  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 renewable-based electricity
generation resources in the electrical grid. We model water supply networks
analytically, and propose a two-step 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 second-order
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.
