Ghetto Solar


I haven’t been doing a lot on the plane lately.  That much should be obvious from the complete lack of postings here.  It’s just not the time of year I enjoy being out in the semi-open shop.  It’s cold, damp, and windy.  That being said, it doesn’t mean that all progress on all interesting things comes to a complete halt.  Growing up in Southern New Mexico, solar energy was something I was exposed to for most of my life.  I was young in the 70s, back when there were huge subsidies to install solar water heaters on the roof of your house.  When I go back to visit Mom in New Mexico, the vestiges of that period are still visible, in the form of dilapidated solar collectors on the roofs of random older homes.  What I’ve always been far more interested in, though, is solar electricity.  Naturally, I never did much with this interest when I lived somewhere sunny (like Arizona, New Mexico, Texas, or Colorado).  No, I waited until I moved to the darkest, soggiest, moldiest place in the US before I finally decided to invest some time and money into solar power.

Solar panels have dropped a staggering amount in the last ten years (it’s something on the order of ten times cheaper per watt than the last time I seriously considered doing this).  When Costco ran a sale on 100W panels for $119 each (normally $149 each), I decided it was finally time to try this out.

My goal was to build a small, simple, cheap system for use while camping and things like Field Day, to power the ham radio gear.  Nothing so grand as trying to power my house.  At least not for the first draft.  Specifically, my goal was to build a 12vdc system with a small inverter for 117vac that would run some lights, a laptop, some ham radio gear, and charge a phone/tablet/camera for the day, all for less than $500.  This budget ruled out some things I would have liked to have, like a pure sine-wave inverter and an MPPT power controller (those two alone would run about $400 by themselves), so the system is a little more primitive, but quite serviceable.  I also made the decision that the system needed to be easy to load in the truck to take to the mountains, and be built rugged enough to withstand banging around a bit in back while going up dirt roads.

In the end, I ended up with a 105amp/hr 12vdc deep cycle battery (a trolling battery from WalMart), two 100W 12vdc Grape solar panels (from Costco), a cheap 117vac inverter that I had in a box in my lab, and a Windy Nation P30L 30amp charge controller.  This gives me enough power to do a fair amount of useful work (whether lighting, radio, or whatever), and kept the cost pretty reasonable.  Obviously, there’s a bunch of other bits, as well, such as wiring, a battery box, fuses, etc.  I also added two extras.  First, I had a 12vdc 20amp Samlex power supply sitting around that I wasn’t using.  It’s got something wrong with it that causes it to generate a horrific amount of RF hash throughout the HF bands.  But the power that comes out is fine.  I added that to the stack to act as a plug-in charging input to the charge controller.  I also decided that since the system was mostly going to live in my truck, I could charge with the truck electrical system, as well.  A standard 7-way trailer controller has a 12vdc wire as one of the seven wires for use in charging batteries in your camp trailer.  I bought a 7-way connector and plumbed that line (through a switch and fuse) into the charge controller, as well.  So now, any time the engine is running, the alternator supplies up to 10A to charge the battery.

The day I built the system, we had sun.  Nice sun, in fact.  Which for late November, was a treat.  I set up the panels in the yard, where I was getting up to 7A charging current to the charge controller.  A bit less than I hoped for, but then again, it’s Winter and I’m at 48degrees North Latitude, so I’ll take what I can get.  For the next three weeks, we never saw the sun again.  I did set up the panels a few times just to see what I could get from my butt-covered sky.  Turns out that grey skies in Western Washington will get you about 200ma from two 100W panels.  Just enough to charge your cell phone, if you leave it connected all day (and don’t use it).  When the sun finally came back, I did a bunch more testing.  I definitively determined that solar is a very poor choice for my home power needs.  The sun is extremely low to the horizon this far North, and my neighbor’s property to the South is covered with 100ft cedars, meaning that my yard and house are forever in shadow during the winter months.  I was able to get a nice amount of power out of the panels, but only if I stayed out in the yard with them and constantly moved them back and forth as shadows formed and moved.  It’s a full-time job to keep the sun and the damned things.  That being said, I think the system will work well for camping.  The sun is considerable higher in Summer, and it should be relatively easy to place the panels in the sun at a camp site.  They’ll still need turning every hour or two to face the sun, but that’s a whole different (and much easier) problem than racing the constant shadows from the neighbor’s trees.  As the P30L charge controller reads amps in, amps being drawn by a load, and total amp hours in and out, it’s easy to get quick feedback on changes to the system.  I quickly settled on LED lighting (I can’t stand compact fluorescent bulbs, for a long list of reasons).  The wire from the trailer connector will supply 10-11amps of charging.  And the solar system can easily power my Macbook Pro, an FT-817, and charge a phone, while still having enough power left over to charge the deep-cycle battery at the same time.

