# Solar Panel Calculator: How Many Panels You Need

Source: Searchable (https://searchable.pk/tools/solar/solar-panel-calculator)
Type: Calculator
Rates reviewed: 15 Sept 2026
Retrieved: 18 Sept 2026

From your monthly electricity units, the number of solar panels you need, the system size in kW, the inverter to buy, the roof area it takes and the panel cost at today's per-watt price.

Version 1.0.0. Inputs: Monthly consumption, Share of consumption to cover, Panel wattage, Peak sun hours per day, Panel price per watt.

## Worked example (default inputs)

- Monthly consumption: 600 kWh
- Share of consumption to cover: 100 %
- Panel wattage: 585 W
- Peak sun hours per day: 4.5
- Panel price per watt: 29 PKR

**Panels needed: 10 x 585 W**

To cover 600 units a month at 4.5 peak sun hours you need about 5.6 kW of panels: 10 panels of 585 W (5.85 kW), a 5 kW inverter and roughly 300 square feet of roof. The panels alone cost about Rs 169,650 at Rs 29 per watt.

### System

- Array size: 5.85 kW
- Inverter (hybrid or on-grid): 5 kW
- Roof area, panels plus walkways: 300 sq ft (1.1 marla)
- Expected generation: 632 units a month

### Cost

- Panels (10 x 585 W at Rs 29/W): Rs 169,650
- Inverter, structure, wiring, installation: see the Solar Payback calculator

## How it is calculated

Divide the monthly units you want to cover by 30 for the **daily need**. A panel array produces its rated kW times the **peak sun hours** of the site (4.5 to 5.5 across Pakistan) times a **derate of 0.8** for inverter, heat, dust and wiring losses. So:

*Array kW = daily kWh / (peak sun hours x 0.8)*, and *panels = array watts / panel watts*, rounded up.

The inverter is sized at about 85% of the array (panels rarely produce their full rating at once), rounded up to the sizes sold here. Roof area allows 30 square feet per 585 W panel including spacing; 272.25 square feet make a marla.

## Frequently asked questions

**How many solar panels do I need for 500 units?**

About 4.6 kW: 8 panels of 585 W in Lahore (4.5 sun hours) or 7 in Karachi. Pair them with a 5 kW inverter.

**How many panels make a 5 kW system?**

Nine 550 W panels or eight 585 W panels give 5 kW. Older 400 W panels needed 13.

**What size inverter for 10 panels?**

Ten 585 W panels are 5.85 kW; a 5 or 6 kW inverter suits them, since panels seldom deliver their full rating together.

**How much roof space does a 5 kW system need?**

About 250 square feet with walkways, a little under a marla, for eight or nine large panels.

## Sources

- Solar panel price per watt in Pakistan, dealer survey, from the Searchable data hub (Searchable): https://searchable.pk/data/solar-panel-price
- Global Solar Atlas: photovoltaic power potential for Pakistani cities (World Bank / Solargis): https://globalsolaratlas.info/

How to cite: "Solar Panel Calculator: How Many Panels You Need", Searchable, rates reviewed 15 Sept 2026, https://searchable.pk/tools/solar/solar-panel-calculator