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stmbtwle

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Reply with quote  #11 
PER BATTERY. a 12v battery will always be a 12v battery.

SYSTEM voltage can be changed, and the current and resistance in the wires will change, but you can't change the BATTERY voltage appreciably unless you want really nasty (and expensive) things to happen.

We all agree that higher voltages are more efficient (less current, less resistance, and less loss in the wires). But as far as the batteries are concerned, the voltage they see will (better be) about the same. It's the wattage that matters as that's what controls the current.

Suppose you expect 100 watts average load (reasonable for a small fridge and a few LED lights). For a day that's 2400 watt hours. Suppose you want to use 6v golf batteries. At 200 amp hrs each battery holds 1200wh, of which 600 is usable. So you'll need a MINIMUM of 4 batteries (2400/600=4), 24v max in series. To carry the starting load of the fridge you'll want about 1000w inverter. But suppose a 1000w inverter isn't available for 24v. No problem, configure for 12v, it's all the same to the batteries. The only place current comes into play is in the wires from the batteries to the inverter. You keep them short anyway, and cost isn't that big a deal for a pair of 4' wires.

Now if you want TWO days' capacity you'll need 8 of the same batteries. Your voltage options are now 12, 24, or 48v. 48 IS most efficient, but if you can't find an affordable 48v charge controller or inverter, you may choose 24v instead.

However charge controllers are usually limited by amps, so a controller that can handle 600w @ 24v can handle 1200w at 48v. So it's cheaper to run one at 48v than two of them at 24v.

No, current is not "drawn", it is PUSHED by the voltage. Try starting your car with a dead battery. "Drawn" is just a convenient term.

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Willie, Tampa Bay

stmbtwle

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Reply with quote  #12 
Denman Island.  That's not as far out in the middle of nowhere as I was visualizing (I've been watching too many "Alaska" movies where everything has to be hauled around by boat and dragged across the mud flats by hand). You Canadians are more civilized than we are.  She has roads and even a bridge to the mainland and maybe an automobile.  That will make building your project a lot easier.

Question is she going to be on a well?  If so that may need to be considered in your calculations. On second thought a cistern may be more likely.  Does she want pressure water?

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Solar is like the wind. It may be free, but putting it to work isn't!
Willie, Tampa Bay
Rick H Parker

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Reply with quote  #13 
"No, current is not "drawn", it is PUSHED by the voltage. Try starting your car with a dead battery. "Drawn" is just a convenient term."

Current is drawen because it is the load that determines the current not the voltage source. If the voltage source determined the current, all loads would have the same voltage,  current and power, you would be burning up loads left and right. 
Electromotive Force which is measured in Volts, does not push current it motives current, there is a critical difference between pushing and motivation. 



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Rick H Parker
Kansas, USA
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Rick H Parker

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Reply with quote  #14 
Denman Island Solar Resources by month.

Denman Island Solar Resources.png


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Rick H Parker
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stmbtwle

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Reply with quote  #15 
Say whatever you want, no voltage, your car isn't going to start unless you push it and maybe not even then. Your starter can't 'draw' power from a dead battery any more than you can suck beer out of an empty glass (I know, I've tried).

But then, some people still believe the world is flat.




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Solar is like the wind. It may be free, but putting it to work isn't!
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Rick H Parker

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Reply with quote  #16 
"But then, some people still believe the world is flat."

That would be people that think if they believe it is so, if they don't it is not so.  There is somebody here that presents their belief as fact but it is not me. 
A battery is called a voltage source not a current source for a reason, it sources the voltage not the current.

no voltage, your car isn't going to start

Of course not, no voltage = no motivation.


If think a battery is a current source explain voltage but no current without a load.







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Rick H Parker
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stmbtwle

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Reply with quote  #17 
Not my job, try high school.


Bfath,
According to PVWATTS, a 1kw (rated) array in Vancouver set at 40° would get you 1132 kwh per year. Using my wild-ass-guess of 2.4 kwh per day, she would use 876 kwh. So in theory at least a 1kw array would be enough. This does not take into account battery charging losses. It would be close.

You can plug in the numbers here: http://pvwatts.nrel.gov/pvwatts.php

Have fun!

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Solar is like the wind. It may be free, but putting it to work isn't!
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Rick H Parker

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Reply with quote  #18 

"Not my job, try high school."

It is your claim. If you can't back it up with anything better then thinly veiled ad hominems ... I'll understand you did your best.

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Rick H Parker
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stmbtwle

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Reply with quote  #19 
I tried, you won't listen. I have better things to do.

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Solar is like the wind. It may be free, but putting it to work isn't!
Willie, Tampa Bay
Rick H Parker

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Reply with quote  #20 
"I tried, you won't listen. I have better things to do."

I know better, I am a  Electronics Engineering Technologist, I get paid well for this kind of stuff.

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Rick H Parker
Kansas, USA
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