Running two 1.5 ton ACs on a 5 kW hybrid inverter

The setup

• An inverter: UTL’s 5 kVA transformerless hybrid, HYB-5-GXLS2. UTL lists it at 5,000 W rated output, up to 6,500 W of panels, and support for lithium and lead-acid batteries, with a 5-year warranty.
• A 5 kWh lithium battery, such as UTL’s 51.2 V, 100 Ah battery, which holds about 5.1 kWh. We match the battery to the inverter’s battery voltage before quoting.
• Panels sized close to the inverter’s 6,500 W input limit.
• Two 1.5 ton inverter ACs.

Is 5 kW enough for two ACs?

A 1.5 ton inverter AC uses roughly 1 to 1.4 units an hour on a hot Punjab afternoon, and less once the room has cooled. That is a load of about 1 to 1.4 kW each, so two together come to about 2 to 2.8 kW.

A 5 kW inverter carries that and leaves about 2 kW or more for the fridge, fans, lights and everything else. What limits the system is energy, which has to come from the panels while the sun is up.

The panels do the daytime work

Over an eight-hour day, two ACs at about 1.2 units an hour each use about 19 units. We plan on about 3.4 units a day from each kW of panels, averaged over the year, and summer gives more than the average. Panels close to the inverter’s 6.5 kW limit make that kind of daily total in the season when the ACs run.

At any moment, though, hot panels make less than their rating, and output dips when a cloud passes. That is the battery’s job.

What the battery does

A lithium battery can be used down to about 80% of its capacity each cycle, so a 5 kWh battery gives about 4 kWh.

In the day, the battery fills the gaps when the panels fall short: a passing cloud, a hazy hour, a power cut. In the evening, it keeps one AC running for a while after sunset, or both for a shorter time. It is not enough to cool two rooms through the night, and a battery bank that could would cost far more than it saves.

Switch them on one at a time

An AC draws more power for a moment as its compressor starts. Inverter ACs start gently, but our hybrid calculator still allows about one and a half times the running load for the start. Two ACs starting in the same second can reach the inverter’s rating. Switch one on, wait a minute, then switch on the other. UTL does not list a surge rating for this model in its catalogue, so we check the start-up load against the inverter when we design the system.

Older fixed-speed ACs draw more when they start and more while running. If yours are not inverter ACs, tell us, because the sizing changes.

Where the grid fits in

A hybrid system stays connected to PSPCL. When the grid is on, it fills in at night and on dull days, so the house never depends on the battery alone. When the grid fails, the inverter switches to the panels and the battery. Surplus power in the day is exported under net metering, and hybrid systems qualify for the PM Surya Ghar subsidy.

Price, and a cheaper alternative

For the price of a 5 kW system, see 5 kW solar system price in Punjab. If you only need to cover the AC’s units on your bill, an on-grid system may be cheaper; how much solar a 1.5 ton AC needs explains the difference.