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Solar Panel Sizing

Panels to offset usage. Free online Solar Panel Sizing. Calculate solar panel sizing online — fast, accurate, mobile-friendly, no signup needed.

Panels needed
17

Derivation

  1. ├── 01Givenkwh_month = 1000, sun_hours = 5, panel_w = 400
  2. ├── 02Formulaceil(t / 30 / a × 1e3 / n)
  3. └── 03Compute Panels needed17
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§01What is

Understanding the Solar Panel Sizing

The Solar Panel Sizing computes Panels needed from 3 inputs: monthly kwh, sun hours/day, panel (w). Panels to offset usage.

Quick calculators for the math that shouldn’t need a notepad — instant, accurate, private to your browser. The Solar Panel Sizing sits in that toolkit — it panels to offset usage. Enter your numbers above and the result updates instantly; every step of the math is shown in the Derivation panel so you can see exactly how the answer was reached.

§02The Formula

How it’s calculated

ceil(t / 30 / a × 1e3 / n)

Where

kwh_month
Monthly kWh
sun_hours
Sun hours/day
panel_w
Panel (W)
§03Practical Example

Step-by-step walkthrough

Scenario

Apply the formula to a realistic set of inputs: Monthly kWh = 1000, Sun hours/day = 5, Panel (W) = 400.

  1. 01Start by noting the input — Monthly kWh: 1000.
  2. 02Start by noting the input — Sun hours/day: 5.
  3. 03Start by noting the input — Panel (W): 400.
  4. 04Substitute these values into the formula: ceil(t / 30 / a × 1e3 / n)
  5. 05Compute Panels needed: the calculator returns 17.
  6. 06Cross-check the answer by opening the Derivation panel above — every line of math is shown so you can follow the computation end-to-end.
§04Variants

Common Solar Panel Sizing Problems

The formula gets rearranged depending on which variable you need. Here are the patterns you’ll run into in the real world — find the one that matches your problem and follow the worked steps.

01 · PATTERN

Monthly kWh halved

kwh_month = 500 (from 1000)

Keep every other input at its default and halve the monthly kwh. See how panels needed responds.

  1. 01New Monthly kWh: 500
  2. 02Baseline Panels needed: 17
  3. 03New Panels needed: 9
  4. 04Panels needed decreases by 47.1% → use this sensitivity to plan for real-world variation.
02 · PATTERN

Monthly kWh doubled

kwh_month = 2000 (from 1000)

Keep every other input at its default and double the monthly kwh. See how panels needed responds.

  1. 01New Monthly kWh: 2000
  2. 02Baseline Panels needed: 17
  3. 03New Panels needed: 34
  4. 04Panels needed increases by 100% → use this sensitivity to plan for real-world variation.
03 · PATTERN

Sun hours/day halved

sun_hours = 2.5 (from 5)

Keep every other input at its default and halve the sun hours/day. See how panels needed responds.

  1. 01New Sun hours/day: 2.5
  2. 02Baseline Panels needed: 17
  3. 03New Panels needed: 34
  4. 04Panels needed increases by 100% → use this sensitivity to plan for real-world variation.
04 · PATTERN

Sun hours/day doubled

sun_hours = 10 (from 5)

Keep every other input at its default and double the sun hours/day. See how panels needed responds.

  1. 01New Sun hours/day: 10
  2. 02Baseline Panels needed: 17
  3. 03New Panels needed: 9
  4. 04Panels needed decreases by 47.1% → use this sensitivity to plan for real-world variation.
§05FAQ

Frequently asked questions

Yes. The calculator implements the standard formula as documented and returns exact floating-point results. No approximations are used unless noted in the formula.
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