Energy Storage

Hydrogen Energy Storage

Videos from CNBC:

Sustainable Energy YouTube Channel

Why hydrogen is becoming a big deal, CNBC

Why hydrogen is becoming a big deal, part one | Sustainable Energy duration 15:49

Why hydrogen is becoming a big deal, part two | Sustainable Energy duration 10:38

Hydrogen Powered Transportation – a Review (Nov. 2020)

A recent announcement of the successful first test flight of a hydrogen fuel cell powered plane prompted a review of how the technology is being used in different forms of transportation. Hydrogen fuel on its own has many benefits as an energy storage medium.

General Aviation

There appear to be several ways hydrogen can be used to power aviation. One is to use hydrogen fuel cells to generate electricity that drives electric motors. Another is more direct and involves modifying gas-turbine engines to run on hydrogen instead of jet fuel. Such a gas-turbine can be used in a conventional jet engine or to power a turboprop engine. Companies such as the European Airbus are exploring concept aircraft based on direct use of hydrogen fuel.

Coradia iLint 2-car Train image

Rail

Hydrogen fuel cell technology has a number of advantages in rail transportation. The Austrian rail company ÖBB is planning to test a hydrogen fuel cell train through November of this year, with passengers, on challenging grades. The train, the Coradia iLint built by the French company Alstom is capable of speeds up to 87 mph, can carry 150 seated passengers and 150 standing passengers with a range of 625 miles in a two car configuration. The train has already been tested in the Netherlands (1) and demonstrated that it had fully zero emissions, was quick and easy to refuel, and fitted within the commercial service’s current time table. The train is designed around a converted diesel train. Alstom claims it to be the first passenger train in the world to run on hydrogen fuel cells. Alstom is also known for supplying Amtrak with trainsets for the US north east corridor in 2015. Alstom sees the US market for hydrogen fuel cell technology in the long term to be in converting diesel freight trains.

The BBC:Future Planet website (2) also brings us a story of Hydroflex, a hydrogen fuel cell powered train tested in 2019 in the UK. The set under test had a range of 50-70 miles. Again by retrofitting diesel trains, train service can be provided where electrification is just too expensive to install.

Meanwhile in the US, San Bernardino County Transit Authority has ordered a multiple-unit hydrogen fuel cell powered train from Stadler Rail. The train, a Flirt H2, is expected to enter service in 2024.(3). Somewhat like the Coradia iLint it will have 108 seats with lots of standing room and a top speed of 79 mph.

Busses & Trucks

The California Fuel Cell Partnership (4) reports on a number of projects designed to bring hydrogen fuel cell technology to busses and trucks. Some of these projects have now been running for several years.

AC Transit (The Alameda-Contra Costa Transit District) with 13 busses has put in more than 1.3 million miles and carried 5 million passengers in the Bay Area. In 2019, AC Transit added 10 New Flyer fuel cell electric buses. As part of the program they are comparing these vehicles in real world service against battery only powered busses. Results should be interesting. Joining AC Transit are the counties of Coachella Valley and Orange County Transit Authority, the latter with the OCBus above.

How do Hydrogen Fuel Cells Work? (5)

We are all probably familiar with the electrolysis of water. Put an anode and a cathode in water with a little bit of salt, connect to a supply of direct current and pretty soon you will see bubbles form on both electrodes. The two elements that make up water (H2O) are hydrogen and oxygen. On the anode will be oxygen while hydrogen appears on the cathode. The two elements that make up water. The process consumes energy to run.

That reaction is reversed in fuel cells and thus generates energy and the anode and cathode are switched. It does get tricky because if you take the power source out of the electrolysis cell it doesn’t automatically reverse to generate electricity. Fuel cells can generate electricity for as long as there’s a supply of hydrogen and oxygen, usually from the air. There’s no discharge-recharge cycle as in batteries. Special catalysts on both electrodes allow the electrochemical reactions to proceed and a special electrically isolating membrane between them forces the released electrons to follow an external circuit to deliver the electrical power.

What is this about Energy Density?

One of the advantages of hydrogen-electric powered transportation over battery-electric powered transportation is in the energy to weight ratio.

