How Much Solar Energy Do You REALLY Need?

This post was written while we were in Chad.

How much of a solar energy system do you need to satisfy the needs of your village home?

The answer depends on a lot of variables, the biggest of which are where you live and what you want to do with it. Some of us live near the equator and want to just run a few lights, while others of us live outside the tropics, yet still want to run a hot tub while they microwave a bag of popcorn as they watch satellite on a large screen TV, while they wait for their clothes to dry.

To run a few lights, all you need is one 70 Ah battery and a 50 to 120 Watt solar panel. I read about someone who was in the latter group, and three arrays with 25 120 Watt solar panels each could not satisfy their need.

Let me just say this: if you are truly homesteading in third-world conditions, you should not be heating water or anything else with electricity!!

Let’s be practical here!

solar makes this electric meter run backwardsFor those of you who are homesteading, it is assumed that you are far away from electrical lines and having your home hooked up to town power. If you aren’t, the new trend these days is to set up a huge array of solar panels on your roof or in your yard, and to run the electricity via the inverter into “the grid”.

That way you avoid the cost of replacing batteries every few years, and experience the satisfaction of watching your meter run backwards. Impressive conversation at the dinner table or on doughnut day at the office…

However, true third-world homesteaders have practical needs and are trying to meet them with practical solutions.  Solar electric isn’t something we “do” to impress our friends; we have a need, and must find a practical, low impact, affordable solution.

Solar System Sizing: The traditional method

When dreaming of your ideal solar electric system, don’t count the number of panels that will fit on your roof; make a list of things you want to accomplish. Then put a number next to them according to which ones are most important all the way down to the least important. Add up the typical wattage of the appliances, and you are ready for the next step.

Next, design a solar electric system to fit your needs. The ongoing rule of thumb of the experts is to have four times as much solar wattage as you do load wattage. That means a system needing 40 Watts should have 160 Watts of solar panels.

To figure out how many batteries to buy, you figure out how many hours you would typically use them in one day. For example, if you would use a 15 watt stereo system for 5 hours each day, you would need at least 75 Ah of batteries just for that appliance. That, coupled with a charge controller that is able to handle the amperage of your solar panels (amperage = total watts of the solar electric system divided by twelve for 12-volt DC systems), makes up the bulk of the cost of your solar electric system.

Even if you own the factory where these things are manufactured, the cost for all this equipment can be downright huge! Too often, the solar system you think you need is well beyond your reach… and so many give up trying right there, sitting in the dark in their village home.

But there is another way!

Solar System Sizing: My “nontraditional” method

village solar energy system runs lights and a laptopWe have two 120 Watt solar panels on our roof in the village and three 70 Ah Deep Cell batteries. With that, we keep our netbooks charged and can light up one big room with compact fluorescent bulbs or those long fluorescent bulbs until we go to bed. We also have a 12-volt refrigerator which is very efficient. One day, we hope to be able to light up several rooms in the house, and maybe even run the outdoor lighting as well.

Using my method of calculating the solar electric system, you start with half the wattage you think you need, and for every 120 Watt solar panel, you have a 70 Ah battery. If you can, pay the little extra for a gel or a sealed battery; their extra endurance will pay for itself when compared to lead-acid batteries. Then slowly save your money, and add to your system as the need for electricity manifests itself.

Caveat emptor

However, my calculation method will only work if you use your solar electrical system wisely by charging the big wattage appliances during the daytime and going to bed at a decent hour each night. You also need to have an alternative in place “for a cloudy day”.

I actually discovered this by accident… While saving up money to buy another 120 Watt solar panel for that occasional cloudy day… I did the math and realized that, for the price of a solar panel, we could actually buy a decent diesel generator!

When the cloud cover is thick, it does not matter if you have two or twenty panels; they will fail you. For the same cost, a diesel or gas generator or a wind turbine is not only more economical than its equivalent in solar panels, it will also provide a more reliable alternative, thus saving you money on the big-ticket items of a village electric system: the solar panels and batteries.

Still, it all depends

With my method, those who, like us, live where there is plenty of sun but no electric company will have their need met by their solar panels most of the time; they will only need to run the generator when it’s cloudy or rainy.

For those of you who live where the sun sets earlier or where there is more cloud cover, you would use the generator to charge the battery bank while you use the electrical system, then run off of the batteries until either the solar panels kick in or the charge controller tells you that it is time to turn the generator back on.

What challenges are you facing with obtaining enough electricity to meet your household needs?  Please let us know, by leaving a comment below:

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