Energy Storage

Harvard, Cambridge scientists improve durabiliy of redox flow batteries with anthraquinone

Anthraquinone (C14H8O) is an aromatic organic compound. Image: Ben Mills and Jynto, Wikimedia Commons

A research team has used a molecule known as 2,6-dihydroxy-anthraquinone (DHAQ) to improve the durability of organic aqueous redox flow batteries. They claim the molecule enables a net lifetime that is 17 times longer than past research has shown.

From pv magazine

Scientists from the University of Cambridge and Harvard University claim to have considerably increased the duration of organic aqueous redox flow batteries. They used a molecule known as 2,6-dihydroxy-anthraquinone (DHAQ) – or more simply, anthraquinone – to avoid the decomposition of chemically unstable redox-active species, which is the main factor affecting the storage capacity of these storage devices.

“Organic aqueous redox flow batteries promise to significantly lower the costs of electricity storage from intermittent energy sources, but the instability of the organic molecules has hindered their commercialization,” said researcher Michael Aziz. “Now, we have a truly practical solution to extend the lifetime of these molecules, which is an enormous step to making these batteries competitive.”

DHAQ decomposes slowly over time, regardless of how many times battery cycles have been performed. When it is in contact with the air, after a cycle, this molecule absorbs oxygen and turns back into its original status. For this reason, the researchers refer to the molecule as a “zombie quinone,” as it is kind of returning to life after being dead.

“But regularly exposing a battery’s electrolyte to air isn’t exactly practical, as it drives the two sides of the battery out of balance – both sides of the battery can no longer be fully charged at the same time,” they said.

Through nuclear magnetic resonance (NMR), the academics discovered that the battery’s active materials can be recomposed via deep discharge. This occurs in a battery when it has been discharged at its full capacity.

“Usually, in running batteries, you want to avoid draining the battery completely because it tends to degrade its components,” said researcher Yan Jing. “But we’ve found that this extreme discharge where we actually reverse the polarity can recompose these molecules – which was a surprise.”

They said redox flow batteries developed via this approach could offer a net lifetime that is 17 times longer than previous research has shown.

“Getting to a single-digit percentage of loss per year is really enabling for widespread commercialization because it’s not a major financial burden to top off your tanks by a few percent each year,” said Aziz, adding that the proposed approach was applied with success to a range of organic molecules.

They described their findings in “In situ electrochemical recomposition of decomposed redox-active species in aqueous organic flow batteries,” which was recently published in Nature Chemistry.

“Now, utilizing 2,6-dihydroxy-anthraquinone (DHAQ) without further structural modification, we demonstrate that the regeneration of the original molecule after decomposition represents a viable route to achieve low-cost, long-lifetime aqueous organic redox flow batteries,” they said.

Author: Emiliano Bellini

China’s massive hydro energy storage goals may be getting bigger

China has been eyeing a major pumped hydro build-out since at least last year. Image: Pixabay

From Bloomberg

BEIJING (BLOOMBERG) – China’s biggest dam builder says the country is launching an even-larger-than-expected campaign to build hydro energy storage to complement renewable power.

The nation will start construction on more than 200 pumped hydro stations with a combined capacity of 270GW by 2025, Mr Ding Yanzhang, chairman of Power Construction Corp of China, the country’s largest builder of such projects, said in a Monday (June 13) commentary in the Communist Party-run People’s Daily.

That’s more than the capacity of all the power plants in Japan, and would be enough to meet about 23 per cent of China’s peak demand.

It would also be a massive increase from what China proposed just three months ago in its 14th five-year plan for energy development, when officials said the country wanted to have 62GW of pumped hydro in operation and another 60GW under construction by 2025.

PowerChina did not immediately respond to an e-mail seeking comment, and the National Energy Administration (NEA) did not answer calls to its Beijing office.

Hydro storage technology dates back more than a century.

Water is pumped into an uphill reservoir using electricity when demand is low, and then generates power when needed by letting gravity carry the water downhill through turbines.

It can be paired with China’s rapidly growing fleet of solar panels and wind turbines to generate electricity when the sun isn’t shining and breezes aren’t blowing.

China has been eyeing a major pumped hydro build-out since at least last year. In August, a draft NEA document identified the potential for 680GW of pumped hydro in the country, and mooted a possible goal of starting construction of 180 gigawatts by 2025.

The final version of the plan released in September toned down the scale, but still called for 120GW of capacity operating by 2030.

