Back to News

Energy Storage Options for EV Charging – Lots of Choices, But Not All of Them Are Great for Fleet EV Operators

(Rick Sander, CEO, Tuesday, May 12, 2020)

If you followed our blogs last month, you read how the growing electrification of transportation will significantly impact the US energy grid in a variety of ways, including a shortage of power generation sources and an inadequate power distribution infrastructure. Electrical utility providers are very aware of these issues, and are putting significant capital and manpower into energy storage. However, many of the approaches they are investigating won’t solve the “energy gap” problem for fleet electric vehicle (EV) operators, where the problem manifests itself as a lack of power to fully charge their EV fleet. For the fleet EV operators, the solutions being  looked at by the electric utilities doesn’t solve their issues in a timeframe that is interesting and which gets more power to their vehicle yards, especially during peak demand hours (5PM to 9PM in most markets). Here are some of the different technologies that electrical utility companies are investigating:

  • Pumped Hydroelectric Energy Storage (PHES): This technology is very similar to hydroelectric dam power generation, but actually pumps water uphill into a reservoir to store the energy. It is a proven technology, but is only 70%-80% efficient, is both capital-intensive, and has a cycle (charge/discharge) time measured in weeks, not hours. Moreover, it requires significant addition to the power transmission infrastructure.
  • Substation Containerized Battery Energy Storage: This approach fills a shipping container with batteries, battery management, and thermal management/fire suppression equipment, and places these containers at power substations. A typical 40-foot long container can hold 2MWh to 4MWh of energy storage. This approach is modular, so containers can be moved around as demand patterns change. It also has quick to deploy, efficient, and has cycle times measured in hours. It would still require the addition of “last mile” power runs from substations to vehicle yards.
  • Vehicle to Grid (V2G) Power Storage: A variation of containerized battery energy storage that utilizes consumer vehicles plugged into bi-directional chargers to put energy unused during the day back onto the grid during peak demand hours. Like substation storage, this approach still requires additional “last mile” power runs from substations to vehicle yards.

An alternative that Rhombus Energy Solutions is developing is the integration of battery-based energy storage containers with fleet EV charging infrastructure in the vehicle yards. As a leader in the development and manufacturing of bi-directional, high-power energy systems for both vehicle charging and photovoltaic solar applications, Rhombus is an expert in high-power charging systems for EVs, and especially in the area of vehicle-to-grid (V2G) charging. Find out how we can help you by contacting us at, or by reading our Energy Storage Reference Architecture white paper.

Back to News