Batterier i BYD-busserne. Kjeld Nørregaard Seniorprojektleder, Teknologisk Institut

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2 Batterier i BYD-busserne Kjeld Nørregaard Seniorprojektleder, Teknologisk Institut

3 Center for Transport og Elektriske Systemer Bio brændsel El-køretøjer Biler Elektronik Marine Batterier Heavy Duty Rådgivning Emission Non-road Havari Smart grid Energi

4 Task ordered by the Danish Traffic Agency Lever batterilevetiden op til opgivelserne fra leverandøren? The main objective is to verify the expected real battery lifetime of the electric buses relative to the battery lifetime stated by the supplier as best possible. For the operator the battery life is a significant economic parameter for dissemination of electric vehicles.

5 3 battery packs distributed in 4 different locations in the bus BYD Fe battery Type Power Battery Cell voltage Capacity FV200 A (540 V, 600 Ah) Li-ion (Lithium Iron Phosphate battery) 3.2 V 324 kwh

6 3 parallelle ways to the result Degradation of the battery is determined by different methods. Primary method by measuring any change in battery capacity and internal battery resistance at vehicle level from start to end of test period (less than two years). Secondary method is a limited test at battery cell level to validate consistence with BYD s own test data at cell level. Supplemented by a visit at BYD test and production facility in China to get access to relevant data Expected general behavior of a Lithium Iron Phosphate chemistry is that: a detectable energy content/capacity is lost with aging only a marginal increase in internal resistance is expected the actual rate of change vary significantly with the conditions of the application.

7 Bus at the heavy duty dynamometer in the laboratory at the Danish Technological Institute in Aarhus

8 Actual battery degradation measured on the vehicle Procedure established to perform battery measurement on vehicles under same conditions every time. The energy content of the battery is determined by discharging and charging the battery while measuring the amount of energy flowing to/from battery measuring currents and voltage. To be able to repeat the test, the discharge is performed at constant power. Temperature has major influence on the batteries so to minimize impact on results all measurements are performed at room temperature on a laboratory heavy duty chassis dynamometer at Danish Technological Institute in Aarhus. Bus id Registration Operator First test Second test Bus #1 NX Keolis Danmark A/S 2014 May Not performed Bus #2 XT Arriva 2014 June 2015 December Tests performed on vehicles.

9 Battery cell degradation test Test at cell level is performed at a dedicated cell test facility at the Danish Technological Institute in Aarhus using a test setup similar to BYD. The measured results is compared to BYD test data released to the Danish Technological Institute only under a very strict NDA (prevents any publication of data or results).

10 Analysis based supplier s data Supplier data provided for the Danish Traffic Agency. Notice significant degradation at very high temperature.

11 Result from vehicle measurement Only Bus # 2 measured a second time.

12 Result data analysis Internal resistance and Battery voltage vs. State of Charge (SoC)

13 Result - degradation test Details not to be revealed measured data weighed with assumed pack temperatures pack temperatures based on Danish average temperatures over a year computed into an estimated lifetime to 80% retained capacity for each pack the uncertainty is substantial due to limited data

14 Conclusion Eventhough the uncertainty is substantial, the computed and measured results concur with the suppliers data. The Danish Technological Institute found no indications giving reason to doubt the data provided by the supplier regarding expected life.

15 Tak for opmærksomheden Kjeld Nørregaard kjn@teknologisk.dk Teknologisk Institut Transport og Elektriske Systemer