Air conditioners are known for their huge energy consumption, however, it is very much possible to run an AC unit on solar power. But is 100 watts of solar power enough?
In this article, I’ll try to provide some insights on the energy consumption of air conditioners, and put into perspective the energy production capabilities of solar panels.
Can a 100 watt solar panel run an air conditioner?
A 100-watt solar panel can – on average – produce 500 Watt-hours (0.5 kWh) of energy per day, and up to 800 Watt-hours (0.8 kWh) on a sunny summer day in certain locations. But is that enough to run an AC unit? can a 100 watt solar panel run an air conditioner?
The answer is no, a 100 watt solar panel cannot run an air conditioner. Air conditioners use a lot of power, consume a lot of energy, and would require more than 100 watts of solar power to run.
However, theoretically, if the 100 watt solar panel is coupled with a large enough battery, a 5000 BTU air conditioner could run for 1 hour on the energy produced by the solar panel over a day.
But this is obviously impractical and you would be better off running a couple of fans on the solar panel instead.
The questions that should be asked are: how much energy does your air conditioner consume? and how much solar power do you need to offset that energy consumption?
How many solar panels do you need to run your air conditioner?
To determine the amount of solar needed to run your AC, you’ll need to determine the following variables:
- The daily energy consumption of your air conditioner (in Wh or kWh)
- The average amount of sunlight that is available to you on a daily basis (Peak Sun Hours).
When these 2 variables are determined, the amount of solar power that you need can be calculated as such:
Required Solar Power Rating (Watts) = Air conditioner’s daily energy consumption (Watt-hours) ÷ Peak Sun Hours per day
Before I get into how all of this works, and to give you some perspective, the following table estimates the amount of solar power that would be needed to run different air conditioners for 8 hours a day:
| Air Con. Capacity | Est. Solar Power Required for 8 hours of run time (Watts) |
| 5000 BTUs | 500 Watts |
| 8000 BTUs | 900 Watts |
| 12000 BTUs (1 ton) | 1400 Watts |
| 18000 BTUs (1.5 tons) | 2000 Watts |
| 24000 BTUs (2 tons) | 2800 Watts |
| 36000 BTUs (3 tons) | 4000 Watts |
| 48000 BTUs (4 tons) | 5500 Watts |
| 60000 BTUs (5 tons) | 7000 Watts |
To get a more accurate estimate, the first step would be to determine the energy consumption of your AC unit.
How much energy does your air conditioner use?
The daily energy consumption of your air conditioner depends on a few factors, such as:
- Capacity: the BTU or tonnage rating of your AC unit.
- Efficiency: This is usually indicated by an Energy Efficiency Ratio (EER, SEER, CEER).
- Run time: the amount of time for which your air conditioner runs every day.
- Temperature: the outdoor temperature and indoor temperature setpoint.
- Insulation: the quality of insulation in your home or vehicle.
These factors make it quite hard to estimate the energy consumption of your unit.
The accurate way to determine the energy consumption of your air conditioner is to measure it, and this can be done using Electricity Monitoring devices, such as the Kill-A-Watt meter.
This device would be plugged into the electrical outlet, and your air conditioner would be plugged into the device.
Once you plug everything together, leave your air conditioner running for as long as it normally does, and push the button that says kWh (kiloWatt-hours). The Kill-A-Watt meter will then display the amount of energy (in kWh) that your air conditioner consumed during this time.
If you’re fine with estimates, for now, you could use the following rule of thumb:
Energy Consumption (Watt-hours) = Power Usage (Watts) x Run Time (hours) x 0.75
- Power Usage: this is the amount of power (in Watts) that your AC unit requires to run. For example, a 5000 BTU unit should use between 400 and 500 watts of power when it’s running.
- Run Time: the amount of time (in hours) for which your AC unit runs daily.
If you don’t know the power usage of your air conditioner, please refer to this page: how many watts does an air conditioner use?
For example, consider an 8000 BTU window air conditioner that uses 700 Watts of power when it’s running.
Assuming this AC unit runs for 8 hours a day, as a rule of thumb, its energy consumption can be estimated as such:
Energy Consumption (Watt-hours) = Power Usage (Watts) x Run Time (hours) x 0.75
Energy Consumption (Watt-hours) = 700 Watts x 8 hours x 0.75
Energy Consumption (Watt-hours) = 4200 Watt-hours
Energy Consumption (kWh) = 4.2 kWh
Once you measure or estimate the daily energy consumption of your air conditioner, the next step is to determine the Peak Sun Hours (PSH) that you get. In the next section, I explain what Peak Sun Hours are and how to determine them.
What are Peak Sun Hours and how many do you get each day?
Peak Sun Hours is a unit that measures the amount of energy per area (kWh/m²) that a location receives from the sun. 1 Peak Sun Hour is equivalent to 1 kWh/m² (kiloWatt-hour per square meter).
If you know the power rating of a solar panel (or solar array), Peak Sun Hours can be used to determine the amount of energy that this panel or array is capable of generating in a certain location:
Energy Production (Watt-hours) = Power Rating (Watts) x Peak Sun Hours
For example, consider a location that – on average – receives 5 kWh/m² of sunlight energy per day. This location could be said to receive 5 Peak Sun Hours per day.
If we install a 300W solar panel in this location, the average daily energy production of this solar panel would be:
Energy Production (Watt-hours) = Power Rating (Watts) x Peak Sun Hours
Energy Production (Watt-hours) = 300 Watts x 5 Peak Sun Hours
Energy Production (Watt-hours) = 1500 Watt-hours
Reversibly, if you know how much energy you need to offset (energy consumption of your air conditioner), you can use your Peak Sun Hours to determine the amount of solar power that you need:
Required Solar Power Rating (Watts) = Air conditioner’s daily energy consumption (Watt-hours) ÷ Peak Sun Hours per day
So, how many Peak Sun Hours do you get?
The number of Peak Sun Hours that you get each day, can be determined using the PVWatts Calculator by NREL. After you submit your address, the tool will provide the annual and monthly averages of your daily Peak Sun Hours.
For example, I submitted an address in Phoenix, AZ, and in the “Results” section of the calculator, the following table was provided:
Following our previous example of the 8000 BTU air conditioner, we’ve estimated that this AC unit consumes about 5.6 kWh of energy per day.
If our air conditioner is located in the Phoenix, AZ address that I’ve submitted to the PVWatts calculator, the amount of solar power that would be required to run the AC unit is:
Required Solar Power Rating (Watts) = Air conditioner’s daily energy consumption (Watt-hours) ÷ Peak Sun Hours per day
Required Solar Power Rating (Watts) = 4200 Watt-hours ÷ 6.57
Required Solar Power Rating (Watts) = 639.3 Watts
According to these calculations, we would need (at least) 639.3 watts of solar to run our air conditioner. However, to account for things like extreme temperatures, system losses, and cloudy days, it would be appropriate to bump this number up to 800 Watts.
In any case, if you’re building an off-grid solar system for your air conditioner, you’ll need more than just solar panels.
What components do you need to run your air conditioner on solar?
An off-grid solar system consists of the following components:
- Solar panels
- A battery bank: the battery bank would store the energy produced by the solar panels and make it available at all times.
- An MPPT solar charge controller: the job of an MPPT solar charge controller, is to maximize the power production of your solar panels, and to protect the battery bank from overcharging, and prevent it from discharging into the solar panels at night.
- A power inverter: the job of the inverter is to convert the DC (Direct Current) power from your battery bank into AC (Alternating Current) power that your air conditioner needs to run.
Please refer to my article about running an air conditioner on solar power, in which I provide a detailed explanation of how to size each of these components.
