2. Energy Construction
& Utilities
California Community Colleges
Workforce & Economic Development
• Utility Grid
• Transmission
• Bulk Storage for
Load/Resource
Management
• Spinning Resource
• Ancillary Services
• Renewable Energy
Integration
• Distribution
• Peaker/Backup Resource
• Power Quality
• Customer Site
– Energy Cost
Management
– Renewable Energy
Output & Load
Matching
– Backup
– Power Quality
Energy Storage Applications
5. Energy Construction
& Utilities
California Community Colleges
Workforce & Economic Development
Charge Charge
Discharge
39% Cost
Savings
*Mock load, electric rate & cost
Customer Load
Management, cont.
6. Energy Construction
& Utilities
California Community Colleges
Workforce & Economic Development
Over Generation
Under Generation
Charge
Discharge
Customer Load
Management, cont.
7. Energy Construction
& Utilities
California Community Colleges
Workforce & Economic Development
• Uninterruptible
Power Supply (UPS)
– Critical device
level
• Facility Backup
– Critical systems
or buildings
APC Back-UPS,
200 Watts /350 VA,
Input 120V
/Output 120V
ABB Conceptpower
DPA 500 100 kW up
to 3 MW
Energy Storage for
Backup Power
8. Energy Construction
& Utilities
California Community Colleges
Workforce & Economic Development
• Impulsive Transient
• Oscillatory Transient
• Sag/Swell
• Under-/Over-voltage
• Interruption
• Harmonic Distortion
• Voltage Flicker
• Electrostatic Discharge
• Noise
Power Quality is Important
The symptoms of a power quality problem could be as subtle as
a light that dims every time a large motor starts or as
catastrophic as equipment failure. Whatever the case, power
quality problems may disrupt your business operations. Today,
there is widespread use of digital or microprocessor controlled
devices in all areas of our customer's businesses.
Many of these new devices are more sensitive and may not
operate properly when small variations or disruptions in the
electrical supply occurs. Some examples of problems that occur
due to power quality problems are: Automatic Resets, Data
Errors, Equipment Failure, Circuit Board Failure, Memory Loss,
Power Supply Problems, UPS Alarms, Software Corruption, and
Overheating of electrical distribution systems.
Source: https://www.hawaiianelectric.com/for-businesses/power-quality-for-
businesses/power-quality-problems
Power Quality
9. Energy Construction
& Utilities
California Community Colleges
Workforce & Economic Development
• Allows microgrids to operate non-carbon emitting resources
• Helps achieve islanding and shifting time-of-use
• Allows distributed generation to synchronize with or without the presence of
the grid (PV generation requires a voltage source with which to synchronize)
• “Smooths” power flow from intermittent sources
Microgrids and Storage
Potential benefits are the same, but scaled for local services
Image source: Siemens, Inc.
10. Energy Construction
& Utilities
California Community Colleges
Workforce & Economic Development
Electric to Stored
Energy Conversion
Stored to Electric
Energy Reconversion
Stored
Energy
AC Electricity
AC Electricity
Energy
Storage
Capacity
AC to ?
Conversion
Losses
? to AC
Conversion
Losses
Simple Electric Energy
Storage Device
𝛥
11. Energy Construction
& Utilities
California Community Colleges
Workforce & Economic Development
• Hydraulic
• Pumped Hydro Storage (PHS)
• Pneumatic
• Compressed Air Energy Storage (CAES)
• Kinetic
• Flywheel Energy Storage (FES)
• Electromagnetic
• Superconducting magnetic energy storage (SMES)
• Electrical
• Double Layer Capacitors (DLC)
Energy Storage
Technology Types
12. Energy Construction
& Utilities
California Community Colleges
Workforce & Economic Development
• Electro-chemical
• Nickel Cadmium (Ni-Cd)
• Iron Chromium (Fe-Cr)
• Lithium Ion (Li-ion)
• Sodium Sulfur (NaS)
• Lead Acid (LA)
• Zinc Air (Zn-air)
• Sodium Nickel Chloride (NaNiCl)
• Vanadium Redox Flow Battery (VRFB)
• Zinc-Bromide Hybrid Flow Battery (ZnBr HFB)
Electro-Chemical Energy
Storage Technology Types
14. Energy Construction
& Utilities
California Community Colleges
Workforce & Economic Development
AES Storage LLC’s Laurel
Mountain Energy Storage supplies
32 MW of regulation in PJM
territory using Li-ion batteries.
