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Off Grid Solar System Sizing Calculator

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How to Size My Off-Grid Solar System & How Much Does it Cost?

Wil has been a part of the solar industry for over 20 years as an electrician, solar installer, support technician, and more. He’s also been living off-grid since 1996. Wil and the rest of the Unbound Solar team are here to answer any questions you have about designing a system that will fit your needs.

How To Calculate Solar Battery Bank Size

Our solar battery bank calculator helps you determine the ideal battery bank size, watts per solar panel, and the suitable solar charge controller. If you choose to build an off-grid system, it’s important to size your system based on the month with the least amount of sunlight. That way, you will have access to a sufficient amount of energy at all times. There are several steps to follow when calculating your solar battery bank. Let’s review them below:

What Is Meant By Off Grid Solar Systems

An off-grid solar power system completely disconnected from public energy infrastructure. The household attached to it is completely reliant to solar power to satisfy its power demand. For example, when taking a 5kW solar system off grid, the daily power demand of the respective household can only be satisfied as long as it stays under 30 kilowatt hours per day.

The thought of going fully off grid with a full solar system for home and become independent from public electricity supply is compelling. It opens up new dimensions of personal freedom for homeowners who have hitherto been subject to the policies of private electricity providers and public power agencies.

BUT: When considering all implications of going off grid with a full solar kit, it quickly becomes obvious that it is by no means a risk-free decision.

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Picking The Right Battery

So, which solar battery is right for you? There are a few different battery types commonly used for off-grid storage systems:

Flooded Lead Acid
  • No maintenance, no venting
  • Highest efficiency, faster charging, more usable capacity

The two main battery chemistries for off-grid are Lead Acid and Lithium. These two chemistries have unique characteristics. Lithium batteries are more efficient, which means less power is wasted in the charge/discharge process. They also have a greater discharge depth allowing you to fully utilize all of your battery capacity.

Lead acid batteries are sensitive and need to be fully recharged every day, where Lithium batteries can stay at a partial charge without any adverse effect. Lead acid batteries also have a more limited amount of usable capacity and are typically discharged only 50%.

Because of the better efficiency and deeper discharge depth, Lithium battery banks tend to be only 50-60% of the size of a comparable lead acid bank! The Lithium batteries we use are purpose-built for off-grid solar, and utilize a special Lithium chemistry called Lithium Ferro Phosphate .

This type of Lithium battery is engineered to provide a long service life while also being safe, with a stable chemistry and sophisticated electronic protection features.

55.2kWh: 1150ah 48v Sealed LA 57.6kWh: 1200ah 48v Flooded LA

This is not intended to be a comprehensive guide on off-grid design.

How Much Do Solar Panels Cost Overall


Using a solar cost calculator is an excellent way to figure out specific numbers for your circumstances. Each home consumes a different amount of electricity based on various factors. Having said that, if you take a 2,000 square foot home, the average solar panels cost equates to somewhere between $15,000 and $40,000.

Lets look at an example to get a better idea of how much solar panels cost. The average home in the United States is 1,500 square feet with a monthly electricity bill of $100. This means that the house needs a 6-kilowatt solar panel system with between 15 and 18 350-watt solar panels.

The estimated cost for a system of this size would be about $18,000. If the system saved you $2,500 per year on energy expenses, the payback period would be just over seven years until you would break even.

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Off Grid Solar Load Calculator

One of the most important things to do BEFORE going solar is to calculate the amount of electricity you are currently using. You will use this information to determine the size of solar power system you will need. Our Solar Load Calculator can help you calculate your system load. To learn more about estimating your average energy usage, go to: Electrical Load Evaluation Calculation and System Design Information.

Off Grid Solar Panel Power Sizing Calculator

This solar PV panels power sizing calculator will help you determine the solar panel wattage requirements for your off grid solar project. Please note: this calculator uses average solar insolation data – if you require a system which must function even on very low solar insolation days you will need to size your system using minimum daily solar insolation for your area.

Use the yearly deficit/surplus data in the calculator to size your system so that it will still on averagesupply enough energy during the lowest solar radiation months over which you will be using the system. If you are planning on using the system over summer only then choose the lowest summer solar radiation month for your location. If you require a year round more mission critical system you should size your system using minimum daily solar insolation for your area in winter.

* Assumes a true Solar North panel mounting at the optimal fixed tilt which is approximately equal to your latitude, L. Note: if you want to optimize your system for winter collection the optimal tilt angle is L + 23.5º. If on the other hand you want to optimize your system for summer collection then the optimal tilt angle is L – 23.5º. If working in Amps – a 24V battery of a certain AmpHour rating will have twice the energy of a 12V battery of the same AmpHour rating. Deeper discharge cycles shorten a battery’s lifetime, also for this value you should consider the age of the battery.

