[Elecraft] OT: Small solar array to handle just the shack, computers, and lighting

[Jim Brown]

On Fri,9/25/2015 8:33 AM, Wayne Burdick wrote:
> Some of our friends are putting in large solar arrays that feed power back into the electrical grid. I'm looking for something smaller and simpler since our electricity use is very low overall.

Sticking with the original title of supplying only lighting, computers, 
and shack, I'll provide some general information that may help you think 
about designing a suitable system. My QTH is in a clearing surrounded by 
very tall redwoods, so an array of solar panels doesn't get a lot of 
illumination. As a result, I've made no effort to run 120V gear from it.

My system is pretty simple. It starts with four 55W panels retrieved 
from the dumpster at an agency where a neighbor ham maintained remote 
instrumentation sites. Because of the shadows cast by the trees, I have 
two strapped together and located to catch the sun before noon, the 
other two for the end of the day.

I use a Genasun MPPT charge controller between the panels and a pair of 
Trojan 6V 220 Ah lead-acid batteries. This system runs everything in my 
shack with the exception of the computers, the rotators, the SteppIR 
controllers, and my power amps. For lighting, I'm using the LED strips 
sold by a Pacificon vendor. Four strips taped to the ceiling provide 
illumination that's adequate for operating in the shack, and draw about 
1.2A. The low power 120V stuff is connected to a small UPS. Because the 
draw VERY little current, a UPS can keep up for quite a while.

If I want to run power during a power failure, I can fire up the Honda 
2000i.

The downside of this system is that the lead-acid batteries discharge 
curve starts around 12.5V and goes down below 11V for full capacity. 
That's fine for a KX3, but not great for a K3. The batteries cost me 
about $240, the Genesun about $120. The Genesun is available in several 
voltage and current ranges, and for both lead-acid and several Li 
chemistries. Buy direct from Genesun.

This system can yield 33Ah or more during the summer half of the year, 
but dips to MUCH less during the winter months. Also, if I want to 
contest with the K3s, I need a lot more power than I can get from this 
system, and I'd like higher voltage to keep the signal cleaner (those 
reading the mail may not know that the IMD in the K3 is lowest at high 
DC supply voltage).

So -- for contesting, and during the winter months, I must float charge 
the batteries from a small regulated supply.  10A is enough to keep up 
with a single K3 at 100W, but 20A is needed for heavy duty SO2R.

Because of their relatively low voltage discharge curve and the K3's 
need for higher voltage, I'm searching for battery chemistry with a 
discharge curve that stays above at least 12V, and higher would be 
better. There are some Li chemistries that are candidates, but cost is 
currently prohibitive.

If you have enough batteries and enough sun, you can start thinking 
about inverters to run your fridge and other 120V stuff when the power 
drops. Samlex has models for several power ratings, and two lines -- one 
that meets FCC Part 15 Class B, and another that does not. Appliances 
like refrigerators require a lot more current to start than to run. 
There are refrigerators specifically designed to run on DC for 
off-the-grid homes.

Samsung makes both computer monitors and TVs that run from a nominal 
14V. I'm running their monitors from my 12V system, and they work fine. 
My cable modem and wi-fi router both run from 12V; they're not in the 
shack, so I run them from a  sealed 12V lead-acid cell that is float 
charged by a linear wall wart that gives it a bit more than the gear 
draws. The result is a poor-man's UPS that holds internet up longer than 
Comcast does. :)  Batteries for their fiber electronics repeaters are 
rated for 6 hours of operation, and it's common for power failures here 
in the Santa Cruz  Mountains to last a LOT longer. And they want to sell 
me a package telephone service? No thanks.

73, Jim K9YC