Table of Contents
What Are First Solar Panels, Exactly?
First Solar panels use cadmium telluride, or CdTe, as the light-absorbing semiconductor. Instead of slicing silicon into wafers, First Solar deposits a thin CdTe layer directly onto glass, which is why the panels are called thin-film rather than crystalline. The company is the largest solar manufacturer headquartered in the United States, with production concentrated in Ohio and expanding capacity in Alabama and Louisiana.
Two product lines matter for installers right now: Series 6 Plus, sold globally and framed like a conventional module, and Series 7 TR1, a larger, frameless panel built specifically for US utility-scale projects and Buy America-compliant procurement. Both share the same underlying CdTe technology. What changes between them is form factor, mounting hardware, and target market — details that affect your design far more than the wattage bump does.
Series 6 vs. Series 7: How the Specs Compare
Here’s a side-by-side on the numbers you’ll actually need for a design or a bid:
| Spec | Series 6 Plus Bifacial | Series 7 TR1 | Why it matters |
| Power output | 455–480 W | 525–550 W | Fewer modules needed for the same array size |
| Module efficiency | 18.1–19.0% | 18.8–19.7% | Slightly less roof or ground area per watt |
| Degradation rate | 0.3%/year (warranted) | 0.3%/year (warranted) | Predictable long-term yield modeling |
| Product warranty | 10–12 years | 12 years | Standard workmanship coverage window |
| Performance warranty | 30 years, ~90% output | 30 years, ~90% output | Longer than most crystalline silicon panels |
| Frame / mounting | Anodized aluminum frame | Frameless, back rail system | Different clamping hardware and labor flow |
| Primary market | Global utility-scale | US utility-scale (Made in USA) | Domestic content eligibility for US projects |
Series 7’s jump to 525–550 W looks like the headline, but the mounting change is the bigger deal for your crew. Series 6 still uses a conventional aluminum frame that most installers already know how to handle. Series 7 doesn’t — more on that below.
Where First Solar Panels Make Sense (and Where They Don’t)
First Solar built these products for utility-scale ground-mount arrays, and that’s where they perform best economically. Large source-circuit counts, long project timelines, and dedicated EPC crews absorb the design complexity that CdTe introduces.
Residential rooftop is a different story. Cadmium content restricts these panels from most residential and occupied-building applications under many local building and fire codes, and First Solar doesn’t market Series 6 or Series 7 as residential products. If a homeowner asks you to spec First Solar panels for their roof, that request usually reflects brand recognition rather than product fit — steer the conversation toward crystalline silicon instead. Commercial and industrial rooftop use exists but is generally limited to metal-roof projects north of 1 MW, and even then you’re working with specialized distributors, not a standard supply house.
Electrical Design Differences: What Changes When You Switch to CdTe
This is where most first-time First Solar designs go wrong. CdTe cells run at higher voltage and lower current per cell than crystalline silicon, which flips your string math. A crystalline silicon design might string 20 to 33 modules per source circuit before hitting the 1,500 Vdc ceiling on a ground mount. A CdTe string typically maxes out around six modules.
Six times more source circuits means six times more conductors, connections, and fuses feeding your combiner box — and that’s before you account for temperature derating. Wire harnesses stop being optional convenience and become a practical necessity for managing that many strings cleanly. If your electrical plan set was copied from a crystalline silicon template, check the string sizing table line by line before you submit it.
Mounting and Grounding: Frameless Panel Considerations
Series 7 TR1 is frameless, glass-on-glass construction with a back rail mounting system — not the rail-and-clamp setup your crew uses on framed modules. Standard mid clamps and end clamps designed for a module frame groove won’t work here. You need mounting hardware that’s specifically compatible with First Solar’s back rail system, and that compatibility should be verified against the manufacturer’s current installation guide before hardware gets ordered, not after it shows up on site.
