How Much Electricity Does an Electric Car Use - Part 1
Photograph (CC0) by Theodor Vasile, cropped by Larry Neal Gowdy
Copyright ©2021 - May 25, 2021
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Note: The following estimates are based upon over thirty years of professional firsthand experience in electronics, electrical devices, industrial controls, mechanics, and private power production. Estimates of fuel BTU outputs are based upon the averaging of standards and measurements as given within government and professional resources.
Due to the extreme quantities of variables within energy production, it is not possible to give exact numbers, but the generalized estimates are close enough to illustrate the wide differences between electric cars and gasoline powered cars.
As used in this series of articles with regards to water, the word "consume" implies water that is not returned to its source, but rather is lost through evaporation, processing, or by other means.
How much electricity does an electric car use? A quick ballpark average is to multiply the electric car battery's kilowatt-hour (kWh) rating by 5, and the sum will be close to how much fossil fuel (i.e. natural gas) energy is consumed to produce enough electricity to charge the battery. Then also multiply the summed quantity of kilowatt-hours by 2 to sum a rough national average of how many gallons of water were consumed to generate the electricity.
As an example, an electric car with a 50kWh battery rating will consume about 250kWh of fossil fuel energy, plus consume about 500 gallons of water. The 250kWh of fossil fuel energy has about a 60% loss of efficiency when converting LNG (liquid natural gas) into heat to run the turbines at power plants — leaving about 100kWh to go into the power lines — and additional efficiency losses occur at each step through the power lines, relays, transformers, into one's house, through the electric car charger, battery charging circuitry, battery, and motor. The 500 gallons of fresh water will be lost into the atmosphere through evaporation and processing, thereby depleting the region's fresh water supplies.
According to the National Renewal Energy Laboratory (of the U.S. Department of Energy Laboratory): "The national weighted average for thermoelectric and hydroelectric water use is 2.0 gal (7.6 L) of evaporated water per kWh of electricity consumed at the point of end use."
From the electric car owner's point of view, his electricity consumption — as reported on his electric bill — may increase about 65-75kWh each time that a fully depleted 50kWh battery is fully recharged.
Low electricity bills do not include the other costs of having produced the electricity, nor of having depleted fresh water supplies.
The following data gives some quick ideas of how to estimate how much electricity and fossil fuel is actually consumed by electric cars. The estimates also illustrate environmental differences between gasoline powered cars and electric cars.
Turbine Electrical Data
All electrical and mechanical devices follow the same laws of physics, but all power plants are different, as do all fuels used by power plants have different ranges of potential energy, which simply means that there will be a sizable variance of power generated from one power plant to another. The goal is to acquire a workable average that is useful for illustrating power plants' probable ranges of electrical output.
Gasoline is rated at ~114,000 BTU per gallon, which sums to about 33.41kWh of electricity. LNG is rated at ~75,000 BTU per GGE (Gasoline Gallon Equivalent), which sums to about 21.75kWh of electricity.
Gallon to gallon, LNG is 65.1% efficient relative to gasoline, and requires about 53.62% more LNG to produce a similar BTU as gasoline.
LNG efficiency of generating electricity at an electric power plant is roughly 40%. Some power plants run at near 30%, while a small number of new experimental plants are said to have reached 55% to 60% efficiency.
Efficiency Loss #1: Converting heat to mechanical motion always has a large efficiency loss. Therefore, the first number to be calculated is that an average power plant's turbines powered by natural gas will have a fuel efficiency loss of about 60% relative to the energy consumed versus the electricity generated.
Power Grid Electrical Data
In past decades a typical power grid would not have exceeded about 80% efficiency. It used to be very common for different neighborhoods in a city to have a 10% variance of voltages, thereby dropping grid efficiency down to around 70%. However, modern high voltage step-down transformers are now far more efficient than the older models, and many power companies have expended the expense to modernize their grids with better insulators, connections, and various other reductions of electrical resistance.
Depending on how far away the power plant is located from a city customer, today it could be estimated that a modernized power grid might achieve around a 90% efficiency. At further distances, efficiency might drop closer to 85%. According to the article Wells-to-Wheels: Water Consumption for Transportation Fuels in the United States (by David J. Lampert, Hao Cai, and Amgad Elgowainy): "The results are shown in Figure 9 and include water associated with electric power loss due to a grid efficiency of 93.5%." Nevertheless, without first knowing which distances, locations, and measuring methods that Wells-to-Wheels used to derive its numbers, then for the moment a 90% efficiency is a good rough average of what to expect and to use for figuring 'turbine-to-home' wattages.
Efficiency Loss #2: On the average, roughly 10% of electricity from power plants is lost in power lines and transformers between the power plants and the customer's electric meter.
Battery Charging Circuitry
Efficiency losses occur when stepping voltages up, stepping voltages down, converting AC to DC, converting DC to AC, and further losses occur within all other modifications of electricity. Poorly designed circuitry commonly has over 50% efficiency loss, good grade voltage regulators for small electrical devices typically range around 85% efficiency, and some low voltage regulators are capable of about 95% efficiency or better if the input and output voltages do not require much modification to power the device's circuitry.
Charging an electric car's DC battery requires that the AC electricity from the power grid be converted to a lower or higher AC voltage, and then converted from AC to DC. Due to electric car manufacturers giving effort to design their charging systems to be as efficient as is practical while being used for common residential AC voltages of 120 and 240, then it can be expected that an electric car's 'wall-receptacle-to-battery-charging-circuitry' ought to be in the 80% to 90% range of electrical efficiency.
The circuitry that controls voltages from the charging circuitry to the battery will also have efficiency losses. The losses ought to be very small relative to the quantity of input, but at least a 1% efficiency loss is expected.
The battery's ability to receive and to store the input will vary relative to temperatures, composition of the battery's materials, kWh size of battery, quantities of volts and amperes, and age of the battery. Typical battery efficiencies range from around 50% to 95%.
Efficiency Loss #3: Roughly 25% to 50% of the electricity used to charge an electric car's battery is lost in the efficiency of the charger, charging circuitry, and the battery itself.
Electric Motor Efficiency
Electric motor efficiency varies relative to whether the motor is AC or DC, whether the motor is rated for the same voltages as the battery, and how the motor is designed. Converting a battery's DC to AC for use in an AC motor will cause higher efficiency losses than if the motor were DC, but the AC motor itself might be more efficient for its intended purpose than what a DC motor might provide.
Depending on types and voltages, typical electric motor efficiencies range from below 50% to around 90%. Without the firsthand measuring of a motor's actual efficiency, all known available references of specific electric motor efficiencies ought to be interpreted as generalizations. The laws of thermodynamics apply: all electric motors will lose a percentage of available energy through heat dissipation, inductance, and friction. Due to the absence of firsthand measurements and verifiable data, a generous estimate is that a quality designed electric car's motor might be around 90% efficient.
Efficiency Loss #4: Roughly 10% of the electricity used to charge an electric car's battery is lost in the efficiency of the motor.
Total Efficiency Losses
Efficiency losses (60% power plant + 10% grid + 25% to 50% charging circuits + 10% motor) sum to approximately 16% to 25% final efficiency (gasoline engines are estimated to be approximately 12% to 30% efficient). The power to an electric car's wheels requires approximately 4 to 6 times the energy to generate the electricity.
How Much Electricity Does an Electric Car Use - Part 2 looks at national electricity consumption and compares energy production relative to BTU and water consumption.