Best air conditioners for home solar systems

South African households who want their small to medium-sized solar systems to run air conditioners should use inverter-type systems.

The amount of power needed to regulate the temperature of a room can be substantial, particularly if the outdoor temperature is significantly lower or higher than your ideal indoor temperature.

The Department of Mineral Resources and Energy (DMRE) has estimated that shifting to more energy-efficient air conditioners in South Africa could collectively save 400,000MWh of electricity annually.

That’s equivalent to roughly 83 hours’ worth of power generated by either of Eskom’s biggest power plants — Kusile and Medupi — if they performed at their maximum designed capacity for that period.

Conventional air conditioners with 12,000 BTU capacity, suitable for a mid-sized room, could consume as much as 3,500 watts (3.5kW).

This is roughly the same power a modern 6-panel solar array can provide at peak capacity.

It is also about 70% of the total capacity of a 5kW power inverter, generally used for entry-level home solar power systems. It will even pull nearly half the capacity of a larger 8kW inverter.

If you want to run the aircon during the night, one hour will drain 3,500 watt-hours of capacity from your battery.

Nowadays, 5.12kWh is often considered to be the entry-level. On a system with this battery capacity, you won’t even be able to run the aircon for two hours at peak output if the sun is not shining.

One major development in aircon efficiency has been the arrival of inverter-equipped models.

Although Toshiba invented the first inverter aircon back in 1980 in Tokyo, the technology has only seen broader adoption by households in the 21st century, driven by more competitive pricing and increased focus on responsible energy usage.

Inverter conditioners are a type of split air conditioner that consists of an indoor and outdoor unit.

Unlike conventional air conditioners, they come with sensors to monitor temperature and can increase or reduce the speeds of their motors as required without switching them off and on, greatly increasing power efficiency.

“An inverter air conditioner’s compressor starts at full throttle to cool a room quickly,” South African aircon importer Turbovent explains.

“Once the room has reached the desired temperature, the compressor continually makes small adjustments, maintaining a constant temperature.”

Conventional air conditioners have motors that can only run at fixed speeds, so they will still be blasting away even when the temperature is right.

While the upfront cost of an inverter aircon will be more expensive than a non-inverter option with the same cooling and heating capacity, it will cut down your electricity bill in the long run.

One of the world’s biggest manufacturers of air conditioners — Samsung — has estimated that its models could save up to 70% in electricity consumption over conventional aircons with the same room cooling or heating capacity.

Turbovent had a more conservative estimated saving of 30–50% on average.

Inverter aircons use an estimated 900 to 1,300 watts, which will put far less strain on a solar system.

In addition to Samsung, other major manufacturers that sell inverter aircons include Alliance, Defy, Hisense, LG, and Midea.

Rating systems to help you decide

There are various measurements you can consider when trying to determine the energy efficiency of an aircon, aside from its maximum power output.

One generally accepted standard air conditioning power efficiency measurement is SEER, or Seasonal Energy Efficiency Ratio.

The higher the SEER value, the more efficient an aircon performs. Generally speaking, a rating of 18 or higher is considered good.

However, the SEER value seems difficult to find on many aircons selling online in South Africa and might not appear on packaging in stores.

The older Energy Efficiency Ratio (EER) is more often shown, although this measurement is no longer considered the gold standard.

When using EER, a rating of 8 or higher is generally considered good.

Consumers can also use the South African Energy Efficiency label, which rates aircon’s energy efficiency in seven classes — from A++ (best) to E (worst).

This is determined by calculating the average electricity consumption of the aircon over a year using an internationally accepted methodology.

The DMRE explains that the figure on the label for aircon assumes using them at maximum power for 500 hours in a year, or an average of one hour and 12 minutes per day.

The department has set Minimum Energy Performance Standards for aircons sold in South Africa, which means only units with an energy efficiency rating of Class B or better can be sold.

It also offers a calculator on the savingenergy.org.za website to help consumers determine how much they will spend on electricity when running an aircon.

Some good practices to follow to minimise aircon energy use are:

• Switch off air conditioners when rooms are empty.
• Do not use the air conditioner for heating, rather dress warmly and use blankets when possible.
• Block the sunlight with curtains or blinds to reduce ambient room temperatures.
• Cool a room with fans and open windows when possible.
• Service the air conditioner regularly.
• Set the temperature to a comfortable level, but not extremely cold or hot. For each degree celsius increase when cooling, efficiency can improve 3–5%.