It's often said that solar panels produce enough electricity to power everything in your home. However, the air conditioning unit presents a standalone challenge – it is the most energy demanding appliance in the house. Consider adding an AC unit to your home and wonder if it's possible to run it on solar energy? In this article we'll explore how much energy it exactly needs and how many panels are required to generate this amount on a regular basis.
First, let's look at the energy consumption of an air conditioning unit itself. Is it all that different from a toaster or a computer? The sheer numbers show that it is. An average american house spends around 10,812 kW a year, according to the U.S. Energy Information Administration. An AC unit requires 20% of this amount — it uses around 2,000 kW every year. In hot places, like Arizona or Texas, this number goes even higher.
Exact energy consumption highly depends on the size and type of the AC unit you've chosen. The cooling capacity of an AC somewhat translates to its wattage like this: 1 ton of cooling power requires slightly more than 1,000 W. Central air conditioning systems that can take care of the whole house use around 3,500W. A medium-size AC unit requires around 1,000-1,500 W. Small units for tiny rooms can have a wattage of 500W.
To get a daily energy consumption of an AC unit you need to multiply its wattage by the estimated number of working hours. However, the whole calculation gets messy because:
• Presence of people and animals in the room where an AC unit is working increases the energy it consumes.
• An air con tries to cool every object in the room: the more there are different things around, the more electricity it takes.
• An AC unit requires extra energy to start working, but then spends much less energy maintaining the desired temperature, rather than actually cooling the air.
Therefore sometimes it is suggested to halve the amount of energy you've got from calculation. What you'll receive in the end is the power that additional solar panels would need to generate daily to support your air conditioning unit.
First, let's think of the most simple situation: an AC unit works only during daytime at the same time as solar panels. Ideally, we would like to simply divide the power usage of the AC unit by the wattage of panels. However, the AC production of a solar system rarely matches its DC rating. Lots of energy gets lost because imperfect angle and positioning and in the process of transfer and conversion. These losses may amount to 20-30%.
AC production of a PV system = PV DC rating - 25%
Let’s say we have 3000W AC unit. We would need about 3,750 watts of DC from a PV system if we include a 25% correction. This aircon would require nine 400W solar panels. However, we should take into account the fact the AC consumption decreases when an aircon maintains the temperature. If we halve the continuous consumption, then five 400W solar panels would be able to power an AC unit.
Let's move on to a more complicated example. We've decided to install a central air conditioning system in a house somewhere in LA. Its rated wattage is 3,000 W. We'll set 6 hours as an estimated daily work time. This time though, running times of a PV system and AC wn't be aligned. We'll instead rely on a battery and make sure that a solar system can charge it enough so that it can power an AC in return. First. let's first figure how energy an AC needs daily:
3000W × 6h = 18 kWh
Assuming that the AC unit spends most of the time maintaining the temperature, we'll divide this number by 2.
18 kWh ÷ 2 = 9 kWh
This is the amount of energy the AC unit needs every day and it is easy to find out its cost. Los Angeles residents pay an average of 20.8 cents per kWh.
$0.20 × 9 kWh = $1.87
This is the cost of running an AC unit for one day in Los Angeles. This amounts to $56 a month and $682 a year. Quite a lot. Given the fact that an average AC unit costs a little over $4,000, it's like purchasing a new one every 5-6 years. Solar panels in Los Angeles, to the contrary, pay for themselves in about 6 years. Running your AC on solar energy contributes to speeding up this process.
6 years
Average payback time of a solar system in Los Angeles
We established that to run the AC unit on solar we need to get approximately 9 kWh from PV modules every day. The average number of peak sun hours in Los Angeles is 5.6 – this is the time when irradiance reaches 1000W/m2 and panels operate at their maximum. Let's figure of a solar array that can provide us with this amount of power.
9 kWh ÷ 5.6 h = 1607 W + 25% = 2008 W
You can generate 2000 watts with the same five 400-watt solar panels. Don't forget that these five modules are intended to cover only the AC unit. When sizing a solar PV system, we need to take into account all the other appliances as well.
Imagine a house somewhere in Minnesota. There is a study where it gets really hot during summer days and it's impossible to work there. We install a small AC unit which requires 500W. It works for 6 hours five days a week. Therefore, on paper this AC unit needs up to 3 kWh each working day. The number of peak sun hours in Minnesota in summer is 5.4.
3 kWh ÷ 5.4 h = 555 W + 25% ≈ 700 W
You can get those additional 700 W by extending your solar panel system with two extra 350W paneIs. But is it mandatory to add them if they are not going to be all that useful in fall, winter and spring? Well, not necessarily.
The AC unit is only needed in summer when solar panels receive more sunlight during the day than usual and, therefore, produce more electricity. On average a solar panel system generates 50% more electricity in July and August than in December and January. So, if the existing solar array produces enough power to cover your energy needs in winter, leave it as it is: that small AC unit won't be much of a burden.
Article updated April 2024
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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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