How Many Solar Panels Do You Need: Panel Size and Output Factors

How many solar panels does the average house need? How many solar panels do I need for a 3-bedroom house? How many solar panels do I need for a 2000 sq. ft. home? These are all common questions for an aspiring solar homeowner. Determining how many solar panels you’ll need for your home requires first knowing what your goals are.

Do you want to minimize your carbon footprint? Maximize the return on your investment? Save as much money as possible?

Most people want to save money while minimizing their environmental impact.

To calculate how many solar panels you need, you need to know:

  1. Your average energy requirements

  2. Your current energy use in watts

  3. The climate and amount of sunlight in your area

  4. The efficiency of the solar panels you’re considering

  5. The physical size of the solar panels you’re considering

One simple way of answering the “How many solar panels do I need” question is to consult a professional solar installer, who can give you a free home solar evaluation.

How much solar power will you need

To determine your home’s average energy requirements, look at past utility bills. You can calculate how many solar panels you need by multiplying your household’s hourly energy requirement by the peak sunlight hours for your area and dividing that by a panel’s wattage. Use a low-wattage (150 W) and high-wattage (370 W) example to establish a range (ex: 17-42 panels to generate 11,000 kWh/year). Note that the size of your roof and how much sunlight your roof gets are factors as well. If you work with an experienced solar installer, they will handle all these calculations for you. If you’re searching for a calculator to figure out “how many solar panels do I need?”, look no further. We use our Design System to estimate your own system size, monthly savings, and the actual appearance of a solar array on your own roof. This interactive tool provides a solar estimate in just a few seconds and can be done on your own or on a call with a EngagePower (877) 793-5331.

How many watts do you currently use?

Look at your electricity bill for average usage. Look for “Kilowatt Hours (or kWh) Used” or something similar, and then note the length of time represented (usually 30 days). If your bill doesn’t show kilowatt-hours used, look for beginning and ending meter readings and subtract the previous reading from the most recent one.

You want daily and hourly usage for our calculations, so if your bill doesn’t show a daily average, divide the monthly or annual average by 30 or 365 days, respectively, and then divide again by 24 to determine your hourly average electricity usage. Your answer will be in kW. (And just in case you’re wondering, a kilowatt-hour is how much power you are using at any given time multiplied by the total time the power is being used.)

A small home in a temperate climate might use something like 200 kWh per month, and a larger home in the south where air conditioners account for the largest portion of home energy usage might use 2,000 kWh or more. The average U.S. home uses about 900 kWh per month. So that’s 30 kWh per day or 1.25 kWh per hour.

Your average daily energy usage is your target daily average to calculate your solar needs. That’s the number of kilowatt-hours you need your solar system to produce if you want to cover most if not all of your electricity needs.

It’s important to note that solar panels don’t operate at maximum efficiency 24 hours a day. (See Solar 101: How Does Solar Energy Work?). Weather conditions, for example, can temporarily reduce your system’s efficiency. Therefore, experts recommend adding a 25 percent “cushion” to your target daily average to ensure you can generate all the clean energy you need.

How many hours of sunlight can you expect in your area?

The peak sunlight hours for your particular location will have a direct impact on the energy you can expect your home solar system to produce. For example, if you live in Phoenix you can expect to have a greater number of peak sunlight hours than if you lived in Seattle. That doesn’t mean a Seattle homeowner can’t go solar; it just means the homeowner would need more panels.

The Renewable Resource Data Center provides sunlight information by state and for major cities.

Now multiply your hourly usage (see question No. 1) by 1,000 to convert your hourly power generation need to watts. Divide your average hourly wattage requirement by the number of daily peak sunlight hours for your area. This gives you the amount of energy your panels need to produce every hour. So the average U.S. home (900 kWh/month) in an area that gets five peak sunlight hours per day would need 6,000 watts.

 

What affects solar panel output efficiency?

Here’s where solar panel quality makes a difference. Not all solar panels are alike. Photovoltaic (PV) solar panels (most commonly used in residential installations) come in wattages ranging from about 150 watts to 370 watts per panel, depending on the panel size and efficiency (how well a panel is able to convert sunlight into energy), and on the cell technology.

For example, solar cells with no grid lines on the front (like SunPower® Maxeon® cells) absorb more sunlight than conventional cells and do not suffer from issues such as delamination (peeling). The construction of our cells makes them stronger and more resistant to cracking or corrosion. And a microinverter on each panel can optimize power conversion at the source, in contrast to one large inverter mounted on the side of the house.

Because of these wide variations in quality and efficiency, it’s difficult to generalize about which solar panels are right for you or how many you’ll need for your home. The main takeaway is that the more efficient the panels are, the more wattage they can produce, and the fewer you will need on your roof to get the same energy output. Conventional solar panels usually produce about 250 watts per panel, with varying levels of efficiency. In contrast, SunPower panels are known to be the most efficient solar panels on the market.*

To figure out how many solar panels you need, divide your home’s hourly wattage requirement (see question No. 3) by the solar panels’ wattage to calculate the total number of panels you need.

So that average U.S. home in Dallas, Texas, would need about 25 conventional (250 W) solar panels or 17 SunPower (370 W) panels.

What is the effect of solar panel size?

If you have a small or unusually shaped roof, solar panel size and numbers are important considerations. With a large usable roof area, perhaps you can sacrifice some efficiency and buy more larger panels (at a lower cost per panel) to get to your target energy output. But if your usable roof area is limited, or if it’s partially shaded, being able to use fewer smaller high efficiency panels may be the best way to make the most possible power over the long term, ultimately saving you more money.

Solar panel dimensions

Typical residential solar panel dimensions today are about 65 inches by 39 inches, or 5.4 feet by 3.25 feet, with some variation among manufacturers. SunPower panels are 61.3 inches by 41.2 inches.

