Updated Nov 4, 2022
All solar panels may look similar, but these energy-producing, light-absorbing powerhouses aren’t created equally. Different solar panel models produce varying amounts of electricity, making some options better for savings and off-grid living. We’ll show you how to calculate a solar panel’s energy output and use that calculation to improve your rooftop solar panel system.
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Solar panels contain layers of semiconductor materials that capture sunlight and transform it into direct current (DC) electricity which is measured in watts. Smaller devices sometimes need a few watts to operate, while larger appliances and home systems require a larger quantity called kilowatts or 1,000 watts. Energy usage is measured in kilowatt-hours (kWh), or the number of kilowatts an appliance needs for one hour.
A residential solar panel typically produces between 250 and 400 watts per hour, depending on the panel’s size and sunlight conditions. Panels for home systems usually have 60 or 72 small square sections called cells that generate and carry electrical currents. You can select a larger panel for more wattage, though each panel’s efficiency is the main power output indicator.
Solar panels’ ratings define how much wattage they can produce under ideal conditions. Factors that affect power output are sunlight hours, roof angle, panel direction, temperature, and shading.
You can determine a solar panel’s approximate output by performing a simple equation. Multiply the panel’s wattage by the average number of direct sunlight hours your home receives each day. If the 330-watt panel gets about four hours of sunlight exposure, this equation is:
330 watts x 4 hours = 1,320 watts OR approximately 1.3 kWh per day.
Let’s dive deeper into the above calculation to understand how solar output works.
The first step in understanding how much solar output you need is to assess your electricity usage. The easiest way to do this is to check your electric bill for your monthly kWh usage. Once you know this number, you can select a solar panel system that meets your needs.
As of 2020, the average U.S. household uses around 30 kWh of electricity daily, so you’d need a solar panel system of about 23 panels to cover your electricity consumption needs. Let’s assume you’d like solar to cover a good chunk of your energy usage, so you invest in 20 300-watt panels.
Next, determine the number of direct sunlight hours your home receives daily, which should range from about three to six hours. If you need help calculating this number, consult the Unbound Solar hours map for your area’s average daily sun exposure. For this example, we’ll calculate outputs for a home in Stillwater, Oklahoma, which receives around five peak sunlight hours per day.
300 watts x 5 hours = 1,500 watts OR approximately 1.5 kWh per day.
1.5 kWh x 20 solar panels = 30 kWh per day.
The following sections will explain different factors affecting a solar panel’s productivity and efficiency. Considering these factors before an installation is an excellent way to improve electricity outputs.
A solar panel’s conversion efficiency is the percentage of received light it can convert into usable electricity. High conversion efficiency is crucial to a solar panel’s cost-effectiveness and functionality as an energy source. Most residential solar panels have 15% to 20% efficiency, though some newer models exceed 22%.
Factors that affect conversion efficiency are:
Residential-grade solar panels are typically 65-inches-long by 39-inches-wide with 60 solar cells. Another common option for homeowners is a 72-cell panel.
Solar cells are the power generators of the PV panel, so having more of them will likely increase the system’s electricity output. Sixty-cell panels are often rated for around 300-watt outputs, while 72-cell panels are closer to 400. However, efficiency is still a primary player in power production. In most cases, a highly efficient 60-cell panel is a better choice than a 72-cell panel with a lower efficiency rate.
As we noted before, the number of sunlight hours a panel gets largely affects its output. Panels transform light, not heat, into electricity, so locations with longer, brighter periods of sunlight have the best solar power outputs.
Shading is another factor that impacts solar panel outputs. Regardless of your location’s average sunlight hours, a panel shaded by tall trees or other buildings will receive less light. Solar panel ratings don’t account for shading, so you must assess this barrier for your specific home.
The direction your panels face and the angle at which they’re tilted affect how much light they capture. There isn’t one definitive answer for optimal tilt and orientation because these factors vary greatly by location.
According to the Rensselaer Polytechnic Institute, panels in the Northern Hemisphere should typically face south and have a tilt equal to the location’s latitude in degrees. Based on this example, a panel in Kansas City, Missouri, needs a 39° angle tilt for max efficiency. A panel in Orlando, Florida, would need a 29° tilt.
Types of Solar Panels
This video from MECH Tech explains how each panel type is made:
Now that you understand how to calculate a solar panel’s energy outputs, you can select the type and number of panels your home needs. Remember to have a professional install your solar panels, no matter what model you choose. Proper installation can significantly affect how well they perform. With optimal efficiency and an army of panels atop your roof, you’ll be on your way to sunlight-fueled savings and self-sufficiency.
Yes, you can store energy from your panels in solar batteries. Solar battery energy storage systems collect excess energy from solar panel systems for later use. These devices allow homeowners to avoid turning to the electrical grid for power when their panels aren’t collecting light – i.e., at night, during power outages, etc.
You’d need approximately 22 300-watt solar panels to produce 1,000 kWh per month.
300 watts x 5 hours = 1.5 kWh per day.
1.5 kWh x 22 solar panels = 33 kwh per day.
33 kWh x 30 days = 990 kWh per month.
Based on our energy output estimates for a location with five sunlight hours, a 500-watt solar panel would produce approximately 2.5 kWh.
500 watts x 5 hours = 2,500 watts OR approximately 2.5 kWh per day.
Here are some tips and tricks to help improve solar efficiency wherever you live:
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