repay via kWh measurement in the car
A crucial aspect in home charging reimbursement is measuring the amount of energy, in kilowatt-hours (kWh), that has been charged.
However, contrary to what one might expect, EVs do not have an earmarked kWh meter on board.
Instead, the energy charged is calculated based on the voltage in the battery cells.
This process involves significant margins of error.
An alternative is to use charging stations with an eared MID-certified kWh meter, which allows for more accurate measurement.
An EV’s Battery Management System (BMS) manages and monitors the battery, including tracking the state of charge (SoC) and energy flow.
The BMS uses voltage and current measurements to calculate the kWh charged, but what many people do not know is that an electric car does not have a kWh meter, let alone a calibrated reading.
But then how does an electric car calculate how many kWh have been charged?
Calculation method: The energy charged is calculated by measuring the voltage (V) and current (I) and integrating them over time: kWh charged = ∫ P(t) dt where P(t) is the power, calculated as P = V x I This method, however, is sensitive to measurement errors and inaccuracies in the sensors.
It is only a theoretical approximation of the actual kWh charged.
Therefore, there are several sources of error: 1. Measurement inaccuracies: Voltage and current meters in the BMS have inherent inaccuracies.
Small discrepancies in these measurements can accumulate and lead to significant errors in the calculation of kWh charged.
2. Temperature effects: Temperature variations affect both battery performance and sensor accuracy.
This can result in variable margins of error.
3. Battery degradation: Over time, batteries degrade, affecting their charge and discharge capacity.
This can result in discrepancies between actual and calculated kWh.
4. Lack of calibration: The BMS requires regular calibration to maintain accurate readings.
Lack of calibration can result in inaccurate energy readings.
5. Measurement is done only in the battery : By measuring only in the battery, it is fundamentally forgotten that electricity is lost in the conversion of the AC to DC in the car’s inverter.
Also the loss in the cable between the charge point and the car is not measured.
STROOHM made test setups in which we compared with different brands of cars and charging stations with calibrated kWh meters what the indicated consumption in kWh was by the car and the calibrated measurement in the charging station.
We recorded deviations between 5 and 10% between the car and the charging station.
The deviations could be both positive and negative compared to the charging station.
This allows us to conclude that the measurement in the car cannot be considered reliable for an employee.
The tax rules for (re)payment of electricity at home always require a correct measurement of the number of kWh consumed.
The measurement via the car is structurally anomalous and not an alternative to a MID-certified kWh meter in the charging station or the electricity meter of the grid operator.
To make a refund correctly, in addition to the tariff, a correct measurement is needed to know the correct kWh’s.
However, the measurement from the cart does not meet these requirements.
Legislation of the Metrology Service for Commercial Settlements in Belgium
The Metrology Service, part of the Federal Public Service (FPS) Economy, is responsible for ensuring the accuracy and reliability of measuring instruments used for commercial transactions in Belgium.
Below is an overview of the main laws and guidelines that a measurement for a commercial settlement must comply with.
1.
MID certification (Measuring Instruments Directive) The MID (Directive 2014/32/EU) is a European directive that sets requirements for measuring instruments used for commercial transactions.
The directive ensures that measuring instruments, such as kWh meters in charging stations, are accurate and reliable.
Some key points of MID certification include: – Calibration and Verification: Measuring instruments must be calibrated and verified by an approved body before being put into service.
This ensures that they meet the accuracy standards set by the MID.
– Documentation and Conformance: Manufacturers and operators of measuring instruments must maintain comprehensive documentation demonstrating that their equipment is MID compliant.
This includes certificates of calibration, inspection reports and declarations of conformity. 2.
Belgisch Wetboek van Economisch Recht Het Wetboek van Economisch Recht (WER) bevat specifieke bepalingen die de nauwkeurigheid van commerciële metingen reguleren.
Enkele relevante artikelen zijn: – Artikel VI.4: Dit artikel stelt dat meetinstrumenten die worden gebruikt voor de verkoop van goederen of diensten aan consumenten moeten voldoen aan de wettelijke vereisten voor nauwkeurigheid en betrouwbaarheid.
– Artikel VI.6: Dit artikel bepaalt dat ondernemers die meetinstrumenten gebruiken voor commerciële transacties verantwoordelijk zijn voor het waarborgen van de nauwkeurigheid van deze metingen.
Dit omvat het onderhouden en kalibreren van de meetinstrumenten volgens de geldende normen. 3.
Koninklijk Besluit over Meetinstrumenten Het Koninklijk Besluit van 12 april 1965 betreffende de controle en verificatie van meetinstrumenten specificeert de nationale vereisten voor meetinstrumenten die worden gebruikt in commerciële transacties.
Enkele belangrijke aspecten zijn: – Erkenning van Controle-instanties: Het besluit erkent bepaalde instanties die bevoegd zijn om meetinstrumenten te kalibreren en te certificeren.
Deze instanties moeten voldoen aan strenge eisen wat betreft hun onafhankelijkheid, deskundigheid en operationele procedures.
– Periodieke Verificatie: Meetinstrumenten moeten periodiek worden geverifieerd volgens de in het besluit vastgestelde termijnen en procedures.
Dit zorgt ervoor dat de instrumenten nauwkeurig blijven gedurende hun gebruiksperiode. 4.
Richtlijnen van de Dienst Metrologie De Dienst Metrologie publiceert regelmatig richtlijnen en technische voorschriften die verdere details geven over de toepassing van de wetgeving.
Deze richtlijnen omvatten: – Technische Specificaties: Gedetailleerde technische specificaties voor verschillende soorten meetinstrumenten, waaronder kWh-meters voor EV-laadpalen.
Deze specificaties beschrijven de vereiste nauwkeurigheid, de methoden voor kalibratie en de procedures voor periodieke inspectie.
– Handhavingsbeleid: Beleidsdocumenten die de handhaving van de metrologische wetgeving beschrijven, inclusief de sancties voor niet-naleving en de procedures voor het melden van en reageren op overtredingen.
Conclusion
The legislation of the Metrology Service in Belgium is extensive and strict to ensure that commercial measurements are accurate and reliable.
The lack of a calibrated kWh meter in EVs means that the calculation of charged energy is based on indirect measurements, which can introduce significant margins of error.
Using charging stations or meters from the grid operator with MID-certified kWh meters offers a more accurate and reliable alternative.
Opting for charging stations also provides faster charging than via the wall socket that requires up to 48h or longer.
A charging station thus provides comfort and an accurate reading that the tax authorities accept.
