Slow1
Well-known member
Reading a couple other threads got me to thinking of what battery and charging needs would be required for me to be willing/able/happy taking an EV on a long distance trip and how to generalize this so that others can 'play' with the numbers too. This is what I came up with - interested in hearing feedback and seeing if the resulting numbers surprise anyone...
For cross country driving I am assuming there really are two main practical factors to consider - first is "how long can I go between stops" which speaks to range; I imagine 3-5 hours would be the 'desired' timeframe for a lot of folks which in my book translates into a range of 180-300 miles (Model S meets this requirement).
Second factor is "time to charge" - if I drive for 4 hours I'd be willing to charge for 45 minutes. This means I need to onboard enough power for an hour of driving in just under 12 minutes.
To make this more general - if you know R "rate of power use at desired speed", Td "time Driving between stops", and Tc "time willing to stop and charge" for a given trip you can calculate the required battery capacity as well as necessary charging rate.
Example:
Leaf driving 65mph burning approx 18kWh average
Desiring to drive 4 hours between stops and charge in 45 minutes
R = 18kW
Td = 4 hrs
Ts = .75 hr
Required capacity = R*Td = 18kw * 4 hr = 72kWh
Required charging rate = R*Td/Tc = 72kWh/.75h = 96kW
Be willing to stop each 3hrs and leave rest constant you get:
Required capacity = 54kW
Required charging rate = 72kW
So this tells me I'd want between 54 and 72 kWh useful battery capacity and chargers that charge between 72 and 96kW (do such exist?). Guess I won't be doing a road trip anytime soon.
While a bit simplified; i.e. charging rate is not a constant, nor would one be able to utilize 100% of battery capacity (perhaps add in a factor of 80% to leave top and bottom 10% unused? - so that would put Required Capacity = R*Td/.8 = 90kW), using this model to evaluate a given vehicle could help folks determine if they would be able to utilize it for long distance driving. Clearly a lot of personal variables, and it assumes availability of charging when desire/required....
Play with this a bit to see what you would be comfortable with - you may be surprised at just what will be required to meet your long-distance driving needs. It would be interesting to see what a poll of the general public says in terms of "time between stops" and "time to stop" and see what that would require of a vehicle to meet 80% of the driving public's perceived (if not actual) needs.
It also demonstrates how much we need to improve charging rates and/or burn rates to be able to really replace the ICE for some folks (such as myself).
All this doesn't matter for local only driving. There it comes down to a simple question of "maximum driven in a day" and number of available charging hours. The ration there allows for much slower charging rates.
For cross country driving I am assuming there really are two main practical factors to consider - first is "how long can I go between stops" which speaks to range; I imagine 3-5 hours would be the 'desired' timeframe for a lot of folks which in my book translates into a range of 180-300 miles (Model S meets this requirement).
Second factor is "time to charge" - if I drive for 4 hours I'd be willing to charge for 45 minutes. This means I need to onboard enough power for an hour of driving in just under 12 minutes.
To make this more general - if you know R "rate of power use at desired speed", Td "time Driving between stops", and Tc "time willing to stop and charge" for a given trip you can calculate the required battery capacity as well as necessary charging rate.
Example:
Leaf driving 65mph burning approx 18kWh average
Desiring to drive 4 hours between stops and charge in 45 minutes
R = 18kW
Td = 4 hrs
Ts = .75 hr
Required capacity = R*Td = 18kw * 4 hr = 72kWh
Required charging rate = R*Td/Tc = 72kWh/.75h = 96kW
Be willing to stop each 3hrs and leave rest constant you get:
Required capacity = 54kW
Required charging rate = 72kW
So this tells me I'd want between 54 and 72 kWh useful battery capacity and chargers that charge between 72 and 96kW (do such exist?). Guess I won't be doing a road trip anytime soon.
While a bit simplified; i.e. charging rate is not a constant, nor would one be able to utilize 100% of battery capacity (perhaps add in a factor of 80% to leave top and bottom 10% unused? - so that would put Required Capacity = R*Td/.8 = 90kW), using this model to evaluate a given vehicle could help folks determine if they would be able to utilize it for long distance driving. Clearly a lot of personal variables, and it assumes availability of charging when desire/required....
Play with this a bit to see what you would be comfortable with - you may be surprised at just what will be required to meet your long-distance driving needs. It would be interesting to see what a poll of the general public says in terms of "time between stops" and "time to stop" and see what that would require of a vehicle to meet 80% of the driving public's perceived (if not actual) needs.
It also demonstrates how much we need to improve charging rates and/or burn rates to be able to really replace the ICE for some folks (such as myself).
All this doesn't matter for local only driving. There it comes down to a simple question of "maximum driven in a day" and number of available charging hours. The ration there allows for much slower charging rates.
