Are Bifacial Solar Panels For Residential Rooftops Worth It?

More solar panel manufacturers are cranking out bifacial modules these days and the price gap is closing. But are they worth installing on your home’s rooftop?

What Is A Bifacial Solar Panel?

In conventional solar panels, sunlight hitting the front of the panel is converted to electricity and the back of the panel has an opaque backsheet. But in a bifacial module, light can also be harvested from the back of the panel. These modules are glass/glass – meaning they have a glass sheet on the front side and on the back.

The boost in output can be significant in optimum conditions. Hold that thought.

Bifacial Panels On Residential Rooftops

In the majority of residential installations, conditions for a bifaciality boost are anything but optimum. Panels are usually installed flush with the roof, around 10 – 15 centimetres above it. In those circumstances even a light coloured roof won’t provide much reflection – and a dark roof even less. Bifacial solar panels can also be trickier to install if they are frameless; although many are available with standard frames.

In these scenarios, while installing bifacial panels will achieve little in terms of extra power output (perhaps a couple of percent at best), it won’t cause any harm either. Where there may be some benefit is if the panels are going on a flat roof with tilt frames, particularly if the roofing material has reflective attributes.

The Solar Reflectance Index (SRI) is a percentage that measures a material’s ability to reflect solar energy and release absorbed energy, with black being 0 and white being 100. Just looking at a couple of Colorbond colours (Classic finish) commonly used in roofing materials, Surfmist has an SRI of 81 and Monument has an SRI of 27 – a big difference.

Image credit: BlueScope Steel Limited

Really, these modules are best suited to utility-scale solar farms where they really come into their own, and some commercial applications. However, around the home they could be used for some carport and pergola projects where the panels are basically the roofing material.

Are There Any Advantages?

Bifacial solar panels can be more durable due to the two layers of glass offering increased protection. But you can also get monofacial dual glass panels – for example, in the Trina Vertex S+ range; which are very affordable. Bifacial modules also generally have a lower temperature coefficient, meaning they tend to perform better than equivalent monofacial panels in the heat – but that also depends on installation conditions.

So, Why Even Consider Bifacial?

Not only are more solar panel manufacturers making them, but some are only making bifacial modules. Winaico (which makes good gear) springs to mind – their current lineup are all bifacial. So, if there’s a brand you’re particularly fond of and that’s all they make; it’s not really a problem.

Note that most bifacial solar panels are rated by their front side capacity; e.g. a 440W panel means 440W capacity from the front side. Back-side production should be a separate figure and more of an estimate rather than hard and fast numbers. You might also come across the terms “bifaciality factor”, or coefficient, which is the measurement of how well a bifacial solar cell’s rear side can generate power compared to its front side. Usually, it’s in the region of 70% – 90%; but bear in mind that’s the potential and not the real world performance on your rooftop.

Related: Learn everything you need to know about choosing solar panels for your home.