Friday, August 26, 2016

Operating on solar power

Two 100-watt panels temporarily "mounted"
It's been almost four months now since I've used my Astron power supply, but I've been operating at my normal summertime pace anyway - a good amount of listening while in the shack doing other things, a QSO here and there, some garden variety DX and participation in the NA QSO Party a few weeks ago. All at 100 watts.

All of it has been with power provided by two, back-breakingly heavy, 6-volt T105 wet cell batteries wired in series and charged with two 100-watt solar panels (also wired in series) resting (but secured with wire) against the chimney on my roof. They face south and provide 40 volts at 5 amps from about 10:30am to 3:30pm local time. Decreased power is available from them during other daylight hours as the sun is at a lower angle.

A Morningstar MPPT charge controller charges the batteries more efficiently than cheaper
Charge controller
pulse-width modulated (PWM) controllers due to being able to trade voltage for current applied to batteries. MPPT controller efficiency is usually 97% versus 70% for PWM charge controllers and that advantage is mainly realized when the voltage from the solar array is at least three times that of the batteries being charged.

Wiring the arrays in series also minimizes the effect of voltage loss over the 50-foot run of 10g copper wire leading from the arrays into my shack. In parallel, my panels would produce 20 volts at 10 amps and the copper loss would amount to a 5% loss rather than the 1.25% loss of the series-wired method.

Like most modern transceivers, my Flex 6300 is designed to operate with an input of 13.8VDC. My batteries are considered fully charged at 12.74 volts and are at half capacity at 12.10 volts. This results in an RF output of 90 watts with fully charged batteries and 78 watts with the batteries half discharged (the lowest I'll ever allow them to go).

T105 golf cart batteries
I don't mind the lower RF out and have only gotten to that point after disconnecting the solar panels for three days and allowing the rig to remain on for three days and nights. Operating normally, with the solar panels connected, the batteries never discharge lower than 12.6 volts, which is considered 90% charged according to the battery manufacturer.

My main reason for buying these components and operating "green" is to learn more about the practical use of solar power in order to eventually use it on an RV when camping away from commercial power. Ham radio is providing an excellent way to learn what can be expected from a given array size with a known load.
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6 comments:

  1. Very nice done John, something I really want in the future. A solar powered shack, not depending on electricity from the grid. And once you get even with the money you invest in panels and batteries it is free as well as long as the sun shines. 73, Bas

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    1. Hello Bas - unfortunately, solar power is not really economical. There has to be another reason besides $$$ to justify it - operating away from commercial power, operating in emergency situations (storms, etc) when no power is available at home, or just as a hobby to learn about it.

      Here in Texas, I pay $00.15 for a kwh of commercial power - and we have a *lot* of sunshine for a good portion of the year. My solar set-up cost me $900. That $900 will buy 6000 kwh of electricity and it will take my solar system about 10 years to produce that amount of power. At that point, I will break even with my money if I don't spend any more. The reality is that I will need one (possibly 2) new pairs of batteries in that amount of time.

      I also have a QRP solar set-up and will be posting info about it in a few days. Much more economical and even more capable than some might think...

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  2. Any RFI from the MPPT controller?

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    1. No, none at all and I did test extensively due to many horror stories I'd heard. I bought the controller and kept all the paperwork, packaging etc with the plan being to take full advantage of Amazon's return policy if I detected any RFI. Happily, it's not an issue.

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  3. Fantastic write up. Anxious to hear about the qrp setup.

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    1. That posting will be made tomorrow - thanks for the comment.

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