Energy Storage Thermal Performance
Electric-drive vehicle (EDV) battery systems need to operate at maximum efficiency, performing at optimal temperatures in a wide range of driving conditions and climates, and through numerous charging cycles. NREL researchers work closely with industry partners to rigorously test batteries and other energy storage technology for EDVs, including hybrids (HEVs), plug-in hybrids (PHEVs), and all-electric vehicles (EVs).
The nation's recognized leader in battery thermal management research and development (R&D), NREL is one of the few laboratories capable of comprehensive evaluation of batteries at the cell, module, pack, and system level. The lab's assessments of thermal behavior, capacity, lifespan, and overall performance factor in the impacts of full-system integration.
The U.S. Department of Energy, the U.S. Advanced Battery Consortium (USABC), and industry partners rely on NREL to measure thermal properties of batteries and evaluate the heat transfer effects of cycling on energy storage components and subsystems. Related tests examine triggers to energy storage failure and reactions to external damage.
Thermal Testing and Characterization
NREL experts measure and analyze the heat generation, efficiency, durability, and heat capacity of energy storage components and systems under specified charge/discharge cycles using the lab's R&D 100 Award-winning Isothermal Battery Calorimeters, infrared thermography systems, environmental chambers, battery cyclers, and other equipment in NREL's Energy Storage Laboratory and Battery Thermal and Life Test Facility.
NREL's IBCs are the only calorimeters in the world capable of determining heat levels and battery energy efficiency with 98% accuracy, providing precise measurements through complete thermal isolation. In addition to the IBCs, differential scanning calorimeters and accelerating rate calorimeters are used to examine thermal properties more closely at the materials level.
Thermal imaging helps researchers determine temperature distributions and identify potential trouble spots in energy storage cells and modules. The information from thermal imaging is used in model validation and in developing optimal battery and energy storage system designs.
Precise measurement of round-trip energy efficiency distinguishing stored energy from waste heatenables carmakers and manufacturers to better estimate vehicle energy consumption. NREL's infrared imaging thermally maps and pinpoints areas of high heat generation within batteries and across energy storage systems. NREL uses a range of battery cyclers to simulate a full spectrum of driving profiles based on real-world circumstances.
Durability and Lifespan
Optimization of batteries can increase the number of times they can be charged and discharged before needing replacement. NREL conducts long-term electrical/thermal performance testing with established USABC testing protocols to assess the life cycle and lifespan of batteries. NREL uses a combination of thermal imaging, cycler-generated simulations, and calorimeter measurements to assess long-term performance and identify improvements with the potential to extend lifespan.
Systems-Level Design and Modeling
NREL also uses a series of models and analytical tools to assess thermal performance. A 3-D thermal-fluid dynamics model helps optimize the performance of energy storage systems with computer-aided engineering of thermal management components, including blowers, pumps, flow channels, and cooling fluids. Validated with laboratory measurements, NREL's energy storage models establish heat generation rate and cooling requirements for various driving, geographic, and seasonal scenarios.
NREL researchers use the battery system life-predictive model, a systems-level thermal empirical design model, to assess battery:
- Performance, lifespan, and cost tradeoffs
- Excess power and energy sizing requirements
- Probability of degradation, including mechanical stress and fracturing
- Warrantees, second uses, and other techno-economic factors.
For more information on NREL's energy storage thermal management activities, contact Matthew Keyser, 303-275-3876.