Estimate the solar system size, installed cost, and payback period based on your electricity bill.
How This Estimate Is Calculated
This calculator works backward from your electricity bill: it estimates your monthly energy usage, figures out how large a solar system would be needed to offset that usage given your area's average sun exposure, then applies your installed cost-per-watt and any tax credit to estimate net cost and payback time.
Monthly kWh used = Monthly bill ÷ electricity rate
System size (kW) = Monthly kWh ÷ (30 × sun hours/day × 0.8 derate factor)
Gross cost = System size (W) × cost per watt
Net cost = Gross cost × (1 − tax credit %)
Payback (years) = Net cost ÷ annual bill savings
Why These Numbers Are Estimates, Not Quotes
Real solar quotes depend on your roof's orientation, shading, local permitting costs, panel and inverter brand, whether you add battery storage, and your specific utility's net-metering policy — all things a local installer will assess with a proper site survey. This tool is meant for rough, order-of-magnitude planning before you request real quotes, not as a substitute for one.
Key Assumptions You Can Adjust
- Peak sun hours: varies significantly by location — sunny states like Arizona or California often average 5-6+ hours, while cloudier northern regions may average 3-4
- Derate factor (0.8): accounts for real-world losses from inverter efficiency, wiring, dust, and panel temperature — a commonly used industry rule of thumb
- Tax credit / incentive: federal, state, and utility incentives change over time and vary by location — always verify the current rate for your area rather than relying on a default
❓ Frequently Asked Questions
How many solar panels will I actually need? ▼
This calculator estimates the total system size in kilowatts, then divides by a typical modern panel wattage (410W) to give a rough panel count. Your installer's exact count will depend on the specific panel model, your roof's usable area, and shading.
What is a 'peak sun hour' and why does it matter? ▼
A peak sun hour represents one hour of sunlight at an intensity of 1,000 watts per square meter — it's a standardized way to measure how much usable solar energy a location gets per day, and it varies significantly by geography and season.
Does this account for battery storage? ▼
No, this calculator estimates a standard grid-tied solar system without battery storage. Adding batteries significantly increases the upfront cost but can provide backup power and, in some regions, additional savings depending on your utility's rate structure.
Is the tax credit percentage still accurate? ▼
Solar tax credits and incentives change over time at the federal, state, and utility level, so the default shown here should be treated as a placeholder — always check the current incentive percentage for your specific location before budgeting.
What is 'simple payback period'? ▼
Simple payback period is the net system cost divided by your estimated annual electricity savings, showing roughly how many years until the system 'pays for itself.' It doesn't account for financing costs, panel degradation over time, rising electricity rates, or maintenance — all of which can shift the real payback time in either direction.
🏆 About This Tool — Accuracy & Trust
🔒 Data Privacy: All calculations run entirely within your browser using JavaScript. Nothing you enter here is ever transmitted to our servers, stored, sold, or shared.
📐 Accuracy Note: This tool uses standard, widely published formulas and guidelines. Results are estimates for informational purposes; for financial, medical, or engineering decisions, consult a licensed professional.
📅 Last Updated: September 2026.