How to size a solar inverter in Lahore

The inverter is sized to two different things at once

Most people ask one question: what size inverter do I need. The honest answer is that an inverter has to satisfy two separate numbers and they rarely land in the same place. On one side sits the panel array, which feeds DC into the MPPT trackers. On the other side sits the house load, which pulls AC out of the inverter and occasionally spikes hard when a compressor kicks in.

Size only for the panels and the house trips every time the water pump and the AC start together. Size only for the load and the array either overshoots the MPPT window or gets clipped on clear April afternoons. Sizing is the compromise between the two, and in Lahore the compromise leans towards surge capacity because of how households here actually run.

Start with the load, not the roof

Before anyone climbs on the roof with a tape, list what runs at the same time on a July evening at 9 pm. Not the total connected load, the simultaneous load. A 10 marla home in Johar Town might have 14,000 watts of connected appliances and still peak at 4,200 watts.

Appliance	Running watts	Start surge
1.5 ton DC inverter AC	1,100 to 1,300	1,500
1.5 ton non inverter AC	1,800	4,500 to 5,400
Refrigerator, no inverter compressor	180	900
0.5 hp water pump	400	1,600
Automatic washing machine	500	1,400
8 ceiling fans plus LED lighting	520	560
Iron or electric kettle	1,500	1,500

Add the running watts of everything that genuinely overlaps, then add the single largest surge on top of that total. That is the number the inverter must survive. For the table above with two inverter ACs, fridge, fans, lights and a pump running, the steady figure is around 3,600 watts and the peak with the pump starting reaches roughly 4,800 watts. A 5kW hybrid inverter at PKR 165,000 handles it. A 3kW unit at PKR 95,000 does not, no matter how good the brochure looks.

The non inverter AC problem

Plenty of homes in older parts of Lahore, Mughalpura and Walton and the inner Cantt streets, still run rotary compressor window and split units bought years ago. Those draw a locked rotor current that can be five times the running current for about half a second. A 5kW inverter rated for 150 percent surge for five seconds is fine. One rated for 110 percent will fault out with an overload alarm. The datasheet line to look for is peak power or surge power, usually written as 10,000W for 10 seconds or similar. Read it before buying, because the retail counter on Hall Road will not volunteer it.

Then check the array, using DC to AC ratio

DC to AC ratio is simply panel watts divided by inverter AC watts. A 5kW inverter carrying 6,500 watts of panels is running a ratio of 1.3. Almost every hybrid inverter sold in Pakistan accepts a ratio between 1.2 and 1.5, and the good ones state it plainly on the datasheet as maximum PV input power.

Oversizing is not a trick, it is normal engineering. Panels almost never make their rated wattage. A 585W panel in Lahore during May at 48 degrees cell temperature is putting out around 490W. In December haze it might make 300W. Sizing the array at 1.25 to 1.35 times the inverter keeps the inverter working near its efficient band for more hours of the day instead of loafing at 30 percent load all winter.

• Ratio 1.0: under used inverter, poor winter output, generally a waste of the inverter you paid for.
• Ratio 1.25 to 1.35: the sweet spot for Lahore. Very little clipping, strong shoulder season and winter performance.
• Ratio 1.5: acceptable if the roof faces east and west in a split array, since the two halves peak at different times.
• Ratio above 1.5: real clipping losses on clear March and October days, and a risk of exceeding the maximum DC input current per MPPT.

Clipping sounds worse than it is. Even at a 1.4 ratio, an honest annual loss in Lahore comes to 1 to 2 percent of production, and those losses happen only in a narrow band around solar noon on the clearest days of spring. Meanwhile the gain across the smoggy December weeks is far larger. Our solar calculator works this out for a given roof if you would rather not do the arithmetic.

Voltage and current limits still bind

Ratio is about power. The MPPT also has a voltage window and a current ceiling, and both can be violated while the power number looks fine. A string of 14 panels at 41V open circuit gives 574V on a cold January morning, which is already knocking on the 550V or 600V limit of many single phase hybrids. Cold weather raises open circuit voltage. Lahore hits 3 or 4 degrees in late December some years, and that is when strings fry input stages. Design the string length for the coldest morning, not the average day.

