By Michelle Meyer, ABB Inc.
With more renewable energy coming online, and fossil fuel plants facing increasingly stringent regulations, utilities and systems operators are being challenged in ways never before seen. Not only do utilities need to integrate renewables without compromising system reliability, but as more traditional sources of generation are taken offline, utilities have fewer resources in their tool kit to help them provide basic grid services.
Although turning on the lights appears as easy as the flip of a switch, ensuring that power is readily available for consumers is no easy task. Grid operators are required to do much more than just provide power supply; the delicate art of sufficiently transmitting the electricity through the utility lines requires a variety of other services such as frequency regulation to maintain frequency levels of 60 Hz in North America, reactive power control to support voltage levels that transport electricity, and back up spinning reserves to supply power during an unplanned disruption in power. Traditionally, utilities have been able to rely upon fossil fuel-based synchronous generators to provide controllable and readily dispatchable power. However, renewables are anything but predictable or readily dispatchable. One of the major challenges of integrating renewables is the rapid fluctuations in power output caused by the variations in wind or solar irradiance, making it difficult for utilities to steadily rely on renewables