The Intergovernmental Panel on Climate Change released its Sixth Assessment Report in early August 2021, and the outlook isn’t good. The report has added renewed urgency to humanity’s effort to curb climate change. The price of solar energy dropped 89 percent in 10 years, and new wind farms are being built both on land and offshore (with ever-bigger turbines capable of generating ever more energy). But simply adding more wind and solar generation capacity won’t get us very far if we don’t have a cost-effective, planet-friendly way to store the energy they produce.
One of the obstacles to total green energy reliance is that many sources of carbon-neutral energy, such as solar and wind power, are unpredictable and intermittent. Wind turbines and solar panels offer low power density and intermittent operation, thereby reducing their usefulness and reliability as a direct form of prime power generation for high continuous or pulsed power loads. Fuel cells offer high energy density but low power density making them a bit more reliable but still not a direct form of power generation in most cases
A possible solution is to build energy storage facilities that can charge up while excess energy is being generated, then discharge when demand overtakes supply. An energy storage system enables you to manage when and how your energy is used. Energy Storage Systems (ESS) have emerged as a promising, versatile technology that can provide solutions to many electric-grid challenges. Without the ability to store large amounts of energy, conventional power systems have been reliant on matching supply and demand in real-time.
“Energy storage fundamentally improves the way we generate, deliver, and consume electricity. Energy storage helps during emergencies like power outages from storms, equipment failures, accidents or even terrorist attacks. But the game-changing nature of energy storage is its ability to balance power supply and demand instantaneously – within miliseconds – which makes power networks more resilient, efficient, and cleaner than ever before,” according to Energy Storage Association.
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Energy Storage Systems
Energy storage systems provide a wide array of technological approaches to managing the power supply in order to create a more resilient energy infrastructure and bring cost savings to utilities and consumers. Advanced energy storage systems enable users to store excess energy to be used at a later time.
The first electrical energy storage systems appeared in the second half of the 19th Century with the realization of the first pumped-storage hydroelectric plants in Europe and the United States. Storing water was the first way to store potential energy that can then be converted into electricity. Pumped-storage hydroelectric plants are very important for electrical systems, as they accumulate energy in periods where the demand is low and give back the energy stored once the demand increases. Battery-based grid-storage facilities using a range of battery types have already been built for this reason, but there is still a need to develop an economical, safe, and long-term solution.
Energy storage systems can be classified based on storage into four main categories: electrical, mechanical, thermal, and chemical. Examples in the electric category include superconducting magnetic energy storage and capacitors. Pumped hydroelectric power, compressed air, and flywheels represent mechanical storage mechanisms. Batteries are the most common type of chemical storage, and ice is the most common form of thermal storage.
Electrical energy storage: Directly electricity storage in devices such as capacitors or super-conducting magnetic devices. Those storage
methods have the advantage of quickly discharging the energy stored.
Mechanical energy storage: Storage of electrical energy in the form of kinetic energy such as flywheel or potential energy such as pumped hydroelectric storage (PHS) or compressed air energy storage (CAES)
Chemical energy storage: Storage in chemical energy form as in batteries, fuel cells and flow batteries. Chemical energy storage usually has small losses during storage.
Thermal Energy Storage
Thermal energy storage formed the basis of propulsion for some 19th century short-distance submarines and fireless steam railway shunting locomotives built mainly during the early 20th century. Saturated water stored inside an insulated tank at high pressure at under 1,000 psia (6.9 Mpa) and high temperature just below 545 degrees F (285 degrees C) served as both the thermal storage material and the means by which to drive the piston engines.
Railways experimented with thermal storage material such as molten sodium hydroxide that melted at 318 degrees C. While some thermal storage materials required a massive input of thermal energy to transform from the solid to the liquid state, the material releases thermal energy very slowly. Advances in solar thermal energy technology include development of molten salt thermal storage material heated far above its melting point, using its heat capacity to rapidly release sufficient heat to generate sufficient steam that drive turbines connected to electric generators that supply the power grid for several hours after sunset.
Sensible Heat. Changing the temperature of materials (liquid or solid) by using solar energy generated at its peak hour, energy is
stored by the temperature difference of the material with the original temperature.
