Inverter temperature derating calculator

By the SmartSolarSizer team · Published 30 October 2026

How the calculator works

It works out the air temperature right next to the inverter, reads how much of its rating it can give at that temperature, then compares that with what you run.

Air at the inverter. You enter the hottest outdoor temperature in the shade. The mounting spot then adds an estimate. A shaded, airy wall adds nothing. A room without AC adds 3 °C, a closed store room, garage or roof shed 7 °C, and direct afternoon sun 12 °C. These are rough rules, not measurements. If you put a cheap thermometer next to your inverter on a hot afternoon, type your own figure into the advanced settings. An air-conditioned room is taken as 27 °C.

Heat factor. This comes from a derating curve. Victron publishes one for its inverters: 100% of the rating at 25 °C, 90% at 40 °C and 69% at 65 °C (Victron). Hybrid inverters are less open about it. Deye's SUN-5K datasheet says ">45℃ Derating" with a working range up to 60 °C (Deye). Huawei's SUN2000-5KTL-L1 says it is "Derated above 45 °C" with the same 60 °C limit (Huawei). Neither says how fast the output falls. For that curve we assume a straight line from full power at 45 °C to half power at 60 °C, and nothing above 60 °C. If your manual has a graph, read two points off it and enter them under "Use my inverter's datasheet".

Size you need. We divide your load by the heat factor and add 25% headroom, the margin our appliance guides use. If you pick a motor, the inverter's surge, which shrinks with the same factor, must also cover the moment it starts.

Inverter derating at 40, 45 and 50 °C

How much power does an inverter lose in hot weather? Less than many people fear while it sits in the shade, and far more once it's somewhere hot. Here is the share of its rating each curve allows:

Victron: published rating, straight lines between its three points. Hybrid: full power to 45 °C per the Deye and Huawei datasheets; the line above 45 °C is our assumption.

Victron also lists watts at each temperature for individual models, which shows the same pattern in real numbers (Victron Inverter Smart, Phoenix 12/800):

The 5000 model loses 300 W between 25 and 40 °C and another 900 W by 65 °C. That's why a figure printed at 25 °C can be misleading in Phoenix, Dubai or Lahore.

Why inverters overheat and trip in hot weather

The parts that switch power inside an inverter, its semiconductors, heat up as they work. When the heat sink gets too hot, the inverter protects them. SMA describes the usual order: power is reduced in steps, and only "in extreme cases" does the inverter shut down completely. It adds that derating itself does no harm (SMA). So a dip in output at noon is the inverter doing its job, not a fault.

Shutdowns come when the heat keeps building. Solis says its inverters' fans switch on at an internal temperature of about 85 °C, roughly 38 °C outside. They shut down with an over-temperature alarm at about 110 °C inside, roughly 60 °C outside (Solis). Deye's manual lists fault F64, "heat sink temperature is too high", and its advice is to switch off for 10 minutes and restart (Deye manual).

Three things push an inverter into that zone on a summer afternoon. The first is hot air around it, the second a heavy load (an AC compressor is the usual culprit), and the third blocked airflow from dusty vents or a cupboard door kept shut. The first and third are cheap to fix; the second means switching something off or buying a bigger inverter.

Best place to install an inverter in a hot country

Shade and moving air matter more than inverter size. Deye asks for about 50 cm of clear space at the sides, above and below its SUN-5K, 100 cm in front, and says to avoid direct sunlight. Its warranty excludes damage from poor ventilation (Deye manual). Huawei warns that under direct sunlight "the power may be derated due to the temperature rise" and suggests a sheltered spot or an awning (Huawei manual).

In practice the best spot is usually a north-facing wall (south-facing in Australia and South Africa) under a roof overhang, out of the afternoon sun, with space around it. The worst are a tin roof shed, a cupboard under the stairs, or a garage where a hot car is parked. An air-conditioned room looks ideal, but in Pakistan and India the AC is often off during load-shedding, exactly when the inverter is working hardest. Keep batteries out of the same hot corner too.

Hottest-day check for 13 cities

This uses each city's hottest month and a hot day: the average hottest day of the year where the climate table gives it, or the record where it doesn't. The output is for a 5 kW hybrid inverter on the curve above. Lahore and Karachi use their records, so their rows are harsher than the rest.

Temperatures from the 1991–2020 climate tables on Wikipedia for each city (sources below). Johannesburg's table has no reliable hot-day figure, so it is left out of the check. Mounting adjustments are the estimates described above.

Look down the shaded-wall column: in most cities the inverter barely notices the heat. Move along the row and the difference between a shaded wall and a hot room shows up in Phoenix, Dubai, Lahore, Karachi and Delhi.

What size inverter do I need for a hot climate?

