How Many Solar Panels Do I Need On My Roof?

Answering the question, "How Many Solar Panels Do I Need?" with an overview map of a city's solar power generation potential.
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Obviously you need more than one solar panel to power your home, and most families will need several solar panels wired together into a highly efficient solar power system in order to meet their energy needs. But exactly how many solar panels do you need for your home?

The truth is that calculating the number of residential solar panels you need on your roof depends on a wide variety of factors, including energy consumption, peak sunlight hours, panel output, and your solar goals.

The goal of this article is to help you figure out how many solar panels you will need, so you can save as much money as possible and minimize your carbon footprint. To find the right number of solar panels for your family, we’ll investigate the several elements that go into the solar power system design process, and explain how each impacts the size of your solar power system.

Whether you’re a solar fan who wants to learn more about the entire solar design process, or you're comparing a few different options to find the right number of solar panels for your needs, we think you’ll find this article helpful.

4 Factors That Impact the Number of Solar Panels for Your House

A typical home needs between 18 to 26 solar panels to cover 100% of its electricity usage. While there are many elements you can analyze to determine the ideal size of your future solar panel system, we want to discuss the four that are most worth your time:

  • Your household energy consumption
  • Peak sunlight hours for your area
  • The output of each solar panel
  • Your solar goals

Let's have a deeper look at each of these elements.

1. Energy Consumption

When people start thinking about home solar, they ask lots of questions.

  • "How much energy does a solar panel produce?"
  • “How many solar panels can I fit on my roof?"
  • "How much solar do I need?"
  • "How many solar panels to power a house?"
  • “What is the number of solar panels I need for my family?

When determining the number of solar panels you need, nearly everything boils down to one crucial factor: The amount of energy you use (or plan to use) in your home.

To start the process of figuring out the right number of solar panels for your house, you should first determine how much electricity you use during an average month. Start by viewing your previous utility bills. Once you locate your last twelve monthly electric bills, add up your total usage in kilowatt-hours (kWH) and divide by 12.

Both your 12-month total energy consumption and your 12-month average energy consmption are the baseline information you need about your energy consumption, because everything else depends upon your electricity usage.

2. Peak Sunlight Hours

The point of solar panels is that they rely on sunlight to generate electricity. To work as efficiently as possible, your panels need maximum sustained exposure to sunlight, a concept called “peak sun hours”. Where you live can determine how much energy your solar panels will produce in a day. For example, the American Southwest regularly receives well over 6 hours a day of “peak sun hours”, while the American Northwest struggles to get 4 “peak sunlight hours” on a good day.

The best way to learn the amount of sustained sunlight your area receives is to speak with a solar energy system expert like Palmetto. We can help you determine the right number of panels for your roof based on the number of peak sunlight hours in your area, as well as the angle at which they should be installed, and additional tips that will maximize your generation.

You can also consult the U.S. Energy Information Administration or use tools like the U.S. State Solar Resource Map from the National Renewable Energy Laboratory to determine peak sun hours in your area.

3. Solar Panel Output

Different solar panels have different electricity generation capabilities, based on factors like the number of solar cells in that panel and their relative efficiency. Additionally, a panel's installation direction, and shade from trees or a chimney may impact how much electricity your solar panel produces.

The output of each solar panel is also going to depend on the angle of installation. Solar panels are installed in a solar array, which is just the name for a group of solar panels that are all installed together. The simplest and easiest array to install is a single rectangular shape. However, a single rectangular array requires a basic rectangular roof to install the array on, so it’s not compatible with more complex roof designs.

If your roof shape doesn’t allow for a single array with all of the panels you need, the right number of panels for your home will instead be placed into a few groups in different parts of your roof. If different arrays face in different directions, they will produce different amounts of electricity, even if they’re made from the same panels.

4. Your Solar Goal

People switch to solar for different reasons. Some want to save money on electricity, others to avoid frequent power outages, and others want to minimize their carbon footprint. Those are all good considerations to help you determine the number of solar panels that will get that desired power output for you.

Let’s consider three common options:

  • If you plan to participate in net metering, you may want to install solar panels that can generate more electricity than you consume.
  • If avoiding power outages is your goal, a good solar panel battery storage system will ensure you store enough electricity that you can use later.
  • If you want to use solar to help the planet, you will need enough solar panels to produce 100% of your electricity needs so you don’t consume dirty electricity from the utility.

Having a clear goal makes it easier for you and your solar panel installer to arrive at the right number of solar panels for your home.

How Can I Calculate the Size of My Solar Panel System?

Many solar energy companies offer an online solar calculator to help people determine the size of the solar panel system they need, and calculate how many solar panels make up that system. Palmetto invites you to try our Solar Savings Estimate tool to see how much you can save by going solar, based on your recommended solar power system size.

Alternatively, you can use a simple formula to determine the size of the system you need to power your house:

(Monthly Electricity Usage / Monthly Peak Sun Hours) x 1,000 / Solar Panel Wattage

Let's break this formula down a little further to help you better understand what’s happening.

1. Determine Your Energy Consumption

Review your 12 most recent utility bills to learn your monthly consumption. Simply add up the last 12 months of usage from your electricity bills and divide by 12 to get your home's average. For our purpose here, we will use 1,200 kWh per month as an example.

