Upgrading the Grid

We really need to upgrade our electrical grid. I’m not talking about those individual wooden or metal poles that bring power to your home. I’m talking about those large metal towers that look like they were built with an Erector Set™ (photo below). Those are the transmission towers that carry electricity between producers and consumers around the country. The system is collectively known as the grid. The wires terminate on the consumer end in what are known as substations, where the voltage is reduced to household levels, typically 110 and 220 VAC (volts of alternating current). Each substation serves around 1500 homes.

The US needs to transition to renewable energy with projects the size of those in the slideshow. You’ve no doubt seen wind farms and solar farms, but geothermal is also part of our renewable mix. Many people are surprised to learn there are 31 active geothermal plants in the US, with two more proposed. The majority are in the western US where there are more natural geothermal “hot spots.” Most were built decades ago and are already part of the grid.

Problem is, the best locations for new wind and solar projects are not necessarily near existing transmission lines. They do feed into the local grid, and that of course ultimately connects to transmission lines, but it’s not the most efficient way to transfer electrical power. We need new transmission lines connecting directly to these renewable sources.

Fortunately, the Inflation Reduction Act or 2023 provides over $3 billion for grid modernization. For the greatest impact, that money should address two critical aspects of grid infrastructure.

First, can the existing grid carry all that extra power? The grid was built out from the east coast during the early days of electrification. That was in the first half of the 20th century, so a lot of the grid is pretty old technology. You can only put so much electricity into those wires before they heat up, expand, sag, and potentially break, causing fires or electrocution hazards. Electrical grid operators follow strict protocols when shunting electricity around the grid to balance supply and demand.

Turns out those protocols are overly conservative, erring on the side of safety. Although there’s no question new lines will need to be constructed, existing lines could carry more electricity safely using a process called dynamic line rating (DLR). Rather then rating the line’s electrical capacity with a fixed number based on the diameter and composition (usually aluminum) of a given wire, a suite of sensors mounted on each transmission tower monitors things like ambient temperature, wind speed, and precipitation (all of which can cool the wire). They also measure actual wire temperature and the amount of wire sag in real time, and relay all the data to the grid operators. In practice, DLR provides an average of 25% more capacity in that section of the grid. And using DLR will buy us some time to get those new transmission lines built.

The second hurdle is actually getting those new transmission lines built. Construction of new transmission lines can take decades — mainly because of the need to secure rights of way and other permitting. There’s also some NIMBY (not in my back yard) resistance. Would you want one of these obscuring your view of the landscape?

There’s a reason transmission towers look the way they do. They are highly engineered structures designed for stability and longevity and safety. You can’t make them look like “trees” or “cactus” as you can with cell towers. The lines on these transmission towers typically carry electricity in the range of 10-500 kV (kilovolts) so they must be heavily insulated and spaced far enough apart to prevent arcing. The towers must also have access for repair crews and maintenance of fire breaks.

Obviously, the fewer towers that need to be built, the cheaper the transmission system. Towers are typically spaced anywhere from 900-1500 feet apart depending on topographic constraints, but there’s a limit to how widely they can be spaced because the cables weigh, on average, 2 pounds per linear foot. Transmission cables are usually made from hard PVC-covered aluminum with a steel core for strength. The aluminum has more resistance to the flow of electricity than copper, so it generates more heat (which is wasted energy), but it’s far lighter and cheaper than copper.

Or … you could just lose the towers altogether and go with undergrounding. You have to trench 6-8 feet deep, and cap the cables with a concrete slab (also buried) to prevent accidental excavation. And individual cables need to be spaced far enough apart to dissipate heat into the earth. No need to worry about wind damage, so it reduces maintenance costs. But again, there are topographic constraints, rights of way, and permitting.

Undergrounding of power lines pretty much returns the landscape to its original appearance, reducing NIMBY objections. It also meets the standards for what climate scientists call infrastructure resiliency — the ability to continue functioning during periods of extreme weather.

Pacific Gas & Electric is planning to underground some 10,000 miles of their transmission lines in high fire risk areas at a cost of $3.75 million per mile. But they’re redoing what are now standard overhead transmission lines. If undergrounding is the original choice the cost is only $300,000 per mile in rural areas — which is where most of the new transmission lines are needed.

An analysis by the National Grid Group found that, excluding build costs, the cost of operation, maintenance and energy losses over the life of the connection was broadly the same for undergrounded and overhead lines. However, the report also concluded that the capital build costs on their own vary greatly, depending on terrain, route length and power capacity.

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