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How Many Solar Panels Do You Need?

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  • Conclusion
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The topic of "how many solar panels do I need for my house in 2021?" is posed often by those considering installing solar panels.

When figuring out how much money you'll save on solar energy, the first thing to do is determine how big your installation will be.

It's not enough to search for "home maintenance tips" online and assume that anything you find will be applicable to your unique situation since every house and family is unique.

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Fortunately, figuring out how many solar panels you'll need is a simple process.

You just need access to a few crucial figures and a rudimentary understanding of mathematics.

How many solar panels you need and how to calculate that number, however, is something you may not know.

An on-site visit from an expert installer who is familiar with your neighborhood and utilities should provide the information you want.

That's the best way to determine how many solar panels you'll really need.

Entering your zip code below will help you locate the finest solar panel installers in your region and determine how many solar panels you will need for your house.

How to Calculate the Number of Solar Panels Your Home Needs

It's not hard to figure out how many solar panels you'll need.

Family life and geographical locations vary greatly. Even if you and your neighbor both live in identical houses, the former may need 10 more solar panels to meet their energy needs since they also host five children and Grandma.

Talking to a few local installers is the best method to determine how many solar panels you need and which panels are ideal for your needs. They will assess your house and energy consumption to determine the optimal size of the installation required to meet your demands.

Let's calculate how many solar panels will power your house. The answer to the query "How many solar panels do I need?" may be discovered by using the same processes we outlined before.

  • Determine your annual energy use.
  • Size up the system.
  • Increasing the size of the installation is necessary to compensate for output decline.
  • Calculate the number of solar cells.

Let's break this down into its component parts and examine it closely.

Step 1: Find Your Total Electricity Use

The primary factor in determining the optimal size of a solar power system is the annual quantity of energy used by the residence. In most cases, a home's electrical needs may be met entirely by the solar panels installed on the roof. Installing a solar system that generates around 10,404 kWh annually is ideal if your annual power use is 10,404 kWh (the average annual residential consumption in the United States).

Finding your yearly power use is the first step in determining the optimal number of solar panels. The use of utilities greatly simplifies this process. Simply log in to your account and review your expenditures over the last 12 months. The author's personal use during the last year is shown up top.

Even though my home isn't solar-friendly (it's too old and has too many quirks), I've always been curious about how many panels I'd need for my own place. Let's find it out together, both to satisfy my own personal interest and to set a good example for the rest of us.

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My family only consumes around 200–300 kilowatt hours (kWh) of power each month; thus, our consumption is rather low. You'll also see a big swing in our monthly use when the temperature rises in the summer and we crank up the air conditioning. The importance of calculating annual energy consumption is highlighted by the fact that it varies from month to month.

To calculate your annual consumption, simply add up the monthly totals over the last year. Getting this done is a breeze if you have access to spreadsheet software like Microsoft Excel or Google Sheets. Over the last year, I used 3,112 kWh of power at my house. So, I'm looking for a solar system that can generate roughly 3,112 kWh of power annually.

If you sign up for net metering, the ups and downs in monthly production from your installation won't affect you. With net metering, your utility will credit your account for the portion of solar power generated by your system that is exported to the grid and not used by your house. If you don't create enough power to meet your demands one month, you may use that credit to pay the bill.

Some astute homeowners figure out that they may really make money off of the utility by installing a solar system that consistently generates more than they need, say 150% to 200% of their use. While it's good to have some more cash on hand, this isn't what net metering is about.

With the help of net metering, you may save money by switching to solar power for your home. Though it may be used to save costs, its primary purpose is not financial gain. Utilities limit the scale of installations to avoid thistching to solar power for your home. Though it may be used to save costs, its primary purpose is not financial gain. Utilities limit the scale of installations to avoid this. Unlike most energy providers, Xcel Energy in Colorado and other states raises this limit to 120% of yearly use.Your solar installer should be familiar with the rules and restrictions set out by your local utility company regarding the size of your system.

Step 2: Calculate Your System Size

Next, we'll calculate how much power your solar array must generate.

We have to determine the maximum amount of energy that a solar panel can generate in your region. One would assume that a solar panel's energy output would be constant regardless of its location; however, this is not the case.

Sunshine is more intense in some places on the planet, and solar irradiance is a measurement of how powerful that sunlight is when it strikes the earth. The solar irradiation in the desert southwest is substantially greater than in the northern states of Oregon, Minnesota, and Washington.

As luck would have it, we have access to a wealth of useful tools. The National Renewable Energy Laboratory created the following map to show how many kilowatt-hours of power each kilowatt of solar panels may generate over the course of a year.

Using this map as a guide, you can easily determine the optimal size of your solar power system. You can easily calculate this by dividing your monthly energy bill by the regional average. We already know that I need to generate 3,112 kWh yearly to meet all of my household's energy needs. 1 kW of solar panels in Denver may generate about 1,900 kWh annually. Installed power of 1.6 kW is based on the use of 3,112 kWh divided by 1,900 kWh.

