The water energy nexus revisited
July 2020 - For decades it has been taken as a given that electricity prices only go one way . . . upwards. All water treatment plants consume electricity and for certain plants, like wastewater treatment and desalination, electricity is one of the largest lifecycle cost factors. To highlight the interdependency between energy and water, the term water-energy nexus was popularized by Peter Gleick of the Pacific Institute in 1994. Put simply, the vast majority of energy production requires large volumes of water and water purification and conveyance requires large amounts of electricity. As one becomes more expensive over time, so does the other.
While the nexus still exists, in several ways it has been turned upside-down in recent years. 2020 has seen a number of record low seawater desalination water prices driven in part by the falling price of electricity. With new solar plants able to generate electricity below $0.03 / kwh in many regions, several tenders have come in well into the low $0.40s per m3 of desalinated seawater. In addition, these solar plants use a fraction of the water that older thermal plants require with a minimal carbon footprint.
At the same time as electricity is becoming cheaper, less water intensive, and lower in carbon footprint, a record number of companies and municipalities are tracking their carbon footprints and seeking innovative ways to reduce their water-associated electricity consumption. While energy efficiency is generally better than energy inefficiency, I think it is also worthwhile to consider that low energy consumption is not necessarily better than high energy consumption. For instance, many electrochemical technologies have had their adoption hindered by their energy consumption. However, with a likelihood of widely available 3 or 2 or even 1 cent per kwh electricity on the horizon, electricity-intensive treatment processes may deserve another look as they often have a number of advantages in terms of contaminant destruction efficiency, remote operation ease, sludge production, chemical reduction, and space efficiency. In an era of cheap, abundant, and near-carbon-free electricity, could the more cost effective and environmentally sustainable approach also be the HIGH electricity consumption technology? The answer of course is – it depends. However, it is at least something worth considering especially for a capital investment with a 20-30 year lifespan that will be operating in a world of dramatically different electricity economics and sustainability than we are used to.