It’s complicated. Gravimetric energy densities are measured in energy per unit mass of fuel. For example, coal has an energy density of 34 MJ/kg, diesel 43 MJ/kg and hydrogen 140 MJ/kg. By comparison Lithium Ion batteries are currently running up to 0.4-0.9 MJ/kg and this must necessarily include the weight of the container, i.e. the battery. Theoretical rechargeable battery energy densities have been calculated as high as 3.6 MJ/kg. Note for context a mega-Joule (MJ) is about 278 watt-hr or the amount of electricity you might consume by leaving a 10W LED light on for 27.8 hours. So once contained in a gas cylinder, hydrogen has a much lower net energy density, more of the order of 2.1 MJ/kg (4) However, in practice compressed hydrogen occupies more space than other energy sources, it has a lower volumetric energy density and this affects how vehicles have to be designed - larger vehicles can accommodate hydrogen fuel cells more easily.

Where does the hydrogen come from?

None of this means much unless the hydrogen can be generated without fossil fuels. Hydrogen is currently found as a by-product from other processes, manufactured via steam reforming of natural gas at high temperatures, and via electrolysis – where hydrogen can be generated with excess renewable electricity.

The cheapest and most common method at present uses the steam reforming method. The direction of developments is to use renewable energy and electrolysis.

How is it stored?

Generally hydrogen is most commonly stored in its pure form as compressed gas (5,000-10,000 psi), or sometimes cryogenically as liquid hydrogen at around -252.8 deg C (-322 deg F). Another approach is to store hydrogen in another substance either adsorbed or chemically combined but easily released - research continues.

At ‘hydrogen fuel stations’ vehicles can fill up much like current gasoline stations. Light weight composites are being used to develop light weight storage options. California has dozens of hydrogen fuel stations in the Bay Area and around Los Angeles for road vehicles.

How safe is it?

Well, all fuels are flammable and must be handled carefully. However, in many ways, hydrogen is safer to use than conventional fossil fuels. If a leak occurs, lighter-than-air hydrogen gas rises up and disperses rapidly. It is also a non-toxic gas and therefore safe to breathe!

More importantly, the only emission is from the fuel cell operation. Even any unconverted hydrogen is recycled.

But about that plane…

CNBC brought us a report (6), that a six-seater Piper M-class aircraft successfully completed its maiden flight this past September. It was powered by a hydrogen fuel-cell as it took off from Cranfield Airfield just 50 miles north of London, UK. It completed a ‘full pattern circuit’ before landing back at the airfield.

ZeroAvia developed the plane as part of their HyFlier Project. They claim it to be the first commercial-scale hydrogen powered aircraft. According to their press release (7) the company plans to develop 10-20 seat planes within three years. More immediately they hope to develop planes capable of flying between the Orkney Islands and the Scottish mainland, some 250-300 nautical miles, by the end of this year.

Ref:

1.  :"Trial runs of Alstom’s hydrogen train in the Netherlands deemed officially successful"
2.  :"Next stop, hydrogen-powered trains"
3.  :"US hydrogen train contract awarded"
4.  :"California Fuel Cell Partnership"
5.  :"How does the Fuel Cell Work"
6.  :Hydrogen-powered passenger plane completes maiden flight in ‘world first’"
7.  :"ZeroAvia Conducts UK’s First Commercial-Scale Electric Flight"

Gravity Energy Storage

Energy Vault

Energy Vault has created the world’s only cost-effective, utility-scale gravity-based energy storage system that is not dependent on land topography or specific geology underground. When energy is needed a tower of 36 ton blocks is disassembled, recovery energy as they are lowered from a tower. When energy is abundant the tower is rebuilt. Advance computer control makes this possible with round-trip efficiencies of 80 to 90%. See

Energy Vault

Gravitricity

The Gravitricity system suspends weights of 500 - 5000 tonnes in a deep shaft by a number of cables, each of which is engaged with a winch capable of lifting its share of the weight. Electrical power is then absorbed or generated by raising or lowering the weight. Unused mine shafts are candidate sites. See;

Gravitricity Ltd. - a company based in Scotland.

ARES Systems

Advanced Rail Energy Storage (ARES) energy storage technology employs a fleet of electric traction drive shuttle-trains, operating on a closed low-friction automated steel rail network to transport a field of heavy masses between two storage yards at different elevations. The facilities are highly scalable in power and energy ranging from a small installation of 100MW with 200MWh of storage capacity up to large 2-3GW regional energy storage system with 16-24GWh energy storage capacity. See;

Advanced Rail Energy Storage LLC. - based in Washington State

Chemical Energy Storage

Photoelectrosynthesis

Extracting clean fuel from sunlight, Phys.org - Richard Harth, Arizona State University - September 3, 2019

“In new research appearing in the Journal of the American Chemical Society (JACS), the flagship journal of the ACS, lead author Brian Wadsworth, along with colleagues Anna Beiler, Diana Khusnutdinova, Edgar Reyes Cruz, and corresponding author Gary Moore describe technologies that combine light-gathering semiconductors and catalytic materials capable of chemical reactions that produce clean fuel.”

