Solar Permit Package & the 3 Types of Residential Solar Panels Explained

Monocrystalline panels are made from a single, continuous silicon crystal grown through the Czochralski process — where a silicon “seed” is drawn through a vat of molten pure silicon to form one large ingot. That ingot is then sliced into the thin wafers that become solar cells.

The result of that single-crystal structure is a highly uniform lattice that allows electrons to flow with minimal resistance — giving these panels their industry-leading efficiency of 20–22%. Their uniform dark black appearance and rounded cell corners are the easiest way to identify them.

Monocrystalline panels degrade at just 0.3–0.5% per year, meaning a panel rated for 400W today will still produce around 85% of its rated output three decades from now. Most manufacturers back this with 25-year performance warranties. From a solar permit package perspective, fewer high-watt panels means a leaner plan set — typically fewer pages of structural calculations and a simpler roof layout drawing.

Polycrystalline (or “multicrystalline”) panels are made by melting multiple silicon fragments together and casting them into square moulds. The cooling process allows multiple crystals to form simultaneously — which is why these panels have their characteristic blue, speckled appearance with visible grain boundaries.

The manufacturing process is simpler and produces less silicon waste, making polycrystalline panels more affordable. Efficiency typically falls in the 15–17% range, with newer manufacturing advances pushing some panels above 20%. Power output generally sits between 240W and 300W per panel.

While slightly less efficient than mono panels, polycrystalline options remain a solid, reliable technology with a long track record. Residential installations with generous south-facing roof space can achieve excellent results. However, because more panels are required for the same output, your permit plan set will include a larger module layout drawing, additional string calculations, and potentially more structural anchor points — all of which add pages and increase the chance of AHJ revision requests if not prepared carefully.

Thin-film panels are made by depositing an ultra-thin layer of photovoltaic material onto a substrate such as glass, metal, or plastic. The most common photovoltaic materials used are cadmium telluride (CdTe), copper indium gallium selenide (CIGS), and amorphous silicon (a-Si). Each variation produces a different “type” of thin-film panel, but all share the thin, lightweight, and often flexible form factor.

Thin-film panels have historically had the lowest efficiency of the three types — commercially available products typically fall in the 10–13% range, though lab prototypes have achieved over 23%. Their shorter lifespan of 10–20 years and larger installation footprint make them a poor fit for most residential rooftops.

One area where thin-film genuinely excels: temperature coefficient. At around −0.2%/°C, thin-film panels lose less power in high heat than silicon-based panels (which typically run −0.3 to −0.5%/°C). This makes them theoretically better in very hot climates — though the efficiency gap typically outweighs this advantage at the system level. From a permitting standpoint, thin-film installations on non-standard surfaces (curved roofs, metal standing seam) require custom structural engineering and specialized racking documentation that many AHJs are less familiar with — which can slow approval timelines significantly.