Is Renewable Energy Compatible With a Reliable Electric Grid?

One of the perpetual criticisms of renewable energy, especially wind and solar, is that its output is variable — solar panels only generate power when the sun is shining, and wind turbines only spin when the wind is blowing. Critics argue that this variability introduces instability into the electric grid.

However, a recent study by electric-power research firm Synapse Energy Economics Inc., prepared for the Civil Society Institute (CSI), found that, in fact, “the U.S. electricity grid could integrate and balance many times the current level of renewables with no additional reliability issues,” according to CSI analyst Grant Smith, quoted in an announcement from the institute. Thomas Vitolo, analyst at Synapse, said that “it is a myth to say that the United States cannot rely on renewables for the bulk of its electricity generation.”

Jennie C. Stephens, associate professor of environmental science and policy at Clark University in Worcester, Mass., told me that the CSI research is “sound” and “complements and confirms” the work of her own research team. She said that “the dominant challenges in shifting to a renewable-based electricity system are not technical, but they are political, cultural and social.”

Do Renewables Require Fossil-Fuel Backup?

The conclusions of the Synapse report argue against some of the assertions of a 2012 report from the American Tradition Institute (ATI) about The Hidden Costs of Wind Electricity. Tom Tanton, the organization’s director of science and technology assessment, said in an announcement,

Because wind is an intermittent source of electricity, it needs appropriate amounts of fossil-fueled capacity ready at all times to balance its large and rapid variations. Those primary fossil plants then operate less efficiently than if they were running full-time without wind, meaning that any savings of gas and coal or any reductions in emissions are much less than simple calculations would indicate.

The ATI report says wind generation imposes various inefficiencies on the fossil fuel plants that have to operate in combination with it, including “increased hours of operation at partial load” to provide spinning reserve, “increased ramping between different levels of outputs,” extra shutdowns and restarts, and operation in combustion-turbine mode, which provides faster ramp-up but is less efficient than conventional combined-cycle mode.

I sent an email query to ATI asking for comments about the more recent Synapse/CSI study, but they did not respond.

The Transition From Coal to Renewables

The CSI report considers whether the variability of wind and solar is really as much of a problem as critics maintain. A previous study by CSI in 2011 introduced a “Transition Scenario” under which the U.S. would retire all of its coal plants and one-fourth of its nuclear plants by 2050, switching over to a power generation regime based on renewable energy and energy efficiency.

The Transition Scenario eliminates U.S. coal generation, increases renewables and reduces demand through efficiency. Courtesy of CSI.

The Transition Scenario eliminates U.S. coal generation, increases renewables and reduces demand through efficiency. Courtesy of CSI.

Under the Transition Scenario, efficiency programs would allow electricity demand to fall by 0.1 percent per year, whereas under Business As Usual (BAU) it would rise by 0.9 percent per year. The Transition strategy would increase solar photovoltaic (PV) generation from 4 Terawatt-hours (TWh) in 2010 to 842 TWh in 2050; and wind generation from 92 TWh to 611 TWh. The 2011 study found that such a strategy would significantly reduce GHG emissions and other pollutants and would yield $83 billion in savings compared to a BAU strategy.

The current study builds on that Transition Scenario, examining the projected power demand for 10 U.S. regions and how those regions’ grid performance would be affected by high levels of variable power hour-by-hour throughout the year. The study only considered the regions in isolation, which means the model doesn’t take into account inter-regional transfers of power, which would provide even greater load balancing.

I asked CSI’s Grant Smith to elaborate on the practices that would have to be used to mitigate the natural variability of solar and wind if renewables constituted a much higher proportion of power generation. He told me that his group’s scenario adds “flexible resources to compensate for variability along with large balancing areas to smooth out the variability of wind.” He cites demand response and storage technologies as resources “that can be called upon quickly to compensate for any changes in wind or solar output.”

One of the biggest challenges to operating the current electric grid is that the grid has to be managed in real-time. The objective is to supply exactly the amount of power that is demanded at every moment, keeping supply and demand balanced as much as possible.

Courtesy of CSI

Courtesy of CSI

The two basic imbalance modes you would want to avoid are too much power and not enough. “In the vast majority of hours,” the CSI authors write, “the model is able to balance resource output exactly with the projected load.” Too much load “typically occurs in a handful of spring and autumn days with very high wind output and very low demand.” The report points out that inter-regional transfers would mitigate this problem. In addition, power utilities have other tools for maintaining balance, such as economic incentives like time-of-use pricing. Commercial and industrial customers can benefit from demand-response incentives that encourage them to buy excess capacity and store it in water heaters, chillers or batteries. Also, the report says, dispatchers and operators could reduce output from wind turbines, if necessary, by angling the turbine blades.

The CSI report identifies some points at which resources fall short of demand. This happens infrequently, though, and “is likely to be averted by importing additional energy from a neighboring region,” or by using demand-response and other strategies for avoiding this imbalance. The authors stress that “inter-regional cooperation, followed by improvements in technology such as energy storage systems, can provide very high levels of reliability under the Transition Scenario.”

What Technologies Could Make It Happen?

I asked Smith to describe some of the most promising technologies that might be brought to bear to improve the performance of a grid based on renewables. He told me,

Wind technology has already improved. Capacity factors are reaching 40 percent and above due to better blade technology, higher towers, and improved electronics. Solar panel costs have plummeted further and the industry is working on bringing down the non-panel costs. Also, a solar PV manufacturing firm opened a facility in North Carolina with new technology that is almost twice as efficient as current panels. The production level will be low at first, but Siemens is supportive and pumped money in to develop the technology along with DOE [U.S. Department of Energy].

