Lee, H.W.J., Townley, L.R., and Goh, C.J. (1993). Optimal control of the solar salt production process. CSIRO Division of Water Resources, Technical Memorandum 93/14, 45pp.

This report describes an application of optimal control theory to the regulation and control of various aspects of the solar salt production process (e.g. salt yield, concentration, outflow). We formulate a mathematical model for the flow of water and salt through a series of ponds, with or without leakage through levees which separate the ponds. The objective of the optimal control problem is to maximise or minimise some desired function of the salt yield, concentration of the terminal pond and or other variables. This is achieved by adjusting the inflow of seawater into the first pond, and/or by adjusting the sill heights of all the ponds to further improve the performance. The production process is subject to weather conditions which act as exogenous inputs to the state differential equations. We assume that the weather is deterministic and varies seasonally. Our approach is closely related to optimal control of the activated sludge process in sewage treatment. Results to date indicate that optimal control of solar salt production is feasible, but that more research is needed to identify realistic objective functions, in conjunction with the managers of an operating system of ponds.