Water Power: An Under-Exploited Resource of Blue Energy

Blue energy, or osmotic power, capitalises on the natural processes involving water to generate electricity. It is derived from the energy available from the difference in salt concentration between seawater and river water. When these two bodies of water meet, the difference in salinity can be harnessed to produce power, offering a clean, renewable energy source. 

With the urgent need to reduce carbon emissions and combat climate change, exploring innovative energy solutions is paramount. Among these, blue energy emerges as a promising yet under-exploited resource with the potential to revolutionise the global energy landscape.

Despite its vast potential, the exploitation of blue energy is still in its infancy. The world's first osmotic power plant was launched in Statkraft, Norway, in 2009, marking a significant milestone in the development of blue energy technologies. 

The potential for blue energy is immense, particularly in regions where freshwater meets the sea. Estimates suggest that the global capacity for salinity gradient energy alone could be between 1.4 and 2.6 TW. This indicates a substantial untapped resource that could be crucial in the worldwide transition to renewable energy.

The journey from concept to widespread adoption will require innovation, investment, and international collaboration, but the rewards promise a cleaner, greener planet for future generations.

Blue energy refers to the generation of electricity through the exploitation of the chemical and physical properties of water, particularly the differences in salinity between freshwater and seawater. This form of energy is sustainable, renewable, and has a minimal environmental impact, making it an important player in the future of global energy production.

It can power our homes. But how can we exploit this natural effect?

The core principle of blue energy revolves around salinity gradients. When freshwater from rivers meets the salty ocean water, the difference in salt concentration can be exploited to generate power. 

This process primarily uses two technologies: 

Pressure Retarded Osmosis (PRO) and Reverse Electrodialysis (RED). In RED, two membranes are used: one that allows positively charged sodium ions (Na+) to pass through and another that permits negatively charged chloride ions (Cl-) to move. 

PRO involves using a semipermeable membrane that allows water to pass through but blocks salt ions. 

The movement of freshwater to the saltwater side under osmotic pressure can be used to drive turbines and generate electricity. RED, on the other hand, uses a series of membranes selective to either sodium or chloride ions, creating an electrochemical reaction that produces electricity

If we separate the fresh water from the salty water in a container via a semi-permeable membrane, the fresh water will naturally go to the salty side. This action increases the level of salty water and generates the pressure of a 120-meter waterfall. If we combine this pressure with turbines, we can generate power and therefore electricity in our homes.

The importance of blue energy lies in its potential to provide a continuous, reliable source of power without the carbon emissions associated with fossil fuels.

Blue energy encompasses various methods of power generation, including:

With technological advancements, particularly in membrane technology and marine energy devices, blue energy is poised to play a significant role in the global energy mix. 

However, this technology still faces some significant challenges. For example, the efficiency of reverse electrodialysis systems needs to be addressed to unlock this potential fully. Let’s break down the recent developments and their abilities. 

Forward osmosis (FO) has emerged as a promising technology for osmotic power generation, leveraging the natural osmotic pressure difference between solutions of varying salinities to produce energy. 

Recent efforts have focused on developing membranes with higher rejection rates and less susceptibility to reverse salt flux, where the draw solution (DS) leaks into the feed solution (FS), reducing efficiency. This includes the exploration of alternative DS and improvements in membrane stability, which are crucial for enhancing the viability of FO energy applications.

Marine energy technologies exploit the kinetic and potential energy of water bodies. The U.S. Department of Energy's Marine Energy Program highlights the vast potential of marine energy, which can meet nearly 60% of the country's electricity needs if harnessed effectively. 

This innovation explores more durable and efficient wave energy converters, underwater turbines for fast-moving currents, and systems designed to withstand the corrosive marine environment while minimising ecological impact. 

These technologies promise to diversify the energy portfolio and offer clean energy solutions for remote and island communities.

Blue energy remains untapped mainly yet holds significant potential as a continuous and reliable power source. Unlike solar or wind energy, blue energy is not dependent on weather conditions, making it a consistent and stable energy supply.

It leverages the chemical and physical properties of water to generate electricity. The beauty of blue energy lies in its source: the inexhaustible supply of saltwater and freshwater meeting points across the globe.

This process and other forms of ocean energy, such as wave, tidal, and ocean thermal energy conversion, represent a vast and largely untapped renewable energy source.

Integrating blue energy into the global energy mix could significantly reduce reliance on fossil fuels, decrease greenhouse gas emissions, and combat climate change.

It is a clean, renewable resource that does not emit greenhouse gases during electricity generation. Moreover, blue energy can complement renewable sources like solar and wind, which are variable, by providing a stable and continuous power supply. 

Its development could also lead to advancements in water purification and desalination technologies, simultaneously addressing energy and clean water challenges. 

