Industrial waste heat can boost blue-energy yield

Blue energy, which can be generated by mixing fresh water and salty water, can offer a much higher energy yield if the fresh water is preheated. This heating is possible using waste heat from, for example, data centres or refrigeration plants. That is demonstrated by calculations by theoretical physicists from Utrecht University, who describe their findings in the scientific journal Physical Review Letters.

Blue energy is a clean, sustainable form of energy that is generated by mixing salty water with fresh water. Blue energy can be generated anywhere where fresh water and salty water meet naturally, for example, a river that flows into the sea.

Heating fresh water

“If the fresh water is heated to 50 degrees centigrade prior to mixing with salty water, twice as much energy can be generated. If the fresh water is heated to 80 degrees, the energy produced can even be trebled,” says professor René van Roij of Utrecht University and an expert in the field of blue energy.

“By heating the water using waste heat, we kill two birds with one stone: blue-energy installations generate more clean, sustainable energy, and industrial waste heat is put to better use,” concludes Mathijs Janssen, lead author of this publication and doctoral candidate at Utrecht University.

New insight

Every litre of river water that flows into the sea can, in theory, generate a quantity of energy that is the equivalent of a waterfall or dam approximately 200 metres high. On a global scale, blue-energy generation can be utilised that corresponds to 2,000 nuclear power plants. And on a national scale in the Netherlands, blue energy – thanks to our estuaries and the Afsluitdijk – can provide 30% of the necessary electricity.

Over the past years a great deal of research has been carried out all around the world to also be able to generate this energy in practice. Until now, however, work has only been carried out at temperatures of approximately 10 to 20 degrees for both the fresh water and the salty water. “The new insight that follows from the Utrecht model calculations is that the energy yield is greater to the degree that the fresh water is warmer and/or the salty water is colder,” Van Roij explains.

Making fresh drinking water

The new findings by the Utrecht physicists also have implications for the reverse process: desalination of brackish water to produce fresh drinking water and salty waste water. “Our theory predicts that the desalination of cold brackish water is considerably less expensive than that from warm brackish water,” Van Roij says. Various laboratories, including that of Utrecht University, are currently testing the theoretical findings of the Utrecht scientists.

Publication

‘Boosting capacitive blue-energy and desalination devices with waste heat’, Mathijs Janssen, Andreas Härtel and René van Roij, Physical Review Letters.

Utrecht University and sustainability

Sustainability research at Utrecht University is exceptionally strong, spanning many different disciplinary fields, including the humanities, social sciences, and natural sciences. In 2017, Utrecht University launched Pathways to Sustainability, promoting interdisciplinary research within these academic disciplines and transdisciplinary approaches with external partners to take up an active role in furthering a more sustainable society. With rigor meets relevance as a guiding principle, Pathways to Sustainability pursues novel approaches in close interaction with governance, business and the scientific community.