Hybrid inverters need a third number: battery current

Once a battery joins the build, the inverter also has to charge and discharge it at a sensible rate. A 5kWh lithium pack at PKR 285,000 typically wants a 50A to 100A charge current at 48V or 51.2V. If the inverter maxes out at 60A of battery charging, the pack charges at about 3kW, which takes roughly two hours of good sun. That is usually fine. If two packs are stacked, or a Pylontech 3.5kWh module is added later at PKR 195,000, check that the inverter can push enough current or the bank will never fill before sunset in winter.

This matters most on hybrid and battery builds where the customer wants overnight backup. There is more detail in the battery bank sizing guide and in the hybrid with battery guide.

Common sizes and what they actually run in Lahore

Inverter	2026 price	Panel array	Realistic load
3kW hybrid	PKR 95,000	3.5kW to 4.2kW	Fans, lights, fridge, one inverter AC on a good day
5kW hybrid	PKR 165,000	6.0kW to 6.9kW	Two inverter ACs plus general household load
6kW hybrid	PKR 158,000	7.2kW to 8.1kW	Two to three ACs, pump, kitchen loads together
10kW hybrid, three phase	PKR 295,000	12kW to 13.5kW	Four to five ACs, large 1 kanal home

Notice the 6kW unit costing less than the 5kW unit. That is not a typo. Different brands and product generations sit at different price points in Lahore, and a newer 6kW model frequently undercuts an older 5kW one. Anyone quoting purely on kilowatts without naming the model is guessing. See the 5kW system pricing article and the 10kW hybrid breakdown for full bills of quantity.

The undersizing mistake that keeps repeating

Here is the pattern seen on dozens of jobs. A family buys a 3kW inverter because the bill is around PKR 18,000 and someone told them 3kW is enough. It works beautifully through October, November and February. Then May arrives, the second AC gets switched on, and the inverter starts throwing overload faults every evening. The family then either adds a second inverter, which means a second set of wiring and a second net metering headache, or sells the 3kW at a loss and buys a 5kW.

The cost of that mistake is roughly PKR 60,000 to PKR 80,000 in lost resale plus the labor to redo the AC side wiring. Going one step up at the start costs PKR 70,000 more and avoids all of it. Sizing to today's load in a city where households add an AC every second summer is the expensive way to save money.

The honest caveat on the other side

Oversizing has a real cost too, and installers who push a 10kW inverter at every house are not doing anyone a favour. A large inverter idles at 40 to 70 watts continuously, which is 1.2 to 2 units a month burned doing nothing. It also runs at lower conversion efficiency at very light loads, so those winter afternoons where the house draws 400 watts are converted less efficiently than a right sized unit would manage. And if the array never grows, the extra PKR 130,000 spent on going from 5kW to 10kW simply sits on the wall. Buy one size of headroom, not three.

Single phase or three phase

LESCO supplies most Lahore homes on single phase up to a sanctioned load of around 15kW. Larger houses in DHA, Bahria Town and parts of Gulberg often have a three phase connection already. Two things to know:

1. Net metering must match the connection type. A three phase house needs a three phase inverter for a clean LESCO net metering approval, or the meter and the inverter fight over phase balance.
2. If only one phase is solarised in a three phase home, the other two phases keep drawing full retail units and the bill barely moves. This surprises people every year.

Above 10kW, three phase is the sensible default. Below 6kW, single phase is almost always the right call. Between those, it depends on the existing LESCO connection, which the survey team confirms on site.

What we check during a site survey

The PKR 3,000 survey fee, which is deducted from the final installation bill, covers a physical walk through rather than a phone estimate. On an inverter sizing visit the team records the sanctioned load from the LESCO meter, counts and rates every AC in the house, checks the distribution board for spare ways and existing breaker ratings, measures the cable run from the proposed inverter wall to the DB, and photographs the roof to work out how many panels fit and in what string configuration.

That last part decides the DC to AC ratio. Roofs in Model Town with mature trees on the south side often support fewer usable panels than the square footage suggests, which changes the inverter choice. Shade also pushes the design towards more MPPT trackers or a split east and west array.

Once the system is running, keep an eye on the fault log rather than only the production number. Repeated overload or over temperature entries in July usually mean the inverter is placed in a hot, unventilated spot rather than genuinely undersized. Our repair team sees more heat related derating than actual sizing failures. A shaded, ventilated wall inside the house beats a metal box on the roof every time.

For more on the equipment side, compare specific models in the Inverex, Growatt and Solis articles, or read the summer AC load guide if cooling is the main reason for going solar.