transmission lines
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Renewable energy sources, at least wind and solar, are variable — the wind isn’t always blowing, the sun isn’t always shining. This is something every glib pundit on the internet cites as a reason we’ll need fossil-fuel or nuclear “baseload” power plants for the foreseeable future. It’s a frustrating topic, since people who actually study the subject (like NREL) have shown that there are all sorts of ways to handle variability without disrupting the grid.

One of those ways is transmission: building power lines to take renewable energy from where it is abundant (often remote areas) to where it is needed (mainly big cities). More specifically, the idea is to build high-voltage direct-current (HVDC) lines that would carry energy over long distances from remote sites and feed it into the alternating-current (AC) lines that serve urban areas. (The DC vs. AC question is interesting, but not particularly essential for understanding the bigger questions.)