Cryogenic Energy Storage

Liquid Air 'Batteries'

Air turns to liquid when cooled down to -196°C (-320˚F), and can then be stored very efficiently in insulated, low pressure vessels. Exposure to ambient temperatures causes rapid re-gasification and a 700-fold expansion in volume, which is then used to drive a turbine and create electricity without combustion. Such facilities are suitable for large scale storage and can compete with hydrokinetic storage (pumped water).

Highview Power claims round-trip energy efficiencies of up to 70%

Mechanical Energy Storage

Compressed Air Energy Storage

Industrial development of compressed air energy storage (CAES) has made some advances. Since the 1870’s, CAES systems have been deployed to provide effective, on-demand energy for cities and industries. While many smaller applications exist, the first utility-scale CAES system was put in place in the 1970’s with over 290 MW nameplate capacity. Care has to be taken since compressing air heats it up and releasing the pressure cools it down. Thermodynamics have to be managed carefully to the decompress phase doesn't require fuels to heat it up.

Unfortunately, large-scale CAES plants are very energy inefficient. Compressing and decompressing air introduces energy losses, resulting in an electric-to-electric efficiency of only 40-52%, compared to 70-85% for pumped hydropower plants, and 70-90% for chemical batteries. See;

"Ditch the Batteries: Off-Grid Compressed Air Energy Storage" - Low-Tech Magazine - no date.

Flywheel Energy Storage Systems

Flywheel energy storage systems (FESS) use electric energy input which is stored in the form of kinetic energy. Kinetic energy can be described as “energy of motion,” in this case the motion of a spinning mass, called a rotor. The rotor spins in a nearly frictionless enclosure. When short-term backup power is required because utility power fluctuates or is lost, the inertia allows the rotor to continue spinning and the resulting kinetic energy is converted to electricity. See;

"Turn Up the Juice: New Flywheel Raises Hopes for Energy Storage Breakthrough" - Scientific American - Chris Nelder - April 10, 2013

Aluminum-air Flow Batteries

Researchers at the School of Energy and Chemical Engineering at Ulsan National Institute of Science and Technology claim to have developed a new type of aluminum-air flow battery for EVs. The new battery outperforms existing lithium-ion batteries in terms of higher energy density, lower cost, longer cycle life, and higher safety. Aluminum-air flow batteries are primary cells, which means they cannot be recharged via conventional means.

"A novel catalyst for high-energy aluminum-air flow batteries" - Phys.org - Ulsan National Institute of Science and Technology - Oct 15, 2018

Conventional Battery Technology

Conventional battery technology includes a number of chemistries.

• Lithium-Ion
• Lithium-Ion Polymer
• Nickel-Cadmium
• Lead-acid
• Silver Oxide
• Alkaline

From IDTechX, a report on the future of battery technologies is available for purchase (from $5,750):

"Solid-State and Polymer Batteries 2019-2029: Technology, Patents, Forecasts" - undated

"This report covers the solid-state electrolyte industry by giving a 10-year forecast till 2029 in terms of numbers of devices sold, capacity production and market size, predicted to reach over $25B. A special focus is made on winning chemistries, with a full analysis of the 8 inorganic solid electrolytes and of organic polymer electrolytes. This is complemented with a unique IP landscape analysis that identifies what chemistry the main companies are working on, and how R&D in that space has evolved during the last 5 years."

Energy Density of Different Storage Technologies

The higher the energy density of a fuel or storage technology, the more energy may be stored or transported for the same amount of volume. The energy density of a fuel or storage technology per unit mass is called the specific energy of that fuel or storage technology.

The higher the numbers for renewable technologies the easier it becomes to replace fossil fuels in transportation, for example Gasoline has a specific energy of 12,888.9 Watt-hours/kg, while Lithium-Ion batteries are 100.00–243.06 Watt-hours/kg. However, available energy has to be considered. Internal combustion engines have a 20-40% efficiency, while the efficiency of batteries/electric motors are expected to be higher, and depends on other features like braking energy recapture.