- Mono panels convert 19–23% of sunlight; poly sits at 15–17%.
- Poly costs roughly $0.20–$0.35 less per watt installed.
- On a small or shaded roof, mono almost always wins on lifetime value.
Both panel types are made from silicon, and both will still be producing power in twenty-five years. The difference is how the silicon is formed. Monocrystalline cells are cut from a single grown crystal, so electrons move through them with less resistance. Polycrystalline cells are cast from melted fragments, which is cheaper to manufacture and slightly less efficient.
Efficiency: what the numbers actually mean
Efficiency describes how much of the sunlight hitting a panel becomes electricity. A 400 W mono panel and a 400 W poly panel produce the same power — the mono one is just physically smaller. That only matters when roof space is tight, which is the case for most suburban homes with dormers, vents and north-facing planes.
When polycrystalline is the smarter buy
If you have a large, unshaded south-facing roof and a fixed budget, poly lets you install more watts for the same money. Ground-mount arrays follow the same logic — space is effectively free, so cost per watt is the only figure that matters.
“On a roof with room to spare, the cheaper panel usually produces more electricity per dollar spent. Efficiency only pays for itself when square footage is scarce.”
The market has moved sharply toward mono since 2020, so poly availability is thinner than it was. Ask your installer what they can actually source before you build a plan around it.
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