PowerSpout microhydro

spgsc531

rogerblack wrote: »

Yes, there is.
If my power use is 10W/hour, then at the end of the first hour it's 10W, at the end of the tenth 100W.
W/h is a valid unit.

Watt-hours - watts * hours - is what's meant in most cases of course.
A 100W light bulb uses 100W * however long it's on energy.
The electricity company typically charges you per unit of energy - (it happens they use 3600000J, 1000watt-hours, or 1kWh).

Confusion of watts, watt-hours and watts per hour

The terms power and energy are frequently confused. Power is the rate at which energy is generated or consumed and hence is measured in units (e.g. watts) that represent 'energy per unit time'.
For example, when a light bulb with a power rating of 100W is turned on for one hour, the energy used is 100 watt hours (W·h), 0.1 kilowatt hour, or 360 kJ. This same amount of energy would light a 40-watt bulb for 2.5 hours, or a 50-watt bulb for 2 hours. A power station would be rated in multiples of watts, but its annual energy sales would be in multiples of watt hours. A kilowatt hour is the amount of energy equivalent to a steady power of 1 kilowatt running for 1 hour, or 3.6 MJ (1000 watts × 3600 seconds (i.e., 60 seconds per minute × 60 minutes per hour) = 3,600,000 joules = 3.6 MJ).

Terms such as watts per hour are often misused when watts would be correct.

Watts per hour properly refers to the change of power per hour. Watts per hour (W/h) might be useful to characterize the ramp-up behavior of power plants. For example, a power plant that reaches a power output of 1 MW from 0 MW in 15 minutes has a ramp-up rate of 4 MW/h. Hydroelectric power plants have a very high ramp-up rate, which makes them particularly useful in peak load and emergency situations.
Major energy production or consumption is often expressed as terawatt hours for a given period that is often a calendar year or financial year. One terawatt hour is equal to a sustained power of approximately 114 megawatts for a period of one year.
The watt second is a unit of energy, equal to the joule. One kilowatt hour is 3,600,000 watt seconds. The watt second is used, for example, to rate the energy storage of flash lamps used in photography, although the term joule is generally preferred.

http://en.wikipedia.org/wiki/Watt

Spgsc

EricMears

Originally Posted by Kernel SandersThere is no such measurement.

rogerblack wrote: »

Yes, there is.
If my power use is 10W/hour, then at the end of the first hour it's 10W, at the end of the tenth 100W.
W/h is a valid unit.

Watt-hours - watts * hours - is what's meant in most cases of course.
A 100W light bulb uses 100W * however long it's on energy.
The electricity company typically charges you per unit of energy - (it happens they use 3600000J, 1000watt-hours, or 1kWh).

I think Kernel was absolutely correct (albeit a little pedantic).
Rate of power consumption is never 10W/hr or even 10W/sec, 10W/year etc. . . It's simply 10W

"A 100W light bulb uses 100W * however long it's on energy." is correct.

If you are indeed using a steady 100W then after 1 hour you will have used 100Wh and after 10 hrs you'll have used 1kWh If you really wanted to, you could say that's a rate of 100Wh/hr or 0.1 kWh/hour but just calling it 100W is correct (and easier).

But the original calculation gave the right final answer in that generating at 120 watts would give 120 x 24 watt hours per day which can also be expressed as 2880 Wh or 2.88kWh

Kernel_Sanders

Thank you, gentlemen, for those comprehensive explanations. The problem lies in faulty thought processes such as

rogerblack wrote: »

Yes, there is.
If my power use is 10W/hour....

Power use isn't 10W per hour any more than it is per second or per week.
It is 10Wh/hour.
Wh is the (accumulated) quantity , W merely the rate.

EricMears wrote: »

I think Kernel was absolutely correct (albeit a little pedantic)

Thank you Eric. Pedantic it may be, but no more so than correcting someone for stating the distance from Mansfield to Nottingham is 15 mph

EricMears

Kernel_Sanders wrote: »

Thank you Eric. Pedantic it may be, but no more so than correcting someone for stating the distance from Mansfield to Nottingham is 15 mph

Only 'pedantic' in the sense that the poster had managed to get the right answer - so it didn't really matter that he'd made up a new unit in the process.

Look carefully and I'm sure you'll find numerous examples of people saying "I generated 25 kW today" or "my panels are rated at 4 kWh". Gets really tiring to correct them all !

P.S. I myself am a fully paid up pedant.