Source: DOE/EPRI 2013 Electricity
Storage Handbook
Lithium Ion Battery, cont.
15. Energy Construction
& Utilities
California Community Colleges
Workforce & Economic Development
A 30 kW/34 kWh Distributed Energy Storage Unit being installed at the Anatolia
SolarSmart Homes in SMUD territory.
Source: DOE/EPRI 2013 Electricity Storage Handbook
Lithium Ion Battery, cont.
16. Energy Construction
& Utilities
California Community Colleges
Workforce & Economic Development
Residential Energy
Storage and Energy
Management System
Source: DOE/EPRI 2013
Electricity Storage Handbook
Lithium Ion Battery, cont.
17. Energy Construction
& Utilities
California Community Colleges
Workforce & Economic Development
Principles of the
Vanadium Redox
Battery
Source: DOE/EPRI 2013
Electricity Storage
Handbook
Vanadium Redox Flow Battery
18. Energy Construction
& Utilities
California Community Colleges
Workforce & Economic Development
Prudent Energy 600-
kW/3,600-kWh VRB-
ESS Installed at Gills
Onions, Oxnard, CA
Source: DOE/EPRI 2013
Electricity Storage
Handbook
Vanadium Redox Flow
Battery, cont.
19. Energy Construction
& Utilities
California Community Colleges
Workforce & Economic Development
Zinc-bromine Cell Configuration
Source: DOE/EPRI 2013 Electricity Storage Handbook
The Zinc-bromine battery is another type of flow battery in which
the zinc is solid when charged and dissolved when discharged
Zinc Bromine Flow Battery
20. Energy Construction
& Utilities
California Community Colleges
Workforce & Economic Development
A 90-kW/180-kWh Zinc-
bromine Energy Storage
System by RedFlow
Housed in a 20 foot
shipping container.
Source DOE/EPRI 2013
Electricity Storage Handbook
Zinc Bromine Flow
Battery, cont.
21. Energy Construction
& Utilities
California Community Colleges
Workforce & Economic Development
Principles of Operation
of an Iron-Chromium
Battery Energy Storage
System. Source:
DOE/EPRI 2013 Energy
Storage Handbook.
Iron Chromium Flow Battery
22. Energy Construction
& Utilities
California Community Colleges
Workforce & Economic Development
Photo Courtesy of EnerVault.
Source: DOE/EPRI 2013 Electricity Storage Handbook
Iron Chromium Flow Battery
24. Energy Construction
& Utilities
California Community Colleges
Workforce & Economic Development
• Control box that can be incorporated into a
water heater to add grid interoperability.
• Also adding a remotely controlled resistive
heating element to the bottom of the water
tank.
• Since the water in the tank will naturally
stratify, the utility or aggregator will have
control of the initially cold water at the
bottom of the tank.
• The remotely controlled resistive element is
used to preheat this cold “make-up” water
as needed to any temperature up to
standard DHW temperatures. Thus,
consistent DHW temperatures are
maintained at the outlet.
Grid Integrated Water
Heaters
25. Energy Construction
& Utilities
California Community Colleges
Workforce & Economic Development
• A heat sink can be generated
during off peak periods to
provide cooling during on-peak
periods.
• Chilled water, ice “shuckers”, ice
on coil, eutectic salt systems
available.
• Economic benefits dependent on
electric rate design (TOU, peak
demand charges, etc.) and when
building cooling load can occur.
