And, as a new NRDC fact sheet published today illustrates, the electric grid can handle much higher levels of zero-carbon wind and solar power, far more than what’s necessary to achieve the relatively modest carbon emission reductions in the U.S. Environmental Protection Agency’s plan to limit pollution from existing power plants. But first, a little background on how our nation’s electric system works.

Grid Basics

The nation’s high-power transmission system is made up of three largely separate grids: one on either side of the Continental Divide (roughly) and the third in Texas. The two largest grids are further subdivided into regions managed by different regional and local utility grid operators.

Source: MJ Bradley Associates using Ventyx Velocity

Grid operators are the air traffic controllers of the power system, managing the flow of electrons from power plants to customers across thousands of miles of transmission lines. They operate the grid under extremely detailed procedures and standards.

Planning for the Next 5 Minutes and the Next 10 Years

To ensure a reliable transmission system, grid operators think in several time frames. In the immediate seconds to hours, they run the grid according to a detailed set of economic and electrical engineering rules embedded in sophisticated computer programs. These programs dispatch power plants with the lowest operating costs first, subject to important constraints to preserve the grid’s stability and avoid blackouts.

Grid operators also plan years into the future to ensure reliability. In the same way that one would not set out to drive across the desert on a half-tank of gas, they want to ensure enough power exists and can be delivered to meet consumer demand years ahead. To do so, they identify factors that could either increase or decrease the need for more power and power lines, and then plan accordingly.

Wind and Solar Power Hit the Big Leagues

There is more renewable energy flowing through the power grid than ever before. At times, wind has supplied more than 60 percent of the total demand on some utility systems, without reliability problems. And solar power now routinely contributes 10 to 15 percent of midday electricity demand in California, which has more solar panel installations than anywhere in the country.

Source: American Wind Energy Association independent analysis based on real time data publicly available by ISOs and utilities

Accurate Forecasts and Advanced Technologies Matter

Due to more precise weather forecasts and sophisticated technologies, grid operators increasingly can predict—and control—wind and solar generation levels. Accurate predictions of wind speed and solar conditions help grid operators efficiently schedule renewable energy into the system. Using advanced and often-automatic control systems, grid operators can both increase and decrease the power output into the grid, which helps to stabilize the grid’s electrical frequency and maintain reliability.

Wind and Solar Need Less Backup Power than Coal, Gas and Nuclear 

Every power plant on the grid needs “backup” power in case something happens to prevent it from generating as much electricity as planned. PJM, in charge of most of the grid from New Jersey to Illinois, currently holds 3,350 MW of expensive, fast-acting contingency reserves 24/7 to ensure that it can keep the lights on in case a large fossil or nuclear power plant unexpectedly breaks down. In contrast, MISO – the grid operator for the middle part of the country with the most wind power in the nation – needs almost no additional fast-acting power reserves to back up its 10,000-plus MW of wind power on the system.

Why is so little backup power needed for wind and solar? In contrast to the large, abrupt, and often unpredictable changes in electricity output from coal and nuclear power plants, wind output changes tend to be gradual and predictable, especially when wind turbines are spread over larger areas. The fact that a wind farm is a collection of many smaller turbines also helps, since the failure of one has little impact on the farm’s total output.

Our Grid Is Successfully Integrating Clean Energy Now and Will Continue

The power grid has always adapted to changing state and national energy trends and needs, thanks to regular operations and planning frameworks. Forty years ago grid operators learned to accommodate the sudden losses of generation that can come from integrating very large nuclear power plants into the system.

Now, as utility-scale wind and solar power rapidly expand, grid operators are successfully integrating these new resources into the grid while retiring many outdated, costly, and polluting coal plants. And they’re doing it without most Americans even noticing. Maybe that’s the best proof that wind and solar power are not just ready for the big leagues, they’re already there.

This article was originally pubished on NRDC and was republished with permission.