A Simple Solar Powered Backup System

The other morning I woke up, tried to turn on my radio and discovered I had no electricity. Hearing trucks I looked out the window to see the power company replacing a pole. 2 trucks, several workers and my black lab supervising.

“It sure would have been nice if they had said something I grumbled”. No coffee no shower (electric water pump as I live in the country) I wandered over to the computer and fired it up to check newsvine. Fortunately it’s a laptop and I use my cellphone as a modem so I was able to get on line. Unfortunately the battery in the laptop doesn’t last that long so I was soon without that link to the world which left me just my battery powered radio for my news fix. How primitive.

Several hours later I was connected to the grid again but I had also resolved to come up with a plan that would at least give me some sort of backup during a power outage. This one was a minor annoyance but I have been in outages lasting days or weeks so it seemed like a reasonable thing to do.

First I checked off the electric gadgets I would absolutely need or want during a longer power outage.
Cellphone - A means to recharge the battery. Like many Americans I don’t bother with a land line phone anymore.
Lights - At least one light capable of providing reading light and a second room light for cooking, etc.
Laptop - A source of power for my laptop computer.
Battery charger - A means to charge batteries for small stuff like radios, flashlights, etc.

Everything else is pretty much optional. I have propane for heating and cooking, The refrigerator/freezer is propane or electric so I can switch to propane no problem. I can easily store potable water. So now the big question, what to use for backup power?

The very first off the shelf solution I thought about was a gasoline powered generator. It would provide more than enough power but it has several drawbacks. It needs regular maintenance, it requires the storage of gasoline which tends to go bad over time, it’s noisy and an expensive solution for the small amount of power I actually need.

I wanted a quieter cheaper less troublesome option, so I decided to build a small backup power system using a deep discharge lead acid battery typically used for RV’s and a couple of solar panels. I would have to convert the 12 Volt DC power from the battery to 110 AC so I needed an inverter of some kind. Fortunately I already had the battery (it also powers the electric trolling motor on my fishing boat) and a small inverter that I use in my truck to power stuff when camping. So really I just needed the solar panel(s) and some hookup wire.

A quick trip to Harbor Freight netted me a couple of 5 watt panels that were on sale for a grand total of 80 bucks. Now 10 watts isn’t much and I could have gone for a 45 watt 3 panel package which retails for about $249.00 and added another battery for greater capacity and I may still do that but I figured 10 watts trickle charging a good sized battery would do the job for now. Speaking of batteries, if you put together a system like this, be sure to get yourself “deep discharge batteries” as they are made to give up more of their charge without damaging the battery. An ordinary car battery if repeatedly fully discharged will soon not hold a charge at all. Even deep discharge batteries should not be drained entirely. Also locate your batteries in an area where they will not freeze, sit directly on concrete or where the hydrogen gas that is generated when they are charged might be near something that could ignite them such as an electric motor.

The great thing about solar is that if you design a system with expansion in mind it is not that hard to add on. With more or larger panels you do need a charge controller which is a small black box gadget that keeps the panels from overcharging the batteries when they are full. These start at about 30 bucks and up depending on size. With more panels, storage capacity you could actually save money by taking an entire circuit and converting it to solar. Say a garage for instance.

A word of caution here. I am a tinkerer and have worked with electricity all my life so I have a good understanding of what works and what doesn’t, what is safe and what is not. If you don’t feel comfortable working with electricity, batteries or understand parallel vs series circuits, etc. consult a friend or professional who does have these skills. Even a small 12 volt system is capable of starting a fire. Always keep your household current separate from your backup power supply current.

Setting my system up was a piece of cake. I mounted the panels on a piece of plywood, angled them at about 45 degrees, aimed at the sun and secured firmly to the roof. Running the wires down to the battery, observing the correct polarity and hooking them up, they were soon working away pumping 15 volt direct current into the batteries. I ran a pair of wires from the battery into my kitchen where my laptop resides and I setup my inverter with a power strip so I could plug several things in at once. Plugged in a desk lamp to test and presto I was in business. Although it is a backup system I use it regularly both to save on the electric bill and to make sure it is functioning properly. No use letting free electricity go to waste.

Now happy in the knowledge that my connection to the internet is secure (as long as the cell tower stays online) I can think about other important stuff like making coffee without electricity. I read some where that they used to do that back in the old days.

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