Sodium Hydroxide For Thermal Energy Storage

Researchers have been testing a theory that Sodium Hydroxide could be used to store solar energy collecting during days or seasons as a form of ‘natural battery’.

Quite simply the hypothesis stems from pouring water into a beaker containing solid or concentrated sodium hydroxide (NaOH) which results in an exothermic reaction – chemical energy is converted to heat.

Sodium hydroxide solution is highly hygroscopic and able to absorb water vapour and the condensation heat obtained as a result warms up the sodium hydroxide solution even more.

Empa researchers Robert Weber and Benjamin Fumey have been working for years to see could if this experiment be replicated on a scale capable of storing enough energy for a single-family household.

They used an insulated sea container as an experimental laboratory on Empa’s campus in Dübendorf – a safety precaution as concentrated sodium hydroxide solution is highly corrosive. This failed. Instead of flowing correctly around the heat exchanger, however, the thick sodium hydroxide solution formed large drops. It absorbed too little water vapour and the amount of heat that was transferred remained too low.

They tried again and the test was a success. They used a viscous storage medium to trickle along a pipe in a spiral, absorb water vapour on the way and transfer the generated heat to the pipe and found the optimum temperatures: 5°C to 10°C is required to drain the store.

While replenishing the store, the 30% “discharged” NaOH solution trickles downwards around the spiral pipe. Inside the pipe flows 60°C water. The water from the solution evaporates; the water vapour is removed and condensed. The condensation heat is conducted into a geothermal probe, where it is stored. The sodium hydroxide solution that leaves the heat exchanger after charging is concentrated to 50% again, i.e. “charged” with thermal energy.

Fumey explains that the method enables solar energy to be stored in the form of chemical energy from the summer until the wintertime. “And that’s not all: the stored heat can also be transported elsewhere in the form of concentrated sodium hydroxide solution, which makes it flexible to use.”

As more research is conducted in this area, there will no doubt be questions and speculation about how charging sodium hydroxide could be used to power thermal desalination in places with seasonally low solar irradiance.

What do you think about the initial findings? Do you think this method is scalable to work at a level that could work for small communities? Do you think it would be cost-effective?

Finalists Announced For Singapore’s 5th Desalination Plant

Keppel Infrastructure, Sembcorp Utilities, Tuas Power and YTL Power International are the four finalists shortlisted by PUB (Singapore’s water authority) for a desalination project on Jurong Island.

The proposals were for the design, build, ownership and operation of a plant that can provide 137,000 m3 per day by 2020. Each proposal sets out a tariff structure and terms and conditions for supply and purchase of desalinated water under a 25-year water purchase agreement.

Keppel was awarded the Marina East project at the beginning of the year which has the same capacity as the proposed Jurong Island.

Singapore currently has two desalination plants in operation, SingSpring and Tuaspring, which operate with a combined capacity of 100 mgd. Both plants use reverse osmosis for its desalination, which uses 3.5kWh/m3.

One of PUB’s goal is to halve the desalination energy used in the future. This will no doubt be a feature that the finalists have factored into their designs.

The Tuas plant is testing and planning to scale up an electrodeionisation facility that will produce 38,000m3/day.

Here is a diagram of how the other existing plant SingSpring operates. It has a pre-treatment process where suspended particles are removed before RO.

Israel Gets Wake Up Call For Its Bets On Desalination

There’s no doubt that Israel is the global poster child for seawater desalination, but that reputation could be starting to turn for the wrong reasons.

It’s time to take an orthogonal viewpoint on how this apparent ‘revolution’ is posing a major threat to the health of the people and environment.

Of course, Israel has relieved and empowered it’s people with their investment in desalination. Residents of one of the driest places on earth freed from chronic droughts by processing the water on their doorstep.

Israel may have gravely overlooked two long-term problems in favour of this solution. The county is set to consume 582 million cubic meters of water annually through it’s current five plants, increasing it’s output by five more plants by 2025.

A few weeks ago, we posed questions about whether Saudi Arabia had actually taken any measures to deal with brine. There was no response from national science institutions. NASA however, were kind enough to get back to us and confirm that nothing could be tracked from space and on-the-ground efforts were required.

Despite the obvious advantage of using potable water for agriculture and combat droughts there are number of significant health threats on the horizon.

Magnesium Deficiency

Israel is bracing itself for an increase in myocardial infarction (heart attacks) in areas and added reliance on magnesium-rich fertilisers.

Prof. Yona Amitai, a public health expert, warned that “more studies be done to examine the possibility of adding magnesium to the water. ”

Hila Gil, director of the desalination division in the Water Authority added “It might cost hundreds of millions of shekels a year. It could affect the price of the water, and we would be the ones who’d have to explain to the public why the prices have risen.”

Israeli isn’t a poor country, but what can it budget for running these experiments and rolling out a solution? Could this be more costly than effective R&D at an earlier stage?


