Do Bifacial Panels Add Much on a Tiled Roof?

If your panels sit close to a tiled roof, I would not pay a sizeable premium on the promise of extra generation from the back. A bifacial panel can be a good choice, but its rear face needs usable light.

An open carport creates a different opportunity. With clear space beneath the panels, the rear can receive light that a tightly covered roof makes harder to reach. The design matters more than the bifacial label.

For a home solar system, I would compare the roof layout and expected annual energy first. Then I would ask whether the rear-side contribution has been estimated for that particular installation.

What the second face actually does

A bifacial module can convert light reaching its front and rear into electricity. That does not mean twice the output, and it does not mean that light passes straight through the roof to reach the cells.

Rear light can include light reflected from the surroundings and diffuse light from the sky. How much arrives depends on what the back of the panel can see, including surfaces, gaps and obstructions.

SAM’s modelling guidance identifies reflectivity, row spacing and clearance as key inputs for rear-side light.

Reflectivity is often called albedo. It describes how much incoming light a surface reflects. A bright, exposed surface offers a different starting point from a darker surface that the array itself shades.

My practical question is simple: where will the useful rear light come from? If the answer is only a percentage copied from a brochure, the proposal needs a better explanation.

Why a tiled roof limits the opportunity

On a close-mounted array, much of the rear faces the roof and mounting structure. Panels also shade the surface below them. That makes it harder to assume a large rear contribution, particularly within a tightly packed array.

The tile colour alone cannot answer the question. The designer needs to consider clearance, gaps, nearby obstructions and the area underneath that actually receives light.

NREL field research found rear illumination varied with array position and roofing reflectivity. Those test conditions are not a performance promise for a Melbourne home.

I would start with a conservative energy estimate for this roof. A small rear contribution might still be useful, but I would want the system to make sense without relying on a generous bonus.

An open carport deserves a separate calculation

A carport with panels forming the canopy can leave the rear more exposed. A conventional carport with solid roofing immediately beneath its panels is a different arrangement, even though both are called carports.

For the open design, I would ask about the ground surface and shade from beams, adjacent buildings and parked vehicles. The useful view from the rear changes when a car occupies the space.

I would also compare the total project, including the structure and weatherproofing. A solar module and its electrical warranty do not, by themselves, specify a complete waterproof roof.

This is a stronger candidate for detailed bifacial modelling. It is not an automatic reason to buy a particular panel or build a more expensive carport just to increase reflected light.

Match the claim to the exact module

Trina’s Australian datasheet identifies TSM-NEG9RC.27 as a bifacial dual-glass module.

That is a specific model family. A brand name, black appearance or dual-glass description on its own is not enough to establish which rear-side performance assumptions belong in your quote.

The datasheet also separates front-side ratings from examples that include backside gain. Those examples describe specified assumptions, not the annual increase every household will receive.

When comparing Trina panels, I would have the proposed model and roof design considered together. The same discipline applies to a quote for Jinko panels.

Compare useful energy, not a headline uplift

Bifaciality and bifacial gain are different. Bifaciality describes the rear’s response relative to the front under comparable illumination. Gain describes the extra output achieved in an actual arrangement.

A strong rear response is not much use if little light reaches it. Nor is extra annual generation automatically equal to extra bill savings: the value also depends on when you use or export that electricity.

I would request the same layout modelled with and without the assumed rear contribution. Keep the weather, shading and other inputs consistent so the comparison isolates the benefit being sold.

Then compare any additional installed cost against that difference. I would not replace serviceable panels solely to obtain a rear-side feature without a convincing whole-system case.

My recommendation for a Melbourne roof

The Australian Government’s design guide puts roof orientation, slope and shading into the system design. I would resolve those basics before rear-side gains.

For a standard tiled roof, choose a well-matched panel and a sound installation. If a bifacial option is competitive on the complete quote, there is no need to reject it simply because the rear contribution may be modest.

For an open carport or another design with genuine rear exposure, investigate the extra yield properly. Different mounting conditions deserve different assumptions, not the same advertised uplift.

Bring your roof details and a recent bill to Lightning Energy. We can work through the proposed panel model, layout and generation assumptions, including whether bifacial performance deserves any extra budget.