Exergy costs analysis of groundwater use and water transfers

• A methodology to estimate the unit exergy cost of water supply alternatives is provided.
• Two alternatives (water transfers and groundwaters) are defined.
• The unit exergy costs are given as a function of design and operating parameters.
• Unit exergy cost of groundwaters go from 1.01 to 2.67 and from 1 to 4.06 in water transfers.
• Unit exergy costs are calculated and contrasted for the medium course of the Ebro.

In the search for new alternatives to meet the water demands, it is interesting to analyze the cost of using alternatives different from those such as desalination and pumping. The exergy cost analysis can be a useful tool to estimate costs of those alternatives as a function of its energy efficiency and its relative abundance with respect to existing resources in their surroundings. This study proposes a methodology for assessing the costs of groundwaters and water transfers from surplus basins within the exergy perspective. An equation to assess the exergy costs of these alternatives is proposed. System boundaries are first identified to the assessment of input and output currents to the system in exergy values for the design and certain operating conditions. Next, an equation to assess water supply costs depending on design and operational parameters is proposed, from the analysis of different examples. Pumping efficiency, altitude gap and flow among other features are introduced in the calculations as those characteristics parameters. In the developed examples, unit exergy costs of groundwaters go from 1.01 to 2.67, and from 1 to 4.06 in case of water transfers. Maximum values, as expected within this perspective, are found at high pumped/transferred flows and high pumping levels and/or low pumping efficiency if pumping is required.