Gil began to express concerns with the high-concentrated brine ‘treated with chemicals’ (likely purified through Lime, CO2 & Soda…) that is being pumped back to sea.

A study is currently underway at the Israel Oceanographic and Limnological Research Institute in Haifa. Dr. Jack Silverman, one of the researchers involved, says they are trying to assess what effect the high salt concentrations will have on wildlife at the bottom of the sea bed.

“Along the bottom, there are very important processes that go on with respect to the survival of the ecological system. Our working assumption is that the concentration may influence these processes and, according to the initial findings, there is an effect”.

None of this should be surprising. It’s a positive sign that senior officials and locals are becoming more savvy to some of the long term risks before the next five plants are built.

It is a disappointing blow for desalination in general, as it will likely be the ‘scapegoat’ in the face of any disaster, whilst poor planning and execution is rather the culprit. We’re still at an infantile phase with this desalination in terms of global, scalable solutions and it would be catastrophic for public attention and funding being drawn away from the need to ‘make it better’.

I do hope the results of the mentioned studies make as many headlines as the utopian ones have, spurring nations that are planning large bets on seawater desalination to consider innovative ways of mitigating the very well known long term consequences.

Teenager Discovers New Water Desalination Method?

A story about a Portland teen discovering a new desalination method has been doing the rounds. It appears copied and pasted across 100s of media sites and is incredibly light on details.

The article states that a high school student, Chaitanya Karamchedu, approached the desalination from a different point of view,  claiming that  he focused on the 90% of water that’s not bonded to salt particles and used a highly absorbent polymer to isolate this.

Tracking down his paper we’re able to shed some more light on it:

It is possible to use such hydrophilic polymers to desalinate water without thermal or electrical energy. Water that was not bonded with salt, bonded with the starch grafted polyacrylamide to form a hydrogel, effectively isolating it from the salt water.

The extracted water’s conductivity was comparable to fresh water indicating that the salts have been separated. The average conductivity of the resulting water was 306.32 μS/cm, comparable to the conductivity of 200 μS/cm for the reference distilled water used.

That this approach has promise in mitigating desalination pre-treatment and post-treatment problems. Mass and conductivity analysis confirmed that the extracted water had a total dissolved solids concentration of 513 mg/L, (WHO guidance is <600 mg/L) compared to 35,000 mg/L for seawater. The concentration of sodium in the extracted water was 25.8 mg/L (compared to 10,500 mg/L for seawater) and that of chloride was 36 mg/L (compared to 19,000 mg/L for seawater). The corresponding EPA secondary concentration levels (aesthetic standards) for sodium is 20 mg/L and for chloride is 250 mg/L.

Chaitanya won a $10,000 award from the US Agency for International Global Development at Intel’s International Science Fair and second place at MIT’s TechCon Conference where he won more money to continue his research.

The winning project at TechCon was a fluoride removal method – using mildly processed bauxite to remediate groundwater fluoride concentrations to the WHO’s maximum contaminant limit for safe drinking water (1.5 mg F-/L).

Although great commendation has been given to the student on an international level, existing research using hydrogels for desalination was published in 2006. Journalists seem to take a lacklustre approach when it comes to accurate report on ‘teen discovery’ story – I’m sure it’s getting plenty of clicks though!

Wood-Graphene Oxide Composite Increases Efficiency Of Desalination

Researchers from the Materials Science and Engineering School of Washington University in St. Louis released a publication today claiming to have an improved process for generating solar steam, thus desalination.

It involves introducing a bilayered structure made of wood and graphene oxide. The graphene oxide is deposited on the micro-pours of wood providing a broad optical absorption and high photothermal effect. This results in rapid increase in the temperature at the liquid surface.

Although the wood serves as a thermal insulator to confine the photothermal heat to the evaporative surface, it facilitates the efficient transport of water from the bulk to the photothermally-active space

Because of this structure and the collective properties each component, the composite exhibited a solar thermal efficiency of ~83% under simulated solar excitation at a power density of 12 kW/m2.

Researchers claim that their structure is highly scalable and cost-efficient, though this statement begs to question – who doesn’t make this claim anymore?

Given the market price for a single gram of graphene oxide is $400 I am interested to know how this can be considered ‘highly scalable’ and ‘cost-efficient’!

Mexico Refuses Drought Stressed California A New Source Of Water

Baja California state’s infrastructure minister says the under-construction Rosarito desalination plant will not supply San Diego.

The plant about 15 miles south of San Diego is being built and is to be operated by Suez. It’s the first of two proposed plants that will collectively produced 150 million gallons a day, enough to supply more than 300,000 homes on both sides of the Mexico-US border.

The plans were initiated as a sort of partnership between Mexico and America but the US was criticised as if this collaboration was an effort to dodge domestic environmental reviews and legal challenges.

This could fire up the long-standing dispute between both countries over the Colorado River where Mexico are protected by a 1944 treaty.