The global electricity demand is rising, with projections indicating an average annual growth rate of 3.4% through 2026. This is highlighted by IEA’s research in the rapid expansion of renewable energy sources, including ocean-based technologies, as central to achieving net-zero emissions in the power generation sector. 

The world's oceans and rivers are a constant, flowing source of energy that, if harnessed effectively, could provide a substantial portion of the electricity needed to power modern societies. 

Though the exact estimations of its capacity are complex due to the nascent stage of the technology and geographical variations, the principle of harnessing energy from the salinity gradient presents a significant opportunity for large-scale deployment, especially in coastal regions. 

The table below provides a snapshot of the diverse methods through which blue energy can be harnessed, each with unique advantages and potential to contribute to a sustainable energy future.

One of the most significant advantages of blue energy is its environmental friendliness. It is CO2-free, contributing to the reduction of greenhouse gas emissions. 

It is a reliable, abundant, continuous power source, not subject to the whims of weather or daylight. It requires less land than wind or solar energy, and its potential is vast; estimates suggest that effectively harnessed blue energy could meet a substantial portion of our energy requirements. 

Though blue energy has struggled to establish economic viability, technological advancements, such as nanotechnology, may soon make it more cost-effective. 

In addition, the IEA forecasted that low-emission sources will account for almost half of the world's electricity generation by 2026. This plays a crucial role in the transition with demand for clean energy. As a continuous power source, it can support sustainable development and help mitigate the impacts of climate change. 

Blue energy, also known as osmotic power, is a promising clean and renewable energy source that harnesses the chemical potential from the salinity difference between freshwater and seawater. It offers significant environmental benefits:

The economic potential of blue energy is significant. Although the technology is still in development, it has the potential to be cost-effective. Current projects suggest that blue energy could generate over 12 watts per square meter, meeting a substantial portion of global electricity demand.

The economic implications of blue energy are multifaceted:

It has been estimated that blue hydrogen, a related concept, can reduce greenhouse gas emissions by 5–36% compared to grey hydrogen.

Blue energy has the potential to play a significant role in reducing greenhouse gas emissions:

Despite its economic and environmental benefits, its implementation faces significant hurdles, including technological inefficiencies and the need for extensive development. 

One of the primary obstacles to adopting blue energy is the inefficiency of current technologies. For instance, methods like osmotic pressure and ocean thermal energy conversion, while innovative, have yet to achieve the efficiency levels required for widespread use. 

RED faces challenges like membrane fouling and optimising multistage configurations for maximum energy efficiency. These technologies face issues such as bacterial contamination and the need for significant temperature differences between water layers, complicating their deployment. 

Research and development efforts aim to overcome these obstacles through innovative solutions like periodic feedwater reversal air sparging. This development will lead to multi-stage RED configurations to enhance energy efficiency and reduce operational costs.

The deep waters and varying flow conditions of potential blue energy sites, such as the Florida Straits, present unique challenges that often require computer simulation and extensive data collection to overcome. 

Despite these challenges, progress is being made. Projects like the demonstration plant in Breezanddijk and the work of researchers like Taek Dong Chung are pushing the boundaries of what's possible with blue energy. These efforts focus on harnessing wave energy, improving turbine designs, and exploring the potential of salinity gradient power, among other innovations.

This potential is a testament to the power of the oceans and the innovative spirit of researchers and developers working in the field.

The future of blue energy is bright, with the potential to transform the global energy landscape and drive economic growth. 

With global commitments to triple renewable energy capacity by 2030, the door is open for this technology to grow alongside other renewable sources. Offshore wind farms, wave, and tidal energy are part of the blue economy's potential to contribute to clean energy transitions. 

Investment in the blue economy is crucial for climate change mitigation and biodiversity. Key areas include sustainable marine transportation, marine renewable energy, and aquaculture.

Countries can reduce energy import bills by fostering energy self-sufficiency and enhancing energy security. Moreover, the development and deployment of blue energy technologies are poised to create new jobs and stimulate economic growth, particularly in coastal and island communities where the technology's potential is most pronounced.

From a social perspective, blue energy can be pivotal in mitigating climate change impacts, safeguarding communities against extreme weather events and enhancing water security. Its deployment in areas such as Latin America, where deforestation and loss of cloud forests pose significant threats, illustrates the technology's capacity to deliver measurable ecosystem services while improving livelihoods. 

Its contribution to the hydrogen economy cannot be overstated. As the world seeks cleaner alternatives to traditional hydrogen production methods, blue energy offers a pathway to low-carbon hydrogen production. Unlike blue hydrogen, which relies on carbon capture and storage from natural gas reforming, blue energy can facilitate the production of green hydrogen through water electrolysis powered by renewable energy sources, thereby eliminating CO2 emissions. 

Engaging with this innovative technology now can help secure a cleaner, more resilient energy future for generations to come. 

As we harness the power of the seas, we're not just investing in energy; we're investing in a cleaner, more resilient world.