Daily demand
30 kWh
Engineering
Solar Panel Calculator
Use this solar panel calculator to estimate array size, minimum panel count, generation, coverage, roof-space limits, and inverter planning range.
solar panelsolar sizingsun hourspanel countsolar panel calculatorsolar system size calculator
Calculator
Calculate instantly
Required array kW = daily kWh / (peak sun hours x system efficiency)
Monthly and annual energy values are converted to daily demand. The calculator applies the loss factor, calculates required array size, then rounds the panel count upward.
- Monthly and annual inputs are normalized to daily kWh.
- System losses reduce usable generation, so the required array grows as losses increase.
- The panel count is rounded upward to the next whole panel.
Inputs
Solar sizing inputs
Estimate system size from electricity use, sun hours, panel wattage, system losses, roof area, and target coverage.
Breakdown
Clear result breakdown
Review the values that explain the primary result.
Daily generation
30.6 kWh
Monthly generation
931.4 kWh
Annual generation
11,169 kWh
Roof-limited panels
20 panels
Inverter range
6.12-8.8 kW
Visual comparison
Energy coverage estimate
Generation is based on entered panel count or the minimum panel count if selected panels are zero.
Generation is based on entered panel count or the minimum panel count if selected panels are zero.
Daily demand30 kWh
Daily generation30.6 kWh
Required kW7.5 kW
Practical guidance
Insights for this scenario
Losses matter
The estimate includes system losses for inverter, wiring, heat, soiling, mismatch, and other real-world reductions.
Panel count rounds up
Minimum panel count is rounded upward because partial panels cannot be installed as a practical system.
Site conditions still decide
Shade, roof direction, roof strength, permits, utility rules, and local design standards can change the final design.
Step-by-step solution
Follow the calculation path from known values to final result.
- 1
Convert energy use to daily demand
Monthly and annual inputs are normalized to daily kWh.
30 kWh/day
- 2
Size the array
kW = daily kWh / (sun hours x efficiency)
System losses reduce usable generation, so the required array grows as losses increase.
7.5 kW
- 3
Round up panel count
panels = ceil(array watts / panel watts)
The panel count is rounded upward to the next whole panel.
17 panels
Formula explorer
Required array kW = daily kWh / (peak sun hours x system efficiency)
Monthly and annual energy values are converted to daily demand. The calculator applies the loss factor, calculates required array size, then rounds the panel count upward.
- E(kWh/day)
- Daily energy use: Average electricity demand after normalizing daily, monthly, or annual input.
- H(hours/day)
- Peak sun hours: Average usable solar energy hours per day.
- eta(%)
- System efficiency: Usable output after loss factor.
- W(W)
- Panel wattage: Rated wattage of one panel.
Assumptions and references
Units
- kWh
- W
- %
Assumptions
- Peak sun hours and losses are planning inputs.
- Roof area is usable area before detailed shade, setback, and structural review.
- Generation estimates assume average conditions and do not replace professional design.
- The array size is a DC planning estimate before detailed inverter, permit, utility, and site-design decisions.
Limitations
- Using daylight hours instead of peak sun hours.
- Ignoring system losses and shading.
- Assuming all roof area can hold panels.
- Treating panel count as a final install plan before checking roof orientation, tilt, setbacks, structure, and local rules.
- Results depend on the accuracy of the values entered.
- Rounding may make displayed values slightly different from exact intermediate calculations.
Worked examples
Real-worldHome solar estimate
Known values
- Daily use: 30 kWh
- Peak sun: 5 hours
- Panel: 450 W
- Losses: 20%
Calculation
- 1. Efficiency is 80%.
- 2. Required array is 30 / (5 x 0.8) = 7.5 kW.
- 3. 7.5 kW / 450 W rounds up to 17 panels.
Result and meaning
The minimum whole-panel estimate is 17 panels.
Learning guide
Understand the calculation
Concepts
- Peak sun hours are not the same as daylight hours.
- System losses reduce usable output.
- Panel count must be rounded to whole panels.
Tips
- Use recent electricity bills for energy demand.
- Check local peak sun hour data.
- Leave room for shade, setbacks, maintenance paths, and inverter sizing.
Common mistakes
- Ignoring system losses.
- Treating roof area as fully usable.
- Assuming estimates replace a professional design.
Educational notes
- The calculator converts daily, monthly, or annual energy use into daily kWh, applies peak sun hours and system losses, then rounds panel count upward.
- Yes for real engineering decisions. Use applicable standards and professional review.
- Use a consistent unit system and convert all inputs before combining them.
- Use it as an estimate and compare it with the formula, assumptions, and examples shown on the page.
- Real-world inputs can include local rules, changing rates, measurement tolerances, and conditions outside the core formula.
Glossary
- Daily energy use
- Average electricity demand after normalizing daily, monthly, or annual input.
- Peak sun hours
- Average usable solar energy hours per day.
- System efficiency
- Usable output after loss factor.
- Panel wattage
- Rated wattage of one panel.
Trust panel
Calculator quality and review
- Reviewed by
- AZCalculate solar planning review
- Review date
- 2026-06-25
- References
- 2
- Trust score
- 91/100
- Formula verified
- Yes
- Risk level
- medium
- Category
- Engineering
- Calculator version
- 2.1
- Formula version
- 2.1
Sign in to save this calculation and access it later.
