Will a Solar Panel Run a 115-Volt Air Conditioner?

Useable Solar Electricity

• A solar panel generates direct current (DC) electricity at a voltage of 12, 24 or 48 volts, depending on the configuration of the cells in the panel. This is compatible with the electricity generated by batteries, so you can hook the panel directly to a battery bank and it will charge the batteries. It isn't compatible with residential 115-volt alternating current (AC) electricity however, because that electricity changes polarity 60 times per second. To power AC appliances from a DC power source, you pass the DC electricity through an inverter, which also steps up the voltage to 115 volts.

Minimum Panel Requirements

• The largest solar panels you can buy are rated for around 200 watts. They are not 100 percent efficient, so they deliver less power than that on sunny days and even less on cloudy ones. Moreover, you lose some power when you pass the electricity through an inverter. An 8,000 to 9,000 BTU air conditioner, which is small, requires 900 watts to run, so even on the sunniest day, you would need a minimum of seven of the largest panels to run it, taking into account efficiency losses. On a cloudy day, those seven panels probably wouldn't generate enough power to keep the air conditioner running.

An Efficient System

• While it is possible to connect an air conditioner directly to a solar array via an inverter, you'll only be able to use it in full sun unless you oversize your array to generate sufficient power on cloudy days. It's more efficient to connect the panels to a battery bank so that the power is always available. Your array should still contain more panels than the minimum for running the air conditioner, because you need extra power to keep the batteries charged while the air conditioner is running. It isn't a very cost-effective strategy for simply powering an air conditioner.

Cost-Effectiveness

• Even with falling panel prices, setting up a solar system capable of running an 8,000 BTU air conditioner will cost you thousands of dollars. Unless you plan to use the system for other purposes, it will take several years to recover the installation costs through energy savings, if you can recover them at all. Even at $0.34 per kilowatt-hour, which is the maximum that Pacific Gas and Electric Company charges for electricity, at the time of publication, the energy cost for running the air conditioner for a month would be $100, assuming you run it for 10 hours every day.