But what happens when the wind doesn’t blow or the sun doesn’t shine?” That’s a common question from those who want to understand how grid operators integrate renewable energy into their systems. Fortunately, the people who keep the lights on every day for US families and businesses have found they can reliably handle large amounts of wind and solar energy. In fact, wind farms in particular have unique attributes that enhance the overall reliability of our electricity grid.

Some of the most common questions about renewable energy focus on how wind and solar can be reliably integrated into the power system. Many people are unaware of technological advances that allow wind and solar to provide grid reliability services as well as or better than conventional power plants. Here, we get answers to some of the most frequently asked questions from lessons learned from grid operators’ experiences of reliably integrating large amounts of renewable energy.

How much wind energy are US grid operators integrating now?

US wind energy provides enough electricity to power the equivalent of over 25 million homes. Iowa and South Dakota reliably produced more than 30% of their electricity from wind in 2016 and a total of nine states are above 15%. At times, wind has supplied more than 60% of the electricity on the main utility system in Colorado, and more than 50% of the main Texas power system and the Southwest Power Pool system. These power systems have seen electric reliability increase.

How much more renewable energy can we reliably integrate?

While US and European grid operators have already reliably integrated large amounts of wind energy, studies indicate that we can go far higher. Researchers have studied the possibility of obtaining 50% or more of our electricity from wind and solar, and found no major obstacles to doing so. Ten years ago, some utilities and grid operators were concerned about reaching 5%. Technology advances and lessons learned have allowed that number to be exceeded over the past decade, and these gains are likely to continue in the future.

Don’t we need baseload?

Instead of using the term ‘baseload,’ it is more accurate to talk about the three main services the grid needs to operate reliably – energy, capacity and flexibility. Energy is the production of electricity, capacity is the ability to produce power during periods of high demand, and flexibility is the ability to change output to keep supply and demand in balance. Cost-effectively obtaining all three services requires a division of labour among a diverse mix of energy sources, as no resource excels at providing all three. For example, baseload resources typically do not provide flexibility, and there can be lower-cost ways of obtaining the energy and capacity provided by baseload. Wind energy fits well into this mix as a low-cost source of energy, though it also provides some capacity and can provide flexibility when it is economic to do so.

What happens when the wind doesn’t blow?

Other plants provide energy at those times, in the same way that all power plants back up other power plants. Portfolio diversity is the key, as no resource is available 100% of the time. All power plants have reduced output at times and grid operators plan for wind’s contribution using the same tools they use to evaluate the contributions of other resources. Adding wind power never increases the need for power plant capacity, but rather reduces it. A number of times, wind energy has shown its contribution to a more diverse and resilient energy portfolio by stepping in when other resources failed unexpectedly.

A prime example occurred during 2014’s ‘polar vortex’ weather event. The bitter cold and loss of gas supply forced many conventional power plants to shut down abruptly. At the same time, high demand for home heating sent natural gas prices and electricity prices skyrocketing. However, wind turbines kept reliably generating electricity, saving consumers in the Great Lakes and mid-Atlantic area over $1 billion in two days. About a year later, a New York nuclear plant shut down without warning. When that had happened in the past, energy prices shot up. This time, however, the state’s wind farms made up the difference and held prices down.

Why are coal and nuclear plants facing economic challenges?

Cheap natural gas, not renewable energy, is the primary factor undermining the competitiveness of coal and nuclear plants. Wind and the production tax credit (PTC) are compatible with well-functioning electricity markets. Wind’s impact on other generators is market-driven. It is the same as that of any low-cost generator and is small compared with other factors.

Some of the clearest evidence that wind is not the main factor driving other energy market woes can be seen by looking at the places where coal and nuclear power plants are being retired. Most retiring nuclear plants are in areas that have little to no wind generation, such as Florida, Vermont, Wisconsin, Massachusetts and New Jersey.

Can renewables offer the reliability services provided by conventional generation?

