(TNS) -- Underground power lines don’t sway in the wind. Tree branches blown sideways by a gale can’t hit them. They don’t sit on wooden poles that can fall down.
They would, in other words, seem to be an ideal way to prevent wildfires in a place like California, which has a history of big blazes sparked by overhead power lines tangling with trees. Investigators are now trying to determine whether that combination triggered the wildfires that tore through the Wine Country this month.
Unfortunately, underground power lines are also very expensive.
And if Pacific Gas and Electric Co., whose overhead lines are facing scrutiny as a possible cause of the North Bay fires, were to bury more of its system, that cost would be borne by the company’s customers. It would not come out of PG&E’s profits. Placing more lines underground could even raise those profits, since under California regulations, utilities make a guaranteed rate of return on the value of all the equipment they own.
“We think it’s so expensive that it’s really not feasible,” said Mark Toney, executive director of The Utility Reform Network watchdog group.
A new underground distribution line across most of PG&E’s territory costs about $1.16 million per mile, according to data filed with state regulators during the utility’s most recent general rate case. That’s more than twice the price of a new overhead line, which costs about $448,800 per mile. Most of the difference comes from the expense of digging a trench for the cable.
Prices rise within cities, where the work is more complex. A 2015 San Francisco report found that recent costs for moving power lines underground in Oakland had averaged $2.8 million per mile, while similar work in San Jose had cost $4.6 million per mile.
And burying high-voltage transmission lines — the kind usually strung from immense steel towers across long distances — can cost as much as $5 million per mile, according to PG&E.
The utility operates more than 134,000 miles of overhead power lines of one voltage or another across Northern and Central California. So while placing power lines underground in areas filled with flammable vegetation may sound sensible, it is far from cheap: It would cost well over $100 billion to do across PG&E’s entire territory.
“Do we want to tear up the whole Oakland hills — a high fire hazard area — to do undergrounding?” asked Michael Picker, president of the California Public Utilities Commission. “There’s never going to be a perfect solution. A lot depends on how much people are willing to spend to approach the next level of safety.”
San Francisco has particularly painful experience with the costs of burying lines.
For 10 years starting in 1996, the city worked with PG&E to place underground 45.8 miles of overhead lines, with the utility estimating a cost of $1 million per mile. Instead, the final price came in at $3.8 million per mile.
California regulations use a formula for allocating some money each year from utility customers’ bills to undergrounding projects in cities that want to bury their power lines. San Francisco’s 10-year project ran so far over budget that it used up all the money that would be available to the city through 2032, according to a city report. That brought undergrounding within the city to a halt.
Price is not the only pitfall.
Repair crews have no trouble spotting a knocked-over power pole or downed line. But when an underground line fails, operators first have to figure out where the problem occurred, without being able to see it — though sensors attached to the power lines can help narrow things down. Then they have to dig.
“You may know it’s within a certain distance, but you don’t know exactly where it is,” said Andrew Phillips, director of transmission studies at the Electric Power Research Institute, a think tank serving the utilities industry. “And fixing it is very expensive, and that means the outage time is a lot longer.”
There’s also the issue of cutting trenches through environmentally sensitive areas. And in more urban settings, workers who don’t know the location of an underground line may dig into it, a problem that plagues natural gas pipelines as well. The power research institute’s office in Charlotte, N.C., recently lost power for an afternoon after someone accidentally hit an underground power cable in the neighborhood, Phillips said.
“Some guy with a backhoe was working on the traffic light, and he dug into the line — and everyone had to go home,” he said.
Most undergrounding takes place in towns and cities, for aesthetic reasons.
Urban streetscapes already contain a maze of infrastructure below the surface — water and sewer pipes, fiber-optic cable — so undergrounding can often be combined with other jobs to minimize the disruption.
PG&E undergrounds about 30 miles of electric lines each year. Other utilities have been more aggressive. San Diego Gas and Electric Co., a far smaller utility, says that 60 percent of its lines are now underground. That even includes small stretches of rural lines running through areas considered particularly prone to wildfires. The city of San Diego also placed a high priority on moving lines underground and set up its own funding system to support the work.
At the current pace, moving all of California’s utility lines underground would take 1,000 years, according to the California Public Utilities Commission.
PG&E has replaced hundreds of toppled or damaged power poles in the North Bay since the Oct. 8 windstorm and the wildfires that followed. It remains unclear whether PG&E’s equipment may have helped start the fires or whether the fires damaged the equipment.
Either way, PG&E does not consider undergrounding a panacea.
“We serve urban areas, and we also serve really rural areas, so where’s the tipping point where undergrounding makes sense?” said PG&E spokesman Keith Stephens. “We want to provide safe and reliable service that’s also affordable. So it’s a balance of those three things.”
power lines underground can help prevent fires
— at a price
Miles of overhead power lines in PG&E territory: 134,000
Cost of underground lines, per mile: $1.16 million to $5 million
Miles of power lines PG&E undergrounds per year: 30
©2017 the San Francisco Chronicle Distributed by Tribune Content Agency, LLC.