Solar powered air conditioning for your home

For many households, air conditioning is the biggest electricity consumer. This makes solar panels an appealing option. Here's a guide on how to use solar to power your AC needs.

Photo of a sign with the words "air con"
René DeAnda / Unsplash

If you live in a climate where air conditioning is a significant part of your electricity usage, that probably means it’s a good climate for solar energy.

Does that mean you can power your air conditioner with solar electricity? You absolutely can, but we should explain exactly what that means.

If your idea is to power an air conditioner directly with solar panels - that is, connect some solar panels directly to an AC unit and essentially run it off-the-grid - it is possible. However, you probably don’t want to do this.

Instead, for most homes, you want to have a grid-connected, net metered solar array and use it to “pay off” the energy usage of your air conditioner. This means understanding how much electricity you need to cool your home over the course of a year so that your installer can size the array correctly.

This article will help you figure out what you need to power the air conditioning for your home using solar, but first let’s talk about those solar powered air conditioners.

Air conditioners powered directly with solar panels (and batteries)

You won’t get the best cooling performance or cost effectiveness by going this route, but there are air conditioning products that are powered directly by solar panels. In fact, you could assemble such a kit yourself.

There are two main types of solar air conditioning setups: those that incorporate batteries, and those that don’t.

You’ll get better performance if you use batteries, but the cost will be significantly more. Basically, the setup consists of a set of solar panels, batteries, charge controller, and inverter. In other words, you need a complete off-grid solar setup.

Once you have this, you can simply plug a window air conditioner into the inverter. The amount of time you can run an AC on this will depend on the number of solar panels and size of your battery.

This will be expensive, and you won’t be able to power a very large AC. For example, Nature’s Generator sells a package that includes 12 solar panels and 6 batteries with an integrated inverter and charge controller. It costs $5,000 and doesn’t even include the actual air conditioner. According to the manufacturer, it will power a small 6,000 btu window air conditioner for about 16 hours. You can usually find one of those for about $200, so this means you would be paying $5,000 to run a $200 air conditioner with solar power.

12 volt air conditioners powered only with solar panels

The other type of solar air conditioning setup skips the battery and powers an air conditioner directly. Because solar panels generate direct current, this means you need a DC air conditioner.

There are 12V DC air conditioners on the market that are intended for RV use. As a result, they’re small and don’t have much cooling power. The other obvious problem is that, without a battery, the AC will run only when the sun is shining.

It’s hard to imagine the practical use for this type of system outside of an RV. Even if you need air conditioning for a small off-grid cabin or tiny home, you will most likely have battery storage anyway, in which case you would be better off with a larger window AC.

Solar-assisted air conditioning

There’s actually a third type of solar air conditioner, but it’s not a product in common use. Solar-assisted air conditioners either use solar thermal to assist with cooling that’s based on the movement of moisture, or that use solar PV to power a compressor.

It’s a neat idea, but compared to pairing a standard air conditioner with a net metered solar array, it’s much more complicated.

One report in 2019 said that there were only about 1,500 solar-assisted air conditioners in use in the entire world, so it’s very much a niche product at this time.

How solar-powered air conditioning works for most homes

For the vast majority of homes and businesses that want solar powered air conditioning, they simply need a grid-connected solar array that is sized to produce approximately the same amount of electricity during a year that the air conditioning system consumes.

You don’t need to worry about whether the solar panels send electricity directly into the air conditioner. From an environmental and financial point of view, it’s better to let your solar panels and the grid work together, but you should pay attention to your net metering and time-of-use arrangements with your utility company.

As a quick recap, full net metering means that you get full credit for the electricity you send into the grid.

If you have full net metering, then just use electricity when your utility rates are the cheapest. If you don’t have net metering, you’ll usually want to run your air conditioner when your solar panels are generating electricity, but it depends on what the utility company pays for electricity you send into the grid. It’s a similar calculation as deciding when to charge your electric car, so I’ll let you read the section “Cheatsheet on the best time to charge your EV” rather than repeat it again here.

How much power does an air conditioner use?

While you can make some assumptions about how many watts your air conditioner uses based on its amperage, the amount of electricity it will consume in actual use depends on several factors including the size of your home, how well insulated and air sealed it is, your thermostat settings, and even the activities in your home.

Because of this, the best way to know how much electricity your air conditioning system uses is to look at your bills and compare the months where you use AC with the months where you don’t. For example, if your electricity usage in February was 1,000 kWh but 1,750 kWh in August, it would be a reasonable assumption that your air conditioner was responsible for 750 kWh of electricity consumption in August. Do this for all of the cooling months to get an annual estimate.

If you don’t have air conditioning yet and instead are planning to add it to your home, you will need a load calculation performed by a knowledgeable HVAC technician.

How many solar panels will you need to power your air conditioner?

Once you know how much electricity your AC consumes annually, just plug that number into The Solar Nerd calculator to get a quick estimate of how many solar panels are required to meet your cooling needs. (You would enter only the electricity load for your AC, not the entire household.)

Or, to get a more accurate estimate, check with a qualified local solar installer.

Even if you have solar panels, pay attention to your time-of-use rates

As mentioned above, the cheapest time to run your air conditioner is a little bit complicated, and depends on your net metering and utility time-of-use plan.

If you do have a TOU plan, your electricity is probably cheapest overnight. (However, that’s not the case in Hawaii, where the cheapest power is in the middle of the day. This happens because Hawaii has a lot of solar power.)

That’s the situation I have in Buffalo, which doesn’t have a long cooling season, but July and August are warm enough that I’m usually running my heat pump in cooling mode on most days.

I have full net metering and a time-of-use plan with cheap electricity overnight (between the hours of 11 p.m. and 7 a.m.). So what do I do? I crank up the cooling overnight when power is cheap, and then “coast” on that cool air during daytime hours.

Depending on the temperatures outside, my house might stay comfortably cool all the way until off-peak hours start again. This has the added benefit that I have a lot of excess electricity during the day that gets sent into the grid, and my utility credits me at the on-peak rates for that.

This works because even an ordinary home has a lot of thermal mass. Basically, this means that it takes a lot of energy to warm up or cool down all the materials that make up a home: drywall, framing, and even the furniture in your home all contribute thermal mass. Once everything inside is cooled down, it takes a lot of energy to heat it up again.

While some homes - especially those that incorporate passive solar features - may deliberately add materials to increase the thermal mass of a building, even an ordinary home can benefit by precooling or preheating when electricity rates are cheapest.

Bottom line: if you have air conditioning, solar panels probably will work for you.

While it’s possible to have an air conditioning system that operates directly from solar panels, it doesn’t make much sense to set it up this way. Instead, what you want is an ordinary grid-connected solar array that’s sized to offset your air conditioning usage.

It’s easy to estimate this if you already have the bills from operating your air conditioner, but if you’re instead planning to install a new AC system, you’ll want a qualified HVAC technician to perform a detailed load calculation (ie. Manual J) to estimate how much electricity your future system will consume.

And to make sure that you’re maximizing the financial gain of your solar installation, it’s helpful to understand any time-of-use billing and net metering arrangements that you have with your utility company.

#Heating and Cooling

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