• Can be used for industrial process
and agricultural cooling too.
Source: U.S. Dept. of Energy
“Cool” Thermal Energy
Storage
26. Energy Construction
& Utilities
California Community Colleges
Workforce & Economic Development
• Hydrogen is “clean” non-GHG producing
fuel for fuel cells and combustion engines.
It can be used for electric generation,
mechanical power, heating, cooling and
transportation purposes.
• Electrolysis of water is one way to
produce hydrogen and can use electricity
produced from renewable resources.
• Electrolyzers can range in size from small,
appliance-size equipment to large-scale,
central production facilities.
• The round trip efficiency today is as low as
30 to 40% but could increase up to 50% if
more efficient technologies are developed.
[Source: Energy Storage Association]
Source: U.S. DOE Office of Energy
Efficiency & Renewable Energy
Anode Reaction: 2H2O → O2 + 4H+ + 4e-
Cathode Reaction: 4H+ + 4e- → 2H2
Hydrogen Energy Storage
Editor's Notes
Energy storage can be applied in many different scenarios resulting in different benefits. The applicable markets can be divided into two major groups; utility grid and customer site markets.
Energy storage can perform a number of services that peaking generators have historically performed for the utility grid. For customers, energy storage can help integrate renewable energy systems, provide backup power and improve power quality.
This chart illustrates which energy storage technologies match with various applications and services.
The larger and slower energy storage technologies tend to be best matched with bulk power management.
While smaller and faster energy storage technologies tend to best for power quality and grid support services.
Many electric utility customers’ electric rates are based on time of use. Typically, the cost of electricity is much higher during daily peak periods than at night.
This chart illustrates the load and cost per hour for a hypothetical customer Time-of-Use (TOU) electric rates.
Energy storage can be used to mitigate on-peak electric costs by charging during the off-peak and discharging during the more expensive on-peak period.
In this example, there is a 39% cost savings to the customer for peak electric demand days. This would be typical for a large commercial to industrial customer.
Energy storage can also help match the output of renewable energy systems with customer load.
The energy storage system would charge during periods where the renewable energy system is over-generating relative to the customer load.
Conversely it would discharge to support the customer load when the renewable energy system is under-generating
Energy storage can also be used as backup power in case of electric grid outage. Uninterruptible power supplies (UPS) are energy storage systems that provide this kind of service.
UPS applications are especially important for public safety, health, security services and other critical loads. Energy storage systems may even help protect us in the event of a cyber attack on the electric power grid.
Poor power quality can damage customer equipment, especially sensitive electronics. Many of these examples of power quality issues can be mitigated with fast acting energy storage:
Impulsive Transient is one of the two types of transient disturbance that may enter the power system. It is defined by IEEE 1159 as a sudden, non–power frequency change in the steady-state condition of voltage, current, or both that is unidirectional in polarity – either primarily positive or negative. It is normally a single, very high impulse like lightning.
Oscillatory Transient is described as a sudden, non–power frequency change in the steady-state condition of voltage, current, or both that has both positive and negative polarity values (bidirectional).
A "sag" is the opposite situation: the RMS voltage is below the nominal voltage by 10 to 90% for 0.5 cycle to 1 minute
When the RMS voltage exceeds the nominal voltage by 10 to 80% for 0.5 cycle to 1 minute, the event is called a "swell".
Over/under-voltage condition is reached when the voltage exceeds/lags the nominal voltage by 10% for more than 1 minute.
Interruptions are classified by IEEE 1159 into either a short-duration or long-duration variation. However, the term “interruption” is often used to refer to short-duration interruption, while the latter is preceded by the word “sustained” to indicate a long-duration. They are measured and described by their duration since the voltage magnitude is always less than 10% of nominal.
Total Harmonic Distortion. The level of harmonic distortion is often used to define the degree of harmonic content in an alternating signal.
