Determining How Much Power You Use

First of all, I would like to say that the designs I used appeared to work fine for me and I must say that I can’t be held liable for anything that is done by another individual. This DIY section is for designing a Hybrid solar and wind system for a personal off-grid home. I am explaining it as simple as possible, like I’m explaining to beginners or my children. The reason I’m posting my information is when I started researching for a project (to piss off my wife), and I was having problems finding all the basic knowledge I needed, in one place, to proceed with a solid design. For years, I have been playing around with this stuff, and by trial and error, I learned the hard way and hopefully you won’t repeat my mistakes. Enclosed I have several separate systems that have been tested and work well. Please feel free to check them out.

Once you have decided what electrical appliances you will use in your off-grid home the next step is to determine how much power you will need to operate the home for an average day!

First you need to understand some basic math formulas used to determine how much power an appliance consumes. You will need to know these three terms for power measurement:

Volts indicate the basic unit of power being produced and are similar to how much water pressure you have when you turn on a garden hose.

Amperes or Amps is the current of power produced and is similar to the flow rate (how fast) that water travels through the hose.

Watts is the quantity of power moving through a wire at any given time.

Watts = Volts X Amps       Amps = Watts / Volts

To find the watts used by any given appliance look at the attached specification label usually on the back of an appliance. The number given will usually be in Watts. If you can not find the label you can use a Watt Meter to determine exactly how many watts an appliance consumes.

This instrument is called a Kill – A – Watt :



Follow the directions on the unit and plug the meter into the outlet and the appliance into the meter and record the watts used for each appliance in your off-grid home.

Write the appliance name, watts used, and average hours the appliance will be used each day as shown here:


Appliance                   Watts                          Hours a day used

__________________ __________________ ____________________

Below is a worksheet that gives you the average watts used for most appliances to make things simpler. Just plug in your Kill A Watt numbers into the worksheet or use the supplied numbers for an estimate.

Load Evaluation Chart (These are the numbers I use)

Appliance Watts Hours per day Watt Hr per Day
Microwave 900
DC powered bed warmer 60
Sundanzer Solar-Powered refrigerator 350
Sundanzer Solar-Powered Chest Freezer 800
Refrigerator 4 cu ft 1000
Refrigerator/Freezer 15cuft Energy Star 1500
Window AC unit, the smallest I could find 660
42” LCD TV 150
Electric blanket 180
Ceiling fan 12/24 volt DC 5-20
Ceiling fan AC 60
Clothes washer standard 700
Clothes washer efficient 200
Computer 100
Laser printer 90



Load Evaluation Chart

Appliance Watts Hours per day Watt Hr per Day


Calculating your average daily power use

If you have used the Kill-a watt meter and the worksheet you should now have numbers in the right hand column that can be added together to give you approximately how many watts you use on an average day.

It is recommended you do a worksheet for both summer and winter use.

Add all the numbers in the right hand column together and record them like this:

Average Daily Power Use in Summer: _______________________

Average Daily Power Use in Winter:    _______________________

Take the bigger of the two numbers (usually winter use) and that is how many watts of power you will need to produce from solar and wind power to run your off-grid home. We use the bigger number because if you have enough power to meet that need you will have enough power to run the home year round. If you will only be using the home seasonally then use only the months you will be actively living in the home.

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