Building a Small Backup Solar Electric System

When Hurricane Maria hit and caused such hardship in Puerto Rico and other areas, I was inspired to review our disaster preparations. Although we live in a part of the world that is much less susceptible to that type of widespread devastation, we have experienced weather events that caused multi-day power outages, and it's not hard to imagine a scenario that could have more impact. We have a small generator, but gasoline is expensive and perishable, generators are noisy, and I suspect gasoline supply chains are more fragile than we'd like to think.

The answer, obviously, was to install solar panels.

The system I installed is completely separate from the house electrical system, not connected to the "grid" in any way, and would be used to power small appliances, electronics, and recharge devices during a power failure. The system consists of:

• two 100 watt solar panels
• a charge controller (controls the voltage going to the battery)
• a combination battery/inverter (battery to store power, inverter to convert it to 110 volt for general household use)

Since I had no experience with solar, I decided to purchase a kit that contained all the major components and detailed instructions. The kit contained one panel, the charge controller, plus cable and connectors. The directions indicated that additional panels could be added, so I went ahead and ordered a second panel to match the first.*

The first step in the install was to construct a wooden frame to hold the two solar panels. The frame was built from treated 2x4s with exterior grade screws. I used an on-line "triangle calculator" to determine the dimensions so that the panels would sit at the correct angle. The angle, according to the instructions, should equal the latitude of the location, in our case about 38 degrees.

I built the frame so that the legs were all the same length. I then placed it on a spot that was the exact opposite of level in all directions. I then realized that I would have to shorten three of the legs, by different amounts, to make it level.

I had no idea how much to shorten each leg. I also knew that if I cut one off the wrong amount, I'd have to shorten each leg even further until I got it right, with the risk that eventually my frame would have no legs. So I wanted to get it right the first time.

It only took me a few minutes to figure it out. It took me at least an hour to figure it out.

Once level, I anchored the frame by driving metal u-posts about two feet into the ground and screwing them to the frame.

I used angle bracing and framing brackets to be certain the frame would support the panels, and also that a strong gust of wind wouldn't tear off the panels.

The electrical cable that came with the kit was apparently rated for "direct burial", so I simply dug a shallow trench between the panels and the house (only about 5 feet) and buried it.

I used a short section of PVC electrical conduit to protect the cable against mowers and trimmers for a few inches where it came out of the ground.

I used another short section of conduit and an electrical box to protect it where it went into the house.

To run the cable into the house, I measured from the corner of the house to determine the approximate location of the wall studs, and drilled a hole where I hoped there was no stud. On the inside wall, I cut a rectangle in the dry wall corresponding to the size of an interior electrical box. I carefully measured hoping I would be in the same "space between studs" as where I drilled the hole for the wire to enter the house.

I then inserted a fiberglass wire-fishing tool into the hole from the outside and pushed it up the inside of the wall, hoping it would appear at the rectangular hole I cut on the inside.

It didn't.

I tried again.

It didn't work that time either.

Eventually it worked. 

It took less than 42 attempts. 

I then pulled a string back through the wall, tied the string to the cable, and pulled the cable into the house.

I built a small cabinet out of scrap wood to hold the charge controller. 

I then connected the cable to the charge controller, and the charge controller to the battery (if you do this, check your charge controller manual, you may have to do it in a certain order). Per the instruction manual, fuses were installed to protect the charge controller and battery.

The battery/inverter I bought is on wheels with a handle so that, once fully charged, it can be moved around the house to the place we need power. 

Here is a breakdown of what I spent (My dearest Kate, you can skip this section). 

• Solar panel kit - $157
• Additional solar panel - $115
• Extra Z-brackets - $10
• 2X4s (6) - $30
• Rafter ties - $7
• Nuts, bolts, washers - $5
• Backup power system (battery + inverter) - $350
• Cable to charge battery - $10
• Cable to connect extra battery - $35
• MC4 couplers - $10
• Misc. electrical parts - $37.50

That adds up to...a bit more than I intended.

OK, I spent just shy of $800. But now I have some free electricity. If I use it to charge my phone everyday, it will pay for itself in less than 284 years**.

I also plan to purchase an extra battery, since I already have the cable to connect it to my existing battery/inverter combo.

I did have several items on hand, including all the screws, the metal u-posts, and the parts to build the cabinet for the charge controller. I also had all the necessary tools.

This is only one component of our disaster preparedness strategy. In addition to the previously mentioned generator, we also have a gas camp stove and a fireplace, plus battery powered lanterns and a good supply of batteries.

If the power goes out and you need your phone charged, come see us!

I have no formal training as a carpenter or electrician, so if you try something like this be sure to get professional advice.

Here are the specific products I purchased for this project:

• Schumacher Storm 700 Backup Power System (battery/inverter)
• Windy Nation Complete Solar 100 Watt Panel Kit

*This also required, I discovered during the installation, purchase of additional mounting brackets and more of the specialized "MC4" electrical connectors. 

**I pulled that number out of the air. I actually have no idea.