Voltage Fluctuations/Flickers are described by IEEE as systematic variations of the voltage waveform envelope, or a series of random voltage changes, the magnitude of which falls between the voltage limits set by ANSI C84.1. Generally, the variations range from 0.1% to 7% of nominal voltage with frequencies less than 25 Hz.
An ElectroStatic Discharge (ESD) event is when a static charge is bled off in an uncontrolled fashion.
Noise, or more specifically electrical noise, is a rapid succession of transients tracking up and down along the voltage waveform. The magnitude of these rapid transients is usually much less than that of an isolated transient.
Energy storage can provide microgrids with the same benefits as for other grid-connected systems when managed as part of an on-site system of DERs and loads. It can also provide essential services when grid interconnection does not exist. These services include:
Allowing microgrids to operate non-carbon emitting resources
Helping achieve islanding and shifting time-of-use
Allowing distributed generation to synchronize with or without the presence of the grid (PV generation requires a voltage source with which to synchronize)
Smoothing power flow from intermittent sources
Many now consider storage an essential building-block for any microgrid.
All energy storage operation can be separated into three distinct modes:
Charge
Where electricity is converted into the stored state
Charge rate is the rate of electric power that can be converted and stored
Conversion losses can vary depending the conversion method
Standby
Where the stored energy is held until it is needed
There are usually stand-by losses, which its rate may increase, decrease, or remain constant over time
Discharge
Where the stored energy is converted into useable electricity
Discharge rate is the rate of stored energy can be converted into electric power and may not be the same rate as the charge rate
Conversion losses can vary depending the conversion method and may not be symmetrical with charge conversion losses
When developing the system integration design all of these performance parameters are important to model to correctly ascertain each of their impact on overall project performance.
These are the primary energy storage technologies that are not electrochemical:
Superconducting Magnetic Energy Storage (SMES) systems store energy in the magnetic field created by the flow of direct current in a superconducting coil which has been cryogenically cooled to a temperature below its superconducting critical temperature.
A capacitor (originally known as a condenser) is a passive two-terminal electrical component used to store electrical energy temporarily in an electric field.
A supercapacitor (SC) (sometimes ultracapacitor, formerly electric double-layer capacitor (EDLC)) is a high-capacity electrochemical capacitor with capacitance values much higher than other capacitors (but lower voltage limits) that bridge the gap between electrolytic capacitors and rechargeable batteries.
Electrochemical energy storage (batteries) come in many varieties and forms.
They are primarily defined by the anode, cathode and electrolyte materials used, as well as their specific electrochemistry.
For example, Ni-Cd batteries use nickel hydroxide Ni(OH) 2 for the positive electrode (cathode), cadmium Cd as the negative electrode (anode), and an alkaline potassium hydroxide KOH electrolyte.
Lithium Ion (Li-ion) battery technology has emerged as the fastest growing platform for stationary storage applications.
Lithium-ion batteries can be dangerous under some conditions and can pose a safety hazard since they contain, unlike other rechargeable batteries, a flammable electrolyte and are also kept pressurized. Because of this the testing standards for these batteries are more stringent than those for acid-electrolyte batteries, requiring both a broader range of test conditions and additional battery-specific tests.
The most common types of Li-ion cells are cylindrical and prismatic cell.
Rechargeable Li-ion batteries are commonly found in consumer electronic products, which make up most of the estimated worldwide production volume of 30 GWh per year. But they are also found in large stationary storage applications.
PV and Storage Demonstration at Anatolia assesses customer and edge of grid-sited storage to address intermittent PV, peak load reduction, and customer energy cost reduction. 2010-2013 time frame. Lithium Ion batteries are used for renewables smoothing, renewables shifting, peak load reduction, and customer Time-of-Use (TOU) energy cost reduction.
The term lithium-ion does not refer to a single electrochemical pairing but to a wide variety of different chemistries.
Li-ion cells do no 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 electrode (anode)
Chemistry, performance, cost and safety characteristics vary across Lithium Ion battery types.