Phase Change Material Storage (PCMS). When a material undergoes a phase change, heat is absorbed or released. Energy can
be stored or released by change phases of the storage materials.
Sorption is the fixation or capture of a gas or a vapor (sorbate) by a solid or liquid substance (sorbent). When heat is introduced to the system, AB is split into compounds A and B, energy is stored as the chemical potential of A and B with negligible loss. When A and B are mixed, A is fixed onto B to form AB, releasing heat.
Solar Fuel. Using optical devices, scattered sunlight can be concentrated and the heat generated from concentrated solar power can be used to carry out endothermic chemical transformation to produce storable and transportable fuels.
Electrical Energy Storage
Pumped hydro- electric storage (PHS) has the largest storage capacity that is commercially available. The basic idea is simple:
use the excess electrical energy generated at off-peak hours to pump water from a lower reservoir to a higher reservoir.
A hydroelectric dam relies on water cascading down through a turbine to create electricity to be used on the grid. In order to store energy for use at a later time, there are a number of different projects that use pumps to elevate water into a retained pool behind a dam – creating an on-demand energy source that can be unleashed rapidly. When more energy is needed on the grid, that pool is opened up to run through turbines and produce electricity.
But the material that is raised to a higher elevation doesn’t have to be water. Companies are currently creating gravitational systems that move gravel up the side of a hill and use the same underpinning principle – when energy is needed, the gravel is released and the weight drives a mechanical system that drives a turbine and generates electricity.
Flywheel energy storage systems store energy in the form of angular momentum. During peak time, energy is used to spin a mass
via a motor. At discharge, the motor becomes a generator that produces electricity. This category of ESS is suitable for applications with low-to-medium power (from ten kW up to a few MW).
Compressed air energy storage (CAES)– the idea of the system is to use the off-peak excess electricity to compress air. At a later
time, the compressed air can be used along with a gas turbine to generate electricity. Compressed Air Energy Storage (CAES) plants are largely equivalent to pumped-hydro power plants in terms of their applications, output and storage capacity. But, instead of pumping water from a lower to an upper pond during periods of excess power, in a CAES plant, ambient air is compressed and stored under pressure in an underground cavern. When electricity is required, the pressurized air is heated and expanded in an expansion turbine driving a generator for power production.
Superconducting magnetic energy storage (SMES) method stores electrical energy in a magnetic field that is generated by direct
Electrostatic Energy Storage (Capacitors, Supercapacitors) This category is quite common, particularly in electronic devices or for electric mobility applications. It works by storing energy through electrostatic charge in a capacitor made by two metallic plates separated by a dielectric. The two plates are charged during the off peak hour to create potential and discharged during peak hour. Supercapacitors are advanced capacitors that can store significantly more energy relative to volume or mass.
Battery and fuel cells are electrochemical cells that converts stored chemical energy to electrical energy. This kind of storage system is based on chemical reactions associated with the elements used to manufacture the battery. The common battery is composed of cells, with two electrodes (anode and cathode) and an electrolyte. Chemical reactions within the battery provide the electromotive force required for the flow of electric current.
Nowadays, due to easier installation, low construction time, and the wide range of possible applications, the most promising category of energy storage systems is the electrochemical category. It can be used both for high-power and high-energy applications, it’s quite small when compared with other types of energy storage systems, and it can be integrated with existing power plants.
Life cycle assessment
New developments in solar energy storage require advances in chemical engineering and materials science. Life cycle assessment (LCA) is an important tool to evaluate energy consumption and environmental impact of renewable energy processes. It is important to note that, while using renewable energy sources such as solar power, storage methods based on non-recyclable materials or methods that consume significant amounts of energy may undermine the effort to reduce energy consumption.
Life cycle assessments (LCAs) are investigations performed to characterize and quantify the cradle-to-grave environmental impacts of certain products and services. LCA accounts for the materials, resources, and energy that enters the system, as well as the waste and pollution that leaves the system. LCA studies should also be performed for all other storage methods. The studies can provide us a more realistic indication, with regard to the efficiency and environmental impact of each storage method, and may reveal additional information, such as the production of raw materials and co- products of the process, which could be important.
