03/08/2022

Most home appliances draw a steady current, which you can work out from its power rating in watts. Once you have that you can size 80w solar panel to meet the demand. Air conditioners, like fridges and freezers, are a bit special beacuse they contain compressor motors.

This means that the power rating changes depending on the cooling cycle and a motor that starts and stops periodically, so you need to use average energy consumed in calculations.

A 5 Ton AC unit requires 6000 watts of solar panels, assuming irradiance of 4 peak-sun-hours per day. 500Ah of battery energy storage will also be needed per Ton for each hour of running time when the sun doesn’t shine. For daytime running a 200Ah battery is sufficient to ensure surge currents are supplied.

You need to consider these factors before sizing solar panels to run an AC unit:

Why are AC units rated in tons?

What the actual AC power rating in kW?

What is compressor motor inrush current?

How long will you run the AC unit?

Do you need batteries to run your AC?

Which batteries are best for storing solar energy?

How much power can solar panels produce?

What size olar panel you intend to use

Why you need an inverter and how to size it

Now you know what happens in an ac unit as the load, let’s take a look at solar panels can be used to supply this kind of load.

Test of the post will be based on using fixed solar panels with 300 watt rating, as bigger panels are better buy in terms of dollars per watt.

The output power of any solar panel depends on several factors:

- solar panel efficiency (between 20% and 22%)
- how big is the solar panel area in square meters
- irradiance (kWh/m2/day) (the sun’s energy, by location)
- orientation (solar panel direction and angle)
- fixed or auto-tracking for the solar panel array

A 300 watt solar panel will generate about 1.2kW/h per day with average peak-sun-hours of 4.

Solar panels generate direct current (d.c.) but domestic appliances use alternating current (a.c.), and this is why you need an inverter for the d.c. to a.c. conversion.

An inverter reshapes d.c. power electronically into a smooth sinusoidal waveform, which is identical to the power fed to your house by utility companies.

Why air conditioners are rated in tons? An air conditioning unit is rated according to efficiency. They are all different, so if we used electrical kw rating to compare them, it might not be a true comparison of their cooling capacity.

Basically, two AC units rated at 5kW will probably not have the same cooling capacity – it depends on their efficiency.

So how do we define a ton of ac cooling power? It is the amount cooling capacity needed to melt 2000 lbs of ice in 24 hours. It’s known as a short ton.

The higher ac tonnage, the bigger the volume of air can be cooled per hour. One ton is also equivalent to 12,000 BTU/hour (British Thermal Units/hour), which is the same as 3.5 kW.

A 1 Ton ac unit has a cooling capacity of:

(12000 x 1055)/3600 = 3516 Joules/sec = 3516 Watts