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

Reader Contribution by Ed Essex

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.

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