What Size Solar System Do I Need? A Simple Guide for Pakistani Homes

Start with your bill, not the installer’s package

Every electricity bill shows the units (kWh) you used each month for the last year. Write down the units for each month. Summer months with AC will be much higher than winter months. Decide whether you want solar to cover your average month, your summer months, or only part of your use. This one decision sets the size of everything else.

The simple sizing formula

Divide your monthly units by 30 to get daily units. Then divide by the peak sun hours in your area and by about 0.8 to allow for heat, dust and wiring losses. Most of Punjab gets around 5 peak sun hours a day on average; parts of Sindh, south Punjab and Balochistan get a little more, and northern areas a little less.

• Daily units = Monthly units ÷ 30
• System size (kW) = Daily units ÷ (Sun hours × 0.8)
• Panels = System watts ÷ Panel watts

For example, a home using 500 units a month in Lahore needs about 4.2 kW. With 585-watt panels, that is 8 panels, or about 4.7 kW, producing around 560 units in an average month. The solar calculator does these steps for you and also estimates roof space and bill saving.

On-grid, hybrid or off-grid

• On-grid: panels and an on-grid inverter connected to the grid. The cheapest way to cut the bill, but it switches off during load-shedding.
• Hybrid: panels, a hybrid inverter and batteries. It cuts the bill and keeps essential loads running during power cuts.
• Off-grid: panels and batteries with no grid connection, used where there is no reliable supply.

Many homes in Pakistan choose a hybrid system because of load-shedding. The batteries add a lot to the cost, so size them for the loads you really need during a power cut — fans, lights, router and a fridge — not the whole house.

Sizing batteries for backup

Add up the watts of the things you want to run during a power cut and decide how many hours you need. Lead-acid and tubular batteries should normally be used to about half their capacity to last longer, while lithium batteries can use more. The UPS and battery backup calculator shows how long a battery bank will last for your load.

Net metering: check the current rules

Net metering lets you send extra units to your electricity company and reduce your bill. The rules, approval process and buy-back rates are set by NEPRA and your distribution company, and they have been revised in recent years. Before you size a system for export, check the latest rules with NEPRA and your DISCO, and ask the installer to explain how the current policy affects your payback.

Roof space and shade

A modern 550–600 watt panel needs roughly 25–30 square feet including gaps. Shade from water tanks, walls or trees can reduce output a lot, even on part of one panel. South-facing roofs with no shade from about 9 am to 4 pm work best in Pakistan.

What to check before you buy

1. Panel brand, model, wattage and warranty in writing.
2. Inverter brand and warranty, and whether it is on-grid or hybrid.
3. Battery type, capacity and warranty, if any.
4. Proper mounting structure that can handle wind.
5. Earthing, DC breakers and surge protection.
6. Who handles net-metering paperwork, if you need it.
7. After-sales service: who cleans, checks and repairs the system.

Payback and financing

Payback depends on the system cost, your electricity rate and how many units you use yourself. If you plan to finance the system, use the loan calculator to compare the monthly instalment with your expected bill saving. A system that saves more each month than its instalment is easy to justify.

Running heavy loads in the daytime

Solar produces power during the day, so shifting heavy loads into daylight hours gets more value from every panel. Run the washing machine, water pump, iron and dishwasher between late morning and mid-afternoon. Inverter ACs set to 26°C use far less power than older units at 18°C. These habits can let a smaller system cover more of your bill.

Looking after the system

• Clean panels with plain water every few weeks, more often in dusty months.
• Check the inverter app or display for daily units and errors.
• Keep batteries in a cool, ventilated place, away from direct sun.
• Ask the installer for a yearly check of wiring, earthing and breakers.

Dust can cut output noticeably in Pakistani summers, and loose connections are a fire risk. A little care keeps the system producing close to what you paid for.

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