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Updated Substations for Renewable Energy: Electric Warehouses

Tony Sleva's picture
President Prescient Transmission Systems

Tony Sleva is president and co-founder of Prescient Transmission Systems, where he provides risk assessments and innovative solutions for updating the electric power grid. Tony has more than 50...

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  • Jun 11, 2021 10:21 am GMT
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Electric warehouses are a technological advancement that will replace traditional substations for delivering reliable electric energy. In addition to the components normally found in a substation, electric warehouses will include energy storage modules to store supplemental power. These large-scale units will release energy when power supplied by renewable energy sources drops, such as on a cloudy day.

What is an Electric Warehouse?

An electric warehouse is an emerging concept that includes a collection of components usually found in a substation (incoming lines, transformers, circuit breakers, outgoing lines, etc.), along with some new technologies. To become a warehouse, energy storage modules will be added to substations to provide additional power when supplemental energy is needed.

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Energy storage modules included in an electric warehouse are more than traditional batteries. They will include compressed air and liquified air storage modules.

Electric warehouses will allow for the integration of renewable energy from several key sources: distributed energy resources (DERs), such as rooftop photovoltaic (PV) systems and wind turbines; and remote power supplies from central generating stations, such as hydroelectric dams or nuclear power plants. Because of the variety of energy sources that can provide customers with power, electric warehouses will provide much more flexibility than traditional substations.

Electric Warehouses Provide Uninterrupted Power

While substations are designed to transfer power, electric warehouses are designed to provide uninterrupted power. Therefore, electric warehouses will be rated in mega-watt hour (MWH) capacity rather than transformer mega-volt-amperes (MVA).

Electric warehouses will be transmission class (100 KV and higher) and distribution class (less than 100 KV). Figure 1 is a one line diagram showing two prototype electric warehouses. Mountain Electric Warehouse is a transmission class warehouse. Valley Electric Warehouse is a distribution class warehouse; we will focus on Valley Electric Warehouse.

This distribution class electric warehouse is assembled with two 50 MVA transformers and two 1200 MWH energy storage modules, providing 2000 MWH of power. As you can see in figure 1, power flows into Valley Electric Warehouse via the 138 KV Powerway. Some of this power is stored in energy storage modules 1 and 2. Power flows into and out of the storage modules at different times. Figures 2 and 3 illustrate when power would flow into the energy storage modules to charge them, and when power would flow out of the storage modules to be used by consumers.

Electric Warehouses Regulate Energy Supply

Figure 2 shows an electric warehouse’s typical peak load on a summer day. Total load is represented by the orange line. The green line shows DERs, in this case rooftop PV. These rooftop solar panels actively provide power between the hours of 5:00 a.m. and 9:00 p.m., the approximate times of sunrise and sunset. After dark, energy is released from energy storage modules, as represented by the yellow line.

The blue line shows power that is provided from remote energy suppliers by way of the transformers. As you can see, remote energy always supplies some of the power at electric warehouses. During the day, remote energy is recharging the energy storage modules, represented by the black line. At night, remote energy supplements the energy being discharged from energy storage modules.

Figure 3 shows the same data as that in figure 2, but with one key difference. Around 11:00 a.m., an underfrequency event occurred, meaning that power system frequency dropped from 60.00 hertz to 59.95 hertz. This may have been because winds became calm, and power produced at wind farms decreased.

Between 12:00 p.m., when the power system frequency dropped, and 2:00 p.m., when the issue was resolved, energy was provided by energy storage modules. The modules are equipped with DIP (differential, integrated, predictive) controllers, which detect a frequency drop on the power grid and signal for the energy storage modules to transition to the support mode. DIP controllers will signal for modules to enter support mode whenever power system frequency decreases to 59.95 hertz or below. Once in support mode, energy storage modules discharge energy so that consistent power can be delivered to consumers.

At 2:00 p.m., when the issue with the power grid was resolved, DIP controllers signaled that energy storage modules should return to charge mode.

Electric Warehouses Supply Power in an Emergency

Because electric warehouses will be designed to provide uninterrupted power, energy storage modules can be created with specific power level storage capacities in mind. In an emergency in which power from the grid is unavailable, an electric warehouse could supply energy to consumers for set amounts of time using the power stored in its energy storage modules.

For example, if the grid fails during peak summer loads, energy storage modules could provide uninterrupted power to consumers for two days. During peak winter loads, power could be supplied for three days; during spring and fall, power could be supplied for five days.

Electric warehouses will allow much more flexibility during all operating conditions. For example, if a major rainstorm blocks the sun for a day or two, operators can decide to stop loading energy into energy storage modules to reduce the demand on the power grid.

The Future of Substations: Electric Warehouses

The need for electric warehouses already exists, as does the ability to make them a reality. When substations are converted to electric warehouses with energy storage modules, smaller transformers can be purchased and installed, and fewer transformers will be needed. The capacity of each transformer will also be reduced. Not only will electric warehouses allow us to easily integrate renewable energy, but they will also increase the flexibility and operability of the entire electric power grid.

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Matt Chester's picture
Matt Chester on Jun 11, 2021

Energy storage modules included in an electric warehouse are more than traditional batteries. They will include compressed air and liquified air storage modules.

Why the distinction? Is it because the latter technologies are more efficient with space and efficiency? 

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