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Calcimator

Solar + Battery Home Calculator

Size a residential solar panel and battery system based on energy usage, sun hours, roof space, and grid independence goals.

Inputs

kWh
hrs/day
sq ft
%
$/kWh

Results

Solar Panels Needed

15

System Size6 kW
Battery Capacity14.2 kWh
Estimated System Cost$28,160.00
Annual Savings$1,255.53
Payback Period15.7 years
How to Use This Calculator
  1. Enter Monthly kWh from your last 12 months of electricity bills and your daily Peak Sun Hours (4–6 for most US locations).
  2. Input Roof Sq Ft available for panels and set Grid Independence (%) — 80% is a common target for backup reliability.
  3. Enter your current Electric Rate ($/kWh) to calculate the financial payback after the 30% federal tax credit.
  4. Review Panels Needed, System kW, and Battery kWh to size the system for quotes from solar installers.
  5. Check System Cost as an estimated all-in cost before incentives, then compare to Annual Savings.
  6. Use Payback Years to evaluate the investment against a 25-year panel warranty and local utility rate trends.

How the result changes with Peak Sun Hours

Peak Sun HoursSolar Panels Needed
1.726
3.4519
5.5512
7.39

What each input means

Monthly Electricity Usage
Average monthly electricity consumption from your utility bill.
Peak Sun Hours
Average peak sun hours for your location. Check PVWatts for your zip code.
Available Roof Area
Usable south/west-facing roof area. About 60% of total roof is typically usable.
Grid Independence Target
Percentage of electricity you want to generate yourself (100% = fully off-grid).
Electric Rate
Current electricity cost per kWh from your utility bill.

What each result means

Solar Panels Needed
Number of 400W residential solar panels required.
System Size
Total solar array capacity in kilowatts.
Battery Capacity
Recommended battery storage to cover evening/overnight usage.
Estimated System Cost
Total installed cost before tax credits (~$2.80/W solar + $800/kWh battery).
Annual Savings
Estimated yearly electricity cost savings at your current rate.
Payback Period
Years to recoup investment after 30% federal tax credit.

How this is calculated

Worked example, using the default values

  1. Identify Input Parameters
    4 parameters
    Monthly Electricity Usage = 900, Peak Sun Hours = 4.5, Available Roof Area = 800, Grid Independence Target = 80 = 5 input(s) provided
  2. Calculate Solar Panels Needed
    Solar Panels Needed
    15 = 15
  3. Calculate System Size
    System Size
    6 = 6
  4. Calculate Battery Capacity
    Battery Capacity
    14.2 = 14.2

Engine last updated . Checked against 2 independently-derived tests — how we verify calculators.

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