I’m still planning on building a protective crate/stand for the solar panels themselves before taking them camping, but for the moment, they seem safe enough in their shipping cardboard in the back of the truck.  It’ll be fun to test in the real world this Summer.  I’d like to upgrade the system to a second 100amp/hour battery, a MPPT controller (far more efficient than the cheap PWM controller, but $200 vs. $50), and I’d like a pure sine-wave inverter (also about $200 vs. $50), and I’d like to add two more solar panels for a total of 400watts.  But this is a good, fun, and useful start to learn the characteristics of the system, how to use it, and what I can expect from it.

Here’s a breakdown of what I bought (though the link to the battery isn’t quite right – can’t find the exact one I bought in the store, and I already owned the inverter, so that cost is not included):

$238 – Two Grape 100W solar panels on sale at Costco ($119 each)

$50 – Windy Nation P30L charge controller

$8 – MC4 Y-Connector

$17 – MC4 Wired Connectors

$32 – 25′ Power Extension with MC4 Connectors

$8 – Group 27 Battery Box

$9 – 7-Way Trailer Plug

$82 – 100amp/hr Deep Cycle Battery

Total:  $444, plus another $25 or so for wire, fuses, etc. plus tax on the whole mess.  I could have saved another $25-50 by making the cables myself, but honestly, I just didn’t feel like it.

I didn’t include a wiring diagram because there really isn’t a need.  The solar panels hook to the first two screws of the charge controller, the battery hooks to the second two screws, and the load hooks to the last two.  Not much to diagram out.  Here’s a link to the controller manual, though, if you’d like see for yourself (see page 7).

UPDATE:  I’ve done a bit of work on the panels themselves.  A quick trip to Home Depot for some bolts, hinges, a handle, and a latch, then an hour in the shop, and I had a “solar suitcase”:

This is the front (above) and the back (below) leaned up against an old sawhorse in the yard.


Here (above and below) you can see where I put the hinges.  I ran short of bolts (duh), so only eight of the twelve bolts are in place.  Another trip to Home Depot is in order, as I don’t seem to have any more of the right size in my junk box.


Last, but not least, here’s the panels folded up ready to carry.

Next project is to make a wood case to protect the glass in the panels while loaded in the back of the truck.  I’m thinking something really easy, like a 2×4 frame with 1/4 plywood sides.  Doesn’t have to withstand wartime conditions, just needs to protect things while bouncing up a dirt road to a camping spot.


One thought on “Ghetto Solar

  1. I really enjoyed your comments! I have been playing with the sunshine for many years, and am as I write this in the process of installing a 12KW system on my house! That is 48 250W panels.
    We are supposed to expect 5 hours average sun per day here, at as I recall about 28 degrees. This is for an all electric house, includes heating. I will expect a result that I will never pay for electricity again! The way it works is that on a fine sunny day when I am using no heat or cool for instance, it will build up a surplus to the elect company, this never expires and an be drawn upon when it is cloudy and cold!
    The cost is 50g, warranty of 25 years on everything, will save me about $4k a year. Payback is slow, but at some stage I should be ahead of it and have free use of the panels, as well as increased equity in the home.
    As you mentioned, the drop in panel prices finally made this a great deal for me
    Don Schwanke, RV12/Viking Air Force One!

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