 [cs.SY] 15 Aug 2018Recent demonstrations of PRVs have shown their benefits in control capabilities [27]-[28], and have incentivized water network operators to invest in PRVs. In the near future, we envision PRVs will be available at all junctions with multiple incoming-outgoing pipes. When the network topology does not