[Elecraft] OT - Solar panel output

[Fred Jensen]

dolfindon at msn.com wrote:
> Hi
> 
> Actually 33 watts is more than enough to power a QRP K2. You only
> transmit about 25 % of the time and receive the rest so running a K2
> at 10 watts will only require about 15 watts to keep the battery
> charged. For a 100 watt K2 you will need about 75 watts of panels and
> about a 35 amp hour battery to run continuously. I know this works
> because this is the setup one of the operators used on field day here
> in Tyler Texas a couple of years ago. The panel was set up out in a
> field about 100 ft away from the rig. The controller was one of my
> Solar Controller Kits and the battery was a 35 amp hour gel cell like
> used on electric wheel chairs. We operated night and day CW at 75
> watts out. The battery kept us running all night and the solar panel
> had the battery back fully recharged by mid day.
> 

My experience [not nearly as much as N0SS and others] is that a good 
half or more of the challenges to the use of solar power is in the 
"usage" rather than the "generation" side of the equation.

Many years ago and when solar cell efficiencies were much lower than 
today, my engineering team and I got the job of designing a UHF multiple 
repeater communications system for a petroleum pipeline operation in So. 
Africa.  We started the design with the normal equipment at the sites 
that we had always used, and a humongous solar array good for about 400A 
in full sun with a bank of glass jar batteries for a 48V primary 
circuit.  Based on historic solar irradiation data, the 24/7 power 
budget was pretty much balanced with a 40% safety pad, which was close 
to but not quite 3-sigma.

400A under full sun resulted in some fairly expensive structural 
construction, wiring, control, and batteries, none of which really 
impressed our customer.  Thus encouraged, we undertook to trim the 
usage, which turned out to be the really fun part of the engineering. 
We got each site down to an eighty amp array with sealed, much cheaper 
but far more long-lived batteries for the same "almost 3-sigma power 
budget pad."  In reality, that still turned out to be overkill after it 
had gone into operation.

I charged my 12V 12Ah gel cell with a 1A RV solar array/controller and 
ran my K2 at 15W for 4 hours for the 2007 Flight of the Bumblebees.  I 
called CQ a lot.  The terminal voltage of the battery never varied, and 
I've used it since without recharging.  Every watt-hour if drain you 
save in drain is a smaller capital investment in charging equipment.  My 
K2 was a good conserver, I'd bet a K1 would be better, and my KX1 could 
make my solar-charged batter last longer than my lifetime :-)

As many of you Elecrafters as can should get into the FOBB.  It's in the 
middle of the summer [in the N. Hemisphere], it's fun, and you'll make a 
lot of Vitamin D while you're knocking off Q's if you do it in the 
field.  Vitamin D is good for you :-)

73,

Fred K6DGW
- Northern California Contest Club
- CU in the 2008 Cal QSO Party  4-5 Oct 08
- www.cqp.org