Yes. As wind energy has grown to provide a larger share of our electricity mix, renewable energy technology has matured so that modern wind and solar plants are able to provide the same grid reliability services as conventional generators, including voltage and reactive power control, frequency and inertial response, and voltage and frequency ride-through. In some cases, the reliability services provided by renewables exceed those of conventional generators. In other cases, conventional generators can provide those services more economically than wind generators but wind generators can provide those services if it becomes economic to do so.

Many blackouts, like the one that hit Washington DC in 2015, happen in part because conventional power plants go offline during voltage and frequency disturbances on the grid. Thanks to their advanced power electronics, wind and solar plants withstand such disturbances far better.

What about the variability of renewable energy?

Variability and uncertainty are nothing new for grid operators. They have always dealt with large or unexpected fluctuations in electricity supply and demand by changing the output of power plants. Factories, air conditioners and appliances turn on and off in waves, varying by time of day and season. Major spikes occur from events as simple as half-time during a football game, when millions of refrigerator doors open.

Most changes in wind output are cancelled out by other offsetting changes in electricity supply and demand, and any remaining variability is accommodated using the same flexible reserves that grid operators have always used. Spread across 41 states, the output of the US’s 53,000 utility-scale wind turbines stays relatively constant. In fact, because changes in wind output occur gradually and can be forecast, they are less costly for grid operators to accommodate than the abrupt failures of large conventional power plants. Contrary to most people’s intuitive experience that winds are variable, and electricity demand and supply is stable, the opposite is actually true at the grid operator scale.

How much does it cost to integrate renewable energy?

Grid operator data shows that increasing the use of existing flexible resources to accommodate wind and solar costs only cents on a typical electric bill. In fact, the cost of accommodating the unexpected failures of large conventional power plants is far higher.

Don’t grid operators need to add backup to integrate wind?

No. One of the main reasons why an integrated power system was first built more than 100 years ago was so all power plants could back each other up. Because most sources of variability cancel each other out, having a dedicated backup source for each would be highly inefficient and counterproductive.

What steps can help accommodate higher levels of renewable energy?

Market-based grid-operating reforms and transmission upgrades are by far the lowest hanging fruit for making the power system more efficient by using more of the flexibility that already exists on the power system. These grid operating reforms provide major net benefits to consumers and improve reliability even without renewable energy on the power system, so they should be implemented anyway.

Isn’t energy storage necessary to integrate wind?

No, but it can be helpful. Large amounts of wind energy can be reliably integrated at low cost without a need for energy storage. Energy storage provides a variety of services and is therefore best viewed as a system resource and not a resource for renewable energy. Energy storage is typically a more expensive source of flexibility than grid operating reforms that allow greater use of the flexibility that already exists on the power system.

Why is some wind power curtailed and how does time of production affect the value of wind energy?

In some areas, the growth of wind energy has outpaced the addition of transmission. At times, this has required reducing, or curtailing, the output of wind plants until new transmission is added. However, as long-needed grid upgrades are completed, wind curtailment is being virtually eliminated, as are occurrences of negative electricity prices. Wind energy always has high economic value, particularly once the environmental and public health costs of fossil fuel generation are taken into account.

What has been Europe’s experience with wind energy?

European nations have demonstrated that wind energy can reliably provide a large share of our electricity, with Ireland, Spain and Portugal obtaining around 20% of their electricity from wind on an annual basis, Germany at 25% from wind and solar, and Denmark at nearly 35% wind. Carbon emissions have fallen drastically in all of these countries, while electric reliability has been maintained at world-leading levels and in many cases improved.

What is wind’s net impact on emissions?

Wind energy greatly reduces emissions of carbon dioxide and other pollutants after all impacts on other power plants are taken into account. Wind power remains on track to supply 10% of the US’s electricity by 2020. That adds diversity to the electricity grid, and a diverse grid offers the most secure and reliable supply of electricity. The people keeping the lights on already know how wind works for them. By helping ensure the country’s electricity grid stays secure, wind works for all.