Solar energy storage methods are urgently needed, because of the increased demand and unsteady nature of solar power. The implementation of proper energy storage remains crucial to achieve energy security and to reduce environmental impact. It is difficult to compare different types of storage methods using only one factor. It should be noted that some materials needed for certain storage methods are scarce, such as ruthenium for capacitors and lithium for batteries. While using renewable energy sources such as solar power, storage methods based on nonrenewable resources may undermine the initial effort to resolve the energy problem
Flywheels – mechanical devices that harness rotational energy to deliver instantaneous electricity.
At the most basic level, a flywheel contains a spinning mass in its center that is driven by a motor – and when energy is needed, the spinning force drives a device similar to a turbine to produce electricity, slowing the rate of rotation. A flywheel is recharged by using the motor to increase its rotational speed once again. A flywheel is able to capture energy from intermittent energy sources over time, and deliver a continuous supply of uninterrupted power to the grid. Flywheels also are able to respond to grid signals instantly, delivering frequency regulation and electricity quality improvements.
Flywheel Energy Storage System (FESS), as a clean power resource, has been applied in different applications because of its special characteristics such as high power density, no requirement for periodic maintenance, no pollution, long lifetime, high cycle efficiency (about 85%). Although this energy storage system has relatively high capital cost (5000 $/kWh), it has low annual operation and maintenance cost (19 $/kW-year). The main characteristic of the FESS is its low energy density and high power density, which makes it suitable for short-term applications.
Flywheels are traditionally made of steel and rotate on conventional bearings; these are generally limited to a revolution rate of a few thousand RPM. Modern flywheels are made of carbon fiber materials, stored in vacuums to reduce drag, and employ magnetic bearings, enabling them to revolve at speeds up to 60,000 RPM.
Solid State Batteries – a range of electrochemical storage solutions, including advanced chemistry batteries and capacitors
On its most basic level, a battery is a device consisting of one or more electrochemical cells that convert stored chemical energy into electrical energy. Each cell contains a positive terminal, or cathode, and a negative terminal, or anode. Electrolytes allow ions to move between the electrodes and terminals, which allows current to flow out of the battery to perform work.
The term “lithium-ion” refers not to a single electrochemical couple but to a wide array of different chemistries, all of which are characterized by the transfer of lithium ions between the electrodes during the charge and discharge reactions. Li-ion cells do not contain metallic lithium; rather, the ions are inserted into the structure of other materials, such as lithiated metal oxides or phosphates in the positive electrode (cathode) and carbon (typically graphite) or lithium titanate in the negative (anode). Li-ion systems such as the 129 MWh Hornsdale power reserve are the current state of the art, benefiting from high energy density of Li-ion batteries. Na-S cells are a close competitor (e.g. the 300 MWh Buzen substation), having excellent energy density and low cost.
Li-ion batteries have been deployed in a wide range of energy-storage applications, ranging from energy-type batteries of a few kilowatt-hours in residential systems with rooftop photovoltaic arrays to multi-megawatt containerized batteries for the provision of grid ancillary services.
Sodium Sulfur (NaS) Batteries technology is manufactured by Japanese company NGK. NGK now manufactures the battery systems for stationary applications. The systems operate at a high temperature, 300 to 350 °C, which can be an operational issue for intermittent operation. Significant installations for energy storage to facilitate distribution line construction deferral. The round trip efficiency is in the 90% range so gives an efficient use of energy.
The active materials in a Na/S battery are molten sulfur as the positive electrode and molten sodium as the negative. The electrodes are separated by a solid ceramic, sodium alumina, which also serves as the electrolyte. This ceramic allows only positively charged sodium-ions to pass through.
Both of these battery types use highly flammable parts which increases their cost due to safety considerations. The main goal is optimizing the cost per MWh over the whole lifetime of the battery, for which non-flammable aqueous battery systems are a tempting prospect. They may also be manufactured more cheaply on larger scales than other batteries, which require rigorously dry conditions.
