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I need a charger and battery for a cell phone booster. - Page 9

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Posted by Ron Rosenfeld on October 25, 2009, 12:33 pm
 
On Sun, 25 Oct 2009 01:18:44 -0700 (PDT), philkryder



The monthly averages, that are derived from NASA data, take cloudy days
into account.  If you are designing critical systems, there is also data
available to show the maximum number of cloudy days in a row.  But for less
critical designs, you can figure 5-10 days of battery backup to be
required.


What about weekends?
Maybe you could turn it off when you leave, and on when you get there.



Panels are rated in a standardized manner, usually termed STC or PTC, that
show what the panel will put out under standardized conditions in a
laboratory.  So this should account for the fact that the panels may not be
a meter square, and should also account for some the efficiency issues
related to the fact that, under ideal conditions, solar panels cannot
convert 100% of the sun energy to electricity.

For example, your HF panels, according to the mfg, measure 12.40" x 36.42"
or 0.29 m^2.  So, theoretically, if they were 100% efficient, they should
produce 290 watts in full sunlight.  However, they are rated at 45 watts
which implies a 15.4% efficiency.

By the way, this value makes me wonder how they are rating their panels. It
seems very much on the high side compared with other commercially available
panels in that size range, which, for many of them, are closer to 10%
efficient.

Neither PTC nor STC account for all "real-world" losses. Actual solar
systems will produce lower outputs due to soiling, shading, module
mismatch, wire losses, inverter and transformer losses, shortfalls in
actual nameplate ratings, panel degradation over time, and high-temperature
losses for arrays mounted close to or integrated within a roofline. These
loss factors can vary by season, geographic location, mounting technique,
azimuth, and array tilt. Examples of estimated losses from varying factors
can be found at:
http://rredc.nrel.gov/solar/codes_algs/PVWATTS/system.html .

And you might also want to see
http://www.gosolarcalifornia.org/equipment/pvmodule.html

Homer's default settings apply derate the panels to 80% of their claimed
rating.  But you can vary this.

By the way, I would recommend that you find out more about the HF system
before deciding to purchase it.  Given their high claimed efficiency, I
would very much wonder about how they are rating their panels, and whether
this can even come close to being replicated in the real world.

Also, it should not be particularly difficult to input your actual usage
pattern, with regard to electricity usage, into HOMER and get a more
accurate modeling.  Especially with your being closed when it is dark, your
winter usage will be much less than I initially predicted and, since your
power usage will be mostly coincident with your power generation, your
storage requirements may also be affected.
--ron

Posted by philkryder on October 26, 2009, 2:20 am
 

Ron - I think that there are 3 of those panels in the 45 watt setup.
thus rating of 5% rather than 15...

Posted by Ron Rosenfeld on October 26, 2009, 11:13 am
 On Sun, 25 Oct 2009 19:20:07 -0700 (PDT), philkryder


If those dimensions are "per panel" then, of course, you are correct.  It
wasn't clear to me, from the way their specs are on this page:
http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber599

whether the dimensions referred to one panel or all three.

But 5% is certainly more believable (and also quite a bit less than the
efficiency of other panels -- which may not be an issue if the price is
right and you have the space to install).

Looking a bit further, I see that the company has a 15W 12V
(http://www.harborfreight.com/cpi/ctaf/Displayitem.taf?itemnumber418 )
panel for sale which appears to be the same as one (1) of the panels in the
kit, and it measures about the same.  So you are undoubtedly correct in
your 5% assessment.
--ron

Posted by Ron Rosenfeld on October 25, 2009, 1:03 pm
 On Sun, 25 Oct 2009 01:18:44 -0700 (PDT), philkryder


------------------------------------
By the way, my re-reading my last post shows that it is not clear that this
paragraph is quoted from
http://www.gosolarcalifornia.org/equipment/pvmodule.html
---------------------------------------

Neither PTC nor STC account for all "real-world" losses. Actual solar
systems will produce lower outputs due to soiling, shading, module
mismatch, wire losses, inverter and transformer losses, shortfalls in
actual nameplate ratings, panel degradation over time, and high-temperature
losses for arrays mounted close to or integrated within a roofline. These
loss factors can vary by season, geographic location, mounting technique,
azimuth, and array tilt. Examples of estimated losses from varying factors
can be found at:
http://rredc.nrel.gov/solar/codes_algs/PVWATTS/system.html .

And you might also want to see
http://www.gosolarcalifornia.org/equipment/pvmodule.html

--ron

Posted by stevey on October 24, 2009, 7:27 am
 
    YES

    You should mount it at atleast 15D tilt towards South, to shed
dust, or snow.


capacity?http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber599

   You'll need a 7 to 10Wdc Max. module only, with a 80%+ efficiency
charger set at
   13.8V float charg voltage

   A sealed gel cell battery rated at 10 to 15 AmpHour.

   Check around your area

   Weather extremes?  Vandalism or wild animals ?
Good Luck,
-solarMD


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