How Many Solar Panels Do You Need
Determining how many solar panels you need for your home means first knowing what your goals are. Do you want to minimize your carbon footprint? Maximize your return on your investment? Save as much money as possible? Most people want to save money while minimizing their impact on the environment.
To calculate how many solar panels you need, the following needs to be determined. How much energy your household uses; your roof’s usable surface area; the climate and peak sunlight in your area; the wattage and relative efficiency of the photovoltaic (PV) panels you’re considering; and whether net metering is available.
The simple way to answer the “How many solar panels do I need” question is to consult a professional solar installer, who can provide 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. To calculate how many solar panels are needed, multiply a household’s hourly energy requirement by peak sun hours for the area and divide by a panel’s wattage. Use a low-wattage (150W) and high-wattage (370W) example to establish a range (ex: 17-42 panels to generate 11,000 kWh/year). The amount of sunlight a roof gets, with the roof’s size and battery storage will figure in as well. If you work with SunPro Solar, our solar experts will handle all these calculations for you. To give a general idea of how many solar panels are needed for an average home, here is a sample set of questions that a solar professional might use to figure it out:
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 time period 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, though, 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 kilowatt-hours (kWh). (And just in case you are 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 100 percent of your energy needs.
It’s important to note that solar panels don’t operate at maximum efficiency at all times. 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 solar potential 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 solar 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. The average U.S. home (900 kWh/month) in an area that gets five peak sun hours per day needs 6,250 watts.
What affects solar panel output efficiency?
Here’s where solar panel quality makes a difference. Not all solar panels are alike. Home solar panels come in wattages ranging from about 150 watts to 370 watts per panel. Panel size, efficiency, and the cell’s technology are also factors.
SunPower ® Maxeon solar cells have no front grid lines, absorbing more sunlight than conventional cells. These types of cells do not suffer from issues such as delamination (peeling). The construction of our cells makes them stronger and more resistant to cracking or corrosion. Unlike a large inverter mounted on the side of a house, microinverters on each panel optimize conversion at the source.
Since there are many variations in quality and efficiency, it’s difficult to over-generalize solar panels. The more efficient the panels, the more wattage produced, and the fewer needed on a roof to get the same energy output. Choosing the correct type or how many solar panels you’ll need for your home should be determined by a professional. 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.
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, you can sacrifice efficiency and get larger panels at a lower cost per panel. If your usable roof area is limited, or partially shaded, using fewer smaller high-efficiency solar panels is the best way to generate the most power over the long term.
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. The efficiency and output from the same footprint, however, has increased dramatically. 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.
Knowing the answers to the above questions will give you an idea of the ideal number of solar panels for your electricity generation needs. 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.
Net metering should also be considered as you’re figuring out the ROI for your solar panel system. Net metering is how the utility company credits you for producing excess solar energy. The credits are then applied when using grid power at night. That is if you don’t have a solar battery storage system. To get started, check out our solar calculator, which can show your potential savings by going solar. Or feel free to call us at 951-678-7733 and schedule a free no-obligation consultation with a SunPro Solar representative.