REC TwinPeak 5 420W vs First Solar Series 6 Plus 465W
The REC TwinPeak 5 420W wins this comparison by a decisive margin. It leads in efficiency (21.4% vs 19.2%) and matches or exceeds on warranty (20 vs 10 years). For most residential installations, the REC TwinPeak 5 420W is the stronger choice.
Key Differences
- • REC TwinPeak 5 420W is rated at 420W while First Solar Series 6 Plus 465W is rated at 465W, a 45W difference.
- • REC TwinPeak 5 420W achieves 21.4% efficiency vs 19.2% for the other, a 2.2 percentage point gap.
- • REC TwinPeak 5 420W comes with a 20-year product warranty vs 10 years for the other.
- • First Solar Series 6 Plus 465W has a superior temperature coefficient of -0.28%/°C vs -0.32%/°C, retaining more power in hot climates.
- • REC TwinPeak 5 420W uses PERC Mono cells while First Solar Series 6 Plus 465W uses CdTe (Cadmium Telluride) cells, representing different technology generations.
Specifications Breakdown
Module Efficiency
The REC TwinPeak 5 420W achieves 21.4% module efficiency compared to First Solar Series 6 Plus 465W's 19.2%, meaning REC TwinPeak 5 420W converts 2.2 percentage points more sunlight into electricity per square meter. In practical terms, the REC TwinPeak 5 420W produces 215.1 watts per square meter of panel area while the First Solar Series 6 Plus 465W produces 187.9 W/m². For rooftop installations where space is limited, this efficiency gap determines how many kilowatts you can fit on your available roof area. Over a 25-year system life, even a small efficiency advantage compounds into meaningful additional energy production.
Power Output
The First Solar Series 6 Plus 465W delivers 465W per panel versus 420W for the REC TwinPeak 5 420W, a 45W difference per module. To build an 8 kW residential system, you would need 20 REC TwinPeak 5 420W panels or 18 First Solar Series 6 Plus 465W panels. Choosing the higher-wattage option saves 2 panels, reducing total racking hardware, wiring, and installation labor costs. Higher wattage per panel is particularly valuable for commercial-scale installations where panel count directly impacts balance-of-system costs.
Temperature Coefficient
The First Solar Series 6 Plus 465W has a temperature coefficient of -0.28%/°C versus -0.32%/°C for the REC TwinPeak 5 420W. On a hot summer day when cell temperature reaches 65°C (40°C above the 25°C STC baseline), the First Solar Series 6 Plus 465W retains 94.4% of its rated power while the other retains 93.6%. While the numerical gap is modest, it still accumulates over decades of summer production, especially in southern latitudes with prolonged peak heat hours.
Warranty Coverage
The REC TwinPeak 5 420W is backed by a 20-year product warranty and 25-year performance guarantee, while the First Solar Series 6 Plus 465W offers 10-year product and 30-year performance coverage. The REC TwinPeak 5 420W provides 10 additional years of defect protection, covering manufacturing issues, material failures, and premature performance loss. Based on their published degradation rates (1% first year then 0.4%/year for REC TwinPeak 5 420W; 1.5% first year then 0.5%/year for First Solar Series 6 Plus 465W), after 25 years the REC TwinPeak 5 420W should retain approximately 89.4% of original output versus 86.5% for the First Solar Series 6 Plus 465W. This 2.9 percentage point gap in end-of-life output meaningfully impacts lifetime energy economics.
Physical Dimensions & Weight
The REC TwinPeak 5 420W measures 1722×1134×30mm and weighs 21 kg, while the First Solar Series 6 Plus 465W measures 2009×1232×49mm at 34.5 kg. 1.95 m² of panel area for the REC TwinPeak 5 420W versus 2.48 m² for the First Solar Series 6 Plus 465W. The REC TwinPeak 5 420W is 13.5 kg lighter per panel, which reduces structural load requirements on the roof and makes handling easier during installation. For a 20-panel system, that is a total weight difference of 270 kg. The more compact REC TwinPeak 5 420W may be easier to fit on irregularly shaped or space-limited rooftops.
Specification Comparison
| Specification | REC TwinPeak 5 420W | First Solar Series 6 Plus 465W |
|---|---|---|
| Power | 420W | 465W |
| Efficiency | 21.4% | 19.2% |
| Power Density | 20.0 W/sq ft | 17.5 W/sq ft |
| Cell Type | PERC Mono | CdTe (Cadmium Telluride) |
| Bifacial | No | No |
| Weight | 21 kg | 34.5 kg |
| Temp Coefficient | -0.32%/°C | -0.28%/°C |
| Snow Load | 5400 Pa | 5400 Pa |
| Wind Load | 3600 Pa | 4000 Pa |
| Product Warranty | 20 years | 10 years |
| Performance Warranty | 25 years | 30 years |
| Degradation (Year 1) | 1% | 1.5% |
| Annual Degradation | 0.4% | 0.5% |
| Country | Singapore | United States |
5-Dimension Head-to-Head Analysis
1. Efficiency & Power Density
Winner: REC TwinPeak 5 420WThe REC TwinPeak 5 420W achieves 21.4% efficiency versus 19.2% — a 2.2 percentage point advantage. On a typical 30-panel residential roof, this translates to approximately 1.4 kW more total system capacity, or 7 kWh more annual production in an average US location.
