Solar System Size Calculatorسولر سسٹم سائز کیلکولیٹر

About the Solar System Size Calculator

This calculator estimates the size of solar system you need to cover your electricity use. Enter your average monthly units, and it works out the system size in kilowatts, how many panels of your chosen wattage that means, the expected monthly and daily generation, and the approximate roof area. Add an installer’s price per kW and your per-unit cost to see an estimated annual saving and simple payback period.

It is meant for households, shops and small businesses in Pakistan comparing installer quotes or deciding whether solar makes sense. The sun hours, losses and panel wattage are editable, and no prices are built in: you enter the quotes and the rate you actually pay. The calculation runs in your browser and gives a starting point before a professional site survey.

How is a solar system sized?

Solar panels are rated in watts under standard test conditions, and a system’s size is the total of its panels, usually given in kilowatts (kW). How much energy that system produces depends on how much sunshine it receives, measured in peak sun hours: the equivalent number of hours per day of full-strength sunlight. Much of Pakistan averages around five peak sun hours per day over a year, but this varies by city, season, weather and smog, which is why the value is editable.

Real systems never produce their full rated output. Heat reduces panel efficiency, dust and shading block light, and energy is lost in wiring and the inverter. These system losses are commonly around 15–25%; the calculator uses 20% by default.

The size needed is: daily units ÷ (peak sun hours × (1 − losses)). The result is rounded up to whole panels. A grid-tied system works with your electricity connection, and under net metering it may export surplus units; an off-grid or hybrid system also needs batteries, which this calculator does not size.

How to use the Solar System Size Calculator

1. Find your average monthly units. Use the average of 12 months of bills, because summer and winter use differ a lot.
2. Check Peak sun hours per day (5 by default) and System losses (20% by default). Adjust them if your installer or local data suggests other values.
3. Enter the Panel wattage you are being offered, for example 585 W or 550 W.
4. Optionally enter the Installed cost per kW from installer quotes and your per-unit cost (bill total ÷ units).
5. Read the system size, number of panels, installed capacity, generation and roof area, plus estimated cost, annual saving and simple payback if you entered prices.

The default sun hours, losses and panel wattage are marked on the page as assumptions you can change, not measurements for your roof.

Key features and benefits

• System size in kW. Calculated from your own consumption, sun hours and losses
• Whole-panel count. Rounded up to complete panels of the wattage you choose, with the actual installed capacity
• Generation estimate. Expected monthly and daily units from the installed system
• Roof area. Approximate space needed, based on about 28 sq ft per panel
• Cost, saving and payback. Uses the installer quote and per-unit cost you enter; savings are capped at your consumption
• Editable assumptions. Sun hours, losses and panel wattage can all be changed

Practical examples

A home using 600 units a month

600 ÷ 30 = 20 units a day. 20 ÷ (5 × 0.8) = 5 kW. With 585 W panels, 5,000 ÷ 585 = 8.5, so the tool rounds up to 9 panels, an installed 5.27 kW. That system is estimated to produce about 632 units a month (21 a day) and needs roughly 252 sq ft of roof.

How much 1 kW produces

At 5 peak sun hours and 20% losses, 1 kW produces 1 × 5 × 0.8 = 4 units a day, or about 120 a month. This is a quick way to check any installer’s generation claim.

Effect of shading or dust

If shading and dust raise losses to 30%, the same 600 units need 20 ÷ (5 × 0.7) = 5.7 kW, or 10 panels of 585 W. Keeping panels clean and unshaded matters.

Simple payback

Suppose a quote is Rs 100,000 per kW and your average cost is Rs 50 per unit — illustrative figures, not market prices. A 5.27 kW system costs about Rs 526,500. It covers your 600 units a month, saving 50 × 600 × 12 = Rs 360,000 a year, for a simple payback of about 1.5 years. Real payback also depends on net-metering terms, maintenance and how tariffs change.

Common use cases

• Homeowners check whether installer quotes are sized sensibly for their consumption.
• Shops and small businesses estimate the system needed to cut daytime electricity costs.
• Families with high summer bills see how many panels their roof would need to hold.
• Buyers comparing panel brands see how panel wattage changes the number of panels.
• Students and researchers learn the basic arithmetic of solar sizing.

Accuracy, limitations and privacy

The calculation is a simplified annual average. It does not model seasonal variation, panel orientation and tilt, temperature effects by month, inverter sizing, export limits or battery storage. Savings assume every unit generated replaces a unit you would have bought at your average rate, up to your consumption; under net metering, exported units may be credited at a different rate set by the rules in force, which change from time to time.

The default values come from the site’s configuration and are labelled as assumptions. The calculator runs in your browser and does not contact any installer or utility.

• Net-metering rules, export rates and approval requirements are not modelled; check the current rules with your electricity company and NEPRA.
• Battery backup and off-grid sizing are not included.
• Always get a site survey from a qualified installer before buying.

Tips and best practices

• Size from your yearly average, not from one summer bill, unless you specifically want to cover peak months.
• Ask installers for expected monthly generation in writing and compare it with this estimate.
• Check the warranty terms for panels and the inverter, and who handles net-metering paperwork.
• Keep panels clean; in dusty cities regular cleaning can noticeably improve output.
• Reduce consumption first with efficient appliances — a smaller system costs less.

Related tools and next steps

Find your monthly units by appliance with the appliance electricity cost calculator. If you also want backup during load shedding, estimate battery needs with the UPS backup time calculator. Find your electricity company and understand bill items in the DISCO bill guide, and compare financing offers with the EMI calculator.