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Off Grid Solar System Sizing Calculator

The altE Off Grid Solar Panel System Calculator helps you size the battery bank, watts of solar panels and the solar charge controller you need. The calculator assumes you will need to size your system to get you through average amount of sun-light in the least sunniest month of the year for your location. You still may want to consider a backup generator, however. Feel free to call our knowledgeable technical sales staff toll free at and have them help you find the system that fits your needs.

Your Information

Used if you optionally choose to save your calculator for later use


Battery Bank Sizing

This calculator will help you size the battery bank for your system.

Step 1:

Your Daily Energy Usage

Watt Hours per Day:

Kilowatt Hours UsageThis value is usually printed on your electric bill. Take your monthly kilowatt-hour usage from your electric bill and divide it by 30 to get your daily kilowatt-hour usage. Since it's in kilowatt (1000's of watts) you'll need to multiply that number by 1000 to get the number into watt-hours. If you don't have a bill, or don't know your consumption, please use our Load Calculator to go through the steps to determine this value.

Is your energy usage too high? Don't despair, our knowledgeable sales folks can help you find other potential solutions. Please call us toll free at: .

Step 2:

How Many Days Should Your System Run without Sun?

How many days of backup power do you want in case of cloudy/rainy days?
(when your solar panels will produce little energy)

Step 3: Colder batteries lose capacity with drop in temperature

Adjust the Effective Capacity of Your Battery Bank Due to Low Temperatures

What is the lowest temperature your battery bank will experience?



Select a battery bank voltage
Note: All calculations assume only a 50% discharge to your batteries to optimize battery life.

Deep Cycle Batteries from altESelect the deep cycle battery that fits your needs

Solar Panel and Solar Charge Controller Sizing

This calculator helps you size the solar panel(s) and charge controller(s) needed for your system.

Step 1:

Determine the Solar Exposure for Your Site

You need to determine the average number of sun-hours per day during the least sunniest month of the year (not the whole year).

Select the State-City Closest to your location (currently only US states are provided)

world solar insolation mapManually enter the average sun-hours for your location.

Step 2:

Sizing Your Solar Panel Power Needed

The total wattage of Solar Panels that you need is:

Watts, or kilowatts

This value takes into account losses due to system inefficiencies.

Step 3:

Determine How Many Solar Panels You Need in Your Array

How many solar panels do you need? That depends on the panel you choose.

Select the wattage of the panel your interested in, and see the results below:

watts per panel.

You will need panels for a total of watts.

how to size solar panels Select the solar panel that fits your needs.


Sizing your Solar Charge Controller

You will need a charge controller that can handle: amps

Sizing Solar Charge ControllerSelect the solar charge controller that fits your needs

Sizing a charge controller can be complex, the above answer is a conservative estimate. Please feel free to call us to find a more accurate fit for your needs.

Now that you have sized up the system that fits your needs, call our Knowledgeable Sales Folks at and let them help you find the exact products for your system.

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