The entire world had 158GW of hydro storage at the end of 2019. China is also ramping up plans to deploy newer forms of energy storage such as batteries, with the country’s largest grid saying it hopes to have 100GW of such capacity available by 2030.

Storing renewables with high-rise elevators

Image: Federal University of Espírito Santo, Energy, Creative Commons License CC BY 4.0

Lift Energy Storage Technology is a proposed long-term storage solution that relies on elevators to bring solid masses to the tops of buildings in charging mode. It then lowers the same mass to produce electricity in discharge mode.

From pv magazine

An international research team has developed a gravitational energy storage technology for weekly cycles in high-rise buildings in urban environments.

Lift Energy Storage Technology (LEST) is a proposed long-term storage solution. It relies on the use of elevators in buildings to lift solid masses in charging mode. It lowers the same mass to produce electricity in discharge mode.

“Energy is stored as potential energy by elevating storage containers with an existing lift in the building from the lower storage site to the upper storage site,” the scientists said. “Electricity is then generated by lowering the storage containers from the upper to the lower storage site.”

The proposed system could detect the position of containers and optimize available storage capacity in the upper and lower storage sites through dedicated software. Building owners could choose to only operate the system during periods of low elevator demand, in order to minimize its impact on building occupants. The elevators can run at different speeds, depending on storage requirements.

“When the lifts are not being used, such as during the night, the autonomous trailers can fill the lift with containers and the lift can be used to provide ancillary services to the power grid by lifting and descending the mass continuously on grid requirements,” the academics said.

Autonomous trailer and storage container. Image: Federal University of Espírito Santo, Energy, Creative Commons License CC BY 4.0

The economic viability of the system depends on the cost of the storage space. If this is low, the scientists said that a mixture of sand and water could be a feasible solution. The number of storage containers depends on a building’s ceiling-bearing capacity.

The researchers assumed that the elevators have regenerative braking capabilities and that the cost of renting the containers’ storage space in the upper and lower sites would be zero.

“The only cost requirements are the containers, the material selected to increase the mass of the containers, and the autonomous trailers,” they said.

Considering an average height difference between the upper and lower reservoirs of 100 meters, the cost of installed capacity energy storage cost was found to be approximately $62/kWh.

“The cost of LEST with an average height difference of 300 meters is $21/kWh, whereas an average height difference of 50 meters costs $128/kWh. This is half of the cost of storing energy with batteries.”

The technical lifetime of the system is estimated between 20 and 30 years and its capacity will be strictly dependent on the number of existing lifts.

“The higher the height difference between the lower and upper storage sites, the lower the cost of the project,” the research team said.

The noted a multi-elevator lift developed by German industrial conglomerate Thyssenkrupp that only uses magnetic force to move the lifts, as an ideal solution for the LEST system.

“This allows the lift to move vertically, horizontally and diagonally, and it is particularly interesting for high-rise buildings because several lifts can travel up or down at the same time in the same shaft,” they said.

The scientists presented the gravitational tech in “Lift Energy Storage Technology: A solution for decentralized urban energy storage,” which was recently published in Energy. The research team includes academics from Austria’s International Institute for Applied Systems Analysis (IIASA), the Federal University of Espírito Santo in Brazil, the Wrocław University of Science and Technology in Poland, and the Hamburg University of Applied Sciences in Germany.

“LEST systems are particularly interesting in buildings with rope-free elevators, and they can also provide tuned mass damper services on the top of very high buildings,” they said. “LEST systems are particularly interesting during the night when most lifts are not being used, as the autonomous trailers can continue to fill the lifts with containers to provide ancillary services to the power grid.” 

Author: Emiliano Bellini

Long-duration storage solution based on saltwater

Image: Imperial College London

Developed by Dutch start-up AquaBattery, the storage technology is claimed to independently amend power and energy capacity. The battery system utilizes three storage tanks, one with fresh water, one with concentrated salt water and one with diluted salt water, and also relies on membrane stacks.

From pv magazine

Dutch start-up AquaBattery has been awarded €2.5 million in funding from the European Innovation Council’s (EIC) Accelerator to develop its long-duration energy storage technology based on saltwater.

The company’s patented storage technology uses just saltwater as the storage medium and is described as a flow battery that is able to independently amend power (kW) and energy (kWh) capacity. The proposed solution is also said to be low-cost, highly scalable and sustainable, as it uses only water and table salt, with its storage capacity being expandable by just adding water reservoirs or using larger tanks.

