Ask five installers what capacity you need and you may hear five different answers, each one conveniently matching the stock in their warehouse. Getting the solar system size right is the single decision that controls your payback period, your summer comfort and how soon you outgrow the setup. Too small and the grid bill barely moves. Too large and you park money on the roof that net metering may never return.
The good news is that sizing is arithmetic, not magic. With an electricity bill, a notepad and half an hour, any homeowner in Pakistan can work out a defensible number before talking to a single salesman. Here is the five-step method that installers use internally, written for 2026 tariffs and equipment.
Why the Right Solar System Size Decides Your Payback
Electricity slabs in Pakistan punish heavy grid users, so every unit you generate at the top slab is worth far more than one offset at the bottom. A correctly sized array shaves the expensive units first.
Oversizing has a quieter cost. Export rates under the revised net metering framework are lower than retail rates, which means surplus generation earns you less than the rupees you spent to produce it. Right-sizing, not maximum-sizing, is what shortens payback.
The 5-Step Sizing Method
- Pull twelve months of bills. Write down the units consumed each month. One hot month tells you nothing; the June and January spread tells you everything about your real load pattern.
- Convert units to daily demand. Divide your highest month by 30. A home burning 600 units in June needs about 20 kWh per day at peak season.
- Divide by your sun window. Most of Pakistan receives roughly 4.5 to 5.5 usable peak sun hours depending on season and city. At 5 hours, that 20 kWh home needs around 4 kW of real output.
- Add system losses. Dust, heat derating, wiring and conversion losses eat 20 to 25 percent. Multiply by 1.25, which lifts our example to roughly 5 kW of installed panels.
- Match the inverter last. Choose the inverter after the array, not before. A quality hybrid inverter in Pakistan should carry the full array output continuously with room to spare for future panels, and its MPPT window must accept your planned string voltage.
Two refinements sharpen the result. If you plan battery backup for night loads, add those evening kilowatt hours to the daily figure before dividing by sun hours, since the panels must both run the house and refill the bank. And if a portion of your roof faces away from south, discount that section’s contribution by 10 to 15 percent in your math.
Know Your Load Before You Shop
If your bills are missing or the property is new, build the daily figure from the appliances themselves. The table below covers the loads that dominate a typical Pakistani household.
| Appliance | Typical draw | Hours per day | Daily energy |
|---|---|---|---|
| 1.5 ton inverter AC | 1,200 W average | 8 | 9.6 kWh |
| Refrigerator | 150 W average | 24 | 3.6 kWh |
| Ceiling fans x4 | 320 W | 12 | 3.8 kWh |
| Water pump 0.5 hp | 375 W | 1.5 | 0.6 kWh |
| Lighting and electronics | 250 W | 6 | 1.5 kWh |
Total the right-hand column, then run steps three to five above. Most families are surprised to learn a single air conditioner outweighs everything else combined.
How Many Panels Does a 5kW Solar System Need?
With 2026 module wattages, fewer than you might think. Mainstream residential panels now ship at 550 to 620 watts each, so a 5 kW array lands at nine or ten panels covering roughly 25 to 28 square meters of roof.
Before finalizing the count, model your exact roof with the free PVWatts tool from the U.S. National Renewable Energy Laboratory. It accepts any Pakistani city, factors in tilt and orientation, and outputs month-by-month generation estimates you can compare against your bills. Ten minutes there beats any verbal promise.
Roof direction matters as much as panel count. A south-facing pitch at around 30 degrees is ideal for most of the country, while east-west splits sacrifice a little total yield in exchange for flatter morning and evening output. As a sanity check, a clean, well-oriented installation in most Pakistani cities produces roughly 4 to 4.7 units per day for every kilowatt installed, so a 5 kW array should log somewhere near 600 to 700 units in a good month.
Sizing Mistakes That Shrink Your Savings
- Sizing to the sanctioned load. Your meter’s sanctioned capacity has nothing to do with consumption. Size to units used, never to the connection size.
- Forgetting winter. Shorter days cut generation 30 to 40 percent. If winter bills are also high, lean toward the upper end of your calculation.
- Ignoring shade lines. A water tank shadow crossing two panels at 3 p.m. can drag down an entire string. Walk the roof at different hours before signing anything.
- Leaving no expansion room. Buying an inverter with zero spare capacity means a second inverter purchase the day you add panels.
- Skipping a site survey. An established solar company in Kohat or your own city will measure the roof, check the earthing and inspect the distribution board before quoting, and that survey routinely changes the recommended capacity by a kilowatt or more.
Planning a solar installation resembles planning any major household transition. The same way a smooth shifting day depends on trusted professionals rather than the cheapest quote, a smooth installation depends on a surveyed design rather than a phone estimate.
Frequently Asked Questions
What solar system size suits a 200-unit monthly bill?
Around 200 units per month works out to about 7 kWh per day, which a 2 kW array covers comfortably after losses. Most households at this level install 3 kW to leave headroom for a future air conditioner.
Should I size my system for summer or winter consumption?
Size for your annual average, weighted toward whichever season hurts your wallet more. In most Pakistani homes that is summer, but gas shortages have pushed many families onto electric heaters, so check both extremes on your bills.
Can I start small and expand my solar system later?
Yes, if you plan for it now. Choose an inverter with spare MPPT capacity, leave conduit space, and keep your panel model documented so future modules match the string. Expansion without that planning usually means replacing hardware.
Get the Number Right First
Every rupee of your solar budget flows from one figure, so calculate your solar system size before you fall in love with any brand or package deal. Work the five steps, verify the output with PVWatts, and demand a physical survey in writing. Do that and your 2026 installation will be sized for your home, not for someone’s inventory.
