BigBattery's Off-Grid Solar Sizing Tool

Step 1: Enter The Proposed System’s Zip Code

Enter the system zip code: Use the Zip Code of where the system will be installed. We will calculate the average WINTER sun hours of that Zip Code for Off-Grid system sizing.

* Must enter zip code to gather data.

BigBattery calculates your average daily Sun Hours, using the Winter Solstice, which is the darkest month?

BigBattery uses the lowest daily sun hour average that the system’s site can expect. We do this for sizing Off-Grid systems because the most important design parameter of an Off-Grid solar system is that it is able to produce ALL of the homes energy requirements under the poorest solar conditions.

By design, Off-Grid solar systems are not connected to the electrical grid or have a “Net Metering” agreement with the utility. When designing an Off-Grid solar system you cannot use average “Annual or Summer” Sun Hour calculations to size your system. If you use those calculations to size your solar system it will not be capable of producing enough electricity to supply your needs during the darkest months.   

What Is The Average Peak
Sun Hour Range In My Area?

Going “Solar” isn’t right for everyone. Some areas of the country simply do not provide enough “Solar Irradiance” or have the “Sun Hours” per day to justify installing a solar system. Your geographical location plays a big part in how many average peak sun hours you get on a daily basis. The ‘Peak Sun Hours Map’ is a good illustration of how varied our country is when it comes to average solar irradiance.

Use the “Drop-Down” box below to select the city closest to you to see the sun hour range for your area. Search different cities to compare how your area’s solar resources stack up to other parts of the country.

Peak Sun Hours Map

Step 2: Completely Fill Out The Daily Load Calculator With ALL Electricity Loads 

Use the Load Calculator tool below to estimate your daily energy usage. Input ALL electrical loads and appliances that will be powered by the solar and/or backed-up by batteries. To properly size the system, we need the maximum estimated daily usage for that electrical equipment year round. Most Off-Grid homes are designed with electrical loads in mind. They generally use energy efficient appliances and major heating loads such as space heating and water heating are usually not electric. Make sure you verify what is (or is not) electric and include the electric air conditioning, space heating, cooking, water heating, well pumps, clothes washing/drying, etc. into the daily load calculator form. 

*Use the “Add New Row” button to add additional electrical loads to the calculator until ALL of the loads are accounted for.

BigBattery Provides Kits
For All Off-Grid Applications

Input Your Highest Estimated Daily Usage for ALL Electric Equipment Year Round. Make Sure To Include: Air Conditioning, Space Heating, Water Heating, Clothes Washing/Drying, Well Pumps, and Electric Cooking Appliances.

Appliance Quantity Power Rating (Watts) Average Daily Usage (Hours) Watt Hours per Day Action

Total Watts - (Peak Load)


Total Watt Hours per Day:

Kilowatt Hours Per Day:

If you already have this total, you can enter it here.

Step 3: Calculate Off-Grid System Size

We’ll estimate your off-grid system size based on the list of appliances and energy usage that you entered. Keep in mind that this is only an estimate, and there are many factors that can influence system sizing. Please contact us for help designing your project.

Click the “Calculate My System Size button” and we’ll calculate your system size based on your load evalutation calculation of 195 kWh/Mo.

Step 3: Calculate Off-Grid System Size

Minimum PV

System Size



As mentioned before, this is a very basic system size estimation. It is intended to give you a general idea of what your Off-Grid solar system sizing needs would be. This system size is designed to generate the electricity needed to power the daily loads you entered into the load calculator. There are many other factors unique to your specific location and application that can effect the size off the Off-Grid solar system you need. Factors such as whether this is a seasonal property or full time, shading implications, azimuth & tilt of the solar panels, unaccounted peak load variations, available space in your main service panel (MSP), and that is just to name a few.

Here are the results of your form submission. If you would like us to email you a copy, enter your email address below.