Inside and out, that is.  Just finished the installation of two 85 Watt solar panels on the trailer’s roof.  This was the last piece in the electrical system which is now operational and ready to support my power demands on some up-coming adventures.

Roof-top Solar Panels

The system is 12 Volts, of course, and relies on an old truck battery for storage.  The battery has about 100 amp-hour capacity.  My desire is to run interior lights, a cell phone charger, and my laptop for a few hours a day.  My laptop uses about 30 Watts during normal operation, so that’s quite a few hours of use before the battery would need charging.  It appears this setup can charge my battery in one day – not that it should ever need to.

The panels, and the charger / controller, are distributed by HQRP.  There is some concern out there about the charger / controller, listed as:

HQRP 20 Amp 12V / 24V Solar Charge Power Controller / Regulator 20A 300W with Battery Charge Monitor plus HQRP Coaster

(and sold on

The manual is absolute junk – making installation a little less than obvious.  But the unit does work well and differs significantly from other chargers that are commonly sold.  If you intend to use power while simultaneously charging a battery, then you need a controller and not just a charger.  This allows power to be diverted to your load, while still charging the battery with the proper current.  Otherwise, you’re just effectively limiting the current to your load, and not taking full advantage of your panels’ output.

I did have some unanswered questions with this hardware, however, namely whether to wire the panels in series or parallel, and also how it functions in either 12V or 24V systems.  After tracking down the company in China that builds these (HQRP just slaps their name on it), I got some good information.  Turns out parallel is the right way to go, and the unit automatically determines the system voltage by measuring the battery’s voltage.  I believe the threshold to trigger it into 24V mode is 18V at the battery.

In conclusion, the system is working great.  I’ll learn more as it sees continued use, but for now it’s quite nice to have ample electricity and a $0.00 utility bill.

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