[NLRS] Solar panels- Update

[Doug Reed]

I feel I must point out that a 20 watt panel provides only a 1 to 1.3 
amp charge rate. But $110 for a 20 watt panel is a good price.

During the summer, with 12 or more hours of sunlight, you can expect 
about 14 amp-hours of effective charge.
During the winter, the solar insolation guides suggest planning on a 
maximum of 4 to 6 hours a day of sunlight and therefore a maximum of 7 
amp-hours effective charge.
The daily effective charge rate is a good indication of how much power 
you can draw on a daily basis. Any more than that and your battery bank 
will eventually be dead.

This panel was obviously designed as a standby-backup charge source for 
a camper or other battery system like at a cabin. It will keep the 
batteries up to max and even run a very small continuous load, probably 
about what a charge controller would draw.  :-)   But one small panel is 
not enough to recharge that battery system if it is being used on any 
sort of regular basis. Panels for whole-house solar collector systems 
are usually counted in 1000's of watts, not 10's. Although for a small 
cabin used once or twice during the winter, it might still be enough to 
keep the batteries up.

For Field Day, I've considered using a small solar panel to claim "solar 
powered" by charging a deep-cycle battery bank over a couple weeks. The 
size of the batteries depends how long you intend to operate and the 
size of the station. Field Day is short term and low power is still useful.

For what its worth, the simplest charge controller for a small solar 
panel has:
1. A heavy diode to isolate the battery from the panel.
2. A voltage comparator on the battery side that trips at the maximum 
charge voltage for the battery bank.
3. A large FET or NPN transistor configured to short the solar panel 
when the voltage comparator is triggered.
The simple charge controller simply SHORTS the panel since that gives 
the lowest power dissipation. If it diverts the power into a resistor, 
that means it must dissipate the full 20 watts. This type of charge 
control is only used for small panels since large panel arrays have much 
higher currents.

As an alternative, Harbor Freight sells a 45 watt solar PV panel kit for 
$220 and sells a 75 watt panel for $500. The 45 watt kit has some extra 
items to sweeten the deal. They even have some charge controllers for 
$30 to $80. But remember, the 45 watt kit is at best around a 3 amp 
charge rate.
<http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=90599>

And there are a number of videos on YouTube that show mounting solar 
panels and even assembling solar panel assemblies from individual 
monocrystalline solar cells. And additional videos that talk about 
wiring and battery installation. I'd suggest using the videos for a 
quick introduction to the project but then follow up with a lot of your 
own research on the Internet and at the library. (I don't trust the home 
videos very much.)

73, Doug Reed, N0NAS.

Tom Peterson wrote:
> Well it's not quite the end of the day and there is still a little 
> usable light, but I've disconnected the panel and brought it in for the 
> night.  The final reading isn't what I expected.  11.9V.  I went out 
> about 6PM and it was at 12.1V, so there was some increase in stored 
> energy.  I solved the puzzle in short order though.  The battery that 
> I'm charging is connected to my camper.  My 7 year old was out there 
> watching a DVD with a friend, using the portable DVD player, but it 
> seems they felt that they needed one of the interior lights on. 
> Additionally, my yard is heavily shaded by trees.  I think I'll try this 
> again later in the week and disconnect the battery from the camper and 
> position everything where it can receive direct sunlight without any 
> leaves blocking it.  All in all though I think it was a good purchase 
> and with some wind generated capacity and a few more deep cycle 
> batteries, I should soon be able to take my shack off grid completely.
>   

>