Panels for Home Calculator

Plan your rooftop system with realistic performance inputs. See panels, watts, area, and yield instantly. Export results for proposals, budgeting, and installation discussions today.

Calculator Inputs
3 columns on large screens, 2 on smaller, 1 on mobile.
Choose the data you know most confidently.
kWh
Typical household range: 200–1,200 kWh/month.
kWh/day
If you have smart meter data, use this.
PKR
Enter total bill amount for one average month.
PKR/kWh
Used only for bill-to-energy conversion and savings.
days
Default uses an annual average month length.
h/day
Use your location’s yearly average.
%
Example: 80% for partial offset, 100% for full.
W
Common modern panels: 400–600 W.
%
Accounts for wiring, soiling, mismatch, etc.
%
Modern inverters often range 95–98%.
%
Use 0% for clear roof, higher if shaded.
%
Hot climates may see 5–12% losses.
%
Adds buffer for new loads and conservative sizing.
ratio
Common design range: 1.10–1.30.
m
Used for roof area estimate.
m
Used for roof area estimate.
×
Covers setbacks, walkways, tilt, and gaps.
m²
If provided, roof utilization will be shown.
Used only for display with bill inputs.
Reset View example table
This tool estimates panel count based on averages. For final design, confirm shade, tilt, orientation, and inverter limits.
Example Data Table
Sample scenarios to illustrate typical inputs and outputs.
Home profile Monthly use (kWh) PSH (h/day) Panel (W) Offset Approx panels Approx size (kW DC)
Small apartment 250 4.5 450 80% 4–6 1.8–2.7
Family home 500 5.0 550 100% 8–11 4.4–6.1
Large home + cooling load 900 5.5 600 100% 13–18 7.8–10.8
These ranges assume typical losses and a modest reserve margin.
Formula Used
Transparent calculations with adjustable assumptions.

The calculator converts your consumption to a daily energy target, then sizes the solar array using location sun hours and an overall performance factor.

1) Daily energy target
daily_kWh = monthly_kWh ÷ days_in_month (or directly entered)
target_daily_kWh = daily_kWh × (offset% ÷ 100) × (1 + reserve% ÷ 100)
2) Overall performance factor
overall_factor = system_factor × inverter_eff × (1 − shading_loss) × (1 − temperature_loss)
3) Required array size and panel count
required_kW_DC = target_daily_kWh ÷ (PSH × overall_factor)
panels = ceil( required_kW_DC × 1000 ÷ panel_W )
4) Roof area and inverter estimate
roof_area_needed = panels × (panel_length × panel_width) × spacing_factor
inverter_kW_AC ≈ array_kW_DC ÷ (DC/AC ratio)
How to Use This Calculator
A simple workflow for consistent results.
  1. Pick a usage mode and enter monthly kWh, daily kWh, or a bill with tariff.
  2. Enter peak sun hours for your location using a yearly average.
  3. Choose panel wattage that matches what installers offer locally.
  4. Open advanced options to adjust losses, margins, and roof details.
  5. Calculate to view results above the form, then export.
If you want conservative sizing, increase shading or temperature losses and add reserve.

Load profile inputs and conversion logic

Accurate energy demand drives every downstream number. Monthly kWh is converted to daily kWh using the month length, while bill mode divides the bill by tariff to estimate kWh. If usage varies, average recent bills. For example, 540 kWh/month over 30.44 days becomes 17.74 kWh/day. The offset target and reserve margin then increase the daily target to reflect your goals.

Peak sun hours and expected variability

Peak sun hours (PSH) represent the daily solar resource as equivalent full‑power hours. A change from 4.5 to 5.5 PSH can reduce required array size by roughly 18% before losses. Use a realistic annual average for planning, and expect seasonal swings. If winter PSH is lower, a higher reserve margin helps maintain coverage. Keep PSH consistent across quotes.

Loss factors that shape real output

The overall performance factor multiplies system performance, inverter efficiency, shading, and temperature impacts. Each input is adjustable because roofs differ. A typical combination might be 0.80 system factor, 0.96 inverter efficiency, 5% shading loss, and 6% temperature loss, producing an overall factor near 0.69. Lower factors increase required kW DC and panel count. If you are unsure, choose conservative losses and refine after shade review.

Roof area planning and layout allowances

The roof estimate starts with panel footprint (length × width) and then applies a spacing factor for pathways, setbacks, tilt rows, and maintenance access. For a 1.72 m × 1.13 m module, footprint is 1.94 m². Ten panels occupy about 19.4 m² before spacing; with a 1.12 factor, plan for 21.7 m². If you enter available roof area, the tool reports utilization to highlight tight layouts early in the design process.

Interpreting results for procurement decisions

Use the recommended panel count as a starting point, then validate inverter sizing and roof fit. The DC/AC ratio suggests an inverter band rather than a single value, accommodating product availability. Compare monthly and annual generation with your consumption to gauge coverage. If tariff is provided, the bill offset value is an estimate, not a guarantee, because billing structures can include fixed charges and tiered rates. Export reports to share assumptions with installers and keep proposals aligned.

FAQs

1) What panel wattage should I choose?

Use the wattage your installer can reliably supply. Higher watt panels reduce the count, but roof area and mounting constraints still apply. Keep PSH and loss assumptions consistent when comparing sizes.

2) Why does shading loss matter so much?

Shading reduces energy through the day and may trigger mismatch losses. Even 5–10% shading loss can add one or more panels. If you have trees or nearby buildings, start conservative.

3) Should I size for 100% offset?

Not always. Some households target 70–90% to control cost and avoid seasonal overproduction. A partial offset can still deliver strong value while keeping roof area and inverter requirements modest.

4) What is a good reserve margin?

A 5–15% reserve is common for future appliances or hotter summers. If you expect EV charging, more occupants, or more cooling load, use a higher reserve to reduce later expansion complexity.

5) How accurate is the roof area estimate?

It is a planning estimate based on panel size and spacing factor. Final layout depends on obstructions, setbacks, tilt, and wiring routes. Use utilization percentage to flag feasibility, then confirm with a site layout.

6) Does the bill offset value equal my savings?

It approximates energy value using your tariff. Real bills may include fixed charges, demand components, and tiers. Treat it as a comparison tool, and confirm with your utility’s billing rules.

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Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.