[Elecraft] Solar Power for KX3

[Greg Troxel]

Panels are rated for a standard sun (1000 W/m^2 insolation) at I think
25C.  This is for the maximum power point, which is almost never the
voltage to charge the battery at.  The ones I've played with (powerfilm
5W, HQRP 20W) do more or less make their rated power in full sun (really
blue sky), and 5-20% of that in clouds.

I have a 20W panel with not particularly good siting that gets sun from
about 1030 to about 1600.  I have seen 1.3A from it, charging a 12V AGM
battery with a simple on/off controller (brunton).   Over the last 2
months I have gotten an average of just over 3 Ah per day.  On really
sunny days I get 7Ah.

So a solar setup really needs enough batteries to run for most of a week
(at least in New England), and enough panel to recharge if you have 1.5
sunny days in that week.

So for a fixed installation

  take daily use in Ah

  multiply by about 15 (1 week, don't discharge more than half) to get
  battery capacity

  take daily use in Ah, multiply by 2h of average good sun per day, and
  find a panel that can produce that current in full sun.



All that said, I have taken a single 7Ah battery and the 20W panel with
charge controller, and found that in mostly sunny conditions that powers
a kx3 indefinitely just fine.

Do not even think of using a panel without a charge controller.  You
will end up with excessive voltage and fry the battery.

73 de n1dam