What would it cost to bury all of California’s power lines?

Recent wildfires in California are sparking debates on potential utility culpability, leading many people to ask the simple question: why aren’t more power lines buried underground?

While the causes of the wildfires that began to blaze earlier this month are still unknown, “better safe than sorry” is a commendable ethos, right? As it turns out, it may not be that simple (or cheap!).

How did the fires start?

The cause of the multiple fires that burned around Los Angeles County are still under investigation by local officials. Lightning, the most common source of fires in the U.S. according to the National Fire Protection Association, was quickly ruled out as a cause. There were no reports of lightning in the Palisades area or the terrain around the Eaton Fire, which started in east Los Angeles County and has also destroyed hundreds of homes. The next two most common causes: fires intentionally set, and those sparked by utility lines. So far there has been no official indication of arson in either blaze, and utility lines have not yet been identified as a cause either. 

Utility Southern California Edison (SCE) filed two Electric Safety Incident Reports (ESIR) related to the wildfires, one for the Eaton Fire and another for the Hurst Fire. ESIRs are filed with the California Public Utilities Commission (CPUC) for incidents that meet certain criteria, such as significant media attention or a governmental investigation. These brief reports contain preliminary information and are provided within two to four hours after a triggering event. To comply with CPUC requirements, these reports are often submitted before SCE can determine whether its electric facilities are associated with an ignition.

SCE filed a report with the CPUC related to the Eaton Fire in the hills near Pasadena, an area the utility serves. Edison said it has not received any suggestions that its equipment was involved in the ignition of that fire, but that it filed the report with state utility regulators out of “an abundance of caution” after receiving evidence preservation notices from insurance company lawyers. SCE said it conducted preliminary analysis of electrical circuit information for the four energized transmission lines in the Eaton Canyon area, which showed no interruptions or operational/electrical anomalies in the 12 hours prior to the fire’s reported start time until more than one hour after the reported start time.

The next day, SCE filed another report related to the Hurst Fire once SCE learned fire agencies are investigating whether SCE equipment was involved in the ignition, which is a triggering event for reporting. SCE noted that the fire was reported at approximately 10:10 p.m. on Jan. 7, and preliminary information reflects the Eagle Rock – Sylmar 220 kV circuit experienced a relay at 10:11 p.m. A downed powerline was discovered at a tower associated with the Eagle Rock – Sylmar 220 kV circuit. SCE said it does not know whether the damage observed occurred before or after the start of the fire.

What is undergrounding?

Undergrounding is often posed as a solution for utility resilience, especially after extreme weather events and wildfires. But it’s not as simple, or cheap, as some may think.

The process of undergrounding involves converting existing overhead electric facilities, including poles, wires, and other equipment, to underground facilities consisting of trenches. The trenches are lined with conduit, which houses the wires, underground vaults, and/or surface mounted structures (like pad mounts) for transformers and other equipment. Additionally, undergrounding can refer to the practice of building completely new lines, line extensions, and service extensions underground.

In California, most new distribution facilities built since the 1960s have been designed and installed underground. However, utility distribution planners can decide to convert an overhead system to underground for safety, cost, reliability, or maintenance reasons. In 1967, the California Public Utilities Commission (CPUC) adopted an Overhead Conversion Program known as Electric Rule 20 to support overhead conversion projects initiated by local communities, which allows cities and counties to identify areas for undergrounding. The utility in turn may fund some, all, or none of the costs of an overhead conversion.

Aside from the aesthetic benefits of undergrounding, which may be important to many homeowners, undergrounding traditionally comes with enhanced safety and reliability: Underground poles can’t be hit by cars or ignite from contacting vegetation, and are less vulnerable to high winds, hurricanes, and winter storms.

However, outages still can occur, and restoration times can be longer for underground lines as utility crews often have a more difficult time locating the faults. Explosions and fires are also concerns in underground vaults, CPUC warns.

What’s the cost?

California has approximately 25,526 miles of transmission lines, and approximately 239,557 miles of distribution lines, of which approximately 147,000 miles of distribution lines are overhead.

Based on an average cost of $3.8 million per circuit mile of conversion for undergrounding distribution infrastructure across the state’s three investor-owned utilities, the ratepayers would be required to pay $559 billion to convert all 147,000 miles of overhead distribution lines in the State, per CPUC’s estimations. Additionally, the cost of undergrounding all 34,000 miles of overhead transmission lines in the state would cost $204 billion, assuming an average cost of $6 million per mile.

According to PG&E, SCE and SDG&E, the costs for undergrounding existing overhead distribution infrastructure can range anywhere from $350 per foot to $1150 per foot, or $1.85 million to $6.072 million per mile.

The ranges for California’s IOUs are as follows:

• PG&E: $650-$1,150 per ft ($3.4 M-$6.1M per mile)
• SDG&E: $500-$700 per ft ($2.64M-$3.696M per mile)
• SCE: $351-$990 per ft ($1.85M-$5.23M per mile)

These costs (in 2019 US dollars) represent all costs associated with the undergrounding effort: trenching, conduit, substructures, cabling and connections, meter panel modifications, cutover work, and finally removal from service of poles and wires.

Additionally, the Edison Electric Institute (EEI) provides a nationwide range of undergrounding costs for the distribution and transmission Systems in its 2012 report “Out of Sight, Out of Mind.” According to the EEI, conversion costs range from approximately $600,000 to $13 million (2019 US dollars) for distribution and $1.5 million to $33 million (2019 US dollars) for transmission.

Installing new overhead distribution infrastructure is much less expensive, CPUC notes. On average, installing new overhead distribution infrastructure costs between $634,000-$760,000 per mile ($120-$144 per foot) according to the electric utilities’ Rule 21 interconnection unit cost guides.

For transmission, the cost for constructing new overhead transmission ranges from $1 million to $11 million per mile and $6 million to $100 million per mile to convert existing overhead transmission to underground for the IOUs.

Is it worth the cost?

CPUC argues that while undergrounding can certainly help fire-harden an electrical system, it may not be the most cost-effective way to do so. A previous Grid Safety and Resiliency Program Application from SCE compared the costs and benefits between three different wildfire mitigation options for its overhead infrastructure located in the High Fire Threat District:

Thus, per SCE, undergrounding is about 7 times more expensive than covering the conductors and replacing wooden poles with fire-resistant poles.

This article contains reporting from the Associated Press.