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I'm a software engineer, but have taken some physics courses and almost went into mechanical engineering, but that was 30 years ago.

I am beginning a deep dive into the efficiency of the grid supplying energy to electric cars. I'll start with what I do know:

  • Assuming a flat and level surface (let's keep it simple), the power a vehicle requires at any speed must be equal to the drag force of the vehicle in the air plus the friction in the drive train.
  • The maximum thermodynamic energy of say a kilogram of fuel is the ratio of the heat it can produce and the cold sink in which it operates, as compared to absolute zero. So a heat engine operating at 500 K in an environment 300 K could in theory be 40% efficient - that is to say it could convert 40% of the energy of a gallon of fuel into work.
  • Actual modern output is (obviously) some fraction of 100% max theoretical efficiency

A Wiki article states

Latest generation gas turbine engines have achieved an efficiency of 46% in simple cycle and 61% when used in combined cycle.

And the going value for a gasoline power plant in say an automobile is 25-35%. I need more research on this.

So my starting question in this deep dive is simple (as long as you factor out variables like change in load and demand which I'll add later):

Given a quantity of fuel, say 100 kilograms, how much work can be produced locally by a car's power plant, and how much work can be produced by that same quantity from an industrial power plant after all steps of getting it to the equivalent electric vehicle? [1][2]

Notes:

[1] As I understand it the loss points from the latter after shaft output would be a) loss in converting to electrical energy by the generator b) loss in transmission across the grid c) loss across the charging station d) loss in battery storage [you charge a battery with 1 kW, you don't get 1 kW out] and e) loss in the electric motor's use of electricity to the point of the shaft. A bonus would be a percentage breakdown of those losses

[2] Again, for simplicity, let's assume highway speeds on level ground with optimal gearing for both the gas and battery powered cars, and peak operation at the industrial power plant. I will mitigate the other variables later.

Thanks for your assistance on this basic question as it will inform priorities for further research.

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  • $\begingroup$ A few rough numbers to hold in your head. Oil gives out about 10 kWh per kg of oil. Oil burning stations and transmission will give you about 40% conversion into electrical energy. Tip: It's 'kW', not 'Kw' which would be 'kelvin-somethings'. $\endgroup$
    – Transistor
    Aug 1, 2022 at 18:40
  • $\begingroup$ Check CHP, you can get some 80% or more of the energy from the fuel if you use CHP, but you have to be able to use low grade heat. So more than the 25-35% you suggest for a car but that is at the flywheel which you are quoting. $\endgroup$
    – Solar Mike
    Aug 1, 2022 at 22:11

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Pretty much everything you need is contained in the Lazard reports. But most importantly, the Lazard reports will help you frame the question in the industry standard manner that can be understood by engineers and investors in the sector.

So write down the actual math formulas that evaluate to the costs of the two competing systems at the desired endpoint and time point. Then populate the terms. The formulas tend to be pretty long and hairy, but this is a tedious business that will require looking up or estimating dozens of individual pieces of cost data that are location specific.

Lazard home page - https://www.lazard.com/perspective/levelized-cost-of-energy-levelized-cost-of-storage-and-levelized-cost-of-hydrogen/

You need the first two reports - Levelized costs of energy production and Levelized costs of storage. For end users, the utility rate structures, code requirements as far as affected infrastructure changes, tax incentives and deed encumbrances need to be priced.

Don't use any efficiency numbers directly. Everything is converted to prices first. You want to be able to make a pie chart when you are done that accounts for where every penny of cost ends up. The efficiency of a power plant doesn't matter, the cost of the electricity is what matters.

Charger cost data - https://rmi.org/wp-content/uploads/2020/01/RMI-EV-Charging-Infrastructure-Costs.pdf

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