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Off-grid Solar Calculator

By SSK Admin November 08, 2022

An off-grid solar system is made up of many components that need to be sized if you want the best results. So how do we go about sizing them?

Yes, manual calculations work best if you enjoy mathematics and statistics, but online off-grid solar calculators make life easier.

Join us as we break down how these calculators work and what values are needed from your side.

But first, what is an off-grid solar system?

Solar Calculator Off-grid

solar calculator off grid

A solar calculator for off-grid systems comes in handy if you need to figure out the size and scale of everything.

The difference between on-grid and off-grid solar systems is in the name. The former is tied to the grid system, relying on local power that must be paid for.

The latter on the other hand works independently and isn’t tied to the grid.

With on-grid systems, the solar panels convert the incoming solar energy into DC power. This then gets converted into usable AC using the inverter.

The excess power that the solar panels generate is sent back into the grid as power credits. Since these systems rely on the grid, they don’t work during power outages.

This means you need to install the system in a place where the sun's peak hours are high and the power outages are infrequent.

Off-grid solar systems work best in places where there are lots of power outages or if you don’t want to end up paying a hefty electric bill at the end of the month.

When the solar panels aren’t generating electricity, this system still works.

The reason being is that the solar panels and inverter do the same DC to AC conversion, but the excess power gets stored in a battery.

While this article covers what you need to know if you want to take your system off-grid, you still need to calculate if solar is worth it for you. 

Once you’ve seen the requirements and size of the system, you can decide whether you wish to proceed with the installation.

Off-grid Solar System Calculator

offgrid solar calculator

Off-grid solar systems are made up of 4 components.

Solar panels that harness incoming solar energy, a battery to store the energy, a charge controller to manage the energy between the solar panels and the battery bank, and the inverter depending on the appliances you’re running.

Whether you’re wanting a solar calculator for RV or a home running off-grid, if a calculator can figure out the size of each component, you’re on the right track

The first step to using an off-grid solar system calculator is to determine your battery size.

An Off-grid Solar Battery Calculator

Calculating the size of the battery is a matter of determining our solar needs.

Solar needs are simple to figure out. It’s a matter of gathering all the appliances you need for your system and finding out the output wattage of each appliance.

Determining Watt-Hours

Most appliances have a label on them that shows the wattage, but in some cases, it only gives you volts and amps.

Well, thanks to Ohm and his law, you can multiply those two values together, and voila, you have your watts. For example, the average toaster uses 120 Volts and 9 Amps. This gives you a draw of around 1,100 watts (120 x 9 = 1,100).

Once you have the wattage, you need to ask yourself how long you plan on using each appliance while the solar system is running.

If you multiply the wattage of an appliance by the number of hours it’s used, you get the watt hours per day that the specific appliance uses. So, if you use that same toaster for an average of ten minutes a day, you get 183 watts per day ((10/60) x 1,100  = 183.33)

Rinse and repeat this process for each appliance and add the watt hours together. Now you’re left with the total number of watt-hours that your solar system should compensate for.

This watt hours per day value is also needed if you’re using a solar payback calculator so you might want to keep this value on standby.

Determining Solar Needs

solar off grid calculator

Now that you have the watt-hours per day, we can get to figuring out the size of our battery.

An off-grid PV solar calculator will ask you to input this value into the battery bank sizing option.

The next value will typically be how many days you want your solar system to run without sun. 

This gives the calculator an idea of the size of a battery needed for your location and circumstances.

Finally, you need to enter the lowest temperature that your battery will be exposed to. This gives the calculator an idea of how the battery will perform.

After you’ve entered each value, the calculator does its magic and returns the battery bank capacity in amp hours and the voltage of the battery. 

Calculators also consider discharge, giving a more accurate estimation than if you were to manually calculate the size of your battery.

Solar Panel and Charge Controller Calculator

Now that we have the size of the battery bank storing energy in our off-grid solar system, we need to figure out the size of the component harnessing the sun’s energy.

The first step is to figure out your location’s number of sun hours. This can be determined by viewing a solar map showing the amount of sunlight per day based on your geographical location.

These maps are color coded from a peachy color to a dark red, ranging from low to high exposure.

If you want an off-grid solar system for your RV and you plan on traveling around the states, read the number of hours of each state you go to and average it out.

Once you have your peak sun hours, type it into your off-gird solar calculator and it will return the number of watts your solar panel needs based on your total consumption.

off grid solar system calculator

These calculators also return the number of panels you need in an array to compensate for your required watts.

The size of the inverter should be slightly above the number of required watts, so if you have 800 W worth of solar panels, you should aim for a 900-1,000 W inverter.

This section of the off-grid solar system will also return the size of the solar charge controller, giving you the size of all your components.

Remote Cabin Solar Power Calculator

All off-grid solar systems, whether they be a cabin, an RV, or a home, have the same components.

A typical remote cabin has a set of solar panels on the roof that is connected to the charge controller within the cabin.

These are then hooked up to a battery bank which is then connected to an inverter.

Most off-grid solar panel kits for sheds and cabins come with the necessary components and installation equipment so you won’t need to worry about buying separate parts.

off-grid solar system calculator

You could include fuses or breaker panels if you wish but those should be recommended and sized by the installation team.

However, if you’re setting it up on your own, the size of your fuse can be determined by dividing the watts of your solar system by 12V.


While manually figuring out the size of your solar system will get you an answer, you could get a more accurate and efficient way of getting the answer with an off-grid solar calculator.

There’s a variety of them online but each has the same approach to sizing your system.

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