[Elecraft] ... and solar power

[Edward R Cole]

This topic has been pretty thoroughly thrashed, but...

I'd like to add a few comments.  I installed and maintained 
solar-power communication sites for over 15 years.  Open circuit 
voltage on a solar panel often will reach as high as 22 vdc (in 
direct sun).  A panel loaded by a radio will drop in voltage to about 
18v depending on the power rating of the panel and the load 
resistance of the radio.  But one should consider a solar 
voltage-regulating charger in series between panels and the battery 
bank.  For a "12-volt" battery to charge, it needs a charging voltage 
higher than the final full-charge voltage.  Solar panels are not 
constant voltage sources and voltage drops with the amount of loading 
(higher current load lower voltage).  They are volt-amp sources and 
not watt sources.

Float charging is beyond the scope of what I can discuss, but battery 
mfr's provide the float voltage required for a given model 
battery.  If you use a bank of batteries there is also equalizing 
voltage that should be applied according to the mfr's 
requirement.  Most hams do not do either.

I am float charging the starting battery of my standby ac generator 
by a crude method.  It is simply a 500ma 12v charging cube plugged 
into a timer outlet.  I guessed at the charge time per day required 
to maintain the battery.  The charge cube runs 19vdc open circuit 
(its a simple transformer and diode).  The battery looks like a large 
capacitor so no filtering is needed.

So far this set up has worked over two months time during which the 
generator was started once.  I should mention the generator is 
outside in an unheated compartment in Alaska winter temperatures (-3F 
as I write this).

Back to setting up a solar charging system one needs to first analyze 
the load requirements: average load and peak load.  Also run time is 
required.  Then one can design a battery bank and solar charger to 
supply these needs.  For communications equipment deep cycle 
batteries are best.  For motor starting high starting current shallow 
discharge is needed.  These are two different battery designs.

Solar panels only work during daylight (duh!)(currently I have 6-hr 
39-min of daylight per day).  Interestingly, one will obtain near 70% 
performance with overcast skies.  Panels will work if not directly 
pointed at the Sun but with diminished output.  but it may work 
better to mount a panel in such a compromise position to avoid things 
like hail damage or snow coverage.  I had solar panels mounted 
vertical on the side of buildings on communication sites that ran 
sites year round.  I also had portable repeaters in fiberglass boxes 
with the panel on the cover looking straight up.  It all depends on 
proper sizing for the load and sun angle.

So it is not trivial to engineer a solar charging system.  Some of 
the sites I maintained were visited only once per year and had to be 
reliable the rest of the year (accessible two months out of a year by 
helicopter).  You got to do your homework for that to happen!

Some sites were buried under 18-foot of snow with over 200mph winter 
winds.  Ice could build up on antennas to over a foot diameter.  If 
something broke is stayed broke for months as the site was inaccessible.

73, Ed - KL7UW
http://www.kl7uw.com
dubususa at gmail.com
"Kits made by KL7UW"