solar power – Why is it easier to retrofit an AC-coupled than a DC-coupled battery to an existing domestic PV installation? – GWC Mag

Not wishing ever to charge a (prospective) house-battery from the grid, naively, I think of a DC-coupled battery as a sort of capacitance between existing solar panels and their inverter.

Again, naively, I imagine a DC-side battery should be able to smooth the supply to varying load beyond the existing inverter. The inverter shouldn’t be able to tell there’s a battery upstream.. AC load downstream of the inverter (including export to grid) shouldn’t care where the inverter got its DC from.

But domestic installers’ information sites always insist that it’s prohibitively difficult to retrofit a DC-coupled battery to existing panels and their inverter, and that an AC-coupled battery, with its own inverter, is much to be preferred.

Can anyone explain why?