I noted that energy storage does not seem to enter much into the CSI scenario. I asked Smith why that was the case. He responded that “The assumptions in the [2011] study were very conservative.” The research team wanted “to draw on technologies whose track record and costs were well established.” That said, he feels that “battery storage technology is particularly compelling. Batteries can ramp up to full power in milli-seconds and can run at any output level, unlike natural gas plants.”

Stephens of Clark University has studied smart grid technologies and points to advances in this area as another resource that can be brought to bear to integrate renewable power generation into the U.S. grid. She tells me that “A smarter grid could contribute to increasing the efficiency, reliability, and resilience of electricity systems, and to facilitating the integration of renewables, energy storage, long distance transmission and the electrification of transport.”

 

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Comments:
  • Tom Tanton
    May 6, 2013

    Response to “Is Renewable Energy Compatible With a Reliable Electric Grid?”
    Al Bredenberg

    By Tom Tanton
    Director, Science & Technology Assessment
    American Tradition Institute (ATI)

    In his article, Mr. Bredenberg refers to a recent study by electric-power research firm Synapse Energy Economics Inc., prepared for the Civil Society Institute(CSI). The CSI study found that, “the U.S. electricity grid could integrate and balance many times the current level of renewables with no additional reliability issues.” The study is an attempt to dispel concerns regarding the variability of renewables, “especially wind and solar…solar panels only generate power when the sun is shining, and wind turbines only spin when the wind is blowing.”

    Mr. Bredenberg then quotes me from my report, “Hidden Costs of Wind Electricity.” First, there are several technical problems with the Synapse study and some apparent confusion by Mr. Bredenberg about my report.

    The “Hidden Cost of Electricity” is an analysis of the cost of wind generated electricity, taking into account various hidden costs and costs imposed on folks other than the wind generator themselves, due to the nature of wind generation. In essence my report doesn’t address the question of whether more wind or other renewables is conceivably and physically possible, but rather what is the total cost, including hidden and offloaded, of wind. It is conceptually possible to increase wind generation while maintaining grid reliability, as the Synapse Report shows. That would be very costly, however, requiring huge investments in energy storage, in massive amounts of ‘flexible’ generation, and the abandonment of well functioning existing power plants (not yet fully amortized), as noted by Synapse. In short, the study calls for the complete replacement of a working system.

    Making it more difficult and complex to maintain power, frequency, and voltage will strain both the generation equipment and personnel, and that will increase the probability of a cascading failure. It does not, as they claim, lead to more reliable service.

    In all regions analyzed by Synapse, imports are required to maintain load (i.e. matching demand and supply). In other words, load was not satisfied by the renewables scenario, but depended on imports from other regions and on increased “flexible generation.” In a select few cases, wind generation is curtailed even when available, but the report does not make clear whether that is timely and available to other regions for use. Curtailment means the wind is wasted. In other words, reliability requires resources beyond the renewables. The Synapse conclusion is at odds with the Synapse analysis.

    The terms “backup” and “balancing” have different meanings. Backup generally refers to the requirement to provide power when the sun is not shining or the wind is not blowing. That is a multiple-hours, or diurnal or longer phenomenon. Balancing refers to the instantaneous (less than 1/60 second) requirement to maintain harmony on the grid for power, voltage and frequency. It can be threatened when the wind suddenly increases or decreases, like when it gusts. Wind creates threats to the grid’s stability as much, if not more, when it’s is generating ‘full out’ than when it’s off due to lack of wind. It is that phenomenon to which I refer in the piece quoted by Mr. Bredenberg – operating flexible generation units in stop and go mode degrades their efficiency compared to ‘cruising.’ That has both capital recovery and fuel cost implications which are not considered in the Synapse report.

    The terms ‘predictability’ and ‘stable’ are also confused when discussing wind forecasting done by regional grid operators. Having been involved with improvements to wind forecasting for twenty years, this is particularly disturbing. Wind forecasting HAS improved greatly over that time, but being able to predict the wind for tomorrow as likely being ‘gusty’ is far different than being able to manage wind’s ‘instability.’ Remember, wind’s output is a cube function of the wind speed, so a gust at 20 mph produces eight times the electricity as does a 10 mph baseline wind. If that’s happening every five minutes, for example, the grid operator will have a very serious challenge regardless of whether he anticipated it ahead of time or not. Knowing the wind will be gusty tomorrow does not mean anything can be done about it when it occurs.

    Finally, the Synapse report acknowledges the need for increased Demand Side Management, which is just one way of saying electricity is turned off when supply is short of demand. That can be voluntary through programs customers sign up for with incentives (they’re paid to not use electricity) or through involuntary central dispatch decisions. Either way, load is not met if it is traditionally defined as meeting customer demand. Turning off customers’ lights is hardly maintaining reliable service.

    The Synapse report addresses different issues than does Hidden Cost Of Wind Energy, and glosses over some significant cost items: huge additional transmission lines that are seldom used, untested and costly large amounts of energy storage, and the capital recovery and efficiency impacts of the ‘flexible generation’ required to maintain the grid. The report’s suggestion that the ‘all renewables’ scenario would result in cost savings of $83 billion compared to business as usual is unsupported.


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