Image source: Chris Meehan
The efficiency of the solar panels made for rooftop solar have dramatically increased in efficiency over the past decade. Meaning your rooftop can generate more power for your home than ever before.
Those power output increases are driven by increased production of solar panels and better manufacturing techniques as well as competition and research and development. All of these have also made solar less expensive than ever before.
The efficiency of a solar panel is measured through a simple equation, the amount of electricity a solar panel can produce in watts divided by the amount of solar energy it absorbs from the sun. The standard testing conditions for solar panels evaluate how much electricity the panel can produce at a temperature of 25°C (77°F) with 1,000 watts of light per square meter hitting the device. That's equivalent to a sunny day with a solar panel tilted at 37° to the sun.
The most efficient solar cells made today are more than 40 percent efficient at converting the sun into electricity, but those aren't the solar cells or solar panels that you're likely to have on your rooftop. They're incredibly expensive since they use exotic materials and usually end up powering satellites that need to maximize energy production in the smallest spaces. The most efficient solar panels suitable for rooftops aren't too far behind, however. They're now more than 20 percent efficient at converting sunlight into electricity.
What types of solar panels can I get?
Image source: WikiMedia
The solar modules made for most roofs are made from crystalline silicon. The most efficient of these, as of March 2018, are made of monocrystalline silicon while polycrystalline cells are close. Monocrystalline solar panels also produce higher amounts of power for longer periods. Hence SunPower is able to offer a 25-year warranty on the output of its solar panels. While monocrystalline silicon is more efficient, it's also more expensive to produce, so polycrystalline silicon-based solar panels often cost less.
Over recent years a handful of solar companies have vied for the top spot for the most efficient solar panels for rooftops-SunPower, Panasonic and LG. Their commercially available solar panels flirt with converting slightly more than 20 percent of the sun's light into electricity.
SunPower's SPR-X21-345 claimed the current record (March 2018) with panels rated at an average efficiency of 21.5 percent and its panels have reached efficiencies of 22.8 percent in production. Currently, LG's High NeON R Module boasts an efficiency of 21.1 percent and Panasonic's leading module is the N330 Photovoltaic Module HIT, which has an efficiency rating of 19.7 percent. These companies have slews of solar panels that are among the highest efficiency models.
What's the average efficiency of a solar panel?
While these companies are pushing the upper limits of rooftop solar panels the majority of solar panels are 15 percent to 18 percent efficient at converting sunlight into electricity. Some of these are made of the more expensive monocrystalline silicon while others are made of the more affordable polycrystalline silicon.
There's really no problem with that either. The efficiency rating of a solar panel is not the only reason to choose the solar panels for your home PV system. As important, if not more important, are the watt ratings a solar panel has. This is how much power a PV panel can output. The LG High NeON R Module, can produce 365 watts, while the Panasonic N330 Photovoltaic Module HIT produces 330 watts. The SunPower SPR-X21-345 produces 345 watts. By that metric the LG panel could produce the most power per panel. But the ultimate advantage of having the most efficient solar panel is that they need less space to produce as much power.
Image source: Chris Meehan
A 5 kilowatt solar rooftop system using SunPower's most efficient panels would need 15 of SunPower's 41 inch by 61 inch panels. That would take up about 261 square feet of roof space.
The LG panels are a little larger at 40 inch by 67 inches, 15 of them would take up 279 square feet of the rooftop, but you'd only need 14 of those panels to produce 5 kilowatts, which would take up 260 square feet of a roof's space.
It would take 18 of Jinko Solar's 16.8 percent efficient Eagle MX (JK07B) solar panels with a 275 watt rating to produce 5 kilowatts of electricity. Those 65 inch by 39 inch panels would take up 320 square feet of rooftop space to produce 5 kilowatts of electricity. That's about 60 more square feet of roof space needed. Also, while the Jinko panels may cost less per panel, you need more of them to produce the equivalent amount of power output.
The Jinko panels are typically less expensive to purchase than the SunPower modules. So in cases where there's plenty of rooftop space ideal for solar power, a solar installer may recommend a solar panel that's less efficient but has a lower cost per watt. In the case where only a small amount of a rooftop is ideal for solar power a solar installer my recommend a solar panel like those from Panasonic, LG or SunPower. Learn more about how many solar panels you'd need by clicking here.
Based on the most popular brands of solar panels installed on US homes here are the most efficient panels that each of SolarReviews.com 's most popular solar panel manufacturers offer in 2018 based on their spec sheets:
Top 15 Popular Solar Panel Manufacturers in 2018 Ranked by Efficiency
|Sunpower X Series||SPR-X21-345||21.5%|
|LG Solar||High NeON R Module||21.1%|
|Panasonic HIT panels||N330 HIT||19.7%|
|Sunpreme||GxB 380 SM Bifacial Smart Module||19.5%|
|Trina Solar||Tallmax M Plus||19.3%|
|Itek Energy||Itek SE 60-Cell Module||18.8%|
|Mitsubishi Electric||D6M 360 E4A||18.6%|
|Phono Solar Technology||PS300M-20/U||18.4%|
|Canadian Solar||CS 6K-300MS||18.3%|
|SolarWorld Americas||Sunmodule SWA 340 - 350 XL MONO||17.5%|
*Kyocera spec sheets do not have efficiency numbers but they claim cell efficiencies over 16%. Panel efficiency is lower than individual cell efficiency.