OK, we are back to the catch 22 here. We want more electric power, both now and for the future, but we don’t want power plants or high voltage transmission lines near our homes and neighborhoods.
The direct current super grid is the most needed item.
A little history here, back at the turn of the 20th century, there was a war being waged between GE (Edison) and Westinghouse (Tesla). Edison wanted to supply electricity in the form of direct current where Westinghouse offered an alternating current alternative.
Westinghouse won out because at the time, they were only powering local grids. Today we call these distribution grids. AC used a higher voltage that used smaller power lines and used transformers to reduce the high voltage down to meet the customers needs. It was, and is still, many times more efficient for that purpose.
However, neither Edison nor Westinghouse have a vision for a national grid with high power transmission lines. But as this grid evolved, it used AC because that was now engrained into the minds of electrical engineers as the superior alternative. But for the transmission grid, aka the long haul grid, it had issues stemming from phase shift of the AC signal.
Phase shift is well understood in the HF community and high frequency transmission lines used in communications equipment (radio, TV, etc) are designed to accommodate phase shift as the wavelengths used in their equipment has very short wavelengths.
60 Hz AC has a wavelength of about 3100 miles, or about the distance from Portland, ME to San Diego, CA. There is about a one degree of phase shift for 8.6 miles. A few degrees are not significant so a grid that covers most eastern states doesn’t have a significant phase shift problems. Also any grid that has only one power station is not a affected by phase shift. The problem occurs when you try to connect two separate grids together so they back-up each other. The phase shift becomes significant and the result is a lot of power loss where signals intersect out of phase.
As the distances grow and the grid becomes more complex, it becomes far more difficult to keep them in sync with each other. Significant losses occur. Now add multiple new sources to the grid in the form of wind and solar farms, especially when these are often located hundreds of miles from the local distribution grid that intends to use that power.
Direct current does not have a phase shift problem when connecting diverse grids together. There are some conversion losses at each end as the AC is rectified to DC and then inverted back to AC at the other end, but these losses are far less than the losses due to phase shifts. I have seen estimates of between 20 to 50% losses on the AC transmission grids depending on who is doing the calculations. The conversion losses for the DC grid are on the order of 5% or so.
The resistive losses for DC and AC are the same, just old fashioned Ohms Law.
But the AC lines were established back when people didn’t object to public projects, or at least their voices weren’t heard. Now, every attempt to build a 600kVD transmission line is met with a lot of resistance from people who live along the routes. Getting permits for each new line is now expected to take 8 years or more, if successful. And because of their lengths, it takes a lot of permits for each line and failure to obtain even one permit dooms the whole project.
L . . .