Can Solar Run Your AC and Other Heavy Appliances?

The short answer

Yes, rooftop solar can run an air conditioner, a geyser, a washing machine, a water pump and other heavy appliances. The system does not treat them differently: it produces electricity and the appliance uses it. What matters is whether the system covers the total energy you use, and whether you use that energy while the sun is up.

For many families in Uttar Pradesh, the air conditioner is the reason the electricity bill jumps from a few hundred rupees in winter to several thousand in summer. Summer also brings the strongest sunshine and the longest days, so solar suits air conditioning if the system is sized for it. This guide shows how to work out the numbers yourself and what to ask your installer.

The figures below are typical values for explanation. Actual power use depends on the model, its age, the room, the temperature and how you use it, so check the label on your own appliances.

Step 1: Find power and hours for each appliance

Every appliance has a rating plate or a manual that shows power in watts or kilowatts. Multiply by the hours of use per day to get units, which are kilowatt-hours. For example, a 1.5 kW appliance running for 2 hours uses 3 units. Some appliances, such as air conditioners and refrigerators, cycle on and off, so the average draw is lower than the rating plate figure. An inverter air conditioner also varies its power with the load.

The table below shows an illustrative day in a home with one air conditioner. These are assumed values for explanation. Replace them with the numbers from your own appliances and habits.

Step 2: Turn daily units into solar capacity

As a rough guide, one kilowatt of rooftop solar in Uttar Pradesh produces around 4 to 5 units per day on average across the year, a little less in monsoon and winter and more in clear spring and summer days. To cover a daily use of about 11 units, as in the example above, you would divide by roughly 4.5, which gives about 2.5 kW. A system of 3 kW would cover that use with some margin, but your results will vary with shade, tilt and dust.

The air conditioner alone, at about 7.8 units a day in the example, needs roughly 1.7 kW of solar to cover it on an average day. Two air conditioners, or running them most of the night, push the number up quickly. A 1 kW system is far too small for a home that runs air conditioning, and last summer's bills are the best guide to sizing. Our article on how much solar you need for your electricity bill explains the method in more detail.

Do not forget your roof space. A larger system needs more shadow-free area, and our roof assessment checklist helps you check it.

Daytime and night: where the energy comes from

Solar produces only when the sun is up. An air conditioner running through the hot afternoon uses solar power directly. The surplus, if any, goes to the grid. Late evening and night use, when many families run their air conditioners for sleeping, comes from the grid, unless you have a battery.

Under net metering, exports during the day are credited against imports at night, so the balance over the billing period determines what you pay. For a home that uses a lot of air conditioning at night, the day-time surplus must be large enough to cover it, which means a bigger system. Our guide on how credits appear on your electricity bill gives a worked example. Settlement rules are set by the regulator and can change, so check them with your DISCOM.

This works without a battery, so most homes in towns with reliable supply choose it. Net metering lets the grid stand in for storage.

Running heavy loads during a power cut

A standard on-grid inverter stops when the grid is down, for safety reasons, so your solar system will not run the air conditioner during a power cut. To keep a heavy load running you need a hybrid or off-grid inverter and batteries, and the equipment must be sized for the load, including the high starting current of motors.

An air conditioner may draw 1.5 kW or more continuously, so a few hours of backup means several units of battery capacity and an inverter that can handle the load. That is a significant extra cost, and batteries need replacement every few years. Many households find it more economical to back up lights, fans, the router and the refrigerator, and to run the air conditioner only when the grid is available. Our article on battery sizing explains the arithmetic and our guide on on-grid, off-grid and hybrid systems compares the options.

• Decide which loads truly need backup during a cut.
• Count the starting current of motors, which can be several times the running current.
• Ask for the battery capacity in kilowatt-hours and the expected backup hours at your chosen load.
• Remember that battery replacement is a future cost.

Starting currents and the inverter

Appliances with motors, such as air conditioners, pumps and refrigerators, draw a surge of current when they start, which can be several times the running current for a moment. A grid-connected system draws this from the grid, so it is not a problem. In a hybrid or off-grid system, the inverter must be able to handle the surge, which affects the inverter size and cost.

Inverter air conditioners start more gently than older fixed-speed models, which helps. If you plan backup for a pump or an air conditioner, tell the installer the exact models and ratings, so that the inverter is chosen for the surge and not only for the running load.

Does solar make air conditioning cheaper

Over time, solar units usually cost less than grid units, because you pay for the system once and then get power for many years with low running cost. The saving is larger when your use is high, because solar replaces units in the expensive upper slabs of the tariff. A home with heavy summer air conditioning often sees a large drop in its summer bills after solar.

How much you save depends on system cost, subsidy, tariff and usage. Fixed charges remain, and some months, such as cloudy monsoon weeks, produce less. Our payback article shows how to calculate it with your numbers. Treat any promise of a zero bill that does not state its assumptions with caution.

Efficiency also matters. A 5-star inverter air conditioner, good insulation, shaded windows and a sensible thermostat setting cut the units you need, which can shrink the solar system you have to buy.

Plan ahead for what you will add

Many households add an air conditioner, a geyser or an electric vehicle charger after they install solar. If you expect to, tell the installer before the system is designed. It is cheaper to provide space, a slightly larger inverter and suitable wiring from the start than to rework later. Remember also that your sanctioned load may need to rise if you add heavy appliances, which is a separate request to the DISCOM.

Our article on home EV charging and rooftop solar planning covers one common addition in detail. If you would like help working out the right size for your home, you can use the quotation form on our home page and we will check your bills and roof and explain the estimate.