Bifacial solar modules, which have efficiencies greater than 20%, are making a comeback. Generally, these modules surround monocrystalline n-type cells with a layer of amorphous silicon (a-Si) and harvest energy on both the back and front of the module.
Panasonic offers its HIT Double module with efficiency rated at 20.8%; Prism Solar and Sunpreme bifacial solar modules have 20.5% and up to 22.9% efficiencies, respectively. Bifacial efficiencies assume energy contribution from the back of the module. To achieve top efficiency, bifacial modules need to be mounted so that the back is not blocked (such as in a shade structure with “perimeter-framed” mount).
Greater module efficiency means generating more electricity in a smaller footprint. With fewer rack materials and a shorter installation time, this can mean lower installation cost per watt. For example, an 8 kW system using modules with 16% efficiency would require about 535 square feet. That same size system using modules with 21% efficiency would only take up 410 square feet. However, because higher efficiency modules are more expensive per watt, higher efficiency doesn’t always mean less-expensive PV generated electricity.