Why did Xcel ask its customers to keep things chilly in the deep freeze?

Xcel Energy has restored heat to nearly 150 homes near Princeton in Sherburne County and told the rest of its natural gas customers they can turn their thermostats back up.

But why did the company need to ask its customers across the state to lower their thermostats at a time when air temperatures across the state dropped into the minus 20s and wind chills were significantly lower?

It comes down to distribution — and pressure.

How does natural gas reach Minnesota homes, businesses?

Minnesota doesn't have its own source of natural gas, so it gets here from other states by pipeline.

Once it's here, it's distributed by a system of smaller pipes that deliver it from the big pipelines to homes and businesses.

In urban areas, there are a lot of interconnected pipes and multiple sources of natural gas. So, even when there's increased demand, the distribution system can reliably supply gas to customers. In rural areas, on the other hand, some of these distribution systems have a single connection to a natural gas source, which can make the area more vulnerable to disruption when demand is high.

What happened to Xcel's distribution system this week?

The distribution system that led to the area affected had fewer redundancies, meaning there were fewer ways for natural gas to reach all of the customers connected to it.

At the same time, the extreme cold meant that everyone was using a lot more natural gas to heat their homes.

The people whose gas service was shut off this week were at the tail end of one of Xcel's distribution systems. Everyone ahead in the system was pulling in so much natural gas that the pipes' pressure, which pushes the gas through, dropped in the pipes toward the end of the line.

Rather than risk even more people losing service, Xcel decided to cut off the gas for those residents at the end of the line, most of whom live in Baldwin Township near Princeton, until demand for natural gas went down. They also asked people in the rest of the state to turn down their thermostats to further limit demand.

Is that the type of thing we should expect, whenever the weather gets really cold and natural gas demand is high?

No. This is not supposed to happen. Ever.

The state of Minnesota has regulations in place to ensure that it doesn't happen. The reliability regulations are there to protect people's safety.

Outages like this week's are rare, but the Minnesota Public Utilities Commission investigates them whenever they happen. The commission issued a statement Thursday saying it will ask Xcel to explain, among other things, the root cause of the outage and how long people were without service.

It's worth noting that other natural gas utilities in Minnesota, such as CenterPoint Energy, did not tell their customers to turn down thermostats when air temperatures across the state dipped into the 20s and 30s below zero.

What's Xcel saying about why it couldn't keep up with demand?

Kent Larson, Xcel's executive vice president of operations, said Thursday that the problem wasn't about supply: There's enough natural gas coming into Minnesota from other states to meet its demand, he said.

But it is a question of how well the company's distribution systems work and whether they can handle the kind of demand that comes along with extreme weather.

Larson noted that we haven't seen a cold snap this severe for decades — some say it's been at least a generation. He said it's possible that the computer models the company uses to test its system's ability to provide reliable service might not have accounted for the scenario we experienced this week.

One thing Xcel will do next, he said, is to look back at its modeling.

Will Xcel have to put in more natural gas lines to ensure this doesn't happen again?

Larson said the utility will likely have to increase its capacity to distribute natural gas in the area where it made the shut-offs this week.

Baldwin Township — and Sherburne County, as a whole — saw massive growth in the 2000s with a lot of new homes being built and connected to natural gas services. This week's cold snap tested Xcel's natural gas distribution system in the area, and it wasn't able to keep up. Those who lost service were put up in hotels and were given space heaters to make sure water pipes didn't freeze.

Will this extreme cold prompt other natural gas utilities to upgrade their systems?

Utilities across the state will be assessing the way their systems handled this latest cold snap.

But there won't likely be an automatic push toward building up natural gas infrastructure in the state because it would go against the general energy trend we're seeing in Minnesota: Utilities, businesses, lawmakers and advocacy groups are pushing for more renewable energy and less reliance on fossil fuels. Natural gas is a fossil fuel.

So, rather than investing in more natural gas, some argue the state should be investing in electrifying more heating systems so that we can tap the strong supply of wind energy in Minnesota.

The debate over how we should be heating our homes and businesses and how we can be the most resilient to these extreme weather events is expected to continue, and this cold snap is causing more people to think about it — and live it.