Alternating current (AC) and Direct Current (DC) are two types of electric current involved in a solar PV system. Current refers to rate of the flow of electrons, otherwise known as electric charge. The electric current in a PV system can take either form. The main difference between the two lies in the nature of the current’s flow. This difference, along with others between the two currents, and their role in a solar PV system, are outlined below.
Alternating Current
AC flow frequently changes direction and takes on a back-and-forth, wave-like motion. It can be easily converted to different voltages with the help of transformers. With AC, it is also easier to transmit power over long distances. Because of this capability, it is AC power that flows from the US electric grid and into households and businesses. Everyday uses consist of most plug-in home appliances including microwaves, ovens and refrigerators.
In a solar PV system, inverters are a key component and are used to convert DC energy to AC. DC is converted to allow energy to be used in either the home or business or be sent back to the local electric grid. While most traditional solar panels produce DC, AC solar panels with micro inverters integrated into them also exist.
Alternating current solar panels bypass the need for external inverters. This allows these panels to adapt to individual panel characteristics and avoid mismatching. However, AC panels are more expensive, less efficient and require more difficult maintenance and upgrade processes.
Direct Current
DC flow always goes in the same direction. One of its downfalls is that the current is not easily converted to higher or lower voltages. As for everyday use, DC is found in batteries. Current within batteries flows in the same direction between the positive and negative terminal during discharge. Devices like cell phones and laptops are powered by batteries.
As for solar PV systems, most traditional solar panels produce DC. DC production occurs when sunlight stimulates the flow of electrons in the same direction and therefore creates current.
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