Solar inverter overheating in Lahore summer

The flat line on your power curve

Open the app on a clear June day. If the curve rises normally through the morning and then goes flat at some value below the inverter's rating, holding that exact number from about 1 pm to 4 pm before falling away, the inverter is derating on temperature. Nothing is broken. The unit is throttling itself to survive.

On a healthy day the curve should be a smooth bell. On a hot day with a well-placed inverter there might be a slight shoulder in the worst hour. On a badly placed unit the flat top starts around noon and stays for four hours, and every one of those hours costs units.

This is different from panel heat losses, which affect every install in Lahore equally and are covered in why solar output drops. Panel derating is physics you cannot avoid. Inverter derating is placement, and placement is fixable.

What the datasheet actually promises

Nearly every hybrid inverter sold in Lahore is rated for full output up to 45C ambient. Above that, output falls on a curve set by the manufacturer. Lahore hit 45C or higher on a meaningful number of days last summer, and the air inside a house is not the number that matters anyway. What matters is the heat sink temperature, which is ambient plus whatever the unit's own losses add.

A 5kW hybrid running at full load produces roughly 250 to 400W of waste heat continuously. In an open, ventilated space that heat leaves. In a 6 by 8 foot store room with the door shut, it does not, and the room climbs steadily all afternoon.

Placement	Typical June air temp at 3 pm	Derating starts around	Estimated summer loss on 5kW
Closed store room under stairs	50 to 54C	12:00 pm	350 to 500 units
Rooftop enclosure, metal box	55 to 62C	11:30 am	450 to 700 units
West-facing car porch wall in sun	48 to 53C	1:00 pm	250 to 400 units
Garage with door open, shaded	42 to 46C	2:30 pm	80 to 150 units
Ventilated utility area, internal wall	38 to 42C	Rarely	Under 60 units

Take the middle of that range. A badly placed 5kW losing 400 units across the summer, at LESCO rates of PKR 48 to 65 per unit, is PKR 19,000 to 26,000 gone every year. Relocating an inverter properly costs a fraction of that once, and the payback runs under a single season.

Why the store room is the wrong spot

It gets chosen for good reasons. It is out of sight, it is near the distribution board, it keeps the equipment away from children, and the homeowner does not want a grey box on a living wall. Every installer in Lahore has had this conversation.

Four things go wrong in there:

1. The heat has nowhere to go. A closed room with one door and no vent accumulates the inverter's own output. By 4 pm the room is well above the rest of the house.
2. Dust. Store rooms hold sacks, cartons, old furniture, and fine dust that the cooling fans pull straight through the heat sink fins. Fans clog in three years instead of eight.
3. Shared space with other heat. Geysers, the main breaker panel, and often the battery all end up in the same room. They heat each other.
4. Nobody looks at it. A fault code can sit on that screen for six weeks before anyone opens the door. That alone costs more than the derating.

Rooftop enclosures are worse. Some installers put inverter and battery in a metal box on the roof to shorten DC cable runs and save on wiring, which runs PKR 25,000 for a typical DC and AC set. That saving buys a box that reaches 60C internally in June. It is the single worst placement seen on Lahore roofs and it shortens the life of everything inside it.

Where an inverter should go in a Lahore house

The rules are not complicated, and a competent installer applies them without being asked.

• An internal wall, not an external wall that bakes in afternoon sun. North-facing internal walls stay coolest.
• Never in direct sunlight, at any hour. A small shade canopy is required if outdoor mounting cannot be avoided.
• Clearance of at least 30cm at the sides and 50cm above and below, so convection can actually work. Units mounted tight under a shelf cook themselves.
• Cross ventilation in the room: a low inlet vent and a high outlet, ideally with an extractor at the high point.
• Away from the battery, not stacked against it. Both produce heat and both suffer from it, as covered in battery not charging.
• At eye level, somewhere a person walks past daily. Faults get caught in hours instead of weeks.
• Away from the kitchen. Cooking grease plus dust turns into a film on the heat sink that no fan can shift.

In practice the best spots in a typical Lahore 10 marla house are a ventilated utility area, a shaded servant quarter passage, or an internal garage wall with the shutter left open during the day. In DHA and Gulberg homes with a basement, a basement wall works very well because the temperature there rarely crosses 34C even in June.

Retrofitting a bad placement

Moving the inverter is not always practical. The cable runs, the net metering wiring, and the LESCO connection point all sit where they sit. Ranked by cost and effectiveness, these are what actually help.

1. Open a vent pair in the room. A 6 inch low inlet and a 6 inch high outlet with an exhaust fan on a thermostat. Materials and labour run PKR 8,000 to 15,000 and typically drop peak room temperature by 5 to 8C. Best value on this list.
2. Clean the heat sink and replace the fans. Fan modules at PKR 4,500 to 8,000. A clogged fan can be the entire problem, especially on a unit past three summers.
3. Add a shade structure if the unit is outdoors. A simple GI sheet canopy with an air gap, around PKR 6,000 to 10,000, removes direct radiation load entirely.
4. Relocate to a better wall. Depends on distance. Under 10 metres it is usually PKR 18,000 to 30,000 including new AC and DC runs and re-terminating everything.
5. Split the load. On larger homes, moving some circuits off the hybrid reduces continuous loading and therefore heat. Free, but it changes what stays up during load shedding.

One caveat worth stating plainly. If the inverter is genuinely undersized for the house and running near its rating all afternoon, no amount of ventilation fixes it. A 5kW hybrid carrying two ACs plus general load in a Lahore June is at its limit, and it will run hot regardless of where it hangs. In that situation the honest answer is a larger unit, not a better fan. A 6kW at PKR 158,000 or a 10kW at PKR 295,000 costs less than replacing a cooked 5kW every three years. Sizing is covered in the calculator and in summer AC load on solar.

Heat damage that does not show up as a code

Derating is the visible symptom. The invisible one is what sustained heat does to the parts inside.

Electrolytic capacitors on the DC bus lose life roughly by half for every 10C above their rated temperature. An inverter run at 55C internal for four summers ages the way a well-placed one would over ten or twelve years. The unit does not throw a code. It just fails one afternoon in year five, and the owner assumes bad luck. It was not.

Solder joints on the power stage suffer the same way through thermal cycling: hot every afternoon, cool every night, expanding and contracting for years until a joint cracks. Board-level repair then costs PKR 18,000 to 45,000, and on brands without local service capacity the unit is simply replaced. Brand service reality is discussed under Inverex, Growatt and SolarMax.

Seasonal routine that keeps it cool

Two visits a year handle it. Late March, before the heat arrives, blow out the heat sink and fan intakes, confirm the vents are clear, and check the fan spins freely by hand. Late September, after monsoon, check for water marks and corrosion on the case and around the glands.

While the technician is there, panel cleaning matters for the same reason. A dirty array on a hot roof is a double loss, and both are dealt with on one visit through the cleaning service or a repair and maintenance call. Costs are listed in cleaning costs and repair costs.

For anyone planning a new build rather than fixing an old one, insist on the placement conversation before the deposit is paid. Any installer who agrees to a metal box on the roof without discussing summer temperature is not thinking past the invoice. Correct placement is standard on every installation and hybrid battery build we do, including work in Bahria Town and Wapda Town where rooftop equipment boxes were common a few years ago.