Does solar panel efficiency really matter for most homeowners?

Efficiency mainly matters when roof space is constrained. A 22% efficient panel produces about 16% more power per square foot than a 19% panel. If you have ample roof space, lower-efficiency panels at a lower price often deliver better economics.

How much does temperature coefficient matter for solar panels?

A panel with -0.30%/°C loses 30% less output on hot days than one with -0.45%/°C. In hot climates like Phoenix with roof temps reaching 65°C, the difference can mean 6% more annual production. In cool climates, temperature coefficient barely matters.

Is price per watt or efficiency the better solar panel comparison metric?

Neither alone tells the full story. Cost per kWh over 25 years (upfront cost divided by lifetime production) is the superior metric because it captures both purchase price and long-term productivity together.

Solar Panel Comparison Calculator

Enter specs for two panels — get 25-year production, cost per kWh, and a clear winner verdict.

System settings

Location (peak sun hours)

Target system size?

Panel specifications

Panel A

Panel name / model

Rated watts?

Efficiency?

Temp coefficient?

%/°C

Price per panel?

Warranty?

yrs

Degradation rate?

%/yr

Panel B

Panel name / model

Rated watts?

Efficiency?

Temp coefficient?

%/°C

Price per panel?

Warranty?

yrs

Degradation rate?

%/yr

Side-by-side comparison

Metric	Panel A	Panel B
Panels needed	20	20
Total cost	$4,400	$6,400
Price per watt	$0.55/W	$0.76/W
25-yr production	300,677 kWh	306,078 kWh
Cost per kWh	$0.015	$0.021
Production at yr 10	123,897 kWh	124,734 kWh
Production at yr 15	184,009 kWh	185,940 kWh
Production at yr 25	300,677 kWh	306,078 kWh
Warranty	25 yrs	25 yrs

Link copied to clipboard

How to Use This Calculator

Enter both panels' specs

Fill in all seven fields for each panel: name or model, rated watts, efficiency %, temperature coefficient (%/°C), price per panel, warranty years, and annual degradation rate. All this data appears on any panel's datasheet or product page. If you're unsure of the degradation rate, use 0.40%/yr for standard panels and 0.25%/yr for premium models.

Set your location and system size

Location determines peak sun hours, which affects annual production. System size (kW) is your target — the calculator determines how many panels of each type you'd need to hit that target, then computes all costs based on that count.

Read the comparison table

The table shows 8 metrics side by side. The WINNER badge goes to the panel with better scores across four criteria: cost per kWh, total 25-year production, price per watt, and warranty. A tie is possible when panels trade off in different areas. Focus on cost per kWh as the single most comprehensive metric — it combines upfront cost and lifetime production into one number.

The Formula

Panels Needed = Target kW × 1000 ÷ Panel Watts (round up) Total Cost = Panels Needed × Price per Panel Annual kWh (Year N) = Target kW × PSH × 365 × 0.80 × (1 - Degradation%)^(N-1) 25-Year kWh = Sum of Annual kWh for years 1 through 25 Cost per kWh = Total Cost ÷ 25-Year kWh Price per Watt = Price per Panel ÷ Panel Watts

The 0.80 system efficiency factor accounts for inverter losses, wiring, and soiling. Annual degradation compounds — a panel with 0.50%/yr degradation produces ~88% of its original output at year 25, while a 0.25%/yr panel still produces ~94%. That 6% difference compounds into thousands of kWh over a 25-year system life.

Example

Maria — Comparing a budget 400W vs premium 420W panel for her Dallas 8kW system

Panel A (Budget 400W)$220/panel, 25-yr warranty, 0.40%/yr degradation

Panel B (Premium 420W)$320/panel, 25-yr warranty, 0.25%/yr degradation

LocationDallas, TX (5.4 PSH)

System size8 kW

Result

Panel A panels needed20 panels @ $4,400 total

Panel B panels needed20 panels @ $6,400 total

Panel A 25-yr production~287,000 kWh

Panel B 25-yr production~294,000 kWh

Panel A cost per kWh$0.015/kWh

Panel B cost per kWh$0.022/kWh

Panel A wins on cost per kWh despite producing slightly fewer kWh over 25 years. Maria saves $2,000 upfront. The premium panel's better degradation adds ~7,000 kWh over 25 years — worth about $910 at $0.13/kWh. The $2,000 premium cost doesn't pay back from the production difference alone, so Panel A wins on economics.

FAQ

What makes one solar panel "better" than another? ▼

No single metric defines the "better" panel — it depends on your priorities. If roof space is limited, higher efficiency wins. If budget is tight, lower cost per watt wins. For long-term value, lower degradation rate and longer warranty matter most. Cost per kWh over 25 years is the most comprehensive single metric because it normalizes upfront cost against lifetime production. A cheaper panel that degrades faster can end up more expensive per kWh than a premium one.

Does panel efficiency really matter for most homeowners? ▼

Efficiency matters mainly when roof space is constrained. A 22% efficient panel fits more watts in the same area as a 19% panel — roughly 16% more power per square foot. If you have a large south-facing roof with room to spare, lower-efficiency panels at a lower price often deliver better economics. If you're limited to a small or shaded roof, pay for efficiency. The break-even analysis depends on your specific roof and local electricity rates.

How much does temperature coefficient matter? ▼

Temperature coefficient tells you how much power a panel loses per degree above 25°C. A panel with -0.30%/°C loses 30% less output on hot days than one with -0.45%/°C. In Phoenix (summer roof temps can hit 65°C), the difference is (65-25) × 0.15% = 6% more production from the better panel. Over a year in hot climates, that's a meaningful difference. In cloudy, cool climates like Seattle, temperature coefficient barely matters.

How should I compare warranties between panel brands? ▼

Solar warranties have two parts: product warranty (covers defects, usually 10-25 years) and performance warranty (guarantees minimum output, typically 80-90% at year 25). A 25-year product warranty from an established manufacturer is worth far more than a 25-year warranty from a company that may not exist in 10 years. Prioritize manufacturers with a long track record and financial stability. IEC certification and UL listing are minimum quality indicators.

Is price per watt or efficiency the better comparison metric? ▼

Neither alone tells the full story. Price per watt is useful for comparing upfront cost on equal footing. But a cheaper panel that degrades at 0.70%/yr produces 18% less energy at year 25 than a panel at 0.25%/yr. Cost per kWh over 25 years (upfront cost ÷ lifetime production) is the superior metric because it captures both the purchase price and the long-term productivity. This calculator computes it for you automatically.

Related Calculators

Embed This Calculator

Free to embed on your website. Just copy this code:

<iframe src="https://solarsizecalculator.com/solar-panel-comparison-calculator"
  width="100%" height="700" frameborder="0"
  title="Solar Panel Comparison Calculator"></iframe>