How many solar panels to run an 8000 BTU air conditioner?

The amount of solar power that you need to run an 8000 BTU will mainly depend on the energy consumption of the AC unit, which itself depends on other factors such as run time and temperature. However, solar panels are not the only things that you need.

A solar system that could run your 8000 BTU air conditioner would consist of:

• Solar panels
• A solar charge controller
• A battery bank
• An inverter

These components would be wired as such:

In this article, I’ll discuss these components and I’ll explain the process of sizing each of them.

How many solar panels to run an 8000 BTU air conditioner?

In general, to run an 8000 BTU air conditioner, you would need around 100 watts of solar power for every hour of daily run time.

Assuming your 8000 BTU air conditioner runs for 8 hours a day, you would need between 700 and 900 watts of solar power to offset the air conditioner’s energy consumption.

The following table estimates the energy consumption of 8000 BTU air conditioners based on their run time, and the amount of solar power needed to run them:

When it comes to sizing solar panels, there are 2 important questions to ask:

• How much daily energy usage are you trying to offset?
• How much sunlight will be available for the solar panels?

Since these solar panels are for an 8000 BTU AC unit, you’ll have to figure out the average daily energy consumption of your air conditioner (in Watt-hours or kiloWatt-hours).

The measurement unit for the daily amount of energy that your solar panels will – on average – receive from the sun, is Peak Sun Hours. So the previous questions become:

• How much energy does your 8000 BTU air conditioner consume per day?
• How many Peak Sun Hours do you get?

The answer to these 2 questions will then be used to calculate the amount of solar power that you need:

Solar Power Needed (Watts) = Air conditioner’s daily energy consumption (Watt-hours) ÷ Daily Peak Sun Hours

Let’s see how you can determine these 2 variables.

How much energy does your 8000 BTU air conditioner use?

Some air conditioners are more efficient than others, and even 2 identical air conditioners can consume different amounts of energy depending on temperature (outdoor temp. and indoor temp. setpoint), humidity, and insulation.

The most precise way to determine the energy consumption of your 8k BTU AC unit is to measure it. And this can be done through an Electricity Monitoring device.

Chances are your 8000 BTU air conditioner runs on 120 Volts and has a plug, in which case, you can use the Kill-A-Watt meter. The device would be plugged into your wall outlet (or inverter), and your air conditioner can be plugged into it.

The Kill-A-Watt meter will then display the current (amps), Voltage (Volts), frequency (Hertz), and power usage (Watts) of your AC unit. But most importantly, it’ll display the Energy Consumption in kWh (kiloWatt-hours) of your air conditioner over time:

For example, if your AC unit runs for 5 hours a day, you can plug it in through the device and check out its energy consumption when your turn it off.

If your AC unit runs on 240 Volts and requires a dedicated circuit (which is probably not the case), you’ll need a device such as the Emporia Monitor. However, this device is not as simple as the Kill-A-Watt and might require an electrician.

Learn more about this topic in this article: How to measure the energy consumption of your air conditioner?

In any case, once you have an estimate or an accurate measurement, the next step is to determine the amount of sunlight that your solar panels will be provided with on a daily basis.

How many Peak Sun Hours do you get?

The amount of energy that a solar panel generates depends directly on how much energy it receives from the sun. This sunlight energy is measured in kWh/m² (kiloWatts-hours per square meter), and each 1kWh/m² is equivalent to 1 Peak Sun Hour.

For example, an area that – on average – receives 6kWh/m² per day, could be said to receive 6 Peak Sun Hours per day.

Peak Sun Hours help us predict how much energy a solar installation is capable of producing in a certain location. For example, if we install 200 Watts of solar in a location that – on average – receives 6 Peak Sun Hours per day, the solar panels would – on average – produce 1.2 kWh of energy per day:

Daily Energy Production (Wh) = Solar Power Rating (Watts) x Daily Peak Sun Hours

Daily Energy Production (Wh) = 200 Watts x 6 Peak Sun Hours

Daily Energy Production (Wh) = 1200 Watt-hours

Therefore, if your know how much energy you need the solar panels to produce, and how many Peak Sun Hours they’ll get, you can calculate the amount of solar power that you need.

So, how do you determine your Peak Sun Hours?

The answer is the PVWatts Calculator by the NREL (National Renewable Energy Laboratory).

All you need to do is provide your address, and the tool will display the monthly and annual average Peak Sun Hours that you get each day:

For example, I used an address in Phoenix, Arizona, and in the Results section, the tool provided the following data:

At the bottom, you can see that on average (annual), this particular location receives 6.57 Peak Sun Hours a day.

However, these results are based on the assumption that your solar panels will be directly facing south and tilted at a 20-degree angle. But you can still change these values in the System Info section of the tool:

Example

For this example, I’ll assume that I have an 8000 BTU air conditioner that on average runs for 8 hours a day, and consumes 4500 Watt-hours of energy during this time.

