Energy Storage Methods

ECE 371Sustainable Energy Systems

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Methods Batteries (Been there. Done that…)

But there is more, a lot more…

Flywheels Compressed Air Hydraulic Energy Storage Reversible Electrolyzer/Fuel Cells (Hydrogen) Hydrogen Pumped-Hydro Storage Thermal Superconducting Magnetic Energy Storage (SMES)

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Pumped-Hydro Energy Storage

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Pumped-Hydro Energy Storage

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Energy Storage

Efficiency Losses Evaporation Leakage (90%) Pump Efficiency (85%) Generator Efficiency (85%)

Used for Bulk Energy Storage

𝐸𝐸 = 𝑚𝑚𝑚𝑚𝑚𝑚 = 𝜌𝜌𝜌𝜌∆ℎ gH

Pumped-Hydro Energy Storage

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Compressed Air Energy Storage

Bulk Energy Storage Use the grid surplus to compress air in a

reservoir. (During hours of low demand.) When needed, compressed air is heated

and expanded through a gas turbogenerator to produce electricity.

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Compressed Air Energy Storage

Bulk Energy Storage Use the grid surplus to compress air in a

reservoir. (During hours of low demand.) When needed, compressed air is heated

and expanded through a gas turbogenerator to produce electricity.

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Huntorf Germany

Two air caverns of 140 000 and 170 000 m3. Cavern depth 500 m, pressure 1 to 70 bar. (1 bar

is 14.5 psi) Plant can generate 290 MathWorks for 2 hours. To produce 1 kWh of peak load electricity

requires 0.8 kWh of base-load electricity 1.6 kWh of gas.

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Alabama, USA

Underground caverns at a depth of 457 m. 360 MathWorks capacity.

In the future, CAES systems will be able to operate without fossil fuels and produce 1 kWh of peak electricity by using only 1.4 kWh of off peak electricty. (71% efficiency)

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Flywheel Energy Storage Sometimes called a mechanical battery. Store energy as rotational kinetic energy. Two classes: Below 10,000 rpm, above 36,000

rpm. Magnetic bearings. Round trip efficiency 70 to 80% 100,000 full charge/discharge cycles. Thick steel sheet container filled with low

friction gas such as helium or a vacuum. Composite rotors. Superconducting magnetic bearing flywheel 11

Flow Battery

Electrolytes are stored in large plastic tanks. Electrolyte is continuously circulated. Increased volume of the tank increases energy

storage. Increasing the number of cell stacks increases

the power delivery

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Vanadium Redox Flow Battery (VRFB)

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VRFD

4 MW, 6 MWh plant online in Japan. Pump losses. Electric currents flow inside the conducting

solutions. These shunt currents depend on temperature and

SOC.

Low power density.

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Sodium-Sulfur Battery (NaS)

High Energy Density High round trip efficiency (89% - 92% Inexpensive Materials. Long cycle life Molten Metal operate at high temperatures (300

-350 C) Liquid sodium is corrosive and flammable when

exposed to air and moisture.

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Hydraulic Energy Storage

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Hybrid Vehicle – Not Electric

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Hydrogen Energy Storage

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Methods of Producing Hydrogen Methane Steam Reformer: 75 – 80% Efficient

CH4 + H2O → CO + 3H2

CO + H2O → CO2 + H2

Gasification of Biomass, Coal, or Wastes Must remove CO2 to be carbon free.

Electrolysis of Water (Opposite of a Fuel Cell) 2H2O → 2H2 + O2

Up to 85% Efficient No carbon produced if electricity comes from

carbon free electricity.

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Electrolysis

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Fuel Cell

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Fuel Cell

Anode: H2 → 2H+ + 2e-

Cathode: 1/2O2 + 2H+ + 2e- → H20

Combining both equations: H2 + 1/2 O2 → H2O This is an exothermic reaction → It releases heat. Since it releases heat, it will happen spontaneously

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Fuel Cell

Question: How much of the energy is release in heat? How much of the energy is released in electrical

energy? Maximum possible efficiency using Gibbs free

energy: 83%.

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Fuel Cell I-V PLot

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New Exotic Energy Storage

Liquid air energy storage Underground pumped hydro Advanced nanoultracapacitors Advanced flywheels Isothermal CAES Thermoelectric energy storage – synthetic oil or

molten salt

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