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Why is Energy Storage So Critical to High-Power DC Charging Stations?

(Joseph Gottlieb, CTO, Thursday, January 17, 2020)

We have talked about the importance of integrating energy storage into DC fast charging infrastructure for electric vehicles (EVs) in several of our recent blogs. A look at the numbers might be useful to help illustrate the size and scope of the need for energy storage in DC fast charging stations. Let’s first look at the battery capacity of some of the longer-range EVs on the market today:

If the goal is to charge a typical EV car from empty to 80% of capacity in 30 minutes, a power flow of 480kW would be required (assuming a 300kWh battery capacity). If an EV fast charging station charges twenty vehicles at a time with a duty cycle of 10%, a power flow of 960kW is required on average. With a 480 volt power supply, this equates to 2,000 amps of power. However, if ten chargers (50%) are operating at the same time, this power requirement jumps up to 4.8MW, with a power flow of 10,000 amps. Even if all of the cars are only connected at the same time for 20 minutes, the draw will still be 1.6MWh. As a reference point, running a new 2MW utility feed can often take two to four years to complete, including permitting and construction, so this is not just an issue of “buying more electricity”.

Fortunately, battery-based energy storage systems today can support this level of demand. A typical ISO shipping container-size storage system can support over 1.5MWh of power, significantly reducing peak grid demand. When utilized with renewable energy sources such as photovoltaic (PV) power and demand management (“peak shaving”) software, these combinations can significantly reduce the power that needs to be brought in from the grid as well as energy costs.

Rhombus Energy Solutions is an expert in the development and manufacturing of high-power bi-directional DC charging systems, with a power range from 60kW to 500kW. These chargers enable automobile, light truck, and SUV (ALTS) EVs to charge to full power in as little as 30 minutes. These chargers are also designed from the ground up to be integrated with energy storage solutions and renewable power sources such as PV panels to minimize grid demand. Our VectorStat® software provides intelligent demand management capabilities, including peak shaving, to reduce energy costs. We have shipped hundreds of high-power chargers with vehicle-to-grid capabilities for a variety of customers. Rhombus looks forward to playing our part in the electrification of the transport infrastructure. Find out how we can help you by contacting us at

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