2. Hot Climate Performance
Winner: First Solar Series 6 Plus 465WThe First Solar Series 6 Plus 465W has a better temperature coefficient of -0.28%/°C versus -0.32%/°C. On a 45°C summer day (20°C above STC), the winner retains 94.4% of rated power versus 93.6%. The difference is modest but accumulates over 25 years of summer production.
3. Durability & Warranty
Winner: REC TwinPeak 5 420WREC TwinPeak 5 420W leads with a 20-year product warranty versus 10 years. REC TwinPeak 5 420W degrades more slowly at 0.4% per year versus 0.5%. After 25 years, expect 89.4% vs 86.5% of original output for REC TwinPeak 5 420W and First Solar Series 6 Plus 465W respectively.
4. Power Output
Winner: First Solar Series 6 Plus 465WThe First Solar Series 6 Plus 465W delivers 465W versus 420W per panel — 45W more. For an 8 kW system, you need 18 panels with the higher-wattage option versus 20 panels, saving 2 panels and the associated racking and labor costs.
5. Cell Technology
Winner: First Solar Series 6 Plus 465WThe REC TwinPeak 5 420W uses PERC Mono: PERC (Passivated Emitter Rear Cell) is the current mainstream technology, offering good efficiency at the lowest manufacturing cost. The First Solar Series 6 Plus 465W uses CdTe (Cadmium Telluride): CdTe (Cadmium Telluride). CdTe (Cadmium Telluride) represents a newer generation technology with a longer performance runway as manufacturing matures.
REC TwinPeak 5 420W
The REC TwinPeak 5 delivers 420W using proven PERC technology with REC's signature half-cut cell design and 20-year product warranty.
Pros
- + Strong 20-year product warranty
- + Good shade tolerance
- + Proven half-cut design
- + European engineering
Cons
- - Lower efficiency vs HJT models
- - PERC limitations
- - Premium vs Chinese brands
First Solar Series 6 Plus 465W
The Series 6 Plus delivers 465W using First Solar's proven CdTe thin-film technology, manufactured in the United States.
Pros
- + Proven US thin-film technology
- + Excellent temperature coefficient
- + Environmentally responsible
- + Strong bankability
Cons
- - Lower efficiency
- - Very heavy panel
- - Not suitable for residential
Choose REC TwinPeak 5 420W If...
- ✓ Your roof space is limited and you need maximum power per panel
- ✓ Long-term warranty protection is a top priority and you plan to stay in your home for 20+ years
- ✓ You want maximum output retention over the system's 25-30 year lifespan
- ✓ Homeowners wanting European-quality PERC panels with a strong warranty.
Choose First Solar Series 6 Plus 465W If...
- ✓ You want fewer panels to reach your target system size, reducing racking and labor costs
- ✓ You live in a hot climate (Arizona, Texas, Florida) where heat performance matters
- ✓ Large commercial and utility projects wanting proven US thin-film technology.
Our Recommendation
The REC TwinPeak 5 420W is the decisive winner in this solar panel comparison, outperforming the First Solar Series 6 Plus 465W in 2 of 5 dimensions. Unless you have a specific requirement that the First Solar Series 6 Plus 465W uniquely addresses, the REC TwinPeak 5 420W is the stronger choice for virtually every installation scenario.
Frequently Asked Questions
Which is better, REC TwinPeak 5 420W or First Solar Series 6 Plus 465W?
The REC TwinPeak 5 420W wins this comparison by a decisive margin. It leads in efficiency (21.4% vs 19.2%) and matches or exceeds on warranty (20 vs 10 years). For most residential installations, the REC TwinPeak 5 420W is the stronger choice.
Which panel is more efficient, REC TwinPeak 5 420W or First Solar Series 6 Plus 465W?
The REC TwinPeak 5 420W at 21.4% module efficiency. Higher efficiency means more watts per square foot of roof space, which is critical for space-constrained installations. The difference of 2.2 percentage points translates to approximately 45W per panel under standard test conditions.
Which has a better warranty, REC TwinPeak 5 420W or First Solar Series 6 Plus 465W?
The REC TwinPeak 5 420W comes with a 20-year product warranty and 25-year performance guarantee. The First Solar Series 6 Plus 465W offers 10-year product and 30-year performance warranties. REC TwinPeak 5 420W provides 10 additional years of product coverage.
Which panel performs better in hot weather?
The REC TwinPeak 5 420W has a temperature coefficient of -0.32%/°C and the First Solar Series 6 Plus 465W is -0.28%/°C. First Solar Series 6 Plus 465W retains more power in heat — important in states like Arizona, Texas, and Florida. A lower (less negative) temperature coefficient is better.
How many REC TwinPeak 5 420W vs First Solar Series 6 Plus 465W panels do I need for an 8 kW system?
For an 8 kW system: you need 20 REC TwinPeak 5 420W panels (420W each) or 18 First Solar Series 6 Plus 465W panels (465W each). The First Solar Series 6 Plus 465W requires fewer panels, saving on racking hardware and installation labor.
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Last updated: February 2026