kW vs. kWh
Gene Alan Townsend
jeremy howard todd wrote:
>
> Okay, I know this isn't strictly solar-related, but I keep
> seeing people here and on several solar web sites saying things
> like, "I use 2 kW/day."
>
> Isn't wattage a measure of continuous power? Do they mean
> kWh/day, or "My average continuous power is 2 kW most days," or is
> my lack of knowledge catching up with me? Just a little confused.
>
Jeremy:
Wattage is a measure of instantaneous power. Energy is the measure of
power over a given time period, usually watt hours, or kilowatt hours.
When someone says they use "2 kW/day", I would assume they mean just
that. Kilowatt days is not the normal measure, but is easy to
understand, since energy use repeats on a daily cycle. This would be
the same total energy as 41 watts used for 24 hours continuously.
A continuous power of 2 kW would be a very large power consumption.
Integrated for a day, this would be 48 kW hours.
Two kilowatts per day would be a reasonable energy consumption for off
grid living. Many live on less than this.
Regards,
Gene A. Townsend
jeremy howard todd
Gene Alan Townsend <wi...@primenet.com> writes:
>Wattage is a measure of instantaneous power. Energy is the measure of
>power over a given time period, usually watt hours, or kilowatt hours.
>When someone says they use "2 kW/day", I would assume they mean just
>that. Kilowatt days is not the normal measure, but is easy to
>understand, since energy use repeats on a daily cycle.
Ack! I guess all my physics classes are playing tricks with
me then. When I see "2 kW/day", I think kilowatts -per- day, not
2 kilowatt-days (which I'd expect to see written as "kW-day"). To me,
kW/day is a measurement of rate of change of power usage (what's that
called, flux?), which is probably not very relevant to most people (:
-jht
--
Jeremy Todd == All those moments == _,/
CS Student and Kangaroo Aficianado == will be lost in == <__ \_.---.
jht...@uiuc.edu == time...like tears == \_ / \
http://www.cen.uiuc.edu/~jhtodd/ == in the rain. == \)\ /\.\
=========================================== -- Roy Batty == // \\
"M-O-O-N, that spells moon" - Tom Cullen ================== ,/' `\_,
Vandibere Hanson
Gene Alan Townsend <wi...@primenet.com> spake:
>Wattage is a measure of instantaneous power. Energy is the measure of
>power over a given time period, usually watt hours, or kilowatt hours.
>
>When someone says they use "2 kW/day", I would assume they mean just
>that. Kilowatt days is not the normal measure, but is easy to
>understand, since energy use repeats on a daily cycle. This would be
>the same total energy as 41 watts used for 24 hours continuously.
Not to pick too many nits, but...
Wouldn't 2kW/day be more83w used for 24 continuous hours? 41w for 24h
would be closer to 1kW (984W, if anyone's counting)...
>A continuous power of 2 kW would be a very large power consumption.
>Integrated for a day, this would be 48 kW hours.
Now that sounds more like it...And that's a _lot_ of power right there
:)
I'm still _on_ the grid, with an extremely low power cost, using a
little less than 4kW hours each day.
Vandibere Hanson (vndi...@oitunix.oit.umass.edu)
Resistance is puerile.