How Many Solar Panels Do You Need?
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 aspiring solar homeowners. Determining how many solar panels you’ll need for your home requires first knowing what your energy goals are.
Do you want to minimize your carbon emissions? Maximize the return on your investment? Save as much money as possible?
Most people want to save money while minimizing environmental impacts.
How Many Solar Panels Do You Need?
To calculate how many solar panels you need installed on your roof, you need to understand:
Your home's average energy requirements
Your current energy use in kilowatt-hours (kWh)
The climate and amount of sunlight in your local area
The efficiency of the solar panels you’re considering
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, like us.
How Much Solar Power Will You Need?
To determine your home’s average energy requirements, review your 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 solar panel’s wattage. Using a low-wattage (150 W) and high-wattage (370 W) example to establish a range (for example, 17-42 panels to generate 11,000 kWh/year). Note that the size of your roof and how much sunlight your roof gets will be factors as well.
How Many Watts Do You Currently Use?
Evaluate 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 your calculations, so if your bill doesn’t show a daily average, just 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 killowatts (kW). (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 around 200 kWh per month of electricity, 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 according to the EIA. 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.
Solar panels don’t operate at maximum efficiency 24 hours a day.
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 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, Arizona, you can expect to have a greater number of peak sunlight hours than if you lived in Seattle, Washington. That doesn’t mean a Seattle homeowner can’t go solar; it just means the homeowner would need more solar panels.
The National Renewable Energy Laboratory (NREL) 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 needed into 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 solar panels need to produce every hour. The average U.S. home (900 kWh/month) in an area that gets five peak sunlight hours per day would need about 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 can convert sunlight into energy), and on the cell technology.
For example, solar cells with no grid lines on the front absorb more sunlight than conventional cells and do not suffer from issues such as delamination (peeling). The construction of these type of cells makes them stronger and more resistant to cracking or corrosion. 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 the more efficient the solar panels are, the more wattage they can produce, and the less 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.
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.
The average U.S. home in Dallas, Texas, would need about 25 conventional (250 W) solar panels.
What is the Effect of Solar Panel Size?
If you have a small or unusually shaped roof, solar panel size and number of panels are important considerations. With a large usable roof area, perhaps you can sacrifice some efficiency and buy larger panels (at a lower cost per panel) to get to your target energy output wanted. But if your usable roof area is limited, or if it’s partially shaded, using fewer smaller high-efficiency panels may be the best way to make the most 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.
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, we can design entire systems to have virtually no gaps between each panel and use 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 panel system 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.
Summary: How Many Panels Do You Need?
Knowing the answers to the questions above will give you an idea of the ideal number of solar 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 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.
Ready to Learn More About Saving with Solar Panels?
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Schedule your free estimate with SunPower today! Our team of solar experts are available to help you transition to a more sustainable lifestyle.