Batteries and solar produce direct current. Inverters convert that to AC and can easily match the frequency of the grid.
Wind turbines can produce AC but keeping tight control of their rotation speed might make conversion to DC to allow frequency sequencing a practical solution.
Dominion attributed the cost estimate increase to a revised estimate of network upgrade costs assigned by PJM Interconnection, the company that operates the electric grid for a region that runs from New Jersey to North Carolina, and from Illinois to Washington D.C., and on higher onshore electrical interconnection costs.
DB2