[aprssig] Shack backup power

KBØNLY kb0nly at mchsi.com
Sun Sep 11 16:13:18 CDT 2011

I don't see solar as an emergency power source, I wouldn't ever rely on it 
as such.  To me it’s a good gimmick to reduce the electrical consumption of 
an average american home, but until the cost of solar comes down from absurd 
I will stick with my $.075 per kWh grid power and a generator for backup.

I would like grid tie solar some day to offset the consumption of the few 
things running all day here, but I am glad I didn’t get all fired up this 
spring, it would have all been lost to the tornado and hail.  We had hail 
large enough to punch dents deep enough in steel roofing to cause it to 
crack, a solar cell wouldn't stand a chance.



-----Original Message----- 
From: Bob Bruninga
Sent: Sunday, September 11, 2011 3:27 PM
To: TAPR APRS Mailing List
Cc: solarDIY at yahoogroups.com
Subject: Re: [aprssig] Shack backup power

> 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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