Mass Gigawatt Storage is closer than you may think
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- Jul 27, 2020 3:53 pm GMTJul 24, 2020 4:31 pm GMT
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This item is part of the Special Issue - 07/2020 - Energy Storage, click here for more
Written by: Virgil Perryman and Shiva Vencat
Vaclav Smil is a Professor Emeritus at the University of Manitoba and a confidant of Bill Gates, who challenged the possibility of rapid transition from fossil fuels.
Professor Smil once answered that the one technology that could change the prevailing trends was Energy Storage. “Give me mass-scale storage, and I don’t worry at all. With my wind and [solar] photovoltaics, I can take care of everything,” he told Science. “But we are nowhere close to it.”
Admittedly we are still far, but there are reasons to be optimistic.
Let’s look at the usual suspects with the primary Pros and Cons in order of market penetration:
1) LITHIUM-ION: by far the biggest culprit of all. Pros - It is readily available and mass-produced. Cons - Lithium-Ion is made of lithium, which is highly volatile, reactive with water, toxic, relatively rare, with sources coming primarily from Chile, the US, China, and a few other countries. Many lithium batteries use cobalt, which, like lithium, is sensitive to movement in demand and is proportionally expensive. The current lithium battery technology is costly and short-lived. They are ineffective at temperatures before -10°C and above +50°C. Other variations of lithium-based batteries may, in time, improve in cost and durability.
2) FLOW BATTERIES: Pros - Their storage and discharge capacity are constant, and they have a very long life and can be made from non-toxic, non-reactive material, unlike lithium-ion. Cons - Their efficiency is lower than lithium-ion batteries; they are disproportionally heavy and large for the current they produce. They, also like lithium-ion, are sensitive to both lower and higher temperatures.
3) FLYWHEELS: Pros - Environmentally friendly, as they are built with harmless materials, without hazardous chemicals. Cons - There are safety risks that can arise if a flywheel is loaded up with more energy than its components can handle, or there is catastrophic structural failure. They are also proportionally large based on the current they can produce.
4) COMPRESSED AIR ENERGY STORAGE (CAES): Pros - CAES is relatively inexpensive if it is installed using an existing natural storage formation. It can provide energy for days, not hours)? Uses mostly off-the-shelf equipment and is easily scaled to whatever sizes are needed. They are (efficient) ? as a gas turbine and do not lose efficiency over their several decades of operational life. Cons - CAES requires specific geographic areas that have salt caverns. (A new adaptation can be deployed using extreme pressure to store heat and air for lots of power for the liquefaction of air) ?. However, based on all end-to-end costs, this newer technology is far more costly than a typical CAES installation (at equal or lower efficiency)?
5) HYDRO and GRAVITY DRIVEN: Pros - Hydro is one of the oldest proven storage technologies. It contributes to the development of remote communities, lasts for well over a half-century, has very low maintenance, and can support both power production and water needs. Cons - It has high initial capital costs, is location-specific, and can be vulnerable to a lack of rainfall. A new development is gravity driven technology which uses winches instead of pumps to lift a mass, as opposed to pumping water, and is not location-specific. But the overall end-to-end efficiency is lower than most other storage options.
6) HIGH-TEMPERATURE PHASE-CHANGE THERMAL ENERGY STORAGE (we are ignoring passive thermal rock storage and ceramic thermal storage): Almost all thermal storage (TES), with the exception of passive energy, can be adapted to providing (CHP) ?. Thermal energy is often more in-demand than power. High temperature phase-change thermal storage presently has three categories:
- MOLTEN SALT: Pros - Has a very long life, is well-accepted in the market offering reasonable thermal transfer and chemical stability, and cheap thermal energy storage (TES) capability. Cons - Most expensive of the thermal storage technologies. It requires direct thermal input, cannot be charged efficiently using electricity, does not store energy higher than 600°C, and the salts are toxic and corrosive. The storage units are disproportionally heavy and large for the energy they store and can only use a steam turbine to generate electricity at 35% efficiency or lower. It also stores energy for less than 24 hours in its best configuration.
- MOLTEN SILICON: Pros - Can store up to 1450°C, offering a very long life, chemical stability, and reasonable thermal energy storage (TES) capability. It is non-toxic, can use both simple and combined cycle to generate power up to 70% efficiency, has a smaller footprint than molten salt and can be efficiently charged with electricity. Cons - Stores for less than 24 hours in its best configuration. Lower thermal conductivity than molten salt (using liquids and gases as well a pressure limitation) ?. It is the second most expensive and heaviest, with (the largest volume-based on storage capacity per volume or mass of the three-storage system)? This is also a new technology, yet to be fully accepted,
- MOLTEN METAL: Pros - It can normally store up to 1750°C with the added ability to store up to 2750°C in certain configurations, offers a very long life of 4-5 decades, is chemically stable, has the highest storage capacity of any storage technology, (can be charged a <96% using electricity)? and is non-toxic. Molten metal can use both simple and combined cycle to generate power up to 70% efficiency, has the smallest footprint of any of the phase-change technologies. It provides the highest mass to storage capacity, with a base-line storage capacity of 4MJ per kg, and the capacity of 8 MJ at highest temperature configuration. (Least expensive based of kW thermal stored against cost per kW of any storage technology inclusive to the inefficiency of thermal to electric conversion) ?. It has the highest thermal transfer of any thermal storage technology <3,000W/m·K, with no pressure limitations, can store for months as opposed to hours or days and is based on 200-year-old high-temperature metallurgy. Cons - This new technology is only ten years old and not yet widely known. (of its mature metallurgy background it is yet to be fully accepted, presently in limited production as all phase-change technologies efficiency is limited to the efficiency of the thermal electric device use to produced power)?
CONCLUSION: Contrary to Professor Smil’s belief that mass storage is a more distant future technology, the trends say otherwise. Storage has moved into the forefront of many concerns about the transition to cleaner and greener energy. Even today, the flywheel is maturing and gravity and air pressure are likewise maturing into technologies that can be scaled up to gigawatts. Thermal energy storage, especially metal storage, which today can store several gigawatts in the size of a football pitch at well under $50 per kW and (is close to economically doubling its storage capacity) ?.There needs to be a broader understanding of the substantial benefits associated with the use of molten metal storage. Further efforts are necessary to inform and educate the energy industry and their consumers on the cost and environmental advantages of this important maturing technology.“