DC coupled systems use solar charge controllers (also known as solar regulators) to charge the battery system directly from a solar array. The very simple PWM type Solar controllers are a very low cost, effective way to regulate a small battery and come in many different sizes.
Advantages
Very high efficiency - up to 99% battery charging efficiency (using MPPT)
Great low cost setup for smaller off-grid systems up to 3kW
Ideal for small auto or marine systems requiring only 1 - 2 solar panels.
Scalable - Additional panels and controllers can be easily added if you require more solar panels.
Very efficient for running DC appliances and loads
If a electricity service provider restricts the size of solar allowed to be installed (ie. 5kW max), additional solar can then be added using DC coupling.