Tropical Storm Irene hit Cape Cod in August 2011. Next came that fall’s “Snowtober.” Then, Hurricane Sandy in October 2012 and the February blizzard, not to mention intermittent summertime power outages and pernicious coastal storms like the one that hit a week ago.

People all over the US are tired of the lights going out and they are increasingly turning to backup power sources in emergencies, particularly natural gas or propane-powered generators.

“Ninety percent of my business right now is generators,” master electrician Leon Knight of Knight Electrical in Brewster said recently. “We’ve been basically doing one a day.”

During the summer it was two a day, he said.

Generator installers report a similar increase in installations in the past year.

Generators can use a variety of fuel sources, including natural gas from an on-site propane tank, diesel or regular gasoline.

The size depends on the homeowner’s needs and desires, Knight said.

“I ask them what they like to power up during a power outage,” Knight said. “Air conditioning? Stove? Some people just want the basics: heat, a few lights.”

Cost varies depending on a number of factors. For example, a 5-kilowatt natural gas generator that is close to the gas meter and 10 to 15 feet away from the electrical panel would run $5,500 to $6,000, Knight said.

A typical 1,200-square-foot home has about 12 circuits, he said. About 10 circuits could be powered by an 8-kilowatt generator that would provide electricity for 60 to 80 percent of the house, Knight said.

Knight installs and services Generac and Kohler generators, but a range of brands is available. Currently, because of the high demand, it can take six to eight weeks to order and install a generator.

“As of 2013, it’s been astronomical,” Ed Moore, owner of Moore Security and Services in Orleans, said.

Although Hurricane Sandy didn’t do as much damage locally as it did in other places “it scared people,” Moore said.

The damaging nor’easter that hit a week after Hurricane Sandy reinforced those fears, he said.

“A lot of people on the Cape are retirees,” Moore said. “They don’t want to put up with three or four days without power.”

For people who need access to oxygen or other medical services, electricity is even more essential, he said.

Often the decision about what size generator to buy comes down to what the customer can afford, Moore said.

Especially in places where most people don’t have natural gas connections, there’s the added expense of an on-site propane tank.

“You have to shop around,” Moore said.

When he first got into the generator installation business in 2007, Moore said, he was “jumping up and down if I could sell one generator a month.”

As of January, he’s been getting two or three calls a day about generators and most of those result in an installation, he said.

Business is up about 200 percent from last year, he said.

The boom has meant jobs as well, according to installers.

“We have had to hire and actually sent one of our electricians to start schooling,” said Kecia McCaffrey, office manager for an electrical department.

Generator sales have probably doubled from last year, she said.

“It started mildly after Sandy but more importantly, it started after the winter blizzard. That brought people to their knees,” said John Robichaud.

Like air conditioners, generators have become a household necessity for many people, he said.

Robichaud said he, also, has had to hire more staff, but the biggest issue is getting electricians from outside the company.

“That really is slowing us down because there’s so much work,” he said.

Robichaud and other installers emphasized that generators are not something a customer can just install and forget until the lights go out. While wireless technology allows remote testing and monitoring, service by a trained professional is still essential, Robichaud said.

“The darn things sit outside and nobody’s looking at them or watching them,” he said.

And when the power goes out and a generator doesn’t work, homeowners often react badly, he said.

“I call this an extremely emotional product,” he said. “I’ve got people crying, people screaming. I was amazed by the emotions.”

National Grid, which delivers natural gas on Cape Cod, takes into account the increase in reliance on generators during power outages, company spokesman Jake Navarro said.

Although the number of generators hooked up directly to natural gas on the Cape is still relatively small, “it’s becoming more popular,” Navarro said.

Because natural gas connections for generators aren’t broken out of the statistics, tracking the total number is difficult, according to local plumbing inspectors responsible for installations.