Bi-Directional Power Flow: The New World Order and What That Means for the Grid
By Troy Miller
Bi-directional power flow is a relatively new topic of concern in the industry, although we have been dealing with it on the grid for years; particularly in states that have led the way in distributed generation. As we add more and more distributed generation, especially renewables, to the grid, we need to take into account the problems they may cause. Adding renewable generation is not a grid reliability concern per se. However, it draws attention to the fact that we need to redefine what is a “truly reliable grid” today. Clearly, an abundance of bi-directional power can directly affect the reliability of a utility, and we need to address the matter promptly
Distributed generation can be an asset to the grid when deployed and operated properly. Utilities are already thinking about how the grid operates on a daily cycle to help balance out renewable power coming on and off. If voltage magnitude is constantly fluctuating, end users will likely experience momentary outages regardless of the additional generation they have in place. We cannot ensure that the sun shines and the wind blows 24/7, so we need to build a grid that can handle the intermittency that comes with renewables. When the grid was developed more than a 100 years ago, these weren’t considerations taken into account, and unfortunately, the grid has not quite caught up to where we should be.
Traditional methods of reinforcing the network by “adding more copper,” , i.e., adding larger cables and bigger transformers, won’t solve the problem the utilities are facing. Tap changers, switching capacitors, and line regulators are a very affordable option, and they perform adequately when responding to slowly changing loads. The changing load and the developments toward more distributed generation is too dynamic to be solved through those “business-as-usual” solutions.
Voltage and frequency variations at the edge of the grid are going to continue to get worse, and we need to re-think how we manage those variations besides resorting to the traditional solution of network reinforcements.
The best way to account for the effects of distributed generation on the grid comes from a variety of solutions. We cannot simply plug in a solar panel, sit back, and reap the benefits. Additional work must be done to bring the grid up to speed to take on these newer generation sources, since we already see such voltage and frequency problems occurring frequently at the edge of the grid. By using active var compensation to better control the aforementioned assets, we can strengthen the grid to benefit all users. Coordinated distributed energy storage paired with distributed generation can serve as a buffer and a balancing agent to limit significant voltage fluctuation on the grid. Speed of response and accuracy of response of these assets will be the differentiating factor between distributed generation that helps versus generation that hurts the grid.
We live in an electric power-hungry world with no tolerance for outages. To continue to improve grid resiliency and reliability, the industry must address the bi-directional power flow problem because the benefits of added distributed generation far outweigh the challenges they present to the grid. We have been talking about building the grid of the future and improving our power quality for some time now – let’s take significant steps toward getting there.
Troy Miller is Director of Grid Solutions at S&C Electric Company, where he has global responsibility for the Grid Solutions market segment that includes energy storage, var compensation, and microgrids. With more than 25 years in the Power Engineering industry, Troy has lengthy experience in the application and implementation of all aspects of power electronics and power quality. Troy is the Chairman of the Board of Directors at the Energy Storage Association and a member of the board at the National Alliance for Advanced Technology Batteries. He also is a regular speaker on market trends and economic benefit analysis at industry events around the world.
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