Grid-Scale Battery Storage Is on the Rise
Driven by steeply falling prices and technological progress that allows batteries to store ever-larger amounts of energy, grid-scale systems are seeing record growth in the U.S. and around the world. Many of the gains are spillovers from the auto industry’s race to build smaller, cheaper, and more powerful lithium-ion batteries for electric cars. In the U.S., state clean energy mandates, along with tax incentives for storage systems that are paired with solar installations, are also playing an important role.
California is currently the global leader in the effort to balance the intermittency of renewable energy in electric grids with high-capacity batteries. Vistra Energy is developing 300-megawatt lithium-ion battery and 100 MW battery. 250-megawatt storage project went online this year in San Diego, construction has begun on a 150-megawatt system near San Francisco, a 100-megawatt battery project is nearing completion in Long Beach, and a number of others are in various stages of development around the state. But the rest of the world is rapidly following suit. Recently announced plans range from a 409-megawatt system in South Florida, to a 320-megawatt plant near London, England, to a 200-megawatt facility in Lithuania and a 112-megawatt unit in Chile.
Already the price tag for utility-scale battery storage in the United States has plummeted, dropping nearly 70 percent between 2015 and 2018, according to the U.S. Energy Information Administration. This sharp price drop has been enabled by advances in lithium-ion battery chemistry that have significantly improved performance. Power capacity has expanded rapidly, and batteries can store and discharge energy over ever-longer periods of time. Market competition and rising battery production also play a major role; a projection by the U.S. National Renewable Energy Laboratory sees mid-range costs for lithium-ion batteries falling an additional 45 percent between 2018 and 2030.
Batteries are even beginning to reach a size — around 200 megawatts — that enables renewables to replace small- to medium-sized natural gas generators, Hohenstein says. “Now we’re able to truly build these hybrid resources — solar, storage, wind — and do the job that was traditionally done by fossil fuel power plants,” says Hohenstein, whose company is seeing a surge of interest in such large projects.
The cathodes in the cells Lu and Hu et al. demonstrated are more stable than in other systems, retaining 90% of their energy storage capacity after 10,000 cycles. One reason for their stability is that part of the distortion prone manganese in the Prussian Blue (KxFeyMn1 − y[Fe(CN)6]) material is substituted with iron. Another reason is the use of an electrolyte containing more potassium salt than water, to inhibit the dissolution of the cathode material over its long life. The anode used in the cells, an organic paint pigment (PTCDI), also has the potential to be manufactured cheaply.
The most remarkable feature of the cells was their tolerance of high rates of charging and discharging, comparable to Li-ion battery performance, without losing much of their capacity. Although the overall energy density of the cells is moderate, due to their comparatively low voltage of 1.3 V, there is potential for optimization in this system, both in increasing the voltage by adjusting the cathode metal and anode composition, and by lowering material costs to produce a very low cost per MWh system
Thermal – capturing heat and cold to create energy on demand
Solar thermal power plants, produce all of their energy when the sun is shining during the day. The excess energy produced during peak sunlight is often stored in these facilities – in the form of molten salt or other materials – and can be used into the evening to generate steam to drive a turbine to produce electricity. Alternatively, a facility can use ‘off-peak’ electricity rates which are lower at night to produce ice, which can be incorporated into a building’s cooling system to lower demand for energy during the day.
Startup That’s Storing Energy in Concrete Blocks
A startup called Energy Vault is working on a unique storage method, inspired by pumped hydro, which has been around since the 1920s and uses surplus generating capacity to pump water up into a reservoir. When the water is released, it flows down through turbines and generates energy just like conventional hydropower.
When there’s excess power—on a sunny or windy day with low electricity demand, for example—a mechanical crane uses it to lift the blocks 35 stories into the air. Then the blocks are held there until demand is outpacing supply. When they’re lowered to the ground (or lowered a few hundred feet through the air), their weight pulls cables that spin turbines, generating electricity.
