Substantial improvements to off-grid photovoltaic technology during the past decade have led to more choices in off-grid PV system design.
Installers can choose between direct-current (DC) coupling with a charge controller and direct alternating-current (AC) coupling of an off-grid or grid-tied inverters to the AC bus for these applications. The appropriate coupling method varies by project.
Advantages to Both Methods
Both AC- and DC-coupled systems provide a renewable energy source where power normally is not feasible, but there are advantages and challenges to both methods.
Traditional off-grid systems are DC-coupled. The battery bank is charged by connecting solar modules to a large charge controller, which regulates both the voltage and current.
With AC coupling, an AC-synchronous solar inverter is directly connected to the AC loads panel. The DC battery bank powers the DC-to-AC inverter, with solar production fed to the AC loads panel. Any extra power on the AC bus is converted to DC to charge the batteries.
Find real-world examples of off-grid AC-coupled and DC-coupled systems, and learn why AC coupling could offer more advantages, in the September 2012 issue of Solar Industry magazine. “Coupling Options For Off-Grid Solar Arrays: DC Versus AC Setups” begins on page 48.
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