There are two different methods when it comes to connecting a solar system and an energy storage system. The connection between the solar panels and the energy storage system can either be alternating current (AC) or direct current (DC).
PV modules will produce DC power. That power must be converted to AC to be used in most commercial and residential applications. In contrast, battery cells must be charged with DC and will output DC power.
So what’s the difference between AC-coupled and DC-coupled for solar-plus-storage, and which is the better option? Let’s find out.
AC COUPLED SYSTEMS
In an AC coupled system, power from the PV modules is converted to AC prior to connecting to the ESS (Energy Storage System). In other words, the output from the PV modules is fed through an interactive (solar) inverter before it reaches the ESS. This means that the power must be converted to DC before charging the ESS, and any power output from the ESS must be converted once again to AC. To achieve this, an additional multimode (battery) inverter is required. This 2nd inverter in most cases is included with the battery pack.
DC COUPLED SYSTEMS
DC-coupled battery system requires the use of only one inverter. This is a more specialized piece of equipment than the inverters used for AC-coupling, as it is a hybrid inverter used for both the battery and the solar panels.
DC output power from the PV modules can directly charge the ESS. No DC-to-AC conversion is required between the PV array and ESS.
AC /DC - PROS & CONS
Credit: Lucas Miller / Mayfield Renewables, Corvalis, OR