The river feeds several U.S. states and northwest Mexico. The assistant director for binational affairs at Mexico’s National Water Commission, Jose Gutierrez, who says “the treaty carries great significance in our country. We have to protect it fiercely.”

Do you think Mexico are right to take this stance given the current US administrations controversial plans?

Power plant in Playas de Rosarito where the desalination plant was proposed to be constructed next to so that the vast amounts of water used at the plant could be used for desalination.

Solar Desalination System Reaches 80% Efficiency?

Nanjing University, in the capital of China’s eastern Jiangsu province, has reported a solar desalination device that has an efficiency of 80%.

The last major milestone was made by Australia’s solar researchers who converted over 40% of the sunlight hitting a solar system into electricity, that was the highest efficiency ever reported. This came from the institution where Martin Green, dubbed ‘the father of Photovoltaics’ resides as Scientia Professor.

This new process is supposedly made possible by a confined, two-dimensional water path. Also, due to minimised heat loss, the high efficiency of solar desalination is independent of the water quantity and can be maintained without thermal insulation of the container.

A foldable graphene oxide film, fabricated by a scalable process, serves as efficient solar absorber, vapour channel and thermal insulator. The graphene oxide film is not in direct contact with bulk water, but is physically separated by a thermal insulator (polystyrene foam) to suppress parasitic heat loss. A 2-D water path is enabled by a thin layer of cellulose wrapped over the surface of the thermal insulator.

Graphene Oxide Film

The entire structure can float on the water surface, with only the bottom side of the cellulose in direct contact with bulk water, so an efficient water supply to the absorber on the top surface is enabled by a 2-D surface water path within the cellulose pumped by capillary force.

Whilst the report sounds impressive, are the claims scientifically valid given the energetics of solar? Please comment with your thoughts!

The full paper can be accessed here.

US Launches Mega Inland Water Desalination Plant

Yesterday the San Antonio Water System (SAWS) activated one of the largest inland water desalination plants in the United States.

Located in far southeast Bexar County, the H2Oaks plant will produce 12m gallons of water every day – serving over 50,000 homes.

SAWS Chairman Berto Guerra marked the event as a huge step forward for San Antonio saying “a city that doesn’t have water, is a city without a future,”

This plant will join SAWS innovative storage and recovery system, which is located on the same property, and, soon, the water from the massive Vista Ridge Pipeline, which will pump in water from an aquifer in Burleson County west of Bryan.

The water comes from an aquifer 1500 feet below the Carrizo-Wilcox Aquifer and the plant will use reverse osmosis to produce drinking water from the moderately saline .

The first phase project cost a reported $149m and was originally set to launch in October 2016.

The total budget for this three-phase project is $441m. and expects to scale up by 66% with phase two in 2021. It will be completed in 2026 where it will support 100,000 households.

There is an excellent, detailed write up about the project stretching back to its inception in 2000 here:


Fossil Feuds – Samsung Leaves $3bn Oil-Fired Desalination Project

Samsung Engineering has been left out of plans to build a 3.1GW oil-fired power and desalination plant in Saudi Arabia after falling out over a change to the specification. They won the project in 2012.

The state owned client, Saline Water Conversion Corporation, served notice to Samsung Engineering who won the $3bn project. The fall out occurred over a change to the specifications of the turbines that were to be procured from French MNC Alstom. This resulted in “the clash of opinions” over what price should be paid for changes to the spec.

Approximately 55% of the entire project has already been completed and the SWCC claim this termination will not hurt their bottom line. Four 4,500 tonne evaporators (pictured) are already in place covering the size of a football pitch.

The project is already running late – completion was due in December 2016. This has since been revised to August 2018.

A Step Forward For Hybrid Nuclear Desalination

Nuclear desalination is where a nuclear reactor is used as the heat source to drive the process of distillation.

This new project proposes that membrane methods (reverse osmosis or electrodialysis) can be used in conjunction with new or existing nuclear plants where the distillation process is powered from.

Scientists in Russia’s National Research Nuclear University have been trialling a new pretreatment process.

They are working on finessing the cost and energy intensity of the overall process by using reagent methods with hydrodynamic activation of the process of pollutant withdrawal in coagulation, flocculation and adsorption. In non science terms – it’s a system that comprises of water recycling and desalination.

Removing the majority of soluble salts in the pretreatment process through nuclear powered distillation will significantly reduce energy intensity in the membrane stage which increases output and lifespans of the membranes.

Russia has 34 operating nuclear plants with plans for a further 9 reactors by 2020. Although nuclear power can be a taboo topic in some countries, nuclear desalination is a non-carbon emitting  form of green energy and will greatly benefit water scarce cities that lack the solar irradiance to plan other plants that are popular right now.

The largest nuclear desalination plant in the world is in Kalpakkam, home to the Madras Atomic Power Station, in South India’s Tamil Nadu. It the world’s largest hybrid seawater desalination plant  – coupled to a nuclear power plant that uses multistage flash + reverse osmosis.