Trust note
Planning estimate
This solar panel result is a planning estimate only. Actual performance varies with location, weather, shading, roof orientation, roof tilt, temperature, panel degradation, equipment selection, permitting, utility rules, and professional installation design.
Medium risk contextDifficulty: intermediateConfidence estimate: 91/100Reviewed 2026-06-25Reviewed by: AZCalculate solar planning reviewCalculator v2.1 / Formula v2.12 sources listed
Formula and Explanation
Required array kW = daily kWh / (peak sun hours x system efficiency)
The calculator converts daily, monthly, or annual energy use into daily kWh, applies peak sun hours and system losses, then rounds panel count upward.
Variable descriptions
- E(kWh/day)
- Daily energy use: Average electricity demand after normalizing daily, monthly, or annual input.
- H(hours/day)
- Peak sun hours: Average usable solar energy hours per day.
- eta(%)
- System efficiency: Usable output after loss factor.
- W(W)
- Panel wattage: Rated wattage of one panel.
Formula Notes
- Panel count is rounded upward to whole panels.
- System losses represent real-world reductions from heat, wiring, inverter, soiling, and other factors.
- This is a planning calculator, not a final site design.
Common uses
- Size solar arrays
- Compare panel wattages
- Plan daily production
- Estimate rooftop solar size
- Check roof-space limits
Assumptions
What this calculation assumes
- Peak sun hours and losses are planning inputs.
- Roof area is usable area before detailed shade, setback, and structural review.
- Generation estimates assume average conditions and do not replace professional design.
- The array size is a DC planning estimate before detailed inverter, permit, utility, and site-design decisions.
Avoid mistakes
Quick checks before you rely on the result
- Using daylight hours instead of peak sun hours.
- Ignoring system losses and shading.
- Assuming all roof area can hold panels.
- Treating panel count as a final install plan before checking roof orientation, tilt, setbacks, structure, and local rules.
Step-by-Step Explanation
Follow the reasoning, not only the final number.
- 1
Set up the calculation
Enter energy use and choose daily, monthly, or annual period.
Starting with clearly defined values and units prevents the most common calculation errors.
- 2
Work through step 2
Enter peak sun hours, panel wattage, and system loss percentage.
This step transforms the known values into the form required by the formula.
- 3
Work through step 3
Normalize energy use to daily kWh.
This step transforms the known values into the form required by the formula.
- 4
Work through step 4
Calculate required array size.
This step transforms the known values into the form required by the formula.
- 5
Interpret the result
Round required array watts into a whole panel count.
Compare the result with your real-world goal, such as size solar arrays.
Worked example
Home solar estimate
Known values
- Daily use: 30 kWh
- Peak sun hours: 5
- Panel wattage: 450 W
- System loss: 20%
Calculation
- 1. Efficiency is 80%.
- 2. Required array is 30 / (5 x 0.8) = 7.5 kW.
- 3. 7.5 kW divided by 450 W rounds up to 17 panels.
Result and meaning
The minimum whole-panel estimate is 17 panels.
Calculator guide
About this Solar Panel Calculator
Estimate solar panel count from energy use, sun hours, panel wattage, and system losses. This page includes an interactive calculator, concise formula notes, worked examples, FAQs, related calculators, and practical guidance you can revisit whenever needed.
References
Sources used for this calculator
Last checked: 2026-06-25 | Next review: 2026-12-25
Last checked: 2026-06-25 | Next review: 2026-12-25
Found something that does not look right?
We work hard to keep every calculator accurate and useful. If you notice a calculation error, missing option, or unclear explanation, please let us know so we can review and correct it promptly.
Calculator usage
Usage information loads after the calculator is ready.
FAQ
Solar Panel Calculator FAQs
How does the solar panel calculator work?+
It uses Panels = daily kWh x 1000 / (sun hours x panel watts x efficiency) and calculates the result from the values you enter.
Can I copy or print the result?+
Yes. AZCalculate calculator pages include copy, share, and print actions.
How does the solar panel calculator estimate panel count?+
It converts energy use to daily kWh, divides by peak sun hours and system efficiency, then rounds the panel count upward.
What are peak sun hours?+
Peak sun hours describe usable solar energy intensity, not total daylight hours. Local location, season, roof direction, and weather affect them.
Why does system loss matter?+
Inverters, wiring, heat, shading, dust, mismatch, and other real-world factors reduce usable output, so the required array increases as losses rise.
Should I enter daily, monthly, or annual electricity use?+
Use the value you trust most. Bills often show monthly or annual kWh, while appliance planning may use daily kWh.
Why does the panel count round up?+
Solar panels are installed as whole panels, so a minimum estimate is rounded up to the next full panel.
Can roof area limit the system?+
Yes. The calculator estimates roof-limited panel count from usable roof area and area per panel, but a real design also needs setbacks and shading checks.
Does this replace a professional solar design?+
No. Use it for planning. A final system needs site survey, structural review, electrical design, permits, and utility rules.
Can I estimate generation from a known panel count?+
Yes. Enter a panel count to estimate daily, monthly, and annual generation under the selected assumptions.
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