Err, you must have quite the efficient house there, Tomby. 3kW (3000 watts) at 120 Volts (US power standard single-phase) is only 25 Amps.
Older homes here in the States were normally equipped with 100 Amp main panels. However, with all the appliances and such in a house now-a-days, most of them are coming with upgraded 150 Amp, or even 200 Amp installations.
This means you'd likely want at least 2 or 3 of those dishes per house. And you'd want a battery bank to provide occasional surge capacity, as well as a source for night time energy. Of course, if your house was un-attended for a lot of the day, you could shift emphasis to a bigger battery supply, and cut the number of dishes so you could charge up the batteries while you were away, and run primarily off of those when you got home and power use exceeded the dish output.
In that case, however, you wouldn't be putting much juice back into the grid. Alternately, you could back-feed the power grid all day, then suck power off it when you returned home and your usage exceeded the dish output, then just pro-rate your total monthly grid costs against the income from the juice you'd provided.
More techie-wuff stuff!vrghrSeptember 9 2010, 23:24:29 UTC
"Ah, pronoun trouble!" /daffy duck *grins*
Actually, it's "Noun" trouble, but that wasn't the duck's original line. The problem is, kWh and kW are not the same thing, and though they sound quite similar, they are very different beasties.
kW is the immediate consumption (or output) of a device at any given moment. kWh is the total work capacity (or usage) of a device.
The simplest way wuff knows to illustrate that: A big battery might have a total capacity of (for illustration) 1 kWh. But a "strong" version might also have an output capacity of 5kW, and a "weak" one might have an output capacity of only .5kW (500 Watts).
Lets use our "weak" one to illustrate: A 100 Watt bulb, running on US power (120V), uses .1kW. If it runs for 10 hours, it would use up 1 kWh. So our "weak" battery could run 1 such bulb for 10 hours, no problem.
We could hook up 5 of those bulbs to our "weak" battery, and max it out at .5 kW (500 Watts). Hook up a 6th one, and our battery trips the breaker or fries internally and explodes.
However, it could run those 5 bulbs for 2 hours before it was drained and used up all of its 1kWh capacity.
The "strong" battery could connect 50 bulbs at one time, because 50X100=5000, or 5kW (that battery's output load capacity). However, because it still only has a 1kWh storage capacity, turning on all 50 lamps would drain it in a matter of minutes.
The solar dish doesn't have any reserve capacity at all. So its output is rated in "immediate" factors (kW). If the sun stops, output stops immediately. So the values they're giving are talking about how many "bulbs" you can hook up to the dish at any given moment.
Your home electrical panel is rated the same way; it hasn't got a built-in reserve, so the rating there is for how much power can flow through it at any given instant. Exceed that rating, and the main breaker trips.
But you mentioned that a home uses 1-3 kWh...
A home, if viewed as a piece of equipment - a black box with stuff inside it - has both immediate flows (kW) and average capacity (kWh) needs. To run all the stuff in that box, you probably need a battery with a capacity of about 1-3 kWh X the number of hours the "box" is "running". That's because the immediate flows fluctuate minute by minute, but all of them pull that capacity out of your battery. So you use the kWh rating to figure the storage needs of a battery bank that supplies that "box", to make sure you don't run it dry and go dark before you shut your "box" down for the night.
At the same time, you need to make sure that the source can also supply the immediate kW peak flow, which, for an 100A panel is a bit under 30kW (due to 3-phase considerations and other silly math stuff). You'd probably want a bit more than that, to handle the occasional "start up surge" that happens when heavy motors like air conditioning and refrigerators kick in. Those can actually exceed the rating on your breaker box, but they come and go so rapidly that the breaker doesn't trip on them. The source, though, has to be able to handle even those short-duration surges without frying something.
So the solar dish's rating of 3kW means you could hook up 30 each 100W bulbs and run them all successfully. OR you can run 3 each 1000W appliances like a toaster, a hot plate, and an electric fry pan (but you'd have to run the 3 without any lights on). OR you could take the entire output, run it into a battery for an hour, and have 3kWh of capacity available to use however you wanted to until it drained, plus the additional 3kW constantly coming from the dish itself, but only if you didn't draw any of the dish's output while it was putting that reserve into the battery in the first place.
And now you know more than you probably ever wanted to about kW and kWh stuff! *giggles*
Re: More techie-wuff stuff!tombfyreSeptember 10 2010, 01:53:38 UTC
Yes, I see where I made the error between the two terms there. ^^ I *used* to know more about all this stuff, but apparently things have been slipping over the years!
