In the solar industry, producing electricity is our bread and butter. That means it’s important for solar professionals to have a strong grasp of electricity fundamentals.
If you’re new to solar, there’s a lot to learn so in today’s article we cover a key topic to understand about electricity: the difference between two types of electric current—alternating current (AC) and direct current (DC). Both are involved in a solar PV system.
If your familiarity with AC/DC starts and ends with the famous band, this article is for you!
The Basics: How Do Alternating Current (AC) and Direct Current Differ?
As we explain in our primer on solar panel stringing, current is the rate of flow of electric charge (i.e. the flow of electrons).
There are two forms that electric current can take: alternating or direct. Direct current always flows in the same direction. Meanwhile, alternating current—as you might expect from the name, changes direction frequently (though the back-and-forth motion of the electrons still conveys energy to the end device).
“A simple way to visualize the difference is that, when graphed, a DC current looks like a flat line, whereas the flow of AC on a graph makes a sinusoid or wave-like pattern,” says Karl K. Berggren, professor of electrical engineering at MIT.
Electricity History: The Fight Between AC and DC
When the use of electric power was first being developed, it was unclear whether AC or DC would become the dominant way in which electricity was supplied. Two famous pioneers of electricity—Thomas Edison and Nikola Tesla—each advanced one of these options.
Tesla had patented AC, while Edison had patents on DC. Despite a smear campaign by Edison to discredit AC as dangerous (in which he went so far as to publicly electrocute animals!), AC won out in the long run. AC gained predominance because it was easier for power companies to transmit AC power over long distances.
Where Are AC and DC Power Used?
Another important thing to understand about AC vs. DC power is what kinds of devices and applications use each.
A solar panel produces direct current; the sun on the panels stimulates the flow of electrons, creating current. Because of these electrons flow in the same direction, the current is direct. Similarly, batteries use direct current; they have a positive and negative terminal and current always flows in the same direction between those points. In contrast, the U.S. electric grid and the power flowing into your home are AC. As a result, most plug-in home appliances run on AC power.
It is for this reason that solar PV systems include inverters! The inverter converts DC energy into AC energy so it can be used in the home or sent back to the electric grid (in addition to some other functions).
You might also be surprised to learn that many of the electronics you use—like your laptop and cell phone—run on DC and have their own inverters as well. The power adapter that is part of the charger for these devices is in fact a form of inverter that converts the AC grid supply to DC power that can be used by the device.
What Are AC Solar Panels?
As we discussed above, traditional solar panels produce DC energy. That energy is then converted to AC power by the inverter. This is the case whether your PV system includes a string inverter (which converts energy from one or multiple strings of solar panels) or microinverters (which convert it for individual, or in some cases a few, solar panels).
You may have heard of AC solar panels, however. If solar panels inherently produce DC, you may be wondering what these are. AC panels are simply solar panels that have microinverters integrated into them. System design with AC panels is the same as designing a system with microinverters, except that the installer doesn’t need to buy and attach the microinverters.
Understanding the differences between AC vs. DC is important knowledge in the solar industry. Not only is it essential to understanding how a solar array works and how it is designed, this knowledge can also help you educate customers—one way to build trust during the sales process.
What other topics would you find helpful to understand? Let us know in the comments below! The Aurora Blog seeks to provide educational updates for solar contractors and we’re always open to new topic ideas based on needs in the industry!