Solar Panel Sizing: How To Calculate Home Solar System Size

Solar power has seen a large increase in popularity over recent years, and this is for very good reasons.

Solar energy is not just better for the environment compared to gas and other fossil fuels, but it can also save you a lot of money in the long run.

Solar Panel Sizing: How To Calculate Home Solar System Size

Additionally, the government regularly runs tax incentives and other support schemes to help homeowners spread the costs of a solar panel system.

But how do homeowners know what size solar panels and how many they need to run their home?

In this guide, we explore solar panel sizing and how to calculate the right size for your home.

How Many Solar Panels Do You Need To Power Your House?

Whether you are just curious or you want to install your own DIY solar powered system, there are a few things you need to look at before you can decide on what size solar panel array you need for your home.

From your current energy consumption and current electricity costs to off-grid systems, let’s find out what you need to know for sizing your solar panels.

The Size Solar System For Average Homes

As a rule of thumb, an average home needs around 6 solar panels, each with a rating of 300 Watts, an average irradiance of 4 kWh per square meter per day.

This is based on a 12 kWh energy consumption per day. Saying this, every home has different needs and uses a slightly different amount of energy.

This also depends on the size of your home, the size of your household and your lifestyle.

Calculate Your Home Energy Consumption

Before you can decide on the size of your new solar panels, you will need to find out how much energy you need to power your home.

There are a couple of different ways you can do this.

Calculate Manually

For this, you need to add up all the wattage of the appliances you want to run with your solar panels.

You can do this in an Excel spreadsheet by just listing the appliances and their wattage.

Then, add the number of hours these devices run every day. This will take some time and can be cumbersome.

Unfortunately, this also is not the most accurate method to calculate your home’s power usage.

However, it does give you a good overview of how often you use your appliances, and what they use.

It’s a good opportunity to review whether you could cut down on some of the use.

Check Your Utility Bill

The most accurate and easiest way of finding out how much electricity you use in your home is by checking your most recent utility bill.

Ideally, you should look at your annual utility bill, which will list your energy consumption in kilowatt-hours (kWh) for this year.

You can then take this figure and just divide it by twelve. This will give you your energy consumption by month.

Take the utility bill figure and divide it by 365 to get a daily average energy consumption.

Although the average electricity usage in the US is around 12 kWh per day, your personal electricity consumption will also depend on where you live.

How Do You Calculate The Right Solar Panels For Your Home?

Once you have a relatively accurate figure of your home’s electricity consumption, you can use this to calculate the use of your solar panels, and how many you need.

Before we get into the details, it’s important to know that solar panels never produce 100% electricity.

Due to the build and other factors, there is always a loss.

This can vary with home solar systems but some systems lose as much as 23% of electricity.

This is typically due to factors such as clouds/shading, dust/dirt, reflections, DC cable losses, inverter losses, thermal losses and others.

This means that you will need to factor in these losses when calculating your panel size.

How Many Solar Panels Do You Need For The Average US Home?

Let’s take a look at the example of an average home based in Oregon.

We will need three different figures for this: the average electricity consumption, the irradiation and the loss.

The average electricity consumption of our sample home is 33 kWh per day.

Next, we check Global Solar Atlas to account for the direct normal irradiation in this location.

For our example home, we use 5.83 kWh per square meter per day.

Although we said previously that the loss of a solar system is typically around 23%, it can’t hurt to set a slightly higher level with 30%.

Not take the average daily electricity consumption 33 kWh x 1.44. This will give you a daily load of 47.5 kWh/day.

You will then need to account for the inverter efficiency, which is on average around 96%.

Calculate the power supplied to your solar inverter with the daily load 47.5/0.96. This gives you an inverter power supply of 49.5 kWh per day.

Now you need to take this figure 49.5 kWh per day and divide it by the daily irradiation figure 5.83 kWh per square meter.

This will give you 8.5 kW (9 kW) of solar panels that work at full capacity.

Then take this figure 9 kW and divide it by the wattage of your solar panel (e.g. 300 Watts). So, 9 kW / 300 Watts per panel will give you around 30 solar panels.

Although this does look like a complex calculation, once you have all your figures in place, it can give you a relatively accurate overview of how many solar panels you need for your home.

The 30 solar panels in this example are for an average US home in Oregon.

Depending on your location and individual electricity consumption, this figure will vary widely.

We recommend checking with a local solar panel installer to ensure that you get the correct number and type of solar panels for your home.

How Many Batteries Do You Need To Power A House?

It’s not just the number of solar panels and their size that you need to consider with a solar panel system, but what stores the electricity that powers your home.

If you want to run your appliances for 24 hours a day without any additional grid electricity, then you can also work out how many batteries you need.

There are generally two different types of home energy storage batteries for a solar system setup: lithium iron phosphate batteries and lead-acid deep-cycle batteries.

Lead-acid batteries are still the most popular and commonly used batteries for solar storage. That’s why we use this type of battery for our example below.

You can discharge deep-cycle batteries down to 80% but typically 50% is recommended to get the most out of your battery.

This means that when you calculate the number of batteries you need, you will need to double the required energy because 50% of the batteries aren’t available usually.

Based on an average daily electricity consumption of 30 kWh, you will use around 2,500 Ah (battery amp-hours with 12 V batteries).

Double the 2,500 Ah, and you get 5,000 Ah. This means that you will need 25 batteries with 200 Ah to store the electricity in your home for 24 hours.

How Many Solar Panels Do You Need For A 2,000 Square Feet Home?

How Many Solar Panels Do You Need For A 2,000 Square Feet Home?

