Blue energy: Can it power a sustainable future?

Ever since global warming became a hot button issue, our leaders have told us umpteen times that "climate change is the greatest environmental threat and the biggest challenge humanity has ever faced." Yet, they are not "bold enough to do enough" to pull us out of the climate change conundrum soon enough.

In the meantime, impacts of climate change are being felt in communities across the world. Average global temperatures have risen every decade since the 1970s, and the 10 warmest years on record have all occurred since 1997. If the trend continues unchecked, very soon we will be living on a planet with unbearable heat, unbreathable air, inundated coastal areas, widespread drought and wilder weather. Indeed, an Australian think tank warns that climate change could bring about the end of civilisation, as we know it, within three decades.

So, what should we do to tackle the disastrous effects of climate change? Since human activity is responsible for climate change, human activity can also mitigate it. To that end, we have to force our national governments to stop using the suicidal fossil fuels without any further delay. In other words, we need a carbon negative economy, or at the least, a zero-carbon economy.

We already have the potential to produce everything we need with no or very little greenhouse gas emissions. It is "green" energy solar, wind, hydropower, geothermal, nuclear that provides an alternative, sustainable and cleaner source of energy. Promising new green technologies, such as tidal, wave and ocean's thermal energy, are also on the horizon.

There is a third type of energy many of us are not familiar with—another alternative, sustainable source of energy that could be the next frontier in clean-energy technology. It is energy released during controlled mixing of a stream of saltwater and a stream of less saline water and can, therefore, be found in abundance anywhere a river meets the sea. Since energy at the river-sea nexus is produced in naturally occurring waterbodies, which are blue, it is called "blue" energy.

Blue energy exploits the phenomenon of osmosis, which is the spontaneous movement of molecules of a solvent through a semi-permeable membrane from the side of lower concentration into the side of higher concentration until the concentration becomes equal on both sides. In the process, energy is released which could be used to generate electricity. That is why it is also called "osmotic power," or "salinity gradient power"

The energy output would depend on the salinity and temperature difference between the river and seawater and properties of the specific membrane. The greater the salinity difference, more energy would be produced. In fact, based on average ocean salinity and global river discharges, it has been estimated that if blue energy plants were to be built at all river estuaries, they could produce about 1,370 terawatts of power each year, according to the Norway Center for Renewable Energy (a tera is a trillion.)

The concept of blue energy is not new. It was first proposed in 1954 by a British engineer named RE Pattle, although it was not possible to implement his idea for power generation until the 1970s, when a practical method of harnessing it was outlined.

The first osmotic power plant was built in 2009 in Tofte, Norway. It produced only four kilowatts of power, which was not enough to offset the cost of construction, operation and maintenance. Consequently, it was shut down in 2013.

Since then, improved technologies to tap blue energy have been developed at various laboratories, primarily in the Netherlands and Norway. Using these technologies and the difference in salt concentration in the surface water on each side of the Afsluitdijk dam, the Dutch built a power plant in 2014 generating enough electricity to meet the energy requirements of about 500,000 homes.

Blue energy is not limited to mixing of river and seawater because osmosis works with any concentration difference of dissolved substances. It may thus be possible to generate electricity from dissolved carbon dioxide, which could be captured from fossil-fuel power plants. Researchers believe that worldwide, the flue gases of fossil fuel power plants contain enough carbon dioxide to make around 850 terawatts of blue power. Hard to believe that the villain of climate change could be part of the solution after all.

In a paper published in July 2019 in ACS Omega, one of the journals of the American Chemical Society, researchers of Stanford University claim to have made a battery that runs on electricity generated by harvesting blue energy from wastewater effluent from the Palo Alto Regional Water Quality Control Plant and seawater collected from Half Moon Bay. Their work clearly demonstrates that blue energy could make coastal wastewater treatment plants energy-independent and carbon neutral.

An advantage of blue energy technology is that it does not depend on external factors like wind or sun. Another advantage is that a commercial plant would be modest in size, but still produce a significant amount of energy. Moreover, compared with, for instance, wind and solar energy, implementing a blue energy power plant would have a smaller impact on landscape, and it requires less land usage. Besides, once fully developed and deployed, the technology would be able to generate energy continuously and would not emit greenhouse gases. Hence, it would ensure access to affordable, reliable, sustainable and clean energy for all.

There are some drawbacks of blue energy though. Power plants exploiting blue energy may have an effect on the marine life, hydrological systems and water management rules of the region. The main drawback, however, is the cost. Compared to a conventional power plant using fossil fuels, the cost of construction of a blue energy power plant would be several times higher because artificial membrane is very difficult and expensive to make. Nevertheless, once built, the expectation is that blue energy would succeed in generating power at a much cheaper rate than solar and wind.

Finally, blue energy is potentially one of the best sustainable energy resources we have at our disposal. The raw material is free and inexhaustible. "Blue" could be the "green" of the future. And the blue-green combination can match the urgency of the climate change crisis.

Quamrul Haider is a professor of physics at Fordham University, New York.