Holy SMOKES Guys !!!
I know I've covered this air density thing MANY times.
Hot air is LESS dense (at the same altitude) than colder air. Air density is not "pretty much static" at the same elevation!!!!
Here's a calculator to help understand the effects:
http://wahiduddin.net/calc/calc_da.htm" onclick="window.open(this.href);return false;
In general, as to the LEAF with non-temperature controlled batteries (that don't consume the air like an oil burning car or airplane), ambient heat will have the following effects (assuming same elevation):
1.
The battery will INCREASE in capacity with temps over 70F.
My rule of thumb is 1% per 8F over 70F. Therefore, in 102F ambient heat (that also had enough time to heat the battery to that temperature), you can expect 102-70 = 32 / 8 =
4% greater capacity. Guys that drag race EV's actually bake or otherwise heat the batteries to get increased performance. Cold batteries are much more severely impacted, with
1% loss of capacity for every 4F below 70F. That means that a brand new LEAF that would have 21kWh of usable battery at 70F at SEA LEVEL elevation will travel about 84 miles at 4 miles/kWh at 65mph indicated will now have the battery capacity to travel 21kWh + (21kWh * 4%) = 21.84kWh * 4 miles/kWh = 87.36 miles of range autonomy (again, assuming 70F air temperature at sea level; this scenario is plausible with DC quick charging that can provide a significantly hotter battery).
2.
Heat will increase range due to a decrease in air density, and the effective "density altitude" can be calculated with the above calculator. Generally speaking, I would use a
rule of thumb of 1% increase in range per 1000 feet increase in "density altitude". That means that a brand new LEAF at 21kWh of usable battery at 70F at SEA LEVEL elevation will travel about 84 miles at 4 miles/kWh at 65mph indicated. At the same speed, at 3500 feet density altitude (102F with 29.92 inch Hg air pressure and 102F dew point) will gain about 3.5% increase in range at the same 65mph, so about 87 miles of range autonomy with a magically still 70F battery temperature with a car at sea level (generally unrealistic scenario of hot ambient air but "cold" battery, but instructive for the demonstration).
3.
The combination of a 102F hot battery and a 102F hot ambient air in the above examples at a constant 65mph would yield a total of 90.42 miles total range, vice 84 miles for 70F ambient air and batteries. First, we factor the 87.36 mile range for increased battery capacity from heat that is then multiplied by 3.5% for decreased air density of 3500 feet density altitude equals an additional 3.06 miles, for 90.42 miles total range. Just to clarify, the economy would increase to 4.14miles/kWh at 65mph indicated multiplied by the new battery capacity of 21.84kWh to equal 90.42 miles.
4.
There will be a decrease in ECONOMY with heater or air conditioner use. This, of course, is difficult to determine with the less than stellar tools available on the LEAF, however the air conditioner / heat pump is relatively efficient, therefore I think a 15% hit to economy is logical at 102F, so 4.14miles/kWh minus (4.14 * .15) = 3.52 miles/kWh economy at the same 65mph with the air conditioner running with a 102F battery and 102F ambient air and 102F dew point at sea level elevation with a new, zero degraded battery. That equals 3.52 miles/kWh * 21.84kWh = 76.9 miles range,
or about 9% effective loss or range autonomy from 84 miles of range at 70F in this example.
5.
Your battery will degrade in high ambient heat areas. This means that your shiny new car with a 21kWh usable battery capacity at 70F will not have 21kWh available in one year. Please factor that into your range calculations, since that singular issue is likely to have the GREATEST impact to range in high heat areas. We have already measured up to
30% reduced range from battery degradation in Phoenix.
).