2. Determine How Much Sunlight You Receive in Your Area

You need to determine how many peak sun hours your area receives. Keep in mind, average daily peak sun hours aren’t merely the hours when the sun is in the sky. They are the hours when the sun delivers the most sustained exposure of sunlight, which means that’s when your solar panels will be most productive.

Peak sun hours directly impact the number of solar panels you need. If you live in a place that receives a lot of sunlight, such as Arizona, a smaller solar power system might be all you need. You would need a bigger one to achieve the same amount of energy production if you live in an area with less sunlight available, such as Massachusetts.

For our example, we will use Arizona, which receives an average of 7.42 peak sun hours per day.

3. Plug Consumption and Peak Sun Hours Into the Formula

1,200 kWh / (7.42 × 30) = 5.4 kW Solar System

Note: We multiplied Arizona's average peak sun hours by 30 to get a ballpark estimate of peak sun hours that the state gets per month.

4. Convert KW to Total Watts

Since 1 kW equals 1,000 watts, we will multiply 5.4 kW by 1,000:

5.4 × 1,000 = 5,400 Watts

5. Determine the Generation Capacity of Your Potential Solar Panels

Different solar panels have different power generation capacities. Some companies sell them at 320 watts, others at 280 watts, and others still at 250 watts. Some high efficiency panel designs can even produce up to 400 watts or more per panel. We shall use 280 watts for this example.

Simply divide the total watts above by the total wattage output of your solar panel to determine how many solar panels you will need:

5,400 / 280 = 19.3 solar panels needed to cover total electricity usage

In this example, the homeowner would need a solar power system with around 20 solar panels to provide all of their energy needs over the course of a year. Solar installers typically factor in many more variables when sizing a solar power system, but this number serves as a good baseline when thinking about your own solar power plans.

When you work with Palmetto to design your perfect solar power system, we take care of the entire process, including the calculations required to find out how many solar panels you need, so you won't have to worry about the details.

The Number of Solar Panels You Need Depends Upon You

You now have a rough idea of the number of solar panels you need to power your home. Great! But still you have to pay attention to a few more details to set up your solar power system for success, including your budget and solar goals. We recommend you engage a solar panel professional to address the following questions about solar panel installations.

How many solar panels do I need for my roof design?

The design of your roof determines how the solar panels will be installed, and how much sunlight they will get. If your roof is well-angled and spacious enough, it can accommodate a large solar panel system. If there is only a small available area, you may be forced to install a reduced system with costlier panels to generate the solar power you want.

The direction your roof faces also impacts the amount of sunlight your solar panels will receive. If your roof faces in a direction that receives less sunlight, your solar company might have to adjust the orientation of your system to get you sufficient electricity. That is why it is important to talk with a professional solar installation company like Palmetto when installing a solar panel system.

How many solar panels do I need for home appliances?

Just knowing the monthly energy consumption on your power bill isn't always enough to help you reach a sound decision. You need to look around your house to learn where and when you use electricity, especially in terms of your appliances.

For example, you may notice higher-than-average consumption when using a washing machine or playing video games during the daytime. Understanding how your appliances use electricity gives you insights into when you are likely to need more electricity.

To track the energy usage for individual appliances, you can install an electricity usage monitor or smart plug between the outlet and the appliance. Leave the usage monitor on for a week and use that data to calculate the total number of kilowatt-hours per day that your appliances use.

Some of the home appliances that eat up the most electricity include:

  • Refrigerator
  • Heater
  • Air Conditioner
  • Dehumidifier
  • Dishwasher
  • Electric Oven
  • Clothes Washer
  • Clothes Dryer

Once you know the energy consumption of your appliances and when they’re used, you can figure out the size of the solar panel system you need to install to generate the electricity your home needs.

How many solar panels do I need if I have a lot of trees?

The beautiful trees around your home can impact how much solar energy your solar panels can generate every day. Even if your area gets lots of peak sunlight hours, tree coverage may diminish your total energy generation.

You may have to trim trees so your solar panels can generate as much electricity as you need. If you don’t trim them, your roof might get shade during certain times of the day, and that requires a larger system to compensate for that decrease in production.

Sometimes you can’t trim trees to improve your energy production, such as tall trees on the edge of a neighbor’s property. In this case, your system design will have to account for this decrease in morning or afternoon production.

How many solar panels do I need for my future energy plans?

Is your electricity consumption rate likely to increase in the coming years? When sizing a solar power system, you need to think about any big changes in electricity usage that might happen in a few years. This includes the purchase of an electric car, installing a larger air conditioner, buying a hot tub, leveraging net metering, and so on.

In short, the greater your future energy needs, the more solar panels you may want to install now to account for that future consumption.

Key Takeaways

There’s a lot to consider before installing solar panels on your home, but the factors we discussed will help you estimate the size of the solar power system you need. Keep in mind that this is simply an estimate, so use it as a guide, not as the final figure.

Once you have your solar power system size estimate, the best way forward is to speak to Palmetto. Our experts will assess your needs, situation, and budget to help you settle on the number of solar panels that will work for you.

We’ll help you figure out the number of solar panels that are enough for your home, answer any questions you might have, and calculate how much you can save by going solar. Get in touch today to find out how we can help you achieve your solar energy dreams.

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