The process of sizing a solar array can be boiled down to 2 steps:
- Determining the daily energy consumption (in kWh) that you need to offset
- Determining the average amount of energy you’ll be receiving from the sun (Peak Sun Hours) each day
So to determine the amount of solar power or the number of solar panels that you need to run a 5 ton ac unit, you’ll need to answer the following questions:
- How much energy does your 5 ton ac unit consume per day?
- How much sunlight do you receive each day?
In this article, I’ll help you answer these questions, and hopefully provide some additional insights about air conditioning and solar energy.
How much energy does a 5 ton ac unit use a day?
In air conditioning, 5 tons equates to 60000 BTUs (British Thermal Units). An air conditioner of this size will use between 4000 and 8000 Watts of power depending on its efficiency. However, watts do not measure energy, they measure power. Energy is measured in Watt-hours.
The exact amount of daily energy consumption of a 5 ton air conditioner depends on 4 main factors:
- Unit efficiency: which is represented by an Energy Efficiency Ratio (EER, SEER, or CEER)
- Run time: the amount of time that it runs each day
- Temperature: outdoor temperature and indoor temperature setpoint
- Insulation: how well is the house insulated, as well as the quality and condition of the ductwork for ducted systems
However, as a general rule of thumb, a 5 ton air conditioner will – on average – use between 3 and 6 kWh (kiloWatt-hours) of energy per hour. Assuming your air conditioner runs for 8 hours a day, it should consume between 25 and 45 kWh of energy per day.
In this article about the power usage and energy consumption of air conditioners, I explain a couple of ways to determine the energy consumption of your AC unit. However, the most precise way to determine this energy consumption is to use an electricity monitoring device.
Contrary to smaller air conditioners, which operate at 120 Volts, most central air conditioners require 240 Volts to operate. This means that your 5 ton air conditioner has a dedicated circuit, so you can’t just plug it into a Kill-A-Watt meter to measure its energy consumption.
To measure the energy consumption of your 5 ton unit, you’ll need a device such as the Emporia Monitor. However, since such a device would be installed inside your breaker box, you will generally need a professional electrician to do it for you.
The following video explains how this works:
If you’re okay with rough estimates for now, please refer to this article: How much electricity does your air conditioner use?
Meanwhile, as an example, I’ll assume that we have a 5-ton air conditioner that consumes 35 kWh of energy per day.
The next step is to determine the amount of sunlight that your solar panels will be receiving.
How much sunlight energy do you receive each day?
The amount of sunlight that an area receives is measured in W/m2 (Watts per square meter) and is referred to as solar irradiance. In order for a solar panel to produce 100% of its rated power, it needs exactly 1000W/m2.
For example, a 100W solar panel could produce 100 Watts of power if 1000W/m2 of solar irradiance is provided. If the same solar panel only receives 800W/m2 of sunlight, it would only produce 80 Watts of power. However, as mentioned above, watts measure power, not energy.
The amount of sunlight energy that an area receives is measured in kWh/m2 (kiloWatt-hours per square meters) and is referred to as Peak Sun Hours (PSH). (1 PSH = 1 kWh/m2)
For example, if our 100W solar panel receives 5kWh/m2 of sunlight energy per day, we could say that it receives 5 Peak Sun Hours per day. This solar panel would produce 500 Wh (Watt-hours) or 0.5 kWh per day.
The relationship between Peak Sun Hours, solar panel power rating, and its energy production, can be expressed using the following equation:
Energy Production (Watt-hours) = Solar Power Rating (Watts) x Peak Sun Hours
Since we’re looking for the size of the system, the formula becomes:
Solar Power Rating (Watts) = Energy Production (Watt-hours) ÷ Peak Sun Hours
Solar Power Rating (Watts) = Energy Consumption of the AC unit (Watt-hours) ÷ Peak Sun Hours
We’ve already discussed the energy consumption of your 5 Ton AC unit, all we need is the average daily Peak Sun Hours that you get.
So how many Peak Sun Hours do you get per day?
As mentioned above, solar panels need 1000W/m2 of solar irradiance to reach 100% of their rated power, and this amount of sunlight is only available in a good weather situation. Likewise, the Peak Sun Hours (kWh/m2) that you receive will depend on the weather.
But most importantly, the Peak Sun Hours that you receive will mainly depend on your location. And thanks to the PVWatts Calculator by NREL (National Renewable Energy Laboratory), you can use your location to determine the PSH that you receive.
Based on your address, the PVWatts calculator can estimate the daily average amount of energy (in kWh/m2) that your solar panels would receive from the sun.
For example, I used an address in Phoenix, AZ, and in the “Results” section, the tool provided the following:
The Peak Sun Hours that you receive will logically vary throughout the year. For example, in the image above, you can see that while this location receives 8.11 Peak Sun Hours per day in June, it only receives 4.46 PSH/day in December.
However, the tool also provides an annual average, which in this case is 6.57 Peak Sun Hours per day. For simplicity, we’ll just use that in the next section.
But before we move on, it is important to note that the tool has a set of default parameters, the most important of which, are:
- The tilt angle of your roof (Roof Pitch)
- Which direction it faces (Azimuth)
The results provided by the PVWatts calculator are for South-facing roofs that are titled at a 20-degree angle (equivalent to a 4/12 or 5/12 roof pitch). However, you can manipulate these parameters to get a more accurate Peak Sun Hours estimate.
Once you figure out the average Peak Sun Hours that you get each day, the last step is to calculate the amount of solar power that you need to run your 5 ton air conditioner.
How many solar panels to run 5 ton ac unit?
As a general rule of thumb, you would need 5kW to 7kW of solar power to run a 5-ton air conditioner for 8 hours every day. To determine the amount of solar power that you need, divide the daily energy consumption of your 5 ton AC unit by the average Peak Sun Hours that you get each day.
Solar Power Rating (kW) = Energy Consumption (kWh) ÷ Peak Sun Hours
For example, consider a new and efficient 5 ton (60000 BTU) central air conditioner that consumes 35 kWh a day. Assuming this air conditioner is located in Phoenix, AZ (6.57 Peak Sun Hours per day), the size of a solar system that could run this AC unit can be calculated as such:
Solar Power Rating (kW) = Energy Consumption (kWh) ÷ Peak Sun Hours
Solar Power Rating (kW) = 35 kWh ÷ 6.57 Peak Sun Hours
Solar Power Rating (kW) = 5.32 kW
Assuming the solar panels are rated at 300 Watts each, a 5.32 kW (5320 W) system would consist of about 18 solar panels.
