History major here, thus the basic question. What exactly does a "85Kwh" battery mean? Does that mean the entire capacity of the battery is it can provide a total 85 Kilo Watts over a one hour period, or something else?
Basically, yes. The kilowatt-hour is a unit of energy equivalent to one kilowatt of power expended for one hour of time.
It is a measure of battery capacity or total (theoretical) output. Means it could dole out 85Kw in a 1 hour (h) period or 5 Kw per hour (h) for 17 hours before depletion. In either case, 85 Kwh total.
Steven beat me to it.
Another cool way to do the math:
If your car uses up 0.309 kW for each mile driven (a reasonable number, when cruising), then an 85 kWh battery can provide 85/0.309 = 275 miles of range.
I don't belive your statement is accurate. When I range charge I can only use about 73-75kwh according to my "trip meter since last charge", even driving straight no stops. The rest is lost in vampire drain, and efficiency loss (my guess). Does anyone else have an experience of close to 85kwh used?
Dave Metcalf used 80.3 kWh on his mega 423.5 mile run last December... http://www.teslamotorsclub.com/showthread.php/12549-Dave-Metcalf-and-son-Adam-break-the-400-miles-challenge!-Incredible
Watts is charge flowing per second. It's a rate, not a quantity.
kwh is a quantity of electrons available.
Some fundamentals that I vaguely remember from my BS in electrical engineering...
A Watt is Joules per second, where a Joule is a unit of energy. So Watts are a rate of energy transfer . A cool way of thinking about it is that if you lifted up a small apple over the distance of 1 meter, you would have expended about one Joule of energy. Do that once per second and you are spending energy at the rate of one Watt.
So "kilowatt hour" is really just a somewhat roundabout way of describing a quantity on energy, or Joules, since a Watt is a rate of energy per time and an hour is of course a measure of time. It's kind of like saying "that town is 55 mile per hour hours away". Which of course is more easily described as 55 miles.
An 85 kilowatt hour battery is therefore the same thing as saying 85 * 1000 * 60 * 60 = 306,000,000 Joule battery. Describing the 85KWh battery as a 306 Mega Joule battery is more direct, but less relatable.
Here is a historical tidbit. It is kWh.
The W for Watts is captialized because it is the name of a person,
Mr. James Watt.
An additional tidbit is that when spelled out, units (at least metric) named after people is lowercase. e.g., watt, joule, coulomb, etc.
Sorry Brian. "units are"
This thread made me wonder... for how long could the 85kWh pack put out 1.21gW of power before running out of juice... by my calculations, about a 1/4 of one second. Is that long enough to make the flux capacitor work? :-)
1.21 gigiwatts? What was I thinking???
Not quite as cool as 1.21 gigawatts, but 306 megajoules sounds pretty neat to me. Cooler than 85kWh.
I like megajoules! ;-)
Thanks captain and David, I thought I was getting my upper/lower cases all mixed up.
@lspitzner, would like to hear if those answers were sufficient, though it seems like you already knew the answer to some degree.
Do you get what we mean when we say that a kWh is a unit of energy whereas a kW is a unit of power?
kW is the flow of water into the bathtub. kWh is the water already in there. ;)
More tidbits... My home (prior to the S) consumed about 20kWh a day on average. So my 60 could keep my home running for 3 days! That's a lot of energy storage in the S. My daily commute consumes 32kWh + vampire losses, luckily I only do that 3 times a week.
wcalvin wrote: "Watts is charge flowing per second. ... kwh is a quantity of electrons available."
That's not quite right. Charge flowing per second is current, and is measured in amps. Power, measured in watts, depends on how much current flows, but also depends on the difference in voltage between where the current flows from and where it flows to. Similarly, energy, measured in kWh, also depends on the voltage, and not just on the quantity of electrons.