Question regarding export of electric cars from ETM to ETM-SA

[DorinevanderVlies]

Situation

This ETM-Scenario has 154 cars in the present and 31 in the future. The present and future share of electric cars is 90%.
The number_of_electric_cars query gives 138.6 electric cars both for the present and the future.

Export to ETM-SA gives 139 electric cars.

Questions

• How is the number of electric cars which is exported to ETM-SA determined? Which value is leading?
• This is more an ETModel question: How is number_of_electric_cars determined? Based on the information above I gather it is not number_of_cars * share_of_electric_cars.

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notifying @AlexanderWirtz

[AlexanderWirtz]

Note that I set the number of cars using the following input statements:

number_of_cars_both: 154
number_of_cars: 31

These input statements have no impact on useful energy demand for transport, which is precisely what we want. Useful demand for transport is 'tweaked' using:

transport_useful_demand_car_kms_both: -6.30742891420747

And then a slider changes future useful demand for car_kms:

transport_useful_demand_car_kms: 2.0

There is no slider for directly setting only the number of cars, but the latter statements do update the number of cars in a scenario. I have changed the priority values for these statements in such a way that first the energy demand (and number of cars get set) and then the number of cars is reset to the desired values. This is a bit dirty @dennisschoenmakers, @ChaelKruip and @jorisberkhout don't you think? I have not alternative at present, though.

Background
The reason we want to set the number of cars separately is that we presume electric vehicles will be mostly autonomous and hence 'a service'. This means they will be utilized more than privately owned cars. The number of car kilometers can therefore grow while the number of cars decreases.

It goes without saying that we need to improve the transportation section of the ETM. This currently does not deal with bicycles or public transportation, for example. The issue of separately setting the number of vehicles and the transport volumes should be addressed when we improve the transport section. I do not believe a separate issue has been created yet. Perhaps we should first discuss the how and why of it before we do.