Solar Panel Production, Efficiency & How to Compare Systems

When shopping for a new car, it’s second nature to compare features like fuel economy, horsepower, price, and so on. But when it comes to buying a home solar power system, consumers often feel confused about how to compare options.

Many solar power system installers recognize this confusion, and take advantage of it by marketing big benefits that don’t really add up when you look more closely.

When shopping for solar power systems, there are two key variables to consider when comparing options: production and efficiency.

Production is simply the amount of electricity produced by a module or system.

Both individual solar modules (or “panels”) and entire systems have an estimated power rating (Pnom)—the amount of electricity that can be produced. Although this figure can’t be replicated in the real world, Pnom represents the absolute maximum potential power production for a given module or system. And those ratings are a handy means of making comparisons and identifying potential shortcomings.

For instance, let’s say you’re entertaining two bids for solar power systems, both of which have a total Pnom of about 4.8 kilowatts, or 4,800 watts.

Bid #1: This system uses 13 of the new SunPower X22-370-D-AC modules, which have a Pnom of 370 watts.

Bid #2: This system is cheaper, which makes it attractive, as it also produces about 4,800 watts. Same amount of power, but less expensive. However, when digging into the specs, you see that it uses Canadian Solar CS6K-300MS panels with a nominal power of 300 watts. The fact that it uses modules with a lower output is an immediate tipoff that it has to use more modules to produce the same amount of power. A look at the bid shows that yes, the Canadian Solar system uses 16 panels, versus 13 for the SunPower system.

The issue: While the two systems in this example produce the same amount of power, the lower nominal power of the Canadian Solar modules means that more modules must be used to compensate. This in turn means that the cheaper system will take up more of the roof—using 23% more panels means it will take up 23% more space. The SunPower system only needs about 80% of the roof space to produce the same amount of power as the Canadian Solar system—a factor very important for homeowners who wish to preserve the appearance of their home.

The Takeaway:

• Production = Maximum amount of electricity produced by a solar module or system
• Lower production = More roof space needed to produce the same amount of electricity
• Higher production = Less roof space needed

Efficiency measures how much solar energy is converted to electrical energy.

Solar panel efficiency is simply a measurement of how much solar energy, when absorbed by a module, is converted to usable electricity. If, on a sunny day, 1,000 watt-hours of solar energy is collected by a 20% panel every hour, the panel will produce 200 watt-hours per hour. On a cloudy day where the panel only receives 500 watt-hours of sunlight per hour, it will produce 100 watt-hours per hour.

A few years ago, high-end panels had an efficiency of about 12% to 15%. Nowadays, many panels are in the 18% to 19% range, with some, like SunPower’s X-series panels, breaking 22%.

The efficiency of the panels used has a direct impact on how much space your system will need.

Example: You’re comparing two systems. One uses panels with an efficiency of 20%, and the other an efficiency of 15%. Straightaway, this tells you that the 15% system is going to have to be a lot larger to equal the production of the 20% system.

In fact, it’s pretty easy to figure out just how much larger—just take the larger efficiency and divide it by the smaller. In the case, 20 divided by 15 is 1.33, which means that a system using 15% efficiency panels will need to be 1.33 times (or 33%) larger than a 20% efficiency system to produce as much electricity. (That’s because a 15% panel produces 25% less electricity than a 20% panel.)

The Takeaway:

• Efficiency = The percentage of solar energy converted to electrical energy by a solar panel
• Higher efficiency = Less surface area needed to produce the same amount of electricity
• Lower efficiency = More surface area needed

While it’s tempting to only consider the total power production of a system, the production and efficiency of the system has a significant impact on your quality of life.

For most homeowners, a home solar electricity system is an investment. This investment may be motivated by financial concerns about climbing electricity bills, or out of a desire to improve the state of the planet by reducing reliance on fossil fuels. But quality of life is also an important consideration for many homeowners.

Most homeowners are much happier with their systems when their aesthetic impact is minimized. Not only do larger solar power systems block more of the roof from view, but they also require more holes to be punched through the roof during the installation process. For those who love the look of their home, it’s critical to seek out systems that use higher efficiency, higher production modules.

In addition, using less roof space provides greater opportunity for expanding your system in the future. For instance, if you purchase an electric vehicle in the future, you will have the room to expand your system and charge the car. Going the cheaper route by installing a system that uses more modules limits the potential for future expansion.

To learn more about what to consider when choosing the residential solar power system that is right for your home, contact Capital City Solar today by calling (916) 782-3333, or emailing us at [email protected].