These dimensions have remained more-or-less unchanged for decades, but the efficiency and output from that same footprint have changed dramatically for the better. In addition, SunPower designs entire systems to have virtually no gaps between panels and uses invisible framing and mounting hardware to keep the rooftop footprint as tight, efficient and attractive as possible

How much do solar panels weigh?

If you’re planning on installing a rooftop solar system, understanding the weight of your solar panels is another key factor to consider. Knowing a solar panel’s weight is the best way to be certain that your roof can support a full installation.

While panel weights vary from brand to brand, most panels weigh about 40 pounds.

SunPower panels are the lightest of all major brands*, with some of our panels weighing as little as 33 pounds. For comparison, at the top end of the range some conventional panels weigh as much as 50 pounds.

Summary: How many panels do you need?

Knowing the answers to the above questions will give you an idea of the ideal number of panels for your electricity generation needs — or at least a realistic range. Next, a professional installer needs to assess your roof architecture, angle to the sun, and other factors to see if and how you’d be able to physically arrange the right number of panels on your roof to achieve your daily energy production goals.

You should also consider net metering as you’re considering how much money you’ll save and make from your solar system. Net metering is how your utility company credits you for producing excess solar energy when the sun is shining and then lets you draw from those credits when you’re using a conventional power grid at night if you don’t store your excess solar energy in a battery storage system.

To get started, check out our solar calculator, which can help you figure out how much you might save going solar.

Is My House a Good Candidate for Solar Panels?

If you're thinking about going solar, you're probably wondering: Is solar cost effective? Is my roof suitable for solar panels? Will solar energy generate enough electricity to power my home? Who makes the best solar panels?

But first, it's important to explore if solar panels for your home make sense. Here are some key questions we ask anyone interested in buying or leasing a solar energy system to make sure their home is best suited for making power with solar panels.

1. How much is your energy bill?

Knowing how much you pay for energy is the first step in evaluating whether your house is a good candidate for solar. The main question is, will it save you money? In some areas, electricity is very inexpensive. For most homeowners, the electricity bill is a dreaded monthly expense. The general rule is that solar makes the most financial sense for someone with a monthly electricity bill of at least $75. Why? Because going solar replaces utility energy with solar energy, we want our customers to see a return on that investment by paying less for that energy. A utility bill of $75 is the threshold at which residential solar customers will see solar savings. There are several ways to go solar, depending on a customer's needs and goals. SunPower offers zero-down lease, loan, and cash purchase options — each with different benefits. (See How to Buy Solar Panels for Your Home for more.) Ask your local solar expert about local and federal incentives and electricity policies where you live. 

 

The overall idea is to pay less than you currently pay, lock in your electricity rate and save money by generating your own clean energy onsite. (Learn more about solar financing, call (877) 793 5331

 

2. What kind of roof do you have?

Solar panels work best with strong, durable roofing materials, such as composite or asphalt shingle, concrete tile or standing seam metal. For roofing materials such as wood shake and slate tile, or for roofs made of clay with mortar or composite metal/stone coated steel, you can still go solar but you'd want to choose a solar professional who has experience installing solar panels on those types of roofs. Also, the type of mounting hardware your solar installer plans to use is important. SunPower Equinox™ uses InvisiMount™ hardware that is designed to work with most roof types and is visually attractive.

3. Does your roof need to be replaced?

It's a good idea to replace a roof that is near the end of its life before installing solar because SunPower solar panels have an expected useful life of 40 years, and you wouldn't want to have to remove them unnecessarily. Solar panels should be installed on roofs that are in good condition and will not need to be replaced in the near future. Considering that your savings from high-efficiency solar panels could pay for the cost of a re-roof in as little as five years after installation, it may be worth it to do any needed roofing work before your solar installation.

4. How much sunlight does your roof receive?

To see if your house is a good candidate for solar, try out a solar panel suitability checker such as Google's Project Sunroof. Then set up an appointment for a solar consultation with an expert who will visit your home to inspect its orientation (solar panels facing south capture more energy), roof angle, and tree shading to see if your roof will receive enough sunlight to meet your family's energy needs. EngagePower's solar consultations are free, and you can learn a lot about your home and the best energy options. The more direct sunlight your home receives, the more power the panels will produce. While SunPower solar panels are known for being extremely efficient at generating power in low-light situations, excessive shading will reduce the amount of power that can be generated.

It's also important to know that SunPower's Equinox solar solution has factory-integrated microinverters in each panel, an innovative solar design feature that means if one panel isn't producing energy because of shade, neighboring panels that might be receiving more sunlight can still generate solar energy for your home.

5.  What is your local climate like?

Solar energy can be generated in all sorts of extreme climates, from rainy areas such as Seattle to extremely hot locations such as Los Angeles, California. Solar suitability checker tools can help you understand how this could affect solar on your house. High-efficiency solar panels convert direct and indirect sunlight into electricity, so they work even on cloudy days. A solar consultant will estimate the amount of energy your system will produce so that you can see the potential savings before you decide to go solar.

If your area is prone to severe weather, check the durability rating of the panels you're considering for your home. SunPower panels are rated No. 1 in third-party durability testing and we pride ourselves in associating with the best, and these panels can withstand some of the harshest weather conditions, including hail up to 1 inch in diameter.1 In fact, SunPower technology is so reliable that NASA chose our solar cells to power its GROVER project, which explored Greenland's vast and inhospitable ice sheets. Solar that's tough enough for NASA is tough enough for your roof, too.

Think your house is a good candidate for solar? Find out how much you might save by entering your address into our solar savings calculator. Sign up for a free home solar estimate and evaluation, or call us at 1-877-793-5331.

Interested in high-efficiency solar panels for your home? Contact EngagePower for more information.

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