Solar Systems
System sizes, what a full quote includes and how to size from your bill.
Solar systems · Calculator
Solar System Calculator for Karachi
You can size a home system on paper in five minutes. This page gives the sums, with worked examples, and shows where the answer needs a site visit.
- ✓ Panels, inverter and battery
- ✓ Cost and payback sums
- ✓ Free estimate on WhatsApp
What this calculator covers
Our solar calculator guide explains how to read your bill. This page goes one step further and sizes the whole system: panels, inverter and battery. It then tests the cost against the savings.
Every number below is a planning figure. The sun, your roof, the shade and your habits move the result, so treat the answer as a starting point for a conversation and not as a final design.
All the sums use a planning rule of 4 to 5 units of electricity per kW of panels per day in Karachi. We use 4.5 in the examples.
The five sums
Do them in order. The worked example follows a house that uses 600 units a month.
- 1
Find your daily use
Divide the monthly units on your bill by 30. For 600 units that is 20 units a day.
- 2
Size the panels
Divide the daily units by 4.5. For 20 units that is about 4.4 kW. With 585 W panels, that is 4.4 divided by 0.585, which rounds up to 8 panels, or 4.68 kW.
- 3
Size the inverter
Add up the loads that may run together, such as an air conditioner, a fridge and fans, and allow for the start-up surge. Then match an inverter that covers it. A 5 kW inverter is a common match for 4.68 kW of panels.
- 4
Size the battery
Decide how many hours of backup you want and the load in that time. A 1 kW load for 5 hours is 5 kWh. Divide by the usable share: about 0.9 for lithium, about 0.5 for tubular. Lithium needs about 5.6 kWh. Tubular needs about 10 kWh.
- 5
Check the roof
A 585 W panel needs about 2.6 square metres including walking space. Eight panels need about 21 square metres of shade-free roof.
Worked examples
Illustrative sizes only. They are not prices, and your own bill will differ.
| Monthly units | Daily units | Panels needed (kW) | 585 W panels | Roof area |
|---|---|---|---|---|
| 300 units a month | 10 | 2.2 | 4 | about 10 m² |
| 600 units a month | 20 | 4.4 | 8 | about 21 m² |
| 1,000 units a month | 33 | 7.4 | 13 | about 34 m² |
Testing cost against savings
Payback is the system cost divided by the yearly saving. The saving depends on how many units you use yourself and how many you export, because the two earn very different amounts.
Reports have put the net billing export rate at roughly Rs 10 to 11 per unit, while import rates have been reported at Rs 37 to 55 per unit. Check the current tariff before you rely on either figure. That gap is why using your own power beats exporting it.
Here is an invented example. Assume the 4.68 kW system makes 630 units a month, you use 480 of them yourself at Rs 45 each, and you export 150 at Rs 10.5. Your monthly gain is 480 times 45, which is Rs 21,600, plus 150 times 10.5, which is Rs 1,575. The total is Rs 23,175 a month. If a system cost Rs 1,000,000, the payback would be about 43 months. These are not our prices.
Where the calculator stops
Paper sums cannot see shade from a water tank, a roof that faces the wrong way, a weak meter board or a sanctioned load that limits the system. A site visit settles these. The estimate is free, so use the sums to prepare and let us check them.
Net billing changes the answer
Under net billing, the best system is usually one sized to the power you use in the daytime, not one sized to export. If most of your use is in the evening, a battery lifts the self-use share but adds cost.
Read the net billing guide before you size for export. And if you want a grid connection, remember that a PPIB pre-qualified vendor files the K-Electric application. We design and install the system but do not file it.
FAQs
Questions people ask us
Short answers. For your own property, send us your electricity bill and roof details.
Ask on WhatsAppDivide your monthly units by 30, then divide by 4.5 to get the panel kW. Size the inverter for the loads that run together and the battery for the backup hours you want.
About 8 panels of 585 W, which is 4.68 kW, using a planning figure of 4.5 units per kW per day.
It depends on the system cost and how much power you use yourself. Divide the cost by the yearly saving. Our worked example is illustrative and not a promise.
No. Output is higher in the clear months and lower in the monsoon and in hazy weather.
Yes. Send a photo of the bill and a roof photo on WhatsApp. The estimate is free.
Sources
Rules and figures on this page were checked in October 2026. They change, so confirm the current position before you commit money.
Related pages
Solar Calculator
A six-step solar sizing method with a worked example and worksheet.
Solar Panel Size Calculator
Panel dimensions, roof area per kW and row spacing worked out for Karachi.
Inverter Sizes
Inverter sizes from 1 kW to 10 kW and what each can run.
Want the sums done for you?
Send a photo of your bill and your roof. We will size the system and give you an itemised quote. The estimate is free.