Handheld electronics mostly use Lithium Ion batteries based on lithium cobalt oxide (LiCoO2), which offers high energy density, but presents safety risks, especially when damaged.
Lithium iron phosphate (LFP), lithium manganese oxide (LMO) and lithium nickel manganese cobalt oxide (NMC) offer lower energy density, but longer lives and inherent safety. These battery chemistries are used in stationary storage applications.
Vanadium reduction and oxidation (redox) batteries are of a type known as flow batteries.
Vanadium ions remain in an aqueous acidic solution throughout the entire process.
During charging V3+ ions are converted to V2+ ions at the negative electrode through the acceptance of electrons. Meanwhile, at the positive electrode, V4+ ions are converted to V5+ ions through the release of electrons.
During discharge, the reactions run in the opposite direction, resulting in the release of the chemical energy as electrical energy.
In construction, the half-cells are separated by a proton exchange membrane that allows the flow of ionic charge to complete the electrical circuit.
Both the negative and positive electrolytes are composed of vanadium and sulfuric acid mixture. The electrolytes are stored in external tanks and pumped as needed to the cells. The two electrolytes are identical when fully discharged. This makes shipment and storage simple and inexpensive and greatly simplifies electrolyte management during operation.
The cell stack has a useful life of 10 years.
The electrolytes and the active materials they contain do not degrade with time.
Vanadium redox systems are capable of stepping from zero output to full output within a few milliseconds. The cell stack can produce three times the rated power output provided the state of charge is between 50% and 80%.
Systems are rated at 10,000 cycles.
The physical scale of vanadium redox systems tends to be large due to the large volumes of electrolyte required. Sizes range from 50 kW to 1000 kW.
Applications include renewable integration, end user energy management, and telecom applications.
When decommissioning a vanadium redox system,
the solid ion exchange cell membranes may be highly acidic or alkaline and therefore toxic
If possible, the liquid electrolyte is recycled
If disposed of, the vanadium is extracted from the electrolyte before further processing of the liquid
Research is ongoing to determine the exact environmental risk factors for vanadium.
In Zinc Bromine Flow Batteries, each cell is composed of two electrode surfaces and two electrolyte flow streams separated by a micro-porous film.
The positive electrolyte is called a catholyte; the negative is the anolyte. Both electrolytes are aqueous solutions of zinc bromine (ZnBr2).
The cell electrodes are composed of carbon plastic and are designed to be bipolar. This means that a given electrode serves both as the cathode for one cell and the anode for the next cell in series. Carbon plastic must be used because of the highly corrosive nature of bromine.
The most common factor in degradation and potential failure of Zinc-bromine batteries arises from the extremely corrosive nature of the elemental bromine electrolyte. Past failure modes have included damaged seals, corrosion of current collectors, and warped electrodes.
Vendors claim estimated lifetimes of 20 years and long cycle lives.
Operational ac-to-ac efficiencies are estimated to be approximately 65%.
Module sizes vary by manufacturer but can range from 5 kW to 1000 kW.
Variable energy storage duration from two to six hours.
Bromine is a toxic material and should be recovered in the event of a spill or when the unit is decommissioned.
Zinc-bromine is a corrosive and should be handled appropriately.
Iron-Chromium Flow Batteries were pioneered and studied by NASA in the 1970’s and 1980’s and by Mitsui in Japan.
The Iron-Chromium Flow Battery is a redox flow battery.
The active chemical species are fully dissolved in the aqueous electrolyte at all times.
During the discharge cycle Cr2+ is oxidized to Cr3+ in the negative half cell and an electron is released to do work in the external circuit. In the positive half cell during discharge, Fe3+ accepts an electron from the external circuit and is reduced to Fe2+. These reactions are reversed during the charge cycle when current is supplied from the external circuit.