In order to power a normal house, the map shows that a 6.5 kW system is required, since average output is roughly 1,600 kWh per kW. NREL's own estimate for the typical US rooftop solar installation size, 6.2 kW, is astonishingly similar to this.

Step 3: Increase the size of the installation to account for production losses.

Although solar irradiance was included in the above calculations, there are numerous additional variables that may impact the actual power output of your solar system. The age of solar panels, dirt, snow, inefficient wiring and equipment, and low sunlight all play a role.

For this example, we'll stick with the baseline production loss of 14% that NREL employs in their online solar calculator, PV Watts. It's easy enough to do the arithmetic to figure out how much bigger our systems need to be to make up for these system losses.

My own home installation need, after dividing by 86%, is 1.8 kW. The typical house requires a larger system, between 7.6 and 10.5 kW.

Step 4: Calculate the number of solar panels.

We're down to our last phase now. With our system size in mind, determining how many solar panels should be placed on the roof is a breeze. Just divide the system size by the wattage of the solar panels, which are typically 275 watts for homes.

To meet the energy needs of my own house, I would need seven panels (1.8 kW divided by 275 watts). It would take 28 panels to power the typical US home.

So, there you have it. That settles the matter. The number of solar panels required can be easily calculated.

Step 5: What to Watch Out for When Estimating Solar Panels for Your Home

The aforementioned procedures are oversimplified, but they do provide a rough estimate of the size of the system required. The last stage in solar installation sizing is to verify that there will be sufficient unobstructed roof space for the planned array. The scope and location of your setup may be affected by the variables listed below. The solar technician putting in your panels will make careful notes on their size, location, and impact on energy output.

Is there enough room for 28 solar panels on your roof? Each residential solar panel requires roughly 15 square feet of area since they are 3 feet wide and 5 feet tall. That's around 420 square feet of solar panels for a 28-panel array. When it comes to figuring out how big your roof has to be, shingle producer Owens Corning has created a fantastic short piece. LG, a major producer of solar panels, has released a user-friendly solar calculator that uses Google Maps to provide rough estimations of how much usable roof space you have.

Can you fit all the solar panels you need on the south side of the roof? If not, you may separate your installation into groups, putting as many as feasible facing south towards the sun, with the remainder facing east or west. Your overall energy output will decrease by a little, but this is a popular strategy when dire circumstances demand it.

In order to comply with setback regulations, the roof must have a clear route of at least three feet in width from the eave to the peak so that firemen may safely enter the property in case of a fire. Obviously, this significantly reduces the amount of usable roof space, but there's a valid reason for this. Versions of this advice that are significantly less restrictive have been implemented by several states and local municipalities. Your installer will be familiar with the regulations in effect in your area.

Spaces that solar panels can't cover, such as vents, chimneys, and satellite dishes Satellite dishes can be relocated and vents re-routed, but you’ll have to work around chimneys.

Shade is an obvious constraint, but it may have serious consequences. Your solar panels require sunshine! If you have a tree shadowing your prime roof position, you can normally either transfer the solar installation to another portion of the roof, chop the tree down, or trim the tree (though of course, you’ll have to keep it trimmed back semi-regularly). Your installer will discuss your alternatives and recommend a course of action if shadows are a problem.

Installers will measure your roof and inspect it for any problems during your first meeting. The installer will spend many hours on your roof after you sign the papers, meticulously measuring the area and making notes about any shading or other potential problems.

How Much Do Solar Panels Cost to Install on Your Home?

Knowing the scale of the installation makes calculating solar panel prices a breeze. By 2021, the price of solar installations will have dropped to about $3/watt, so if you're thinking about making the switch:

If you've read thus far, you should now realize that estimating your solar panel needs and costs is not as complicated as you would have thought. Once again, the four phases are as follows:

  • Determine your annual energy use.
  • Size up the system.
  • Increasing the size of the installation is necessary to offset output losses.


Answering the aforementioned questions will help you determine the optimal amount of panels for your power generation requirements, or at least a reasonable range within which to work. Next, a professional installer needs to examine your roof construction, angle to the sun, and other parameters to discover whether and how you’d be able to physically place the proper number of panels on your roof to accomplish your daily energy production objectives.

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What is the optimal number of solar panels?

Based on the typical monthly power use of 893 kilowatt hours (kWh) in the United States, a typical household would need between 16 and 20 solar panels. After factoring in the federal solar tax credit, the cost to install that many solar panels would be between $12,000 and $17,000.

Just what would happen if there were too many solar panels?

Why might having too many solar panels be a bad thing? Large solar energy systems have two major drawbacks: (1) you cannot utilize all your extra electricity, and (2) you are paid less by the power provider for the electricity you give back to the grid.

How important is it to have a large array of solar panels?

The size of your solar power system is important when it comes to providing electricity for your house. Make sure your system is big enough to provide your daily power needs.

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