The battery system utilizes three storage tanks, one with fresh water, one with concentrated salt water and one with diluted salt water, and also relies on membrane stacks. During the charging phase, the diluted salt water is split into concentrated salt water and fresh water in the membrane stack and stored separately. The separation is achieved through electrodialysis (ED), which is a separation process in which charged membranes and electrical potential differences are used to separate ionic species from an aqueous solution and other uncharged components.

A pilot project developed by AquaBattery. Image: Imperial College London

In the discharging phase, the two streams are combined and the resulting energy is converted to electricity with the help of the membrane stack through reverse electrodialysis (RED), which is a technology to generate electricity from the salinity difference between two solutions, for example, seawater and river water.

“AquaBattery’s solution could provide virtually unlimited storage capacity from eight hours up to days, weeks or even seasonally,” reads a statement from the Imperial College London, with which the Dutch start-up is cooperating. “The fund will provide around €2.5 million in grant funding to AquaBattery, with options for direct equity investment of up to €15 million depending on their needs. The grant will enable the team to speed up R&D and product development and bring forward commercialization of AquaBattery to 2025 or earlier.”

Author: Emiliano Bellini

Latent heat thermophotovoltaic battery for renewables storage

Inside view of a latent heat thermophotovoltaic battery developed in the Amadeus project and available at IES-UPM. Image: Technical University of Madrid

Developed by researchers in Spain, the battery uses renewable electricity to melt low-cost metals such as silicon or ferrosilicon alloys to produce and store latent heat, which is in turn used by a thermophovoltaic generator to produce power. According to its creators, the device may store electricity at a cost of €10 per kilowatt-hour for a 10MWh system.

From pv magazine

A group of scientists from the Technical University of Madrid has fabricated a latent heat thermophotovoltaic (LHTPV) battery that is able to store electricity in the form of latent heat at temperatures of over 1,000 degrees Celsius and then convert the stored heat to electricity on demand using a thermophotovoltaic system consisting of a thermal emitter and a photovoltaic diode cell.

“We have built a small, laboratory scale prototype of less than 1kWh of storage capacity,” the research’s corresponding author, Alejandro Datas, told pv magazine. “To reach commercial maturity, we need to build a system with several megawatt-hours of power capacity, which may require some time and a large amount of funds. However, we are already working on that and, hopefully, we can speed things up if we find the right partners to scale the technology.”

The proposed system uses renewable electricity to melt, at temperatures over 1,000 degrees Celsius, low-cost metals such as silicon or ferrosilicon alloys, which are able to store energy during their fusion process, thus producing the so-called “latent heat.” According to the research team, a liter of silicon material is able to store more than 1kWh of latent heat, which corresponds to the energy contained in a liter of hydrogen pressurized at 500 bar. “However, unlike hydrogen, silicon can be stored at atmospheric pressure, making the system potentially cheaper and safer,” it further explained.

The thermophovoltaic generator used for the device is described by the researchers as a miniature photovoltaic system that can generate up to 100 times more energy than a conventional PV installation. According to the researchers’ calculations, if a square meter of a conventional PV array produces 200W, a square meter of thermophotovoltaic system may generate up to 20kW. “The efficiency of thermophotovoltaic cells ranges between 30 and 40% depending on the temperature of the heat source,” they emphasized. “Furthermore, the use of thermophotovoltaic generators, instead of conventional heat engines, avoids the use of moving parts, fluids, and complex heat exchangers.”

The prototype is claimed to be able to store energy at a cost of €4 per kilowatt-hour, although its commercial costs may be higher as the system currently does not integrate a container and thermal insulation. “It would be possible to reach costs of around €10 per kilowatt-hour if the system is large enough, typically more than 10MWh, since the cost of thermal insulation would be a small fraction of the total cost of the system,” the Spanish group emphasized, noting that if costs will be further reduced, it may be enough to recover only 30-40% of the energy in the form of electricity, to make these devices more profitable than lithium-ion batteries. “Additionally, the remaining 60-70% of the heat that is not converted to electricity can be delivered directly to buildings, factories, or cities, reducing your natural gas consumption.”

The battery was presented in the paper “Latent heat thermophotovoltaic batteries,” which was recently published in Joule. “If the price of stationary lithium-ion batteries remains high, it will be necessary to combine them with other, cheaper technologies, such as thermophotovoltaic batteries, which allow larger amounts of electricity to be stored,” Datas concluded.

Author: Emiliano Bellini