Grounding follows the same logic. A frameless module has no metal frame to bond, so your equipment grounding path runs through the mounting structure and rail system rather than through frame-to-frame jumpers. NEC Article 690 still applies in full — every metal component in the array needs a low-resistance path to ground — but the physical bonding points are different from what a crew used to framed silicon panels will expect by default.
Permitting Considerations for First Solar Projects
Plan reviewers see far more crystalline silicon submittals than CdTe ones, and that unfamiliarity shows up as extra scrutiny or comment cycles on First Solar plan sets. Three things reduce that friction: reference the specific UL 61730 listing and the current First Solar user guide by document number, show string sizing math explicitly rather than as a summary line, and include manufacturer-specific mounting details rather than a generic rail drawing.
This is exactly the kind of detail a permit design team that works across module types every day catches before submission rather than after a rejection letter. At One Place Solar, plan sets for CdTe and thin-film projects get the same PE-stamped, jurisdiction-specific treatment as crystalline silicon designs — string sizing, grounding details, and equipment-specific mounting drawings included, so the AHJ isn’t guessing at how an unfamiliar module fits into a familiar code.
Warranty, Degradation, and Long-Term Performance
First Solar backs both series with a 0.3% annual degradation rate under warranty — among the lowest in the industry — and a 30-year performance warranty guaranteeing roughly 90% of rated output at year 30. Product warranties run 10 to 12 years. For asset owners modeling 25- to 30-year project economics, that low degradation rate translates directly into more lifetime energy per installed watt, which is a real selling point once you get past the sticker price conversation.
First Solar also runs an established take-back and recycling program for CdTe modules, which matters increasingly for projects with sustainability requirements or end-of-life disposal clauses in their power purchase agreements.
Common Mistakes Installers Make with First Solar Panels
- Reusing a crystalline silicon string-sizing table instead of recalculating for CdTe’s voltage profile
- Ordering standard frame clamps for frameless Series 7 modules and finding out on site that they don’t fit
- Undersizing the combiner box for the higher source-circuit count CdTe strings require
- Submitting generic mounting drawings instead of manufacturer-specific back rail details
- Quoting First Solar panels for a residential roof without checking local code restrictions on cadmium-based modules first
Frequently Asked Questions
Are First Solar panels good for residential installations?
Generally, no. First Solar builds Series 6 and Series 7 for utility-scale and select large commercial projects. Cadmium content restricts these panels from most residential and occupied-building applications under local building and fire codes, and First Solar doesn’t market either series for residential rooftop use.
What’s the difference between First Solar Series 6 and Series 7?
Series 6 Plus Bifacial is a framed module sold globally, producing 455–480 W. Series 7 TR1 is a larger, frameless module built specifically for the US utility-scale market, producing 525–550 W with a different back rail mounting system. Both use the same CdTe technology and carry the same 0.3% annual degradation warranty.
Do First Solar panels need special grounding?
Frameless Series 7 modules have no aluminum frame to bond, so equipment grounding runs through the mounting rail and structure instead of frame-to-frame jumpers. NEC Article 690 grounding requirements still apply in full — only the physical bonding points change.
What’s the degradation rate on First Solar panels?
First Solar warranties a 0.3% annual degradation rate on both Series 6 and Series 7, backed by a 30-year performance warranty guaranteeing about 90% of rated output after three decades.
Can First Solar panels be recycled?
Yes. First Solar operates an established take-back and recycling program for its CdTe modules, which can matter for projects with end-of-life disposal requirements in their power purchase agreements.
Where are First Solar panels manufactured?
First Solar is a US-headquartered manufacturer with Series 7 TR1 production based in Lake Township, Ohio, and additional capacity expanding into Alabama and Louisiana as part of a broader push toward domestic-content-eligible supply for US utility-scale projects.
The Bottom Line
First Solar panels aren’t a drop-in replacement for crystalline silicon on your next design — they’re a different product with different string math, different mounting hardware, and different permitting expectations. Get those three things right up front, and CdTe’s low degradation rate and strong warranty become a genuine advantage rather than a source of change orders.