“Heavy” blocks in this case means 35 tons (70,000 pounds or 31,751 kg). The blocks are made of a composite material that uses soil and locally-sourced waste, which can include anything from concrete debris and coal ash to decommissioned wind turbine blades (talk about coming full circle). Besides putting material that would otherwise go into a landfill to good use, this also means the blocks can be made locally, and thus don’t need to be transported (and imagine the cost and complexity of transporting something that heavy, oy).
The cranes that lift and lower the blocks have six arms, and they’re controlled by fully-automated custom software. Energy Vault says the towers will have a storage capacity up to 80 megawatt-hours, and be able to continuously discharge 4 to 8 megawatts for 8 to 16 hours. The technology is best suited for long-duration storage with very fast response times.
Swedish Scientists Develop Liquid That Can Store Solar Energy For More Than a Decade
Scientists in Sweden have developed a specialized fluid, called a solar thermal fuel, that can reportedly store energy captured from the sun for over a decade. “A solar thermal fuel is like a rechargeable battery, but instead of electricity, you put sunlight in and get heat out, triggered on demand,” Jeffrey Grossman, an engineer works with these materials at MIT explained to NBC News.
The exciting liquid is a molecule composed of carbon, hydrogen, and nitrogen. When sunlight makes contact with the liquid the bonds between its atoms are rearranged and it transforms into an energized version of itself called an isomer. The sun’s energy is then captured between the isomers’ strong chemical bonds. Incredibly, the energy stays trapped there even when the molecule cools down to the room temperature. To put the trapped energy to use, the liquid is put through a catalyst which returns the molecule to its original form, releasing energy in the form of heat.
“The energy in this isomer can now be stored for up to 18 years. And when we come to extract the energy and use it, we get a warmth increase which is greater than we dared hope for,” says the leader of the research team, Kasper Moth-Poulsen, Professor at the Department of Chemistry and Chemical Engineering. The research lab placed a prototype of the complete energy system onto the roof of the university and it has already caught the eye of several large investors.
When an energy demand occurs, the fluid is pushed through a catalyst that converts the molecules back to their original form, warming the liquid by 63 degrees Celsius. This warm liquid can be used for can then have application in everything from domestic heating systems, powering a building’s water heater, dishwasher, clothes dryer and much more. The liquid is then pumped back to the roof to be rescued. So far the researchers have put the fluid through this cycle more than 125 times without significant damage to the molecule. The most recent study in the series has been published in Energy & Environmental Science.
South Australian company made silicon energy storage system “ready to close grid gap”
South Australian company 1414 Degrees has developed technology to store electricity as thermal energy by heating and melting containers full of silicon at a cost estimated to be up to 10 times cheaper than lithium batteries. Our energy storage technology presents an opportunity to disrupt the energy market and the use of readily available silicon rocks ensures its sustainability and its affordability, says company.
Australian CleanTech Managing Director John O’Brien said energy storage would undoubtedly be a very significant part of the energy system as nations moved towards low or zero carbon targets in the next decade or two. He said the relatively cheap price of silicon and its ability to be used over and over would help keep the overall lifecycle price down.
A South Australian company behind a silicon based thermal energy storage system has created and successfully tested a full prototype of its technology, which it says is ready for commercialisation after a decade in the making. The company completed its first trials in September with a small prototype test system using about 300kg of silicon to store about 150kw of energy.
The prototype of its thermal energy storage system (TESS) works to store energy by heating and melting containers full of silicon, whose properties of high latent heat capacity and melting temperature make it ideal for the storage of large amounts of energy.TESS was developed in conjunction with the University of Adelaide, and Adelaide-based engineering consultancy ammjohn.
Silicon is the second most abundant element in the earth’s crust after oxygen. A tonne of silicon can store enough energy to power 28 houses for a day. Its high latent heat capacity and high melting temperature of 1414 C – make it ideal for the storage of large amounts of energy.
“The know-how is crucial. Anyone can go and buy some silicon, it’s cheap, it’s $2000 a tonne,” he said. “A single tonne of that (a 50sq cm block), just to melt that, to hold it at melting temperature, what they call the latent heat, in other words the energy of melting, is the equivalent of taking a tonne of water and raising it 200m in the air. “One block like that will store enough energy to keep 28 houses operating for a day.
