Equipment and components
Bifacial panel
Also known as: bifacial module, double-sided panel.
Definition
A bifacial panel captures light on both faces: the front directly from the sun and the rear from light reflected by the surface below. It can increase generation when installed over light-coloured surfaces or on elevated structures.
A bifacial panel's gain depends entirely on the mounting. What the rear face makes use of is albedo: the fraction of light bouncing off the surface below. Over a white roof, light gravel or a concrete slab, that bounce is significant; over dark tiles, or if the panel sits flush against the roof with no separation, the rear face barely receives any light and the advantage is lost.
That is why bifacial fits better on ground-mounted installations, flat roofs with elevated structures, pergolas, car park canopies or agrivoltaic structures, where there is free space behind the module and a reflective surface below. On a standard pitched residential roof, paying the premium is rarely justified.
Its datasheet declares a front capacity and a bifaciality factor, indicating what proportion of that capacity the rear face can contribute. The real gain you will see depends on the albedo, the mounting height and the spacing between rows, so it is worth being wary of optimistic estimates that do not explain those assumptions.
The essentials of Bifacial panel
- The gain depends on the albedo of the surface below and on mounting height.
- Favourable scenarios: elevated flat roof, ground, pergolas and canopies.
- Unfavourable scenario: a dark pitched roof with the panel flush against it.
- The bifaciality factor indicates the maximum contribution of the rear face.
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Frequently asked questions about Bifacial panel
How much extra energy does a bifacial panel produce?
It varies a great deal with the mounting: it can range from a negligible gain, when the rear face receives no reflected light, to an appreciable contribution over very light surfaces with the panel well elevated. Any figure promised without describing the albedo and the mounting height is unreliable.
Is a bifacial panel worth it on a house roof?
Normally it does not pay off. On a pitched roof the module sits a few centimetres above the tiles and the rear face receives very little reflected light, so a premium is paid for a minimal gain. It makes far more sense on flat roofs with elevated structures or on ground mounting.
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