March 26, 20264 min read

Solar Panel Calculator: Size Your System and Estimate Savings

Calculate how many solar panels you need, estimate annual energy production, payback period, and 25-year savings based on your home and location.

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Solar installers give you a quote, but do you actually understand what you're getting? Knowing how system size, panel count, and expected production are calculated lets you evaluate any proposal critically — and figure out whether the numbers make sense before you sign anything. The CalcHub Solar Panel Calculator walks through the full sizing and savings estimate.

Step 1: How Much Energy Do You Use?

Start with your electricity bill. You're looking for your annual kWh consumption — most bills show this month-by-month. Add up 12 months or find the "previous 12 months" summary.

Typical US household consumption by region:

Region	Avg. Annual kWh
New England	6,500–7,500 kWh
Mid-Atlantic	8,000–10,000 kWh
Southeast / South	12,000–15,000 kWh
Midwest	9,000–11,000 kWh
Southwest	10,000–13,000 kWh
Pacific Northwest	10,000–12,000 kWh
California	6,500–8,000 kWh

The South runs high because of heavy air conditioning. The Southeast is particularly energy-intensive. California runs lower partly due to mild climate and strong efficiency programs.

Step 2: Peak Sun Hours for Your Location

Peak sun hours (PSH) measures how many hours per day your location receives sunlight equivalent to 1,000 W/m² (full intensity). This is the key variable that changes by geography.

Location	Avg. Daily Peak Sun Hours
Phoenix, AZ	6.5
Los Angeles, CA	5.5
Miami, FL	5.5
Dallas, TX	5.2
Denver, CO	5.5
Chicago, IL	4.2
New York, NY	4.0
Seattle, WA	3.5
Boston, MA	4.2

More sun hours = more production per panel = fewer panels needed for the same output.

Step 3: How Many Panels?

Formula:

System Size (kW) = Annual kWh / (PSH × 365 × System Efficiency)
Panels Needed = System Size (kW) / Panel Wattage

System efficiency accounts for real-world losses: temperature effects, wiring losses, inverter efficiency — typically around 80–85%.

Example: 10,000 kWh/year, Dallas (5.2 PSH), 400W panels:

System size = 10,000 / (5.2 × 365 × 0.82) = 10,000 / 1,556 = 6.43 kW
Panels needed = 6,430 W / 400 W = 16 panels

Step 4: Cost and Payback Period

A typical residential solar installation costs $2.50–$3.50 per watt installed (2025 figures), before incentives.

System Size	Installed Cost (before incentives)	After 30% Federal Tax Credit
4 kW	$10,000–$14,000	$7,000–$9,800
6 kW	$15,000–$21,000	$10,500–$14,700
8 kW	$20,000–$28,000	$14,000–$19,600
10 kW	$25,000–$35,000	$17,500–$24,500

The 30% federal Investment Tax Credit (ITC) applies through 2032. Many states and utilities have additional rebates. Payback period = Net system cost / Annual electricity savings

If your 6 kW system costs $12,000 after credits and saves $1,500/year in electricity: 12,000 / 1,500 = 8-year payback. With a 25-year panel warranty, that's 17 years of essentially free electricity after payback.

Battery Storage: Worth It?

Adding a home battery (like a 13.5 kWh unit at ~$10,000 installed) significantly increases cost but provides backup power and time-of-use optimization. Payback on batteries is longer than panels alone — often 12–15 years. The main reasons to add storage:

Frequent grid outages in your area
Your utility has unfavorable net metering policies
Time-of-use rates with expensive evening electricity

The calculator has a battery add-on section to see how it changes the overall economics.

Is my roof suitable for solar?

Ideal conditions: south-facing roof, slope of 15–40°, minimal shade from trees or neighboring structures. East and west-facing roofs also work well, just at 10–20% lower production. North-facing roofs are generally not worth it in the Northern Hemisphere. The calculator lets you enter roof orientation and shade factors.

What happens to excess electricity I generate?

With net metering (available in most US states), excess electricity flows back to the grid and credits your bill. The credit rate varies — some utilities pay retail rate (very favorable), others pay a lower wholesale rate. Enter your utility's net metering credit rate in the calculator to see the accurate financial picture.

How long do solar panels actually last?

Modern panels are typically warranted for 25 years at 80% of original output, and many last 30–40 years. Performance degrades at about 0.5% per year. The calculator's 25-year projection accounts for this gradual degradation.

Electricity Cost Calculator — current monthly bill analysis
Carbon Footprint Calculator — emissions savings from going solar
Fuel Cost Calculator — compare driving costs: gas vs. EV charged by solar