I’ll also assume that my solar panels will have access to 6.57 Peak Sun Hours a day. The amount of solar power that I need to run this AC unit is:

Solar Power Needed (Watts) = Air conditioner’s daily energy consumption (Watt-hours) ÷ Daily Peak Sun Hours

Solar Power Needed (Watts) = 4500 Watt-hours ÷ 6.57 Peak Sun Hours

Solar Power Needed (Watts) = 684.93 Watts

According to these calculations, I’ll need at least 684.93 Watts of solar power to run this 8000 BTU air conditioner. However, to account for system losses, cloudy days, and extreme temperatures, it is appropriate to bump this number up to 800 Watts of solar.

A good choice for this setup would be 8 of these 12V-100W Renogy Solar panels.

Now that we know how much solar power is required, the next step is to size the battery bank.

What size battery bank do you need to run an 8000 BTU AC unit on solar?

The job of the battery bank is to store all the energy produced by the solar panels and make that energy accessible at all times.

Assuming your 8000 BTU air conditioner runs for 8 hours a day, you would need around 400 Ah of available battery capacity (at 12 Volts). This equates to about 5 12V-100Ah Lithium batteries (LiFePO4/Li-Ion) or 8 12V-100Ah Lead-Acid batteries (AGM/Sealed/Flooded).

The following table estimates the battery capacity (lithium or lead-acid) needed to run an 8000 BTU air conditioner on solar:

In the table, you can see that the battery capacity that you need depends not only on the energy consumption of your air conditioner but also on the type of battery you’ll be using. This is because of something called Depth Of Discharge (DOD).

Simply put, the DOD of a battery represents the percentage of the overall capacity that can be used.

For example, a 100AH Lithium-Iron-Phosphate (LiFePO4) battery can supply 80 to 100% of its capacity. On the other hand, a 100Ah AGM battery can only supply 50 Amp-hours before it needs to be disconnected or recharged.

Although lithium batteries are more expensive, they can supply double the amount of energy, meaning that one of these batteries can do the job of 2 lead-acid batteries.

In general, the recommended depth of discharge for lithium is 80%, and that of lead-acid batteries is 50%.

The daily energy consumption of your 8000 BTU AC unit and the DOD of the battery you’ll be using, can both be used to determine the battery capacity that you need:

Battery Bank Capacity (Watt-hours) = Air conditioner’s daily energy consumption (Watt-hours) ÷ Depth Of Discharge (%)

Since most of the batteries for these applications are rated at 12 Volts, the battery bank’s capacity in Amp-hours is calculated as such:

Battery Bank Capacity (Amp-hours) = (Air conditioner’s daily energy consumption (Watt-hours) ÷ 12) ÷ Depth Of Discharge (%)

Following our previous example, the AC unit consumes 4500 Wh per day on average. Assuming I’ll be using a LiFePO4 battery bank, which can be 80% discharged, the capacity that I need is:

Battery Bank Capacity (Amp-hours) = (Air conditioner’s daily energy consumption (Watt-hours) ÷ 12) ÷ Depth Of Discharge (%)

Battery Bank Capacity (Amp-hours) = (4500 Wh ÷ 12) ÷ 80%

Battery Bank Capacity (Amp-hours) = (4500 Wh ÷ 12) ÷ 0.8

Battery Bank Capacity (Amp-hours) = 468.75 Amp-hours (@ 12 volts)

An affordable choice for this setup would be 5 or 6 of these 12V-100Ah Ampere Time batteries. A more premium and long-lasting choice would be 5 or 6 of these 12V-100Ah Battle Born batteries.

Once you determine the size of the battery you’ll need, the next step is to select a suitable solar charge controller.

What size solar charge controller do you need?

Solar charge controllers connect the solar panels to the battery bank, and their job is to protect both the battery bank and the solar panels.

Learn more about solar charge controllers here: What is a solar charge controller and why do you need one?

The size of the solar charge controller that you need will mainly depend on the size of your solar array and battery bank, and their configuration.

But before we get into the sizing process, there are 2 types of solar charge controllers that you should know about:

• PWM solar charge controllers
• MPPT solar charge controllers

PWM stands for Pulse Width Modulation, and these are the cheaper type of charge controllers and are generally inefficient. Learn more about these devices here: What is a PWM charge controller and how does it work?

MPPT stands for Maximum Power Point Tracking, and these solar charge controllers are the more expensive choice. However, an MPPT solar charge controller does not only protects your system, but while doing so, it maximizes the energy production of your solar panels.

Related: Why are MPPT solar charge controllers better?

Since they are the better long-term choice, I’ll focus on MPPTs for the rest of this section. If you are more interested in a cheap short-term solution, you can use our PWM solar charge controller calculator.