Hydrogen ions are exchanged between the two half cells to maintain charge neutrality as electrons leave one side of the cell and return to the other side. Hydrogen ions diffuse through the separator, which electronically separates the half cells.
The standard cell voltage is 1.18 volts and cell power densities are typically 70-100 mW/cm2.
The DC/DC RTE of this battery has been reported in the 70-80%.
Efficiency is enhanced at higher operating temperatures in the range of 105-140 F.
Iron-Chromium Flow Batteries are available for telecom back-up at the 5 kW – 3 hour scale and have been demonstrated at the utility scale.
The iron and chromium chemistry is relatively benign compared to other electrochemical systems. The iron and chromium species have very low toxicity and the dilute water-based electrolyte has a very low vapor pressure. These factors combine to make the iron-chromium redox flow battery one of the safest battery based energy storage systems.
This table summarizes the performance characteristics of the various types of electrochemical battery technologies.
Electric water heaters account for 9% of all electricity consumed by households nationally. This represents the third single largest source of residential electricity consumption, behind only space cooling (13%) and lighting (11%). More than 40 percent of U.S. households have electric water heating. Office buildings, campuses, and manufacturing facilities have hot water heaters and consume a significant amount of energy as well.
Water heaters could be used as energy storage for intermittent sources such as wind energy. For example, they can be controlled to slowly allow the water at the bottom of the tanks to cool so that at midnight, we can have relatively small capacity - just enough to serve a household’s or business’s hot water needs. Then, through the course of the night, when the wind is typically blowing strongly, it can be charged up, heating all the water in the tank for morning use.
Then, when morning electricity peak demand arrives, the water heater can be turned off almost completely in order to draw off that stored hot water capacity. From that point on, over the course of the day, energy can be put in, but at a rate less than what is coming out. Such a strategy can be scaled-up for businesses as needed.
Excess capacity could also be made available to absorb power that comes when wind power spikes, or substations trip offline.
These kinds of deep discharge and recharge cycles can shorten the life of batteries asked to do similar tasks,. Unlike batteries, there are 50 million or so electric water heaters in the United States already in place, ready to serve wind power storage and fast-response needs.
Electric water heaters have an 8 percent to 10 percent average turnover rate every year, therefore deployment of this technology could be fairly rapid.
Cool Thermal Energy Storage (TES) has become one of the primary solutions to the electrical power imbalance between daytime need and nighttime abundance. Although “cool thermal energy” sounds like a contradiction, the phrase “thermal energy storage” is widely used to describe storage of both heating and cooling energy. Heating TES usually involves using inexpensive, off-peak power to add heat to a storage medium for later use. In contrast, cool TES uses off-peak power to provide cooling capacity by extracting heat from a storage medium, such as ice, chilled water, or “phase-change materials.”
Typically, a cool storage system uses refrigeration equipment at night to create a reservoir of cold material. During the day, the reservoir is tapped to provide cooling capacity. There are many advantages to using a cool TES system. Lower nighttime temperatures allow refrigeration equipment to operate more efficiently than during the day, reducing energy consumption. Less chiller capacity is required, which means lower capital equipment costs. And, at a macro scale, using off-peak electricity to store energy for use during peak hours, daytime peaks of power consumption are reduced, forestalling the need to build expensive new power plants.
Cool Storage Using Ice is an efficient cool storage medium. Cool storage systems using ice can store and release 144 British thermal units (Btu) per pound (334,000 joules per kilogram) during melting and freezing, whereas chilled water systems can store only about 18 Btu per pound (41,780 joules per kilogram)—about one-eighth the capacity per pound of an ice storage system. But it is less efficient than systems that use chilled water to create the heat sink.
A potential benefit of ice is that it’s generally colder than chilled water or phase-change materials, unless the chilled water is treated with an additive. A cooler storage medium produces cooler air, so less air needs to be moved to cool a building. Because fans that move the air can be smaller, they cost less and use 30% to 40% less energy than a conventional system does, according to Electric Power Research Institute. Also, duct size can be 20% to 40% smaller and air handlers 30% to 50% smaller, requiring less initial equipment cost and less cost for the building space needed to house mechanical equipment.
