AC stands for at least a quarter of your electric bill in summer. Is there a way to decrease your expenses on cooling? In this article, we’ll talk about how many watts an air conditioner uses, what alternatives you can use and how you can run an AC on solar power.
The amount of energy an air conditioner uses depends on its size and type. The bigger the AC unit, the energy it needs. A common measure is cooling capacity: 1 ton of cooling power needs about 1,000 watts. Whole-house central air systems typically use around 3,500 watts, medium units need 1,000-1,500 watts, and small units for tiny rooms use about 500 watts. RV air conditioners in an average-size trailer require between 2,000 to 3,500 watts to start. While working, they use anywhere between 600 to 1,700 watts continuously.
500-3,500 W
AC unit power ratings range
To find the daily energy consumption of a device, normally you would have to multiply the unit's wattage by the estimated working hours. With air conditioners, it gets tricky. People, pets and the number of objects in the room change the amount of cooling power that an AC has to use. Starting a unit requires extra energy. Maintaining low temperature, on the other hand, requires less electricity than what the nameplate says. Some propose multiplying hours in use and power rating as usual and then halving the result to get an estimate of AC unit energy consumption.
Here is an example for a medium air conditioning unit that we let run for 6 hours:
1,000 W × 6 h / 2 ≈ 3,000 Wh ≈ 3 kWh/day
Let’s say we turn this unit every day for 6 hours. How much electricity does an AC use per month? 3 kilowatt-hours times 30 amounts to 90 kWh. Considering the average price of 1 kilowatt-hour in the US is $0.17, a medium-sized AC unit costs you about $15 per month. If you were to run an AC for 6 hours every day of the year, the bill for just this unit would come to $180 per year.
What if we take a larger AC system — the one rated for 3,500 watts, the one that is capable of keeping the whole house cool? Running it again for 6 hours, we get:
3,500 W × 6 h / 2 ≈ 10,500 Wh ≈ 10.5 kWh/day × 30 ≈ 315 kWh/month
899 kWh
average monthly consumption of a US household
The average monthly energy consumption of an American household amounts to roughly 900 kWh, according to U.S. Energy Information Administration (EIA). Even our medium-sized 1,000W air conditioning unit made 10% of it. The large 3,500W AC system that we used would stand for over 30% of an average bill.
Statistics only confirm the fact that an AC unit is one of the most expensive items on your electric bill. Around 16% of a homeowner's electricity expenses come from cooling, according to EIA. This is an average number for the year though. Most of the cooling takes place in the summer, so the percentage easily reaches 20-40% in June-July. In some places it gets so hot that you have to let the AC run 24/7.
Because of air conditioning units, summer can be a tough time for a commercial grid. The demand can get so high that electric rates skyrocket. One example would be Texas where electric rates rose 100% in June 2023, according to state grid operator the state’s Electric Reliability Council. The price for 1 Megawatt-hour of electricity (1,000 kilowatt-hours) reached $5,000. Of course, solar owners were quite happy about their decision to get a PV system at that moment.
What can you use instead of an AC to save money on cooling? The best alternative is a simple ceiling fan.
Consider the difference in energy usage: an average 48-inch ceiling fan consumes about 75 watts. The exact power consumption will depend on the size of the dan and the brand. For instance, a 30-inch fan will need about 40-50 watts. The power rating of a 72-inch fan can be anywhere from 100 to 180 watts.
Let’s say you let your 48-inch fan run for 12 hours. Its power consumption will amount to:
75 W × 12 h = 900 Wh/day
These 900 watt-hours a day is less than some ACs consume in an hour. The upfront cost of a ceiling fan is much smaller compared to an AC unit. The maintenance is also much less expensive. Still, ceiling fans don’t do as well in extreme heat. They also don’t provide air moisturizing which some air conditioners offer.
Solar power has been a proven method to lower electric bills. But is it possible to run an air conditioner on solar panels? How many PV modules would it take?
An air conditioner is a totally doable task for a solar system — if it’s large enough. Generally, an air conditioner works during the daytime when solar panels are also active. The consumption of an AC is going to change throughout the day. For example, if an AC system requires 3,500 watts to start and a solar system produces at least 3,500W at this very moment that are not used elsewhere, then an AC runs solely on solar power. If a system does not produce enough, then an AC is going to grab the rest from the grid.
Don’t forget that the AC production of your system is lower than the DC rating of all solar panels combined. Due to imperfect irradiance and power losses in the system, the amount of usable AC power is going to be about 25% lower than what the system is rated for.
Let’s say we want to run an AC unit that is rated for 3,000 watts in Los Angeles. If we add 25% on top of it, we need 3,750 watts of DC from solar panels. This home AC unit will thus require nine extra 400W solar panels just to keep the AC running. However, we noted that the AC consumption is going to decrease when maintaining the temperature. If we halve the continuous consumption, then the AC can be supported by, say, five 400W solar panels.
What if we have a battery? Then, assuming that the power rating of a battery is high enough to support the AC, we can calculate the number of watt-hours that an AC needs in its working day. Then we’ll find out how many solar panels will produce this much during daytime. In this situation, it doesn’t matter when exactly we plan to turn the AC works — it will either use the energy from solar panels or, if they are inactive, rely on batteries.
Let’s try it with our 3000W AC unit that we run for 6 hours. Assuming that California has at least 5.6 hours of peak irradiance when solar panels are going to work at their maximum capacity, the number of 400W solar panels that produce the same amount of energy equals to:
(3000 W × 6 h / 2) × 1.25 / 5.6 psh / 400 W ≈ 5 solar panels
Remember that solar panels produce about 50% more electricity in July than in January. If a solar system covers your energy consumption in winter, then you can comfortably turn off the AC in summer — the bonus production from your array will be able to take care of it. Learn more in our article “Running air conditioning on solar is possible. Here is how many panels it takes”.
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Andrey had been a news editor and freelance writer for a number of medias before joining A1SolarStore team. Climate change and its impact on people's lives has always been among his interests and it partially explains his degree in Philosophy and Ethics.
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