The Gemini solar battery energy storage system (BESS) is on line in Nevada. This territory in the western United States has a hot dry climate, making it ideal for a project of this kind. The designers had to chose between AC or DC coupling solar batteries. They chose DC-coupled architecture because it charges the BESS directly from the solar panels. This bypasses one inverter avoiding some energy loss.
What’s the Difference Between AC and DC Coupling?
AC-coupled and DC-coupled solar systems convert their electricity from AC to DC and vice versa. The choice between these options depends on how they use the energy they capture from the sun.
The Principles of AC Coupling
Direct current coming from solar panels converts to alternating current by passing through an inverter. This is ideal for powering devices online in a standalone system, or for transmitting energy to a grid.
However, this power must reconvert back to direct current to charge the batteries. And then reverse the process again to use the energy for powering devices, or sending power to the grid. Each of these three current conversions absorbs some of the energy flowing through the system.
How DC Coupling Works in Practice
A DC-coupled system sends the direct current from the solar panels to the batteries via a charge controller. However, this energy must convert to alternating current to power devices, or send energy to a grid.
Direct current coupling hence requires just one inverter, compared to two for alternating current coupling. There is also only one load loss. DC-coupled systems are thus simpler with fewer components, and generally more efficient than AC-coupled alternatives.
Would AC or DC Coupling Be Best For Me?
If you already have solar panels at your home or business, and want to add battery storage, then alternating coupling will be cheaper and faster to install.
If, however, you are starting from scratch, then the additional expense of direct current will deliver greater levels of efficiency, that should compensate for this cost.
More Information
Alternating Between Types of Electric Current
Direct and Alternating Electric Current Compared
Preview Image: Large Solar Battery Project