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How To Use Our Off

Need any more information or advice?

Our team of experts are more than happy to give you the information and advice you need about our Off Grid range, its components, and outstanding warranties.

Feel free to contact us on 1300 669 256 or email us at for all of your Off Grid, Solar Pumps and Grid Connect needs!

Power Consumption Of Household Appliances

DIY Solar | Sizing an Off-Grid Solar Power System | Battery Sizing

Select the appliances from this drop down menu. To the right will appear typical wattage values for the appliance you selected. However, for the most accurate information look on your appliance to find its wattage rating .

See our Kill-a-Watt database for real-world power consumption data on a variety of older appliances collected by our staff and customers.

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Choosing Solar Panels And Camping Batteries Made Easy By My Generator

WHAT SIZE SOLAR PANEL & BATTERY DO I NEED?this is the most commonly asked caravan / camping solar panel and battery question and can sometimes seem like quite a technical, challenging task. But for most applications, its actually pretty simple and straightforward here we try and make it easy for you.

First follow these four simple steps

Step 1 & 2: Total Power Consumption of Your Favourite Caravan, Camping & Off Grid appliances.

Step 3: Solar Panel selection and calculation

Step 4: Battery bank sizing & calculation

Read on for more detail how to go about completing each of the steps. Then we have also included a Power Draws of Common Caravan, Camping & Off Grid Appliances table to assist you in your calculations.

Note: solar power calculator assumes 12V solar panels are connected in parallel.

Figure Out How Much Energy You Use In A Typical Day

The first step is to figure out your electricity consumption, aka load size. You can do this by either using your current energy bills from the utility company or by using a load calculator. Once you know your electricity usage, you can begin to plan solar production.

If you are going to use energy bills to figure out your load. You can locate either the average daily electric usage on your bill or the total monthly energy usage.

Below is an example of my monthly energy bill, it tells me my daily kilowatt hour usage is 22.88 kWh for the past month. When I add up this value from the past 12 energy bills and divide the total by 12, I get the average daily kWh usage for the past year.

If your energy bill quotes total energy used by the month, then add up all the monthly kilowatt hours for the past 12 months. Divide the total by 356 to get the estimated daily kilowatt hours you consume.

Alternatively, you can use the following load calculator to estimate energy usage in a 24 hour period. You can itemize every appliance and list their running wattage along with the total number of hours you plan to use it in a 24 hour period. Appliances should all come with an energy label that states the amps and voltage. This method is more useful if you are setting up solar for a new place or you dont have past energy bills

Total Daily Kilowatt Hours = /1000

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Full Or Partial Offset

Most grid-tie homeowners choose to offset 100% of their energy needs with solar. But it is also possible to start with a smaller system for partial offset, and then expand down the line as the budget allows for it.

If partial offset is your goal, you can account for that here. For example, lets say you want to start by offsetting half your energy usage with solar:

7.2 kW solar array * 0.5 = 3.6 kW solar array

In this scenario, a 3.6 kW array would cover 50% of your energy usage, cutting your electric bill in half.

Other Factors Influence Battery Sizing:

Solar Choice
  • Ambient Temperature – Heat or cold has a big impact on battery performance and capacity.
  • Seasonal Factors – People use more power at different times of the year. The sun produces more power in the summer than in the winter.
  • Budget – Battery bank size is often a compromise between what you want to spend on batteries and how often you’ll need to run your backup generator.

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Battery Bank Sizing & Calculation

Enter in your battery bank size . Then choose the type of battery you have or are looking to purchase. The calculator will tell you how many days you can camp with all your appliances powered up.

For your convenience we have added in a section for autonomy. Autonomy refers to the amount of days that you will power your system in the event of little to no solar power .

Choosing The Charge Controller

The charge controller acts as a gatekeeper between the solar array and the battery bank to prevent voltage and current spikes from damaging the batteries.

Cold temperatures can cause a significant surge in solar panel voltage. If you live in a place that experiences cold temperatures, please use the following calculator to see how high voltages can spike.

Youll need the technical specs of solar panels that you are considering as well as the record low temperature in your region.

Once you have the potential voltage surge of solar panels. You can figure out the total voltage that would enter the charge controller by multiplying the surge voltage by the number of solar panels you plan to connect in series. Your charge controllers allowable input voltage must be higher than the solar array total output voltage.

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The Quick Guide To Using The Solar Battery Bank Calculator For Defining The Number Of Solar Batteries Connected In Series Or Parallel

Here is a quick guide on how to use the calculator.

Input fields:

These are colored in yellow.

