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[aprssig] Shack backup power

Bob Bruninga bruninga at usna.edu
Sun Sep 11 20:27:12 UTC 2011


> I would put in grid tie solar, as 99% of the time 
> it would be perfect for my needs...  When I get 
> an outage I crank up the generator....  Solar 
> would have done me NO good as a backup, even with 
> a large battery bank it would have been played 
> out before commercial power came back on...

My take on it is 4 golf cart batteries would make a great emercency backup system for those with GridTie solar...

A typical refrigerator is rated at 400 to 900 watts (when running (and defrosting)) but the 24 hour total (including the on/off cycle times) is about 2.4 kwh per day.   

For a solar system, which can provide power for several hours during the day, then you'd only need about 1.5 KWH storage for the night (when you should not be opening the door every hour anyway).  And that is about ONE golf cart battery (though you will need two to get to 12 volts and to keep the depth of discharge to about 50% to prolong the life of the battery).

What about cloudy days?  For a 10 kW grid tie system, even on cloudy days, the array is still producing about 1 kW all day long, still more than enough to run emregency day-time loads including the charge for the overnight Refrigerator batteries.

But the big solar panels are typically 28 volt peak output, so you may as well get four golf cart batteries so you can operate a 24 volt battery system.  They will last much longer at only 25% depth of discharge plus giving you greater peak power when evreything kicks on at once.

Dont over look that your TV, PC's and almost every modern electronics gizmo can run on 100 to 330VDC (that has a modern 100 to 240V AC univeral power supply).  SO they can run directly from 5 to 10 or so panels in series.

Join us on solarDIY at yahoogroups.com

or see http://aprs.org/off-grid-maybe.html

Bob, Wb4APR



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