panel size

Jun 2, 2004 10:32 pm
panel size

Im installing an attic fan,drawing 2.8 AMPS AT 120 VOLTS,im not sure what size panel to use.Also,can i expect to run this fan allday to help alleviate the temp. in my attic space.
Jun 4, 2004 10:18 pm
Re: panel size

 2.8 AMPS AT 120 VOLTS allday  
2.8 multiplied by 120 = 336 watts
A 12 hour day multiplied by 336 watts =      4,032 watt hours.
At the electric power utilities rate of $0.08
per kilowatt hour this would cost a total of
$0.35 a day rain or shine. Or $63.88 for 6 months of summer.

To do this with photovoltaic it would require an investment in;
1,000 watt PV array
1 Array mount
400 watt inverter
440 amp hour battery bank a 12 volts nominal
60 amp charge controller (with 17.4 volt modules)
Combiner box
If on roof a GFP breaker
This would be a fully autonomous system and it could even run into the night if the attic were hot enough (rain or shine). But thats just it, if it were raining the attic would be cooler so the fan would not run or at least not as long. Whats more is during the winter months it, more than likely, would not run at all. So what do you do with all that surplus power? You could heat water with 12 volt water heating elements but that would mean investing more.
This is just my conclusions though, as with most anything else in life that one may not be absolutely sure about, seek other opinions.

If you have read the ad for a solar powered attic exhaust fan at Alt-E store then you read were all it says is that the panel and motor are matched to ensure maximum power output throughout daylight hours. Its only $309.00 if you were to divide that by $63.88 that the utilities might charge, you can see where the solar fan would pay for itself about the same time the warranty would last on the fan motor. How long of a warranty does the fan you want to use have? The only sure things in life are death and taxes.

The other alternatives are; ridge vents, turbines, opening up the soffits more, and/or bigger gable vents. I have been meaning to find out if there are any biulding codes that would prohibit a chase that would allow cooler air from a crawl space to flow into the attic of a house but have not done this as of yet. One draw back to this idea is that it may not let air move from the soffits across the under side of the roof which would result in a shorter shingle life.

Or you could always open up a swett lodge and charge admission:) It would be my luck the feds would find out about it and charge their tax and then someone would have a heat stroke and pass away:( Death and taxes.

To me the provebial glass of water is neither half empty or half full, its just a glass of water. Thomas S.

351 Posts
Jun 5, 2004 04:29 pm
Re: panel size

I do not know while you are asking about panel size, a load of less than 3 amps can be added to almost any household circuit without overloading it.  If you are asking about a switch for it, your common light switch will handle it without any problems.

The other Item that you should add to the installation is a thermostatic switch with the thermostat (or sensor) mounted as high up in the roof ridge or peak as is convenient.  You pick the tempurature (I like about 120 degrees). The fan will not come on until that temp is reached and will shut off when the temp falls below it.  Depending on the house design and roof color, the results will very, but my fan runs about 10 minutes an hour on a 90 degree day and no more than 30 minutes an hour on a 102-105 degree day.

8 Posts
Jun 15, 2004 08:23 am
Re: panel size

or just change the motor to a DC one.

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