by Jason Black, Battelle Memorial Institute
The march toward a future where renewable energy will represent the backbone of electrical generation continues in earnest. According to the Energy Information Agency, nonhydroelectric renewable energy production surpassed hydro for the first time this year. Total renewable use for electricity generation will increase by 2.1 percent in 2014, and it is projected that 2015 will see a 4.2 percent increase as a result of growth in nonhydroelectric energy production.
This is good news for the environment, economy and U.S. energy production, but as utilities integrate more renewable energy sources, this shift will present challenges in determining the right mix and placement of critical assets to maintain grid stability.
Renewable energy sources-including solar, wind, geothermal, hydro and biomass-are growing in stature because of concerns about climate change, energy independence and the fluctuating costs for petroleum-based products. In addition, federal and state mandates that make older coal or gas-fueled power plants less competitive are driving a significant shift in our energy mix. As more areas follow Germany and California in mandating that large percentages of energy come from renewables, utilities will need to re-evaluate their operating and restoration plans to consider these new sources.
Renewable energy integration presents many challenges for grid planners and operators.
Solar and wind energy are particularly difficult to predict and provide fluctuating energy production from day to day or moment to moment. Peak supply times driven by sunny or windy days might not match peak demand, and areas with high consumption needs are not always close to areas with the best opportunities for renewable energy production. This combination of variable energy supply and long-distance transmission makes the grid more fragile. The greater the percentage of total power generated by variable-power renewables makes it harder for utilities to balance energy supply and demand.
As we introduce more variability into the system, transmission planning methods and emergency restoration plans developed for a simpler grid system might no longer be adequate. When variable renewable energy sources move from a small piece of the power supply picture to a more significant fraction of the overall energy mix, it becomes harder to predict and model grid performance. Variable energy sources introduce complexity to the system and increase the likelihood of imbalances between supply and demand that could lead to a voltage collapse if the load is not rebalanced.
In addition, the most common transmission planning software programs on which utilities rely are built on historical models and have limited ability to predict grid performance when the grid is stressed.
Operators might find their experience is outdated, which limits their abilities to make effective decisions during crises. The fairly recent onset of renewable fuels usage negates the historical reliance on experience and institutional knowledge upon which many operators rely. The costs of miscalculation can be ruinous; a single blackout can result in millions of dollars in direct costs and lost economic output, or even billions of dollars in the case of a wide regional outage.
Restoration plans typically are based on off-line power flow studies most appropriate for static scenarios.
In rapidly shifting, multivariable, real-world scenarios, relying on these static historical models can be inadequate. When the worst happens, renewable integration might make it harder to restore the grid.
As reliable coal-fired power plants are retired because they can’t meet environmental regulations and replaced with variable power sources, operators likely will have fewer restoration options.
Because it is difficult to predict how much power renewable energy sources will generate after a disaster, these sources are unsuitable for restoration.
Renewable resources are being tied into an aging infrastructure that wasn’t designed for solar, wind and biomass as important electricity generators.
In addition, the existing grid infrastructure is being augmented to operate with new smart grid technologies that place greater strain on its capabilities and undermine the central planning and control mechanisms that have been established and proved.
Given the number of unknowns and level of risk associated with these changes, the need for minute-by-minute situational awareness over grid conditions has never been greater.
This new energy mixture requires utilities to invest in systems and processes to control these risks and maintain command and control over the grid.
Transmission operators need new tools to increase situational awareness and help them quickly restore grid stability when a blackout occurs.
Researchers worldwide are developing sophisticated software solutions to accommodate complex, multivariable scenarios, including variable renewable energy sources, and to adjust to rapidly changing grid conditions, even up to the point of collapse.
As the world’s largest nonprofit research organization, Battelle has been involved in developing these tools to fit the changing energy generation landscape. A good case study can be found in HELM Agora, a tool developed by Gridquant and distributed by Battelle Memorial Institute, and in use by utilities in Spain and California. Rather than relying on traditional Newton-Raphson methods to solve limit equations, the software takes advantage of a patented, deterministic load-flow solver that allows operators to visualize grid conditions in real time even up to the point of voltage collapse. In the event of a blackout, it operates much like a GPS, providing dynamic, step-by-step guided solutions that are continuously recalculated in response to changing grid conditions and equipment availability.
The software was created for Spanish utilities that lacked the ability to provide real-time, guided solutions to utility operators for avoiding and recovering from blackouts. Since its implementation in 2000, the tool has become integral to transmission operations at Endessa, Spain. And after the 1998 San Francisco blackout, Pacific Gas & Electric Co. recognized it needed a solution to restore customers as quickly and safely as possible.
In each instance, investments in real-time decision support software replaced outdated or unreliable intuition with real-time information that helps operators respond to emerging conditions to prevent a blackout or rapidly restore the grid if a blackout occurs.
These newer approaches to grid monitoring and modeling can give power companies a new tool in their arsenal for emergency planning and restoration as they adjust to new technologies and energy sources.
By giving operators better visibility into grid conditions, power companies can ensure they are prepared for all of the changes and challenges the future will bring.
Jason Black leads Battelle’s research initiatives in the grid systems area. He received a doctorate in engineering systems from Massachusetts Institute of Technology and a Bachelor of Science in Electrical Engineering and a Bachelor of Arts in International Studies from the University of Notre Dame. Reach him at email@example.com.More PowerGrid International Issue Articles
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