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Energy Management Principle Number 16: Energy Storage
Energy storage is an important application of energy management. Often the greatest demand for energy does not coincide with the time when the lowest cost resources are available. One of the earliest applications of energy storage is pumped hydro. At night, when demand for electricity is low, water is pumped from a low reservoir to a high reservoir. During the high demand period, water is released from the high reservoir and generates electricity by turning a turbine as it flows to the low reservoir. Another early form of energy storage is underground storage of natural gas. During times of low demand (summer) natural gas is pumped into underground caverns. It is then withdrawn during peak winter periods. Additional methods of energy storage that have been used include compressed air, flywheels, and batteries.
Each of these methods has disadvantages. Pumped hydro is expensive, sites are limited, and construction takes years. Underground storage of natural gas also suffers from high development costs and limited site availability. In 2015, the Aliso Canyon underground storage facility operated by the Southern California Gas Company suffered a massive gas leak. Over 100,000 tons of a mixture of methane and ethane were released. It is considered the worst natural gas leak in U.S. history. Schools were relocated, along with 2,200 families from the Porter Ranch neighborhood nearby. The cost to the gas company is over $700 million and still rising. Local residents would like to see the facility shut down permanently.
Compressed air, flywheels, and batteries have limited storage capacity and high costs. Utilities have experimented with battery storage for a number of years, but high capital cost, battery life, and limited storage capacity have prevented widespread use.
Now that is about to change.
Recent progress in extending the range of electric vehicles his spurred the development of high-capacity lithium-ion batteries. Tesla Inc. built a battery manufacturing plant to supply batteries for its vehicles. It also started producing a compact battery called the Tesla Powerwall for use with residential solar systems. It has a storage capacity of 14 kWh. This unit can be mounted on a garage wall or other convenient location within a structure. Tesla offers two versions, one without and one with a self-contained inverter to convert direct-current to alternating current. The estimated installed cost is $7,000. The average California resident uses approximately 20 kWh per day (2018). Residences with solar panels typically are more efficient by design and one Powerwall could conceivably power a residence for one to two days.
Now the concept has been extended to electric utility storage. Tesla and the Southern California Edison Company recently dedicated a storage facility containing 396 Tesla Powerpacks.[i] It was constructed at Edison’s Mira Loma substation and took only 6 months from initial design to start of operation. Each Powerpack has a storage capacity of 210 kWh, or 50 KW of three-phase, 480 volt power. Units are the size of a large refrigerator, roughly 3 feet wide, 4 feet long and 7 feet high. The facility has a capacity of 20 MW and is capable of storing 80 MWh hours or enough to power 15,000 typical homes for 4 hours.
How does this help?
California has a mandate to produce 50% of its electricity from renewable energy sources such as solar and wind by 2030. During evening hours when renewable energy is not available, natural gas or coal-fired generation supply electricity. However, four hours of storage would go a long ways towards covering the evening demand, meaning that the batteries would be charged during peak daytime generating hours, and thus fossil fuel generated power would not be required in the evening.
Another advantage is that the entire Mira Loma installation only required 1.5 acres on the substation site since the lithium-ion batteries are compact. Permitting is streamlined, and the facility can be built in months, not years
Read more about energy storage and the other fifteen general principles in Energy Management Principles.
[i]Penn, Ivan. (January 31, 2017): Los Angeles Times, “Edison, Tesla unveiled energy storage site,” page C-1.
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