For many, summer is the best season of all: beaches, vacations, and sunshine. But this season can also bring high temperatures and unbearable humidity, often creating widespread demand for air conditioning. Solar power is one way you can keep your electricity costs down as you’re blasting the air conditioner this summer. After all, you shouldn’t have to sacrifice on comfort just to save money on electricity.
How much does air conditioning cost? Window vs. central air
There are a few factors that will impact how much running an air conditioner will cost you, including the rate you pay for electricity, how often you use the air conditioner, the size of the air conditioner, and its associated power usage.
Every modern air conditioner should have a nameplate that displays the amount of power it draws when in use. This number should be in watts (W). You can use this to roughly calculate how many kilowatt hours (kWh) your air conditioning system will use on a given day. This calculation will help you prepare for solar.
Let’s say that you’re planning on running your air conditioner only at night, for eight hours. You can calculate how many kWh the air conditioner would use during that time by multiplying the power usage in watts displayed on the nameplate by eight hours, and then dividing that number by 1,000 to generate a kWh estimate. To calculate what this will cost on your electricity bill, you can simply multiply the kWh usage by the rate you pay for electricity.
Below are some examples of what calculating your air conditioning usage could look like, depending on system type and location.
Air conditioner usage examples
Type of air conditioner | Power usage (W) | Number of hours in use | State | Rate for electricity ($ per kWh) | Total kWh usage for hours in use | Cost for hours in use |
|---|---|---|---|---|---|---|
| Window unit | 900 | 8 | MA | $0.18 | (900 W*8 hours)/1000=7.2 kWh | 7.2 kWh*$0.18=$1.30 |
| Window unit | 1,400 | 24 | CA | $0.25 | (1,400 W*24 hours)/1000=33.6 kWh | 33.6 kWh*$0.25=$8.40 |
| Central air system | 3,500 | 12 | AZ | $0.14 | (3,500 W*12 hours)/1000=42 kWh | 42 kWh* $0.14= $5.88 |
How many solar panels do you need for AC units? 2 step calculation
If you’re considering installing solar to cover your anticipated electricity needs for air conditioning (plus more), you’ll need to determine how much extra electricity you may need and how many solar panels are necessary to produce it.
The example calculations above can be used to determine how much electricity your air conditioner will use on an annual basis. Simply plug in the number of hours in a year you expect your air conditioner to be on, or multiply your daily kWh usage by how many days of the year the air conditioner will be in use. For example, if you only run your AC in the summer, you could estimate 90 days (or 3 months).
From there, the number of panels you will need to add onto a solar panel system to cover this usage depends on how much sunlight exposure the panels receive. This will vary depending on a number of factors, including the type of installation, where you are located in the country, the efficiency of the equipment, and the system design.
Any solar installer on EnergySage will be able to determine how many additional panels you will need for your specific property using design tools if given an approximate estimate for the increase in electricity usage. Here’s a way you can generate a quick estimate yourself.
Step #1. Calculate how many additional watts of solar capacity you need
Let’s say you’ve determined that your central air conditioner will increase your annual electricity usage by roughly 4,000 kWh annually. To calculate how many panels you will need to generate 4,000 kWh, you should first divide that usage amount by the average production ratio in your area. A production ratio shows how much energy a solar panel system will produce in relation to its size.
Additional watts needed = Anticipated need in electricity (kWh) / Production ratio
As mentioned before, production estimates and ratios are very specific to your solar panel system design and property. Below are examples of a realistic production ratio in a given region; the production ratio for your own solar panel system may be higher or lower:
Solar production ratio by U.S. region
| Region | Production ratio |
|---|---|
| Northeast (e.g. MA, CT, RI) | 1.2 |
| Pacific Northwest (e.g. WA, OR) | 1.1 |
| Southwest (e.g. TX, AZ, NM) | 1.65 |
| Mountain West (e.g. CO, UT) | 1.45 |
| West Coast (e.g. CA) | 1.6 |
So, to generate 4,000 kWh in Massachusetts, you would need roughly 3,333 W (4000 kWh / 1.2). To generate the same amount of electricity in New Mexico, you would only need approximately 2,424 W because New Mexico receives more sunshine throughout the year and has a higher production ratio.
Step #2. Divide the number of watts you need by the wattage of each panel in your solar panel system
Next, you’ll need to divide the number of additional solar wattage you need by the number of watts in the solar panels you plan on adding. Solar panels come in a range of sizes; most on the market today are between 250-365 W. The higher number of watts per panel, the less of them you’ll need to generate your full electricity needs.
This number will be the number of solar panels necessary to cover your air conditioning needs.
Number of panels = Additional watts needed / Watts per panel
To follow the example above, let’s say you’re looking to generate an additional 3,333 W to run your air conditioner in Massachusetts. If you’re installing 300 W panels, you should plan to install an additional 11 to 12 panels (3,333 W / 300 = 11.11 panels). If you prefer higher efficiency 350 W panels, the number would be reduced to 9 to 10 panels.
Installing air conditioning after a solar panel installation
Air conditioning doesn’t have to be your motive for going solar; it works the other way as well. If you’ve already installed solar panels and are struggling with the summer heat, now is still a good time look into your home cooling options.
Once you install an air conditioner – whether it’s window units or central air – your electricity usage will increase. Your current solar panel system may not be able to cover 100 percent of your new electricity bill after your AC installation. If you have the space to install additional panels, you can reach out to your solar installer about adding a few more panels to your existing array to cover the needs of the air conditioning unit.
If you can’t add onto your solar panel system because of lack of available space, that doesn’t mean you should suffer through the heat. Consider scheduling an energy audit, and look to make energy efficiency improvements to your home that will decrease your baseline energy consumption. You may be able to decrease your electricity usage in other areas so that it more than offsets the costs of a new air conditioner.
Using solar to power your air conditioner: next steps
You don’t have to be a casualty of high electricity bills this summer or the next. Solar energy is an effective way to generate renewable energy for your air conditioner to use, while also providing power to the rest of your appliances. Solar panel systems will generate thousands in electricity savings for over 25 years, and outlast your air conditioner plus all the other appliances they power.
If you want to be comfortable and save on electricity, use the EnergySage Solar Marketplace to explore your solar options. By signing up online, you can receive multiple solar quotes from local, pre-screened installers for free. If you’re planning on adding air conditioning in the near future, simply note it in your account so that the installers know to size your solar panel systems a bit larger than your past electricity bills indicate.