Start with what you run at the same time, add 25%, then divide by the heat factor for the spot you've chosen. For the 3 kW load in the example above that's a 5 kW inverter on a shaded wall on Lahore's record day, but 6 kW in a closed store room. Before you pay for the bigger inverter, price a better spot: a few metres of cable usually costs less than the next size up.

kVA vs kW: is a 5 kVA inverter 5 kW?

Not always. kVA is the inverter's apparent power and kW is the real power your appliances use. Some inverters give the same figure for both; others give about 80% of the kVA figure in watts. Check the watt rating before you size anything:

If your label only shows kVA, choose kVA in the calculator and keep the power factor at 0.8 unless the datasheet says otherwise. For what a 5 kVA inverter runs in practice, see what a 5kVA inverter can carry.

ACs, pumps and fridges: surge in the heat

Motors draw several times their running power for a moment as they start. An inverter covers that with its surge rating: Deye and Solis hybrids give twice their rating for 10 seconds (Deye, Solis). We scale that surge by the same heat factor, which is a cautious assumption because manufacturers don't publish surge at temperature.

Running and starting watts are the figures our main calculator uses for these appliances.

Picture a 5 kW hybrid in that hot store room on Lahore's record day. Its surge falls from 10 kW to about 6.6 kW. Run a 1.5 ton non-inverter AC with 1.0 kW of other things and the inverter carries 3.2 kW, against the 3.3 kW it can give. Starting the AC needs about 6.0 kW for a moment, against 6.6 kW of surge. Both just fit, so one more appliance switching on could trip it. An inverter AC starts far more gently. Our 1.5 ton AC guide and AC solar guide cover sizing for both.

Grid-tied and hybrid inverters behave differently

A grid-tied inverter in the heat simply sends less solar out. On the hottest afternoons anything above its derated limit is cut off, which is called clipping. Your home keeps running from the grid, so nothing trips, but you lose some solar output. A hybrid or off-grid inverter that powers your home is different: if it can't supply what you're running, it cuts back or shuts down and the house goes dark. Choose "Grid-tied only" in the advanced settings to see the clipping limit instead.

Inverter derating at high altitude

Thin air cools less well. EG4's IP65 inverters keep full power up to 2,000 m, give 85% from 2,000 to 3,000 m and 70% from 3,000 to 4,000 m, and aren't allowed above 4,000 m. Its IP20 models aren't allowed above 2,000 m at all (EG4). The calculator uses those steps. Few homes are that high, and Johannesburg, at about 1,700 m, is still under the first step.

Heat and your solar panels

Panels lose output in heat too, separately from the inverter. A Jinko Tiger Neo panel, for example, loses 0.29% of its power for every degree its cells run above 25 °C. Its cells reach about 45 °C in mild conditions (800 W/m² of sun, 20 °C air) (Jinko datasheet). On a 45 °C day the cells run much hotter than that, so the panels are giving less than their rating too. That's why a heatwave cuts total solar output twice. Our appliance guides show how many panels each appliance needs in each city, and the battery size calculator covers backup.

Common questions

Sources

Every figure on this page comes from these documents, opened on 30 October 2026. Where we had to assume something, the text says so.

• Victron Energy: output rating, operating temperature and efficiency
• Victron Phoenix Inverter Smart technical specifications
• Victron Phoenix 12/180–1200 VA datasheet
• Deye SUN-3.6–6K-SG03LP1 datasheet
• Deye SUN-3.6–6K-SG03LP1 user manual
• Huawei SUN2000-3–6KTL-L1 specifications
• Huawei SUN2000-2–6KTL-L1 user manual
• Solis: inverter temperature de-rating
• Solis S6-EH1P(3-8)K-L-PLUS datasheet
• SMA: temperature derating technical information
• EG4: inverter altitude derating usage restrictions
• Jinko Tiger Neo JKM560–585N-72HL4R-(V) datasheet
• Climate data: Phoenix (Wikipedia, 1991–2020 table)
• Climate data: Houston (Wikipedia, 1991–2020 table)
• Climate data: New York (Wikipedia, 1991–2020 table)
• Climate data: Seattle (Wikipedia, 1991–2020 table)
• Climate data: Toronto (Wikipedia, 1991–2020 table)
• Climate data: London (Wikipedia, 1991–2020 table)
• Climate data: Berlin (Wikipedia, 1991–2020 table)
• Climate data: Madrid (Wikipedia, 1991–2020 table)
• Climate data: Dubai (Wikipedia, 1991–2020 table)
• Climate data: Lahore (Wikipedia, 1991–2020 table)
• Climate data: Karachi (Wikipedia, 1991–2020 table)
• Climate data: Delhi (Wikipedia, 1991–2020 table)
• Climate data: Sydney (Wikipedia, 1991–2020 table)
• Climate data: Johannesburg (Wikipedia, 1991–2020 table)

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