When you turn on a light or charge your phone, the electricity coming from the outlet may well have traveled hundreds of miles across the power grid that blankets most of North America — the world’s largest machine, and one of its most eccentric.

Your household power may have been generated by Niagara Falls, or by a natural-gas-fired plant on a barge floating off the Brooklyn shore. But the kilowatt-hour produced down the block probably costs more than the one produced at the Canadian border.

Moreover, a surprising portion of the system is idle except for the hottest days of the year, when already bottlenecked transmission lines into the New York City area reach their physical limit.

“We have a system which is energy-inefficient because it was never designed to be efficient,” said Richard L. Kauffman, the state’s so-called energy czar, who is leading its plans to reimagine the power grid.

It’s like a mainframe computer in the age of cloud computing, Mr. Kauffman added, and with climate change, the state has to “rethink that basic architecture.”

But how does it work now?

In 1882, heaps of black coal were hauled by horse-drawn wagons to the Edison Electric Illuminating Company of New York’s powerhouse on Pearl Street in Lower Manhattan, where “jumbo” steam-powered engines (named after P. T. Barnum’s elephant) spun generators. These created electricity, which traveled to homes and businesses within about one square mile, illuminating drawing rooms without the use of a match for the first time.

A few years later, a hydroelectric station on the Niagara River using Nikola Tesla’s designs and equipment supplied by George Westinghouse helped turn Buffalo into an industrial force.

Today hundreds of plants, mostly privately owned, pump out power. Each one varies in its cost to build and operate, how much power it can produce, how quickly and how efficiently. Unlike other states, which do not have access to such a diversity of resources, New York has a full menu of options.

Coal, the original fuel, is on the way out. The state has announced plans to close the remaining plants or convert them to natural gas, which is currently cheap and plentiful.

In 2015, 64 plants that use natural gas produced almost half the electricity in the state, said the New York Independent System Operator, a nonprofit that runs the state’s grid and power markets.

Four nuclear plants accounted for about a third of it. Though disposing of nuclear waste remains a concern, the state wants to subsidize nuclear plants upstate because of the steady, carbon-free power they provide. But Gov. Andrew M. Cuomo’s recent decision to force the closing of the Indian Point power plant in suburban Westchester County has raised questions about the state’s ability to meet its clean energy goals and how it will make up for the energy the plant provides.

In New York there are 180 hydroelectric facilities, which produced 19 percent of the state’s electricity, and which remain crucial to clean power production.

By 2030, Mr. Cuomo wants half of the electricity consumed in the state to come from renewable sources produced here or imported from places like Canada and New England.

According to the latest figures, less than a quarter of the electric energy produced in New York came from renewables.

While there are tens of thousands of residential and commercial solar energy systems, only one utility-scale solar photovoltaic power plant is included in the Nyiso’s estimates of solar production.

Large-scale wind has had more success, and the state is pushing for more; about 30 wind farms are planned upstate. And the state recently approved the nation’s largest offshore wind farm, which could power 50,000 homes on Long Island by the end of 2022. A second site near the Rockaway Peninsula in Queens is in the works but is years away.

The cost of building wind and solar plants has fallen, but these power sources are intermittent. Until more storage is plugged into the grid, like batteries or pumped hydro plants, which pump water into reservoirs to store power for later use, other generators must be available to supplement solar and wind power.

A standard part of the electric arsenal are generators called “peakers,” which are needed to keep the grid reliable but might run only a few days a year. New York City has about 16 such plants, mostly around the waterfront, which spring into action on the hottest days of the year or if transmission lines or power plants upstate malfunction. Some sit on barges, and all are designed to switch on quickly. The trade-off for the rapid response is usually higher costs and carbon emissions.

As a result, customers pay for plants and wires that “a lot of the time are hardly used,” said Mr. Kauffman, the energy czar.

The entire system was designed to meet demand extremes and handle the worst-case situation.

Inside a $38 million control room near Albany, a team of seven employees of the New York Independent System Operator is always on duty, monitoring electricity zooming through the state’s grid and coming in from and out to neighboring grids.

Nyiso (pronounced NIGH-so) is one of 36 entities responsible for the Eastern Interconnection, one of the country’s three main grids extending from the Rockies to the East Coast in the United States and Saskatchewan to Nova Scotia in Canada.

Unlike water, electricity can’t be stored in a bucket. While batteries are improving, most electricity is used the instant it is created.

The team constantly calculates how much power is needed and which plants can produce it at the lowest cost. Every five minutes, a computer system directs plants to dial up or scale down production to ensure enough electricity is available to keep the lights on without overloading transmission wires. If the system is out of balance or the flow of electricity is destabilized, it can damage equipment or cause power failures.

Operators undergo psychological evaluations to ensure they can handle stress, and they spend weeks every year inside simulation labs preparing for a hurricane or cyberattack. Still, the No. 1 enemy is tree branches, as Gretchen Bakke pointed out in her book, “The Grid: The Fraying Wires Between Americans and Our Energy Future.”

In 2003, the country’s worst blackout started with a sagging power line in Ohio that shorted out after touching a tree branch. A series of human errors and a computer problem plunged about 50 million people into darkness from New York City to Toronto and cost the United States economy about $6 billion.

Jon Sawyer, the chief system operator for Nyiso, said that today, computer systems receive 50,000 data points about every six seconds, and operators monitor regional activity on a 2,300-square-foot video wall. Mandatory reliability standards have been put in place for the thousands of entities involved in the operation of the country’s electric systems.

The biggest daily variable is weather. Storms can flood equipment, and bright, hot days can cause transformers to overheat and customers to crank up air-conditioners.

Leaning on solar and wind means a greater dependence on weather, just as weather patterns have become less predictable. Nyiso has developed sophisticated tools using climate data to predict how much power each wind farm…