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NREL Researches Ultracapacitors in Advanced Vehicles

Batteries are most commonly used to store energy and deliver power in hybrid electric and hybrid fuel cell vehicles. But ultracapacitors may become a viable energy storage option because of their projected low cost, high power density, and long life. The recent introduction of the Honda fuel cell vehicle with ultracapacitors (FCX-V4) has heightened interest in this technology.

DOE's Vehicle Technologies Program has supported NREL in its efforts to investigate the potential use of ultracapacitors in hybrid and fuel cell vehicles. NREL researchers develop and validate ultracapacitor models in combination with batteries using MATLAB's SimPower Systems tool and in stand-alone applications using ADvanced VehIcle SimulatOR (ADVISOR).

Combining ultracapacitors with batteries may enhance performance and improve fuel economy. Ultracapacitors may also extend the life of a hybrid vehicle's on-board battery system because they are better suited to capturing high power from regenerative braking and releasing it for initial acceleration (Hybrid Energy Storage Studies Using Batteries and Ultracapacitors for Advanced Vehicles [PDF 1.81 MB] and Potential Ultracapacitor Roles for Hybrid Electric Vehicles [PDF 769 KB]). Ultracapacitors may be especially useful in regenerative energy capture when a vehicle's peak power is much greater than its average power demand. However, limited energy storage capability limits the ultracapacitor's ability to downsize fuel cell systems (Energy Storage System Requirements for Hybrid Fuel Cell Vehicles [PDF 313 KB]). Download Acrobat Reader.

We are also developing a dual-source energy storage analysis tool to evaluate how advanced vehicle technical targets can be met with a combination of batteries and ultracapacitors (Dual-Source Energy Storage—Control and Performance Advantages in Advanced Vehicles [PDF 359 KB]). The tool parametrically studies the roles of the fuel converter and energy storage system for advanced hybrid vehicles. It addresses the question of whether hybrid energy storage packs can be sized to allow for downsized, more specialized component sets that meet all of a vehicle's average and transient loads (Electrochemical Double Layer Capacitor Modeling and Vehicle Simulations [PDF 1.27 MB]). Download Acrobat Reader.

Diagram of Energy Storage System architecture setup (for coupling battery and ultracapacitors) that can be simulated which includes a battery and ultracapacitor linked to a motor controller and motor.
An example architecture setup (for coupling battery and ultracapacitors) that can be simulated.

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