[Milsurplus] OT: Solar Panels

[Albert LaFrance]

Unfortunately, your daily output will be a lot less than 4.9 kwh.  The 400W
rating of the panels is a "DC peak" output - they'll only produce near that
much when they're getting full sun normal to the panel surface.  The amount
of available sunlight at a given moment depends on your location, the time
of day and time of year, and weather conditions.  In the Philadelphia area,
for example, the daily average over the year is equivalent to around 4.5
hours of full sun. 

The efficiency in converting the panels' output to AC (the "DC-to-AC derate
factor") varies by system configuration, but an often-used figure is 77%.

So for your configuration, in Philadelphia, the annual production would be
something like 400W x 4.5 hours x 365 days x 77%, or about 506 kwh. 

Albert LaFrance

-----Original Message-----
From: milsurplus-bounces at mailman.qth.net
[mailto:milsurplus-bounces at mailman.qth.net] On Behalf Of David Stinson
Sent: Sunday, October 03, 2010 2:37 PM
To: armyradios at yahoogroups.com; milsurplus at mailman.qth.net;
boatanchors at theporch.com
Subject: [Milsurplus] OT: Solar Panels

Probably considered OT, but I trust this group's good sense.
Please reply off-list (unless a lot of people say they 
want to see the thread :)

One of the more effective ways of using solar panels
to help with your bill is to connect them through 
a "grid synchronizing" or "grid tie" inverter.
These create a pure sine wave at a slightly higher
voltage than the line, so that they actually feed power 
back to the grid.  
They used to cost like $2000, but the Chinese have
gotten into the act and moved that decimal place
to the left; you can get one for less then $200 now.

I need some smart people to tell me 
if I have this right:

I have 400 watts worth of solar panels.
I feed these to a grid-tie inverter.
Fudging for losses, let's say I can deliver 350 watts
to the grid for about 14 hours a day (in the summer).
That's 4.9 kWh a day.  Times 30 days is 147 kWh.
My electric rate is 12.6 cents per kWh.
That's $18.52 a month discounted to my bill,
best case.  Average it out over the year for 
low-output days and let's call it $12 a month.
That's $144 a year.  Payback time on that 
small system would be long.  

Hardly seems worth the trouble.

73 Dave S.



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