Solar panel efficiency is simple, but there a few things you need to understand.
There are 3 main types of solar efficiency.
1. Module Efficiency
2. Area Efficiency (Density)
3. Cell Efficiency
1. Module efficiency measures how well a solar module (aka panel) converts the Sun’s energy into usable energy. If the Sun dumps 100 Watts of energy onto the module and the module spits out 15 Watts, the the module is said to have 15% module efficiency (15 W / 100 W = 0.15 = 15%). If you want to brag to your friends that you have a top tier efficiency panel, care about this.
2. Area efficiency (aka Density) measures how much usable energy a module produces in a given area. It’s Watts per square foot, so the more Watts, the more energy you’ll get from a specific area (or available space on your roof). So if a module spits out 210 Watts in 15 square feet, it’s density is… c’mon, it’s Watts per square feet (and I made it an easy number). Okay, it’s 14 W/sqft (= 210 W / 15 sqft). If you have limited roof space, get the panel with the highest density.
3. Cell efficiency is measured the same way as module efficiency, but only with a single cell. This is the number news media and blogs love to tout in their headlines as ‘record breaking’ and ‘highest efficiency achieved’. This number is generally not useful for the average consumer. If you work in a solar cell lab, don’t give up on increasing this number.
So that’s the basics of solar efficiency. Now, let’s make it even simpler by dividing solar panels into 5 Efficiency Tiers (or levels).