Hooray for the tech woof further clearing things up. :3 You likely would want more than one dish on sight then, unless you were direct feeding it into the grid or something.
Older homes here in the States were normally equipped with 100 Amp main panels. However, with all the appliances and such in a house now-a-days, most of them are coming with upgraded 150 Amp, or even 200 Amp installations.
This means you'd likely want at least 2 or 3 of those dishes per house. And you'd want a battery bank to provide occasional surge capacity, as well as a source for night time energy. Of course, if your house was un-attended for a lot of the day, you could shift emphasis to a bigger battery supply, and cut the number of dishes so you could charge up the batteries while you were away, and run primarily off of those when you got home and power use exceeded the dish output.
In that case, however, you wouldn't be putting much juice back into the grid. Alternately, you could back-feed the power grid all day, then suck power off it when you returned home and your usage exceeded the dish output, then just pro-rate your total monthly grid costs against the income from the juice you'd provided.
Reply
Reply
Actually, it's "Noun" trouble, but that wasn't the duck's original line. The problem is, kWh and kW are not the same thing, and though they sound quite similar, they are very different beasties.
kW is the immediate consumption (or output) of a device at any given moment. kWh is the total work capacity (or usage) of a device.
The simplest way wuff knows to illustrate that: A big battery might have a total capacity of (for illustration) 1 kWh. But a "strong" version might also have an output capacity of 5kW, and a "weak" one might have an output capacity of only .5kW (500 Watts).
Lets use our "weak" one to illustrate:
A 100 Watt bulb, running on US power (120V), uses .1kW. If it runs for 10 hours, it would use up 1 kWh. So our "weak" battery could run 1 such bulb for 10 hours, no problem.
We could hook up 5 of those bulbs to our "weak" battery, and max it out at .5 kW (500 Watts). Hook up a 6th one, and our battery trips the breaker or fries internally and explodes.
However, it could run those 5 bulbs for 2 hours before it was drained and used up all of its 1kWh capacity.
The "strong" battery could connect 50 bulbs at one time, because 50X100=5000, or 5kW (that battery's output load capacity). However, because it still only has a 1kWh storage capacity, turning on all 50 lamps would drain it in a matter of minutes.
The solar dish doesn't have any reserve capacity at all. So its output is rated in "immediate" factors (kW). If the sun stops, output stops immediately. So the values they're giving are talking about how many "bulbs" you can hook up to the dish at any given moment.
Your home electrical panel is rated the same way; it hasn't got a built-in reserve, so the rating there is for how much power can flow through it at any given instant. Exceed that rating, and the main breaker trips.
But you mentioned that a home uses 1-3 kWh...
A home, if viewed as a piece of equipment - a black box with stuff inside it - has both immediate flows (kW) and average capacity (kWh) needs. To run all the stuff in that box, you probably need a battery with a capacity of about 1-3 kWh X the number of hours the "box" is "running". That's because the immediate flows fluctuate minute by minute, but all of them pull that capacity out of your battery. So you use the kWh rating to figure the storage needs of a battery bank that supplies that "box", to make sure you don't run it dry and go dark before you shut your "box" down for the night.
At the same time, you need to make sure that the source can also supply the immediate kW peak flow, which, for an 100A panel is a bit under 30kW (due to 3-phase considerations and other silly math stuff). You'd probably want a bit more than that, to handle the occasional "start up surge" that happens when heavy motors like air conditioning and refrigerators kick in. Those can actually exceed the rating on your breaker box, but they come and go so rapidly that the breaker doesn't trip on them. The source, though, has to be able to handle even those short-duration surges without frying something.
So the solar dish's rating of 3kW means you could hook up 30 each 100W bulbs and run them all successfully. OR you can run 3 each 1000W appliances like a toaster, a hot plate, and an electric fry pan (but you'd have to run the 3 without any lights on). OR you could take the entire output, run it into a battery for an hour, and have 3kWh of capacity available to use however you wanted to until it drained, plus the additional 3kW constantly coming from the dish itself, but only if you didn't draw any of the dish's output while it was putting that reserve into the battery in the first place.
And now you know more than you probably ever wanted to about kW and kWh stuff! *giggles*
Reply
Hooray for the tech woof further clearing things up. :3 You likely would want more than one dish on sight then, unless you were direct feeding it into the grid or something.
Reply
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