Moriarty said that while battery chemistries like lithium-ion had a limited life, only lasting a certain number of charging cycles, the TESS was based on a “phase change” – melting and cooling of silicon – and so did not suffer the same limitations. And, as well as storing and dispatching electricity, the system’s excess heat can be used to heat water for space heating and other industrial processes.
The company, which is in the process of changing its name to 1414°, says it is now ready to apply its TESS to industry and generation sites at scales of 10MWh and 200 MWh. Suitable sites for these demonstrations, the company says, would be a wind farm, or an existing gas-fired generator. The technology will increase efficiency and revenues of a wind farm through load shifting to times of maximum demand.
A key benefit of the TESS device is also considered to be its scalability. The trial confirmed that the technology is capable of storing and supplying hundreds of MW of electricity, at just $70,000 per MWh to provide for a reliable electricity supply with up to 90 per cent renewable sources – making it a good fit with the South Australian energy market.“The next phase is to develop the first large, commercial systems over the next two years,” Dr Moriarty said in an interview with the Adeliade Advertiser in October this year.
“This was recognised in CSIRO some years ago although they worked mostly with molten salt because that operates at around 500 degrees. This melts only at 1414 degrees. It will stay at that temperature while it’s melting and provide energy until fully solidified at a constant potential like hydro. No other heat storage system does that. “You can store it, then you can regenerate it.’’
Chemical System Collects, Stores Solar Energy on Molecule for 14 Hours reported in Sep 2020
Researchers from the Leibniz Institute of Photonic Technology (Leibniz IPHT) and Friedrich Schiller University have developed a copper complex-based chemical system for molecularly storing solar energy for at least 14 hours. The system decouples photochemical processes from the day-night cycle, bypassing a barrier that had previously made solar-powered photochemistry unsuitable for continuous industrial production processes.
Previous approaches to the storage of solar energy have been based on solid-state materials. Alternatively, the researchers generated reactive photoredox equivalents on a small molecule, enabling them to not only store the light energy for at least 14 hours, but to regenerate it when needed.
“The dependence on brightness and darkness has so far been a major hurdle when it comes to using solar-powered photochemistry for continuous industrial production processes,” said lead author Martin Schulz, a postdoctoral researcher at the University of Jena and Leibniz IPHT. “We assume that our results will open up new possibilities to research systems for the conversion and storage of solar energy as well as for photo(redox)catalysis.”
In the chemical system, the photosensitizer and the charge storage unit are located on the same molecule, eliminating the need for intermolecular charge transfer between a separate sensitizer and a charge storage unit. The system retains three-quarters of its charge capacity even after four cycles. Rather than using rare and expensive materials such as ruthenium, which had used in previous approaches, the researchers used a copper complex that can be stored after photochemical charging and be used as a reagent in dark reactions, such as the reduction of oxygen. The researchers developed the approach with partners from the University of Ulm, the Leibniz Institute for Solid State and Materials Research Dresden, and Dublin City University.
NASA Funds UCF Research for New Power Systems on Space Missions
NASA has turned to UCF to develop a new way of powering and heating spacecraft when they are far from the sun and solar energy isn’t practical. Mechanical and aerospace engineering Associate Professor Subith Vasu leads the team that will use the three-year $550,000 award to develop storable chemical heat sources that can be controlled to provide heat and electrical energy, even in the very hot or very cold conditions found on some planetary destinations. Vasu, who is also affiliated with the Florida Space Institute, has expertise in rocket propulsion, hypergolic propellants and hybrid propulsion.
According to NASA, objects in space easily reached by our current technology and power systems – mostly solar or radioisotope – have been achieved. But to go farther, a better power system is needed. “Our proposed approach is to use stored chemical-energy sources,” Vasu says. “A thermal source with high specific combustion enthalpy could provide thermal energy necessary for some longer missions.”
A solid-chemical heat source, which produces high exergy heat would enhance NASA’s abilities to operate thermal generation centers on “hot” environments such as Venus, or alternatively provide the mission critical heat necessary for icy world explorations, or deep-space exploration in addition to simultaneously providing electrical power, he says.
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