Chilled-Water cool storage has the advantage of using water as a cool storage medium in that constructing chilled-water storage tanks is economically attractive in larger buildings. Chilled water systems have proven to be more reliable over the long term than other cool storage technologies. They are well suited for large district and campus cooling systems.
Phase-Change Materials cool storage uses salts developed to undergo liquid/ solid phase changes at temperatures as high as 47°F (8°C), and to store and release large amounts of energy during the phase change. Stored in hermetically sealed plastic containers, phase-change materials change to solids as they release heat to chilled water that flows around them. At these temperatures, chillers can operate more efficiently than at the low temperatures required by ice storage systems. Phase-change materials also store about three times more Btu per pound (joules per kilogram) than a typical chilled-water storage system.
Electrolysis is a promising option for hydrogen production from renewable resources. Electrolysis is the process of using electricity to split water into hydrogen and oxygen. This reaction takes place in a unit called an electrolyzer. Electrolyzers can range in size from small, appliance-size equipment that is well-suited for small-scale distributed hydrogen production to large-scale, central production facilities that could be tied directly to renewable or other non-greenhouse-gas-emitting forms of electricity production.
How Does it Work?
Like fuel cells, electrolyzers consist of an anode and a cathode separated by an electrolyte. Different electrolyzers function in slightly different ways, mainly due to the different type of electrolyte material involved.
Polymer Electrolyte Membrane Electrolyzers
In a polymer electrolyte membrane (PEM) electrolyzer, the electrolyte is a solid specialty plastic material.
Water reacts at the anode to form oxygen and positively charged hydrogen ions (protons).
The electrons flow through an external circuit and the hydrogen ions selectively move across the PEM to the cathode.
At the cathode, hydrogen ions combine with electrons from the external circuit to form hydrogen gas.
Alkaline Electrolyzers
Alkaline electrolyzers operate via transport of hydroxide ions (OH-) through the electrolyte from the cathode to the anode with hydrogen being generated on the cathode side. Electrolyzers using a liquid alkaline solution of sodium or potassium hydroxide as the electrolyte have been commercially available for many years. Newer approaches using solid alkaline exchange membranes as the electrolyte are showing promise on the lab scale.
Solid Oxide Electrolyzers
Solid oxide electrolyzers, which use a solid ceramic material as the electrolyte that selectively conducts negatively charged oxygen ions (O2-) at elevated temperatures, generate hydrogen in a slightly different way:
Water at the cathode combines with electrons from the external circuit to form hydrogen gas and negatively charged oxygen ions. The oxygen ions pass through the solid ceramic membrane and react at the anode to form oxygen gas and generate electrons for the external circuit. Solid oxide electrolyzers must operate at temperatures high enough for the solid oxide membranes to function properly (about 700°–800°C, compared to PEM electrolyzers, which operate at 70°–90°C, and commercial alkaline electrolyzers, which operate at 100°–150°C). The solid oxide electrolyzers can effectively use heat available at these elevated temperatures (from various sources, including nuclear energy) to decrease the amount of electrical energy needed to produce hydrogen from water.
Potential for synergy with renewable energy power generation Hydrogen production via electrolysis may offer opportunities for synergy with variable power generation, which is characteristic of some renewable energy technologies. For example, though the cost of wind power has continued to drop, the inherent variability of wind is an impediment to the effective use of wind power. Hydrogen fuel and electric power generation could be integrated at a wind farm, allowing flexibility to shift production to best match resource availability with system operational needs and market factors. Also, in times of excess electricity production from wind farms, instead of curtailing the electricity as is commonly done, it is possible to use this excess electricity to produce hydrogen through electrolysis.
[Source: https://energy.gov/eere/fuelcells/hydrogen-production-electrolysis]
