Morningstar has released a 600V MPPT Solar Controller that allows for direct battery charging in DC rather than going via the inverter charge controller in a typical grid-tie solution. The intent is to eliminate the double conversion from solar panels being DC power through the inverter to mains then back through a charge controller into the batteries.
This isn't really something new its more of a variable option, it allows you to use your house's power via your distribution power board in the event of the grid going down.
Many people won't know that when the power provider or mains power line is not working if power is cut, that stops your solar panel system from functioning. If power is purposely disconnected because of rolling blackouts or accidental line failure or like in California U.S.A power has been cut to prevent fires from failures in the national grid in dry summer environments.
The Direct DC Coupling allows you to be more efficient and charge your storage batteries directly and keep your grid-tie system live. Other manufacturers call this an "island", an island is where you can operate independantly of the grid and distribute and manage your own resources.