What's a "good" solar payback period?

Anything under 8 years is excellent. 8–12 years is typical for most U.S. homes with average bills. Over 15 years usually means low electric rates, weak net metering, or excessive shading.

Why does Boston have faster solar payback than Phoenix?

Electricity rates matter more than sun hours. Boston pays 26.5¢/kWh vs. Phoenix at 14.5¢. Each kWh you self-generate replaces more dollars at higher rates, even if you generate fewer kWh total.

Should I include rate inflation in my payback calculation?

Yes — long-run U.S. residential electric rates have risen ~3% annually. Excluding inflation overstates payback by 6–18 months on most systems.

How Solar Payback Actually Works (With Worked Examples)

"How long does solar take to pay for itself?" is the right question. The answer depends on five inputs you can verify in about 20 minutes. Here's the entire calculation, step by step.

The formula in one line

Payback (years) ≈ Net cost ÷ Annual savings. Everything else is figuring out those two numbers accurately for your situation.

Step 1: Gross system cost

Installer pricing in the U.S. averaged $2.75/W in 2025 (Lawrence Berkeley Lab, EnergySage Marketplace). For a typical 10 kW residential system, that's a $27,500 sticker price. Higher-cost states (CA, MA, NY, CT, HI) run $3.00–$3.40/W. Lower-cost states (TX, FL, AZ) run $2.55–$2.70/W.

Step 2: Subtract incentives → Net cost

This is where most online calculators are lazy. The right stack:

Federal Residential Clean Energy Credit: 30% of gross. On $27,500, that's $8,250 back at tax time.
State tax credits: Vary widely. NY = 25% (max $5,000). HI = 35% (max $5,000). MA = 15% (max $1,000). Most states = $0.
Utility rebates: Typically $0.10–$0.50/W in states like NY, MA, CT, NJ, NC. Often capped or first-come-first-served.
SREC value: States like NJ, MD, DC, MA, IL, PA pay you separately for the renewable energy credits your system generates. Worth $50–$300+ per MWh in active markets.

For a 10 kW system in New York: $27,500 gross → $8,250 federal → $5,000 state → $1,500 NY-Sun rebate → ≈ $12,750 net.

Step 3: Year-1 production

The standard formula: Annual kWh = system kW × peak sun hours/day × 365 × 0.78 derate. The 0.78 factor accounts for inverter loss, wiring loss, soiling, and shading.

10 kW system in Phoenix (6.5 sun hours): 18,500 kWh/yr
10 kW system in Boston (4.3 sun hours): 12,250 kWh/yr
10 kW system in Seattle (3.7 sun hours): 10,540 kWh/yr

Step 4: Year-1 savings

Multiply year-1 production by your electric rate. Savings = annual kWh × rate ($/kWh).

10 kW in Phoenix at $0.145/kWh = $2,683/yr
10 kW in Boston at $0.265/kWh = $3,246/yr
10 kW in Seattle at $0.11/kWh = $1,159/yr

Notice Boston outperforms Phoenix despite worse sun, because of higher rates. Rate matters more than sun hours in most cases.

Step 5: Simple payback (years)

Divide net cost by year-1 savings:

Phoenix: $19,250 net ÷ $2,683 = 7.2 yr
Boston: $20,000 net ÷ $3,246 = 6.2 yr
Seattle: $20,500 net ÷ $1,159 = 17.7 yr

The two corrections that make the answer more accurate

Rate inflation (+)

Electricity rates have risen ~3% per year over the last 20 years (BLS data). Including this shortens payback by 0.5–1.5 years on most systems because future-year savings are larger than year-1 savings.

Panel degradation (−)

Tier-1 panels degrade about 0.5% per year. Year-25 production is ~88% of year-1. This lengthens payback by a few months.

Net it all out: 25-year savings

Project year-by-year savings (with both corrections), sum them, subtract net cost. The result is your lifetime savings — what you keep after the system has paid for itself and produced free electricity for the rest of its life.

For our New York example: 25-year cumulative savings ≈ $52,000. Net cost ≈ $12,750. Lifetime net = ~$39,000. Payback at year 5.4.

Want this calculated for your home?

Use the free solar payback calculator — it runs all of this with your state's actual rates and incentives.