Solar charge controllers (solar regulators) were once the only option for off-grid power systems and are used to create what is known as a DC-coupled system. DC-coupled systems use solar controllers to charge a battery directly from the panels, which is extremely efficient, while a battery inverter supplies AC power to home appliances.
AC (alternating current) coupled solar
AC-coupled systems use a string solar inverter coupled with an advanced multi-mode inverter or inverter/charger to manage the battery and grid/generator. Although relatively simple to set up and very powerful, they are slightly less efficient (90-94%) at charging a battery compared to DC-coupled systems (98%). However, these systems are very efficient at powering high AC loads during the day and some can be expanded with multiple solar inverters to form micro-grids.
Advantages
- Higher efficiency when used to power AC appliances during the day such as air-conditioning, pool pumps, and hot water systems (up to 96%)
- Generally lower installation cost for larger systems above 5kW
- Can use multiple string solar inverters in multiple locations (AC couple micro-grids)
- Most string solar inverters above 3kW have dual MPPT inputs, so strings of panels can be installed at different orientations and tilt angles
- Advanced AC-coupled systems can use a combination of AC and DC coupling. (Note: this is not possible with some lithium batteries.)
Disadvantages
- Lower efficiency when charging a battery system (approx. 92%)
- Quality solar inverters can be expensive for small systems
- Lower efficiency when powering direct DC loads during the day
DC (direct current) coupled solar
DC-coupled systems have been used for decades in off-grid solar installations and small-capacity automotive/boating power systems. The most common DC-coupled systems use solar charge controllers (also known as solar regulators) to charge a battery directly from solar, plus a battery inverter to supply AC power to household appliances.
Advantages
- Very high efficiency
- Great low-cost setup for smaller-scale off-grid systems up to 5kW
- Ideal for small systems requiring only 1-2 solar panels
- Modular (additional panels and controllers can be easily added, if required)
- Very efficient for powering DC appliances and loads
- If an electricity service provider restricts or limits the capacity of grid-tie solar allowed, additional solar may be added by DC-coupling a battery system
Disadvantages
- More complex to set up systems above 5kW, as often multiple strings are required in parallel, plus string fusing
- Can become expensive for systems above 5kW as multiple higher voltage solar charge controllers are required
- Slightly lower efficiency in powering large AC loads during the day due to the conversion from DC(PV) to DC(batt) to AC
- Many solar controllers are not compatible with managed lithium battery systems such as the LG Chem RESU or BYD B-Box
RV Electricity Converter vs Inverter
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