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Simple Solar Calc - Page 3

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Posted by Ron Rosenfeld on June 30, 2010, 10:30 am
On Tue, 29 Jun 2010 22:27:37 -0700, "Malcom \"Mal\" Reynolds"


Let's review the formula and the definitions:

so for 2.5A x 12V x 24h = 720 whr per day

dividing by the insolation factor of 4 = 180 Watts of PV panels.

The OP requires a total of 720 wHr per day.

Insolation means the number of hours where you effectively get "full
sun" per day, sometimes also abbreviated ESH (effective sun hours),
and also the full rated output from your PV Panel.

Since the sun is not directly overhead all day, nine hours of daytime
will not generate the maximum out of the PV panels for the entire nine
hours; rather (in this case) it would be as if the sun were directly
overhead four hours.  (The fact that this is 1/6 of a day is
irrelevant; the "day" could be any length).

Since the OP requires 720 wHr per day; and since there are 4 ESH per
day, you divide the 720 by four to determine how much Panel you

Posted by ABLE1 on June 30, 2010, 11:38 am

I (OP) have been reading the extra discussion here and really appreciate all
the comments.  I understand now what is needed and will look into that
aspect.  So, I say thanks!!!

My next question is a little different.  Based upon what has been calculated
and putting together the necessary components.  What would be a ballpark
price for such a system.  I know that there may be a wide range based upon a
number of variables but am I looking at $00 or $0,000 to make it work.

Again thanks!!


Posted by Ron Rosenfeld on June 30, 2010, 12:56 pm
 On Wed, 30 Jun 2010 07:38:44 -0400, "ABLE1"

It used to be that you could ballpark a figure of about $-$0/watt
installed power.

Figure that with losses accounted for you'll need maybe 250-275 watts
installed power in an off-grid system.

Since that figure, PV prices have gone down; battery prices have gone
up; and labor prices have probably gone up.

There may or may not be state or local subsidies available.

Posted by Ron Rosenfeld on June 30, 2010, 1:26 pm

Those numbers are for professional installation.

If you do all the work yourself, you can cut the price considerably.

Posted by Malcom \"Mal\" Reynolds on June 30, 2010, 10:04 pm

I understand what you are saying, but to me if there are "x" Effective Sun
Hours, "x" should replace 24h in the above formula, giving you how much panel
you require. Seems a little easier


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