Power on Demand: How It Works

In the wake of storms and blackouts, standby generators keep your
house in business

standby generator
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Standby Generator Setups

 

Standby Generator Setups

Surviving a disaster in the form of a hurricane, ice storm, or earthquake is mostly a matter of luck. Surviving the aftermath—when the power lines are down and the roads are impassable—is a longer struggle to keep your food from spoiling, your basement from flooding, or your pipes from freezing as you wait for service to be restored.

With a standby generator parked in the yard, you'll never have those worries. Unlike the portable, gasoline-powered models trotted out by emergency crews, these mini power plants are always "standing by," ready to turn on automatically in the event of an outage, even if you're not home to flip the switch. Standbys are more expensive than their portable cousins—about $3,000 versus $900—but they're also more powerful, longer-lived, quieter, and safer. That's why more and more people, left in the dark by natural disasters or, increasingly, by the frequent hiccups of an aging electrical grid, are making the investment; sales of standby generators went up fivefold between 2000 and 2005.

The basic standby setup is simple. The brawn—the engine and the alternator that generate the electricity—lives outside, in a weather-shielded, sound-deadening box anchored to a concrete pad. The brains, otherwise known as the automatic transfer switch, reside inside and connect the generator to the house's main breaker panel. This switch senses when the power goes down, alerts the generator to turn on, and shunts its electricity through the load center, the subpanel for all the house circuits that need emergency juice. When the power returns, the switch signals the generator to stop and restores the house's connection to the grid. You don't have to do a thing, except perhaps keep an eye on the fuel tank if the engine runs on propane or diesel. For generators that burn natural gas, you don't even need to do that.
Surviving a disaster in the form of a hurricane, ice storm, or earthquake is mostly a matter of luck. Surviving the aftermath—when the power lines are down and the roads are impassable—is a longer struggle to keep your food from spoiling, your basement from flooding, or your pipes from freezing as you wait for service to be restored.

With a standby generator parked in the yard, you'll never have those worries. Unlike the portable, gasoline-powered models trotted out by emergency crews, these mini power plants are always "standing by," ready to turn on automatically in the event of an outage, even if you're not home to flip the switch. Standbys are more expensive than their portable cousins—about $3,000 versus $900—but they're also more powerful, longer-lived, quieter, and safer. That's why more and more people, left in the dark by natural disasters or, increasingly, by the frequent hiccups of an aging electrical grid, are making the investment; sales of standby generators went up fivefold between 2000 and 2005.

The basic standby setup is simple. The brawn—the engine and the alternator that generate the electricity—lives outside, in a weather-shielded, sound-deadening box anchored to a concrete pad. The brains, otherwise known as the automatic transfer switch, reside inside and connect the generator to the house's main breaker panel. This switch senses when the power goes down, alerts the generator to turn on, and shunts its electricity through the load center, the subpanel for all the house circuits that need emergency juice. When the power returns, the switch signals the generator to stop and restores the house's connection to the grid. You don't have to do a thing, except perhaps keep an eye on the fuel tank if the engine runs on propane or diesel. For generators that burn natural gas, you don't even need to do that.
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Practical Considerations

 

Practical Considerations

standby generator engine illustration
Illustration by Harry Campbell
The hard part comes earlier, in trying to figure out how big the generator should be and where to put it. People who want the whole house to run as if nothing were awry will pay dearly for the convenience: A 35-kilowatt unit will set you back $10,000 and incur high fuel and maintenance costs. But if you limit yourself to necessities—the sump pump, air conditioner, heating system, fridge, and a few lights—you can get away with something much smaller. A 7-kilowatt generator, for example, can be had for around $1,700. An installer can size the unit, or you can use the calculator at thisoldhouse.com/shortcuts.

Before writing the check, however, make sure you get the nod from your town's building inspector on where to park the unit. Like all internal combustion engines, generators spew carbon monoxide, so they must be sited well away from doors and windows. Noise is another factor: A generator can pump out 60 to 80 decibels, about the level of loud road noise. You (and your neighbors) probably won't begrudge the racket when there's a power outage, but those once-a-week, 20-minute exercise sessions, which the engine and battery need to stay in shape for the big event, can become a serious annoyance at three in the morning or during an evening barbeque. Have the installer set the exercise time to a neighborhood-friendly hour. Planting evergreens or a fence around the unit also helps screen the noise.

Like any insurance policy, a generator is something you buy hoping it won't be needed. Indeed, if there's one thing that mitigates the cost, it's this: Generators last 15 years or more. "Running a standby generator 100 hours a year—and that's a lot—is roughly equivalent to about 5,000 miles of driving," says Mike Carr, a spokesman for manufacturer Generac. "So it's not likely you'll be wearing out the engine."
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Standby Generator Engine

 

Standby Generator Engine

Just like an automobile, most standby generators have an internal combustion engine, complete with pistons, cooling fans, and spark plugs. But instead of propelling a pair of axles, the engine's sole purpose is to spin the alternator's rotor at 3,600 revolutions per minute, making a stream of of appliance- and light-friendly electricity in the process. Smaller units (those producing less than 16 kilowatts) generally have air-cooled engines; more expensive water-cooled engines will work harder and longer without complaint.

Just like a car, a generator has oil to change, filters to replace, and, if it's water-cooled, antifreeze to check. These tasks must be done every two years, even if you never use the unit in an emergency, or every 50 to 200 hours of running time if you do. If you'd rather not mess around under the hood, so to speak, sign a maintenance contract with a dealer who specializes in your brand of generator.

How Big Should It Be?

A generator's output, measured in kilowatts, needs to be enough to supply all the electrical devices you want to keep running in an emergency, plus a 20 percent cushion. That extra power means the engine doesn't have to operate at top speed to meet the expected demand. It also assures there's enough reserve power for the extra surge that electric motors, such as those in air conditioners and refrigerators, need to get started.

To figure out how big your generator should be, make a list of all the appliances you want to supply with emergency power, then use the online calculator at thisoldhouse.com/shortcuts. You can get a sense of your household's power needs from the list of common appliances below.

Running Watts
Start-up Watts
700
Refrigerator
2,800

750

Lights (10 at 75 Watts)
0
800
Television (large)
0
500
Gas furnace
(with 1U2-hp fan)
1,250

5,000

Central air conditioner
(3 ton)
12,500
2,000
Window air conditioner
6,000
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Cost and Manufacturers

 

Cost and Manufacturers

What is Standby Generator
A miniature power station, fueled by natural gas, diesel, or propane, that automatically turns on in the event of a power outage. Operates continually until electricity is restored (or fuel runs out), then shuts itself off.

Why you'd want one
It continues to power house systems even when you're not there, preventing frozen pipes, a flooded basement, spoiled food, and mold infestations.

How it works
When the power fails, the automatic transfer switch instantly shuts off the main supply, fires up the generator, and directs its electrical output to the designated emergency circuits in the house. When the power returns, the switch shuts down the generator and restores the house's connection to the power grid.

What it costs
You can pay as little as $1,700 for a 7-kilowatt air-cooled system or more than $10,000 for a 35-kilowatt water-cooled unit big enough to run a McMansion. Prices include transfer switches but not installation, which could run as high as $1,000.
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Where to Find It
Guardian
Generac Power Systems Inc.
Waukesha, WI

Kohler Power Systems
Kohler, WI
800-544-2444

Coleman Powermate
Kearney, NE
800-445-1805

Cummins Onan Generators
Cummins Power Generation
Minneapolis, MN
763-874-5000
 
 

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