https://en.wikipedia.org/wiki/High-voltage_direct_current https://en.wikipedia.org/wiki/High-voltage_direct_current I'm not an electrical engineer, so all of t

https://en.wikipedia.org/wiki/High-voltage_direct_current https://en.wikipedia.org/wiki/High-voltage_direct_current I'm not an electrical engineer, so all of this has been my lightly informed opinion. I don't have the right words or depth of knowledge to convey my impressions, sorry. I don't know about big problems, but there are certainly complications and concerns when converting DC to AC at grid scale, as you can see in the Disadvantages portion of the wiki. Sorry I don't have a better source. I don't think batteries are "bad" for frequency stabilization, I just don't think they're good at it. With regard to spinning metal, I think you may be referring to flywheel storage? Flywheels do have lower energy density than batteries. I was referring to base load generation by spinning generators.