A new conveyor-based system offers an alternative energy storage technology. The heart of the system is a reversible conveyor belt that converts between electrical energy and gravitational potential energy by transporting bulk granular materials between two stockpiles at different elevations.
The U.S. Department of Energy reported that the total solar energy production in the U.S. increased from 28,924 GWh in 2014 to 96,147 GWh in 2018. During the same time period, it said the total energy produced by wind in the U.S. increased from 181,655 GWh to 274,952 GWh. Grid operators must keep the supply and demand for energy in balance. Traditionally, operators balanced supply and demand for electricity by modifying the supply to match demand. However, wind and solar generators cannot change the energy they supply as easily as conventional coal and gas power plants. To balance the supply and demand for power, many grid operators with large solar and wind assets are utilizing energy storage facilities to increase the demand for power when the supply would otherwise outstrip demand.
Currently, there are four commercialized energy storage technologies deployed in the U.S. They are pumped hydro storage (PHS), compressed air energy storage (CAES), advanced battery energy storage (ABES), and flywheel energy storage (FES). As of June 2018, 94% of U.S. energy storage assets were PHS. PHS commands a huge market share because unlike ABES its lifetime is measured in decades instead of years. PHS technology was proven more than a century ago, and the cost per MWh stored and dispatched are lower than all its competitors.
PHS systems require large volumes of water that are not readily available in all regions of the world. Conveyor Dynamics Inc. (CDI) has developed a new energy storage system analogous to PHS, but instead of transporting water between reservoirs, the conveyor energy storage (CES) system stores and releases energy by moving bulk granular material between stockpiles. Like PHS, CDI’s system utilizes low-cost and proven equipment that has been deployed for decades. The company expects the CES system to provide a competitive alternative to PHS in arid regions of the world.
- The conveyor energy storage system utilizes a motor-generator scheme similar to technology employed at a pumped hydro storage facility. When energy is to be stored, the motor-generator drives a conveyor to move bulk granular material from a lower stockpile to an upper stockpile. When energy is to be supplied by the system, the motor-generator is driven by the conveyor as the bulk granular material is transported from the upper stockpile back to the lower stockpile through gravitational force. Courtesy: Conveyor Dynamics Inc. (CDI)
Figure 1 shows the operating principle of the CES system. The heart of the system is a reversible conveyor belt that converts between electrical energy and gravitational potential energy by transporting bulk granular materials between two stockpiles at different elevations. The reversible conveyor is driven by an electric motor-generator controlled with a four-quadrant inverter drive.
To store energy the reversible conveyor receives ore from feeder conveyors below the low-elevation stockpile and discharges the material onto the high-elevation stockpile. To release energy, the conveyor reverses direction, receives material from feeder conveyors under the high-elevation stockpile, and discharges this material onto the lower-elevation stockpile.
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