To make the process of sizing an MPPT for your system even simpler, I’ve made an MPPT solar charge controller calculator that does all the sizing for you, all you have to do is provide some details that describe your system.

1- Solar panel wattage: This is the power rating (in watts) on each of your solar panels.

2- Solar panel open-circuit voltage: You can find this value in the specification label on the back of your solar panels, or by looking up the specific model.

3- Battery bank’s nominal voltage: The voltage of each battery is usually written on the casing. If you have more than one battery, the voltage of the battery bank is equal to the voltage from one string of batteries.

4- Lowest temperature during sunlight hours: In this field, you should enter the lowest value of temperature that you estimate your solar panels are ever going to be exposed to. This will allow the calculator to estimate the highest voltage to expect.

5- Number of strings: In your solar array, how many parallel strings are there?

6- Number of solar panels in each string: In each string, how many solar panels are wired in series.

In the solar array sizing section, we’ve determined that we need at least 684.93 Watts of solar power to run the 8000 BTU unit for 8 hours a day and then decided to bump it up to 800 Watts. As an example, I’ll use 8 12V-100W Renogy solar panels.

A good configuration for this system would be 4S2P. This means that we’ll have 2 parallel strings of panels, with each string consisting of 4 solar panels wired in series. Our solar array would look like this:

For the battery bank, we’ve determined that we’ll need at least 468.75 Amp-hours of battery capacity (@ 12 Volts). A good choice would be 6 of these 12V-100Ah Battle Born batteries. This would give us 600 Amp-hours of battery capacity (@ 12Volts), which is more than enough.

A good configuration for this battery bank would be 3S2P (2 parallel strings each consisting of 3 batteries in series). With this configuration, we’d end up with a 36V battery bank:

Now that we know what our setup looks like, here are the values I’ll submit to our MPPT solar charge controller calculator:

1- Solar panel wattage: Each of the solar panels is rated at 100 Watts.

2- Solar panel open-circuit voltage: Each of these solar panels has an Open-Circuit Voltage (Voc) of 22.3 Volts.

3- Battery bank’s nominal voltage: Our battery bank has a nominal voltage of 36 Volts.

4- Lowest temperature during sunlight hours: For simplicity, I’ll assume the temperature does not go below 32°F (0°C).

5- Number of strings: Our setup Consists of 2 strings of solar panels.

6- Number of solar panels in each string: In each string, there are 4 solar panels connected in series.

I’ve submitted these details to the calculator, and here are the results:

Our calculator determined that the solar charge controller that we need, should be able to handle 99 Volts on the PV side, and put out 20.4 Amps on the battery side.

The calculator recommends the 150V/35A MPPT from Victron as a premium choice or the 150V/50A MPPT from EPEVER as a more affordable choice. Either of these choices would allow 400 Watts to be added to the solar array, or an extra 1000 Watts of solar (1.8kW total) if we also add a battery to each string.

The next and last step is to find the right inverter for our system.

What size inverter do you need to run an 8000 BTU air conditioner?

While the battery bank will provide DC (Direct Current) power, an 8000 BTU air conditioner requires AC (Alternating Current) power to run. The job of the inverter is to convert the relatively low voltage (12/24/36/48 V) DC power from the battery, into a higher voltage (usually 120 Volts) AC power.

In general, to run an 8000 BTU air conditioner on solar, you would need a 3000 Watt Pure Sine Wave inverter, which can handle both the running and starting power of these air conditioners. However, the input voltage rating of the inverter should also be compatible with your battery bank’s voltage.

In this article about sizing an inverter that can run your air conditioner, I explain the specifications that should be considered, in both the AC unit and the power inverter. The inverter’s specifications to look at are:

• Waveform: The inverter you go with should be a Pure Sine Wave inverter. A Modified Sine Wave inverter can cause permanent damage to your AC unit.
• Continuous Power Rating: 8000 BTU AC units usually use 600-100 Watts of power when running, which means the Continuous Power rating of the inverter should be higher than that.
• Surge Power Rating: 8000 BTU air conditioners can require up to 5000 Watts of power to kick off. A 3000W high-frequency inverter will usually have a surge wattage of 6000W, a 3000W low-frequency inverter will usually have a surge wattage of 9000W.
• Input Voltage rating: Generally speaking, most inverters are designed to convert a specific DC voltage. For example, a 12VDC inverter will not be able to run on a 24V DC system.
• Output Voltage: Most power inverters in the U.S. market provide 120VAC, which should be compatible with your 8000 BTU unit. However, make sure to check the voltage of your air conditioner before choosing an inverter.

Since our battery bank is rated at 36 Volts nominal, a good choice would be this 3000W Pure Sine Wave inverter. It has a Surge Power rating of 6000 Watts and is designed to run on 36 Volts nominal.

To learn more about sizing an inverter for your air conditioner, please refer to this page: How to size an inverter that can run your air conditioner?