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How Many Solar Panels Do I Need?

The amount of solar panels you need depends on the size of your home and location. Learn how to calculate how many solar panels are required for your home.
Solar Panels
7 minutes
Written by:
Joey Cheek
Updated on:
October 27, 2022

The number of solar panels required to power your home will vary depending on size and geographical location. That’s why determining how many solar panels to install is the first step in ensuring you save on energy costs. Solar panels provide consistent, cost-saving benefits while contributing to lowering your family’s carbon footprint.  

Common goals for using solar energy include:

  1. Maximizing your return on investment
  2. Save on energy costs
  3. Reduce your carbon footprint 
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How Much Solar Power is Required 

Planning for the number of solar panels your home will require following information:

  • The home’s average energy requirements 
  • Current energy usage in watts
  • Climate and the total amount of sun in the area
  • Efficiency and size of the solar panels

You may turn to your utility bill to figure out how much energy you are using. However, this isn’t the only factor to consider. If you want to figure out how many solar panels you need, all you need to do is use this formula:

Number of Panels = System Size / Production Ratio / Panel Wattage

Although, most American homes require 20-24 solar panels installed. The formula helps to determine your home’s energy requirements; in addition to other factors such as how big is your home’s roof? Is your home large enough to support the number of solar panels necessary?

You also have to consider how long your roof is in direct sunlight each day. If your home receives little direct sunlight, more solar panels would be required to generate enough energy. 

If you decide to work with a professional solar installer, they can handle the calculations on your behalf. You can also find online calculators to help you determine what you need. These calculators can provide information on the size of the system you need, total monthly savings, and the look of the solar array on your roof.

Determine the Current Watts 

Look at your utility bill for your average energy usage. When looking at the bill, look at the kWH, which stands for kilowatt hours you used. After this number, you should see the amount of time it’s for – usually it will be 30 days. If your bill does not show the kilowatt hours used, find the beginning and end reading on the meter, then subtract the last reading from the most recent.

You will then want to find the hourly and daily usage for your calculations. If your bill isn’t showing a daily average, then divide the annual or monthly average by either 365 or 30 days (respectively). Now, divide it by 24 to figure out your average electricity usage per hour. The answer you get will be in kWh.

If you have a smaller home and live in an area with a temperate climate, then you use around 200 kWh/month. For larger homes located in the southern part of the US, where air conditioners account for most of the home energy usage, you may be using 2,000 kWh/month or more. 

It’s estimated that the average home in the United States uses around 900 kWh each month. This equates to 1.25 kWh an hour and 30 kWh per day.

You can use your average daily energy usage to determine your total solar needs. This is the total number of kilowatt hours that you require your solar system to be producing energy if you want it to cover all or most of your electricity demands.

It’s important to note that solar panels will not operate at maximum levels of efficiency for 24 hours per day. For example, weather conditions may reduce the efficiency of your system temporarily. Because of this, it’s smart to add a 25% cushion to the daily average you come up with. If you do this, it will help ensure that you can generate all the clean, eco-friendly energy you need for your home.

Hours of Sunlight 

Another factor that will impact the amount of energy you can expect your home solar power system to produce is the peak sunlight hours in your location. For example, someone who lives in Phoenix can expect more peak sunlight hours than someone living in Seattle. This does not mean that someone in Seattle can’t take advantage of solar power, it just means you will need more panels in Seattle than you would in Phoenix.

It's possible to multiply your hourly usage (determined above) by 1,000. Then, you can convert your hourly power generation needs into watts.

Divide the hourly wattage average requirement by the total peak sunlight hours in the area, which you can find at the Renewable Resource Data Center. This will provide you with the total amount of energy your panels must produce each hour. An average home in the U.S. (at a rate of 900 kWh/month) in an area with five total peak sunlight hours each day will require 6,000 watts.

Solar Panels Output Efficiency

This is when the quality of the solar panels comes into play. Not all solar panels are created equal. For example, PV or photovoltaic panels, which are commonly used for residential projects, come in wattages that range from around 150 watts up to 370 watts per panel. It all depends on the panel size and the efficiency (this refers to how well the panel can convert the light from the sun into energy), and it depends on the cell technology.

For example, if a solar cell doesn’t have grid lines on the front, it can absorb more sunlight than traditional cells without experiencing as much delamination (this means peeling). The construction of quality cells ensures they are strong and can resist corrosion and cracking. Also, having a microinverter on every panel will help to optimize the power conversion right at the source rather than having one big inverter that is mounted on the side of your home or building.

Due to the wide variations in efficiency and quality, it’s often challenging to generalize what solar panels are right for you or how many you will need to power your home. The main takeaway from this is that when you opt for efficient panels, they will produce higher wattage. This means that you won’t need as many on your roof to achieve the same level of energy output.

With conventional solar panels, you can expect them to produce around 250 watts per panel. The efficiency levels vary. To determine the number of solar panels you require, you can divide the hourly wattage requirements of your home by the wattage of the solar panels.

Solar Panel Size

Do you have a home with an unusually shaped or small roof? If so, knowing how many solar panels you need is an important consideration. If you have a larger portion of your roof to use for solar panel installation, it may be possible to sacrifice some level of efficiency and purchase larger panels. If you do this, you will likely get a lower cost per panel. This will also help you get the desired energy output.

However, in situations where the usable roof area is limited, or if your roof is in the shade, installing less, higher-efficiency panels, can be the best option to make the most of the power produced in the long term. This is also going to help you save more money over time.

Usually, the dimensions for residential solar panels are about 39” by 65”, although there are slight variations based on manufacturer.

Solar panel dimensions have been relatively the same for decades. However, the output and efficiency from the footprint have improved significantly. There are solar panel designs that have almost no gaps in between the panels and use invisible hardware that reduce the surface area required on a home’s roof. 

Solar Panel Weight

If you plan to have solar panels installed on your roof, you should consider the weight. While this can vary based on the manufacturer, however, most panels weigh around 40 lbs.

Now that you know the basics of solar panels, here is a recap of what to consider when determining how many are required:

  1. Calculate energy demands: Know how much energy you need to power the items in your home you plan to use solar power.
  2. Average daily sunlight in your location: There are online resources that can help.
  3. Solar panel size and weight: The size of the panels will determine how much power they can produce. The weight determines if your roof can support the solar panels.

The Bottom Line

There are several factors to consider when it comes to installing solar panels. Keep the information here in mind, which is going to help you find the right solar panels for your home. You should also consult with a solar panel installation professional to assist in your green energy project. 

“Quote from an author or expert that spans across two lines.”
Joey Cheek

Meet the author:

Joey Cheek

Joey Cheek spent 10 years on the US National Speedskating Team where he competed in two Olympic Games, winning gold, silver, and bronze medals. He attended Princeton before diving into the startup and tech world. In 2011 he launched a livestreaming platform for sports before leading a team of engineers building next-gen news and content apps for Fortune 100 companies. He is the CEO and co-founder of SmartSolar.org, whose mission is to move the earth to cheap, abundant, carbon-free energy.

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