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What is Solar Panel Efficiency?

Solar panel efficiency ratings measure the amount of sunlight captured by a solar panel. If a panel is rated at 20% efficiency, that means that 20% of the sunlight that hits the face of the panel will be converted into usable power.

In this article, we’ll explain what factors impact panel efficiency and highlight some of the most efficient solar panels on the market, as well as how to increase solar panel efficiency.

Why Solar Panel Efficiency Matters

Solar panels come in two standard sizes:

  • 60-cell panels: (39″ x 65″)
  • 72-cell panels: (39″ x 77″)

There are other sizes available, but the majority of residential and commercial solar projects use either 60-cell or 72-cell panels.

As panel technology advances and solar cell efficiency improves, manufacturers are able to produce higher-wattage panels in the same form factor. Panels typically increase in output by 5-10 watts per year thanks to efficiency improvements, even though the physical size of the panel never changes.

Like any other technology, though, you’ll pay a premium for the latest and greatest products to hit the market. The most efficient solar panels also tend to be the most expensive on a cost-per-watt basis, so these may not always be the best solar panels for you.

Investing in high-efficiency solar panels isn’t about getting more production from your system. Instead, high-efficiency panels allow you to fit more solar in a smaller space. So this is something you will want to consider if you’re asking yourself “how many solar panels do I need?

If you have a small roof, or live in an urban area with limited yard space, high-efficiency panels are appealing because they can make the most of the limited space available to you.

But if space isn’t a concern, there is absolutely nothing wrong with using lower-efficiency panels. Your array will be larger, but you won’t sacrifice performance, and you’ll save money by buying panels that output more power per dollar spent.

Solar Panel Efficiency Rankings

At the time of publication, most solar panels on the market have efficiency ratings that fall between 15-23%. This table compares some of the efficiency ratings of solar panel manufacturers we offer.

ManufacturerMax Efficiency Rating
Canadian Solar19.3%
Mission Solar18.7%

How to Maximize Solar Panel Efficiency

Aside from the panel’s efficiency rating, there are several other factors that influence how efficient your system is as a whole. Here are some things to consider:


Shade on solar panels prevents them from absorbing sunlight, which reduces your system’s production. If possible, build your solar array in a location that will receive full sunlight year-round.

If buildings, trees or other obstructions make that impossible, consider buying a system with either power optimizers or micro-inverters. These types of inverters include technology that minimizes the impact of shade on your system’s output. Read our article comparing different types of inverters to learn more.

Panel Facing

To get the most out of your panels, it is ideal to face them toward the Equator, so they are exposed to direct sunlight during the day. In America (where we’re located), that means you want to face your panels South.

If you don’t have a South-facing roof, East and West will also work, though you’ll need to add a few more panels to achieve the same output. East- and West-facing systems aren’t quite as efficient, but will still save you money on your energy bills in the long run.

The tilt angle of your panels is also important. The easiest option is to tilt your panels at an angle equal to your latitude. For example, if you live in San Diego (latitude 32.7157° N), we’d recommend setting them at around 33°.

Most people just set it at one angle and leave it there, but if you’re the hands-on type, you might enjoy adjusting them a few times per year to optimize their output. Learn more with our guide to optimizing your solar panel angle.

Degradation Rate Over Time

All solar panels degrade slightly over time, losing about 0.5% to 1% of their rated output each year. Newer technology tends to degrade at a slower pace, meaning your panel will stay more efficient over its lifespan (typically 25 years under current warranties).

Panel degradation rate can be found in the manufacturer’s warranty. For example, Heliene’s warranty (PDF) projects a 0.7% degradation rate per year, guaranteeing the panel will remain at least 80% efficient at the end of its 25-year lifecycle.

If you are comparing two panels with the same efficiency rating, the one with the lower degradation rate will be more efficient and produce more power over the life of the system.


If dust, snow or other debris builds up on your panels, they’ll become less efficient. We recommend wiping down the face of your solar panels once or twice per year to keep them clean.

If you live in a snowy climate, you’ll need to clear off any snow that builds up on the face of your panels. It’s worth noting that snow may melt or slide off on its own due to the natural tilt angle of the panels. If it piles up, though, you’ll need to clear it off to keep your panels exposed to sunlight.

When cleaning your panels, use a cloth or soft brush. Hard-bristled brushes could scratch the glass face of the panels.

In Conclusion

If you have limited space to build your system, high-efficiency solar panels can help you squeeze as much production as possible out of your system.

If space isn’t a concern, though, panels with lower efficiency ratings offer a better value without sacrificing quality.

Ready to start your solar project? Browse complete solar power systems or request a free customized quote from our in-house design team.