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Living Off-Grid: How to Calculate the Size of Your Electrical System

| 3/9/2012 12:38:00 PM

When you talk to people about going off grid most of the questions they ask are about solar power. Everyone wants to know how much it costs and how do you figure out what size system to put in? How many panels? Are you going to have batteries and if so how many? Oh and how much does it cost?

If you are thinking of going off grid you are going to ask the same questions and it doesn’t matter whether you are going to have solar power,  a wind turbine, or a water powered hydro generator. In order to size any of the above systems you are first going to have to calculate your electrical needs. Until you do that you can’t have an intelligent conversation about what type of system, or what size system you are going to need, or how much it is going to cost.

There are whole books written on this subject so I am just going to share the actual steps we took to figure out what our power needs would be.

The first thing I did was read the book Solar Power for Dummies. I’m not kidding. What did I know about off grid power systems? One book led to another and there was a fair amount of time spent on the Internet researching as well.

In all the research, one simple tool stood out time and again in slightly different formats but similar in nature and practical use. It was a chart which listed all of your typical electrical appliances with their associated wattage and how much time you used each appliance each day. A sample is worth 1000 words so you can click here to see it. I created this one on Excel so that I could enter the formulas to make it automatically calculate the watts per day. On this spreadsheet all you have to do is write down the appliance and figure out how long it will run each day and how many watts it uses.

Some of our appliances only listed amps not watts and there is a simple conversion formula for that too. Watts = Volts X Amps. If your stereo is rated at 3 amps and you plug it into an 110v wall outlet then just multiply 3 x 110 = 330 watts! You will find most watts or amp ratings somewhere on the appliance tag. If not, look up the appliance online and pull up the specification sheet or just use something similar. Remember this is an estimate and not an exact accounting.

When we were done our Spreadsheet looked like this. Now we had something to talk about. This was the starting point to research what kind of system and how large a power system we would need. Your daily electrical use will determine the size of the system. We knew we needed something that produced at least 6 kWh per day in order to meet our needs

4/6/2012 8:42:12 PM

Right you are! That's actually how we got started.

J.Russell Bailey
3/20/2012 11:21:53 PM

Congratulations Mother Earth!!!!!! This article is EXACTLY the kind of thing to which I have been referring: to the point, NOT propagandistic, very informative, and with useful links which can make the job of proper research and archiving MUCH easier!!!! The only thing I would have desired is MORE information, ie, several more pages for the authors to provide more useful information concerning the various aspects of their Off Grid Solutions.......Please start publishing MORE of this kind of article!

Gary May
3/16/2012 5:25:00 PM

If you do not plan any major appliance changes, you can simply use your average utility bill and divide your monthly consumption by the number of days in the billing cycle, and you will get a very good estimate of your daily kwh requirements.

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