Altitude difference and energy required

[i3marc]

Looks like we are same as pilots and need to take into account the difference in altitude affecting the range and energy required...

Maybe not so true in flatland UK or Europe but more like it in Cali which is also the Mecca for electric cars.

On my blog I found the energy required to go up 1000 ft is roughly 1 kWh, and I guess coming down that distance gives you an extra boost of half that much, considering regeneration losses.

Anyone's opinion on this?

 

[jadnashuanh]

Sounds about right...someone on one of the blogs actually ran the numbers using the weight of the vehicle. While slight, the air IS thinner, so wind resistance at altitude is lower. The good thing is that the electric motor doesn't need to breath (although a turbo can usually overcome any deficiencies, but the REx probably wouldn't be quite as efficient especially since it does not have a turbo - altitude matters).

I've not seen actual numbers on the efficiency of regen, but even if you end up only coasting down the mountain, you should get a lot more miles per Kw, even if you can't produce any electricity in the process depending on the slope.

 

[Jeffj]

See these links for a very technical, exhaustive analysis of energy used to climb hills.
http://bmwi3.blogspot.com/2014/10/the-i3-rex-one-owners-thoughts-on-bevx.html
http://bmwi3.blogspot.com/2014/10/sf-bay-to-tahoe-in-i3-rex-what-was.html

Prevailing altitude also has to be taken into account. The REx produces less than 35 HP on flats in Colorado due to the altitude.

 

[i3marc]

Sounds about right...someone on one of the blogs actually ran the numbers using the weight of the vehicle. While slight, the air IS thinner, so wind resistance at altitude is lower. The good thing is that the electric motor doesn't need to breath (although a turbo can usually overcome any deficiencies, but the REx probably wouldn't be quite as efficient especially since it does not have a turbo - altitude matters).

I've not seen actual numbers on the efficiency of regen, but even if you end up only coasting down the mountain, you should get a lot more miles per Kw, even if you can't produce any electricity in the process depending on the slope.

Air has has nothing to do with the energy required to move an object of mass M to a certain delta h as the formula is E = M * delta h

Sure the i3 could probably move on the Moon granted we would be in a low sunshine area (but not night since it's like -100 there, F or C) and the occupants would be in suits, and the energy required to move up a hill would be still based on that formula.

Using metric I used M = 1300 kg and delta h = 270 meters. That gives us about 3.7 million joules or watts, and that is roughly 1 kWh.

A simple formula in Imperial units would be 1 kWh for every 1000 ft of altitude difference.

Want to go to Big Bear from Santa Monica? That's 7 kWh just for the altitude as Big Bear is 7000 ft ASL.

 

[jadnashuanh]

Drag WILL affect how the vehicle moves, whether uphill or on the level, and will be part of the total energy used to move the vehicle any distance. Certainly, if you're just looking at the energy used to gain altitude, that is only the weight (mass) and the height involved...but, the car generally needs to be rolling along the roadway to accomplish that altitude change, and thus, the drag is a factor.