Round-Trip Energy Efficiency and Energy-Efficiency Fade Estimation for Battery Passport

The battery passport is proposed as a method to make the use and remaining value of batteries more transparent. The future EU Battery Directive requests this passport to contain the round-trip energy efficiency and its fade. In this paper, an algorithm is presented and demonstrated that estimates the round-trip energy efficiency of a battery pack. The algorithm identifies round trips based on battery current and SoC and characterizes these round trips based on certain conditions. <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$2\mathrm{D}$</tex> efficiency maps are created as a function of the conditions ‘temperature’ and 'RMS C-rate‘. The maps are parameterized using multiple linear regression, which allows comparison of the efficiency under the same conditions. Analyzing data from three battery-electric buses over a period of 3.5 years reveals an efficiency fade of up to 0.86 percent point.

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