DC Transmission for Cutting CO2 Emissions

DC Transmission for Cutting CO2 Emissions

The previous article ended with the comment, “There have been at least two proposals to rebuild the US grid using DC transmission so as to cut CO2 emissions. The most recent proposal was by the Climate Institute in a Wall Street Journal article.”

Is this an appropriate proposal?

Let’s begin by establishing the good and bad features of DC transmission.

  1. DC transmission is better than AC transmission for:
  • Shipping large amounts of power over long distances
  • Conducting power underwater
  1. On the negative side, DC transmission is point to point which limits its ability to distribute electricity to multiple locations.
  2. DC transmission is more expensive when used for shorter distances, say under 400 miles.

Here are a few examples of existing DC transmission installations:

A. Rio Madeira transmission line, Brazil: Currently, the world’s longest, carrying power from Jirau hydro plants

B. Jinping-Sunan transmission line, China: Currently the world’s second longest carrying power from Guandi, Jinping and Sichuan hydro plants

C. Neptune Regional Underwater Transmission System: Carries power from New Jersey to Long Island to Bypass NY City

Items A and B connect hydro power plants that operates 24/7/365 to carry power for 1,500 and 1,300 miles respectively.

Item C is an example of where DC transmission can carry power underwater to connect islands or bypass congested areas.

Cutaway of HVDC line from Canada’s Nelson River. Note only two cables compared with three cables for three-phase AC transmission.

The Climate Institutes article in the WSJ was titled, 

“Upgrade America’s 19th-Century Electric Grid”

It called for “spending $500 billion to create a super grid using DC transmission that was built underground alongside Interstate highways” which would be superimposed on today’s mostly AC grid.

The reason for spending $500 billion is to cut CO2 emissions.

The article said, “The DC super grid would transfer energy between power-abundant and power-hungry regions.” 

Presumably one such example would be to transmit power supplied by solar power plants in the Southwest to locations in the northern United States. If a DC transmission line went from Arizona to Chicago, a distance of approximately 1,700 miles, the electricity would have to be shipped back to Saint Louis and Kansas City, and elsewhere, over existing AC lines. 

One problem with this DC line would be that it would only operate during the daytime when the sun shines. 

The DC lines, A and B above, carried power from hydro plants that operate 24/7, 365 days of the year. Solar power plants, whether they be PV or concentrating, don’t operate 24/7.

In this example, we would be spending several billion dollars to transmit expensive electricity from the Southwest, electricity that costs two to three times more to produce than electricity produced by natural gas combined cycle (NGCC) units. This cost comparison is based on the Levelized Cost of Electricity (LCOE).

Building NGCC power plants closer to where power is needed would be a less costly solution than building a DC super grid.

Summary

It would appear that, “America’s 19th-Century Electric Grid” is well suited to America’s 20th century needs, and that it can be expanded as necessary with the use of DC transmission when appropriate.

It’s also how to provide Americans with abundant, reliable electricity at the lowest cost.

. . .

2 Replies to “DC Transmission for Cutting CO2 Emissions”

  1. I’m not so sure about the lowest cost part. In fact, I’m skeptical. It seems the concept of “least cost planning” is being jettisoned in the quest for minimizing carbon..

    • Thanks for your comment.
      From what I have seen, it seems as though there is no cost too great when it comes to cutting CO2 emissions.

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