When you apply an average 950 kWh (30 kWh per day) of electricity consumption for 2,000 square feet, then you will need around 30 solar panels.

Each panel should be rated at 300 Watts.

How Many Solar Panels Do You Need For 5,000 Watts?

Based on our example calculations above, you may think that the answer is simply around 17 solar panels.

However, it is important to take into account any loss. A solar panel that has been rated at 300 W puts out this amount at its best performance.

This ideal performance has been measured in a laboratory with a standard irradiation factor of 1,000 Watts/m2.

As irradiance levels vary widely depending on your location, the calculation will also differ.

In addition to the irradiance levels, you will also need to factor in any losses which means that you need to multiply the power of your solar panel to ensure that you include the losses.

This is exactly the same as multiplying your 5,000 Watts with 1.44. You will then get 7,000 Watts. This is the true power you will need.

As per our calculations above, you will need 23 solar panels (each one rated at 300 W).

What Size Solar System Do You Need To Run A Fridge?

So far, we have only looked at the different calculations of solar power for different size homes.

But what size solar panel do you need to run a single appliance, such as a refrigerator?

On average, a standard fridge needs around 350 kWh per year. This does depend on your type of fridge.

Some of the older models consume a lot more electricity. So, if you have an older refrigerator, then it’s a good idea to add 5% to the 350 kWh.

A smaller 100 W solar panel can generate up to 400 Watts each day. This is at an average irradiance level of 4 hours full sun per day.

This is a power output of around 146 kWh for the entire year.

In order to calculate the number of 100 Watts solar panels you need, you just need to divide the 350 kWh by the annual figure of 146 kWh.

This gives you a figure of 2.4 solar panels. You will always need to round this up as you cannot use half a panel.

We recommend always using one panel extra, so this would make 4 solar panels for your average fridge.

This accounts for any power shortages and cloudy days.

In order to run your fridge with these four solar panels, you will also need an inverter which turns the solar power into the type of power that your refrigerator can use.

For 4 panels, you will need a 4 Watts inverter. Although you can also use 300 Watts, you should try to run a solar system as efficiently as possible.

In addition, you will also need a deep-cycle battery (100 Ah), although we prefer to use a Lithium Phosphate battery for smaller devices.

You will need the battery to store any solar energy during the night when your solar panels do not provide any power.

Do Solar Panels Work On Flat Roofs?

Yes, solar panels do work on flat roofs. However, they are much more efficient when they are mounted at the best angle for where you live.

Although the power loss is relatively small, it’s important to make the best use of your solar setup.

For example, a flat roof in Phoenix, Arizona, generates 10% less solar energy than when it is mounted at an optimum 57 degrees angle in the same location.

The exact difference will depend on your location’s irradiance.

How Long Does It Take For Solar Panels To Pay For Themselves?

There are so many different factors that play into the pay back times of your solar system setup.

One of the biggest factors is the irradiance of your location. The more sun your solar system gets, the more efficient it can run your home.

But the pay back time also depends on how much electricity you use for your home, utility prices and the installation of your solar system.

Some solar systems pay for themselves after ten years, while others can take up to 15 years.

A professional solar installer will be able to give you an accurate estimate for your home, your location and the setup of your solar panels, as well as batteries and inverters.

It’s a good idea to take net metering into account as well. This is any excess solar power that you may be able to feed back into the electricity network.

This means that your solar panels do not only save you money but they can also earn you some money on the side.

Why Does Solar Panel Size Matter?

The size of your solar panels for your solar-powered system is an important factor, especially when you have a relatively small or unusually shaped roof.

After all, you want to get the most out of your setup, and make use of all the roof space available.

With a larger roof, you are relatively free to use whatever you want.

You have the option to buy larger panels which are more efficient and less expensive than most smaller panels.

However, if your roof area is smaller, then you will need fewer panels that are smaller but still highly efficient.

This will ensure that you get the most possible power output from your solar panels over a longer period of time. This can also save you money in the long run.

The average solar panel measures 5.4 feet by 3.25 feet (65 inches by 39 inches). This can vary depending on manufacturer and where you live.

Although these dimensions have stayed the same (more or less) for the last decades, the technology and their energy output has developed over the years.

You also need to make sure that you choose a space-efficient panel which has a narrow frame. Also the installation can make a big difference.

Not all panels can be installed close to each other, so when you have a small roof, you will need to ensure that you get a solar panel which allows for very small gaps between panels.

The mounting hardware can also make a difference as to how close you position the panels.

Why Does The Weight Of Solar Panels Matter?

Another factor that you need to consider when choosing a solar panel is its weight.

This will largely depend on the dimensions of the panel and the technology inside.

A solar system, especially with a large number of panels, can weigh heavy on your roof, and you need to make sure that the roof structure of your home supports the weight.

The weight of a solar panel can vary depending on the brand and manufacturer.

The average solar panel weighs around 40 pounds, although there are also some lighter and heavier panels.


Calculating the size of your solar panels for your home is unfortunately not as easy as it may seem.

There are a number of different factors to consider when you want to calculate your home solar system.

You will first need to know your current electricity consumption.

Then your location and the sun hours at your location also play a significant role, as this has an impact on how efficient your solar panel can run.

You will also need to factor in any losses of the solar panels and other equipment you need for your system setup, such as inverters, storage batteries and cables.

It’s important to remember that no solar panel and battery is 100% efficient.

There is always some loss, and you will need to make allowances for this in your calculations.

This means that you will likely need more solar panels than originally calculated, which means you need to make best use of your limited roof space.

Joe Danner