Select the battery bank voltage, V the solar battery bank voltage is the system voltage you have selected for your system. Here, you are supposed to choose from a list of standard values.

Enter the battery bank capacity, Ah this is the capacity you have already calculated by using our Calculator for sizing the solar battery bank or you know it in advance.

Select the standalone battery voltage, V standalone means a single battery. Certainly, your battery bank can comprise more than one standalone battery.

Here, you are expected to select among a list of standard values typically used in solar power systems: 6, 12, 24 or 48 volts. This is the voltage of the specific battery model you are about to select for your PV system.

Enter the standalone battery capacity, Ah this is the capacity of the specific battery model you are about to select for your PV system.

Output fields

These are colored in blue.

Number of batteries in series here, you get calculated the number of batteries of the specific model you should connect in series to get the total battery capacity you need. The total battery capacity is calculated based on your daily energy needs.

Number of battery strings in parallel we do not recommend connecting more than 4 strings in parallel.

Why is that?

So, the higher voltage battery connected in parallel will discharge itself via a lower voltage battery.

What Size Of Battery Bank Do You Need

Solar PV (Off Grid) System Sizing

The reality is that battery banks come in all shapes and sizes. This calculator will help you calculate how much energy needs to be stored to power your home, cabin, shed, or other off grid location.

The first step is to estimate the total size of your battery bank. This takes into account the useable storage of the battery system. For lead acid, this is often only 50%, whereas for LiFePo4 its usually 80-95%.

Youll want to have a battery bank that can support your daily useage over the number of days youve chosen as autonomy days.

For example, if you use 1kWh per day, youll need a 2kWh battery if you want 2 days worth of autonomy.

If only 90% of the battery is useable, youll then need a 2.3kWh LiFePo4 battery, or a 4kWh lead acid battery. If youre using 12v batteries then those would be 28 amp hour LiFePo4 or 48 amp hour lead acid batteries.

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Full Off Grid Solar System Risks And How To Mitigate Them

One of the biggest drawbacks of a full off grid solution is that it confines oneself to a single electricity source. A PV array generates electricity only under full sunlight exposure, so an off-grid system has about 6 hours per day to generate a households energy supply for an entire day.

Therefore, it is crucial to know how much power your household consumes in a day beforehand. The easiest way to determine a households daily electricity consumption is by using a load calculator.

This requires reliable high-capacity devices. Because they have to establish their own grid, off-grid systems can only operate under a high voltage 400v solar panel array.

Fulll Off Grid Solar Power Systems For Homes

As opposed to a grid-tied solar power energy system for home, off grid solar panel kits allow a household to disconnect from public electricity networks and cover its entire energy demand with solar power. This is crucial as this has different requirements in terms of maintenance and equipment and, most importantly, its own risks.

When opting for an off grid kit, the first step is to weigh the inherent downsides against the benefits.

Solar Power Systems for Homes Off-Grid

  • No integration with public energy supply
  • Power supply entirely dependent on solar
  • No export of excess power
  • Household unaffected by public power outages
  • No electricity bills
  • Higher number of solar panels required
  • Higher maintenance requirements

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How Do You Calculate How Many Solar Panels You Need

Youll need to have enough solar panels to be able to fully charge your battery in one day.

The remote cabin solar power calculator above will help you determine how many solar panels you need to power your home, cabin, shed, or other off grid location and what size of battery bank you will need for storage. You can also see how much money you can save by generating your own electricity.

To find out how many solar panels you need:

1) Enter the type of off grid location youre thinking about getting solar panels for

2) Choose how many days of autonomy you need. This is the number of days that you can go without any sunlight at all, just running off your battery system.

3) Enter how much youre paying for grid electricity, so we can calculate savings

4) Enter the amount of electricity your use daily

5) Confirm your location. We need to know roughly where you are in the world as the closer to the poles you are, the less sunlight youll get during winter.

6) Select which direction your roof faces. In the northern hemisphere, south facing is typically best.

7) Enter your main goal with going off grid.

8) Click next and well tell you how many solar panels are needed and what size battery bank is needed to store them

How To Figure Out Your Average Sun Hours Per Day

Solar PV Calculator (Off

Various parts of the country receive different amounts of daily sunlight at various times throughout the year. To figure out your locations average sun hours per day, youll want to determine the peak sun hours, not just the times at which the sun rises and sets. Peak sun hours are the times at which an hour of sunlight is equal to at least 1,000 watts per square meter.

You will receive somewhere between three-and-a-half and six peak sun hours in most parts of the United States. The southwest tends to get the most hours, while the northeast and northwest get the least. To get more specific details, you can check an insolation map or use an insolation meter.

Knowing your average peak sun hours is a crucial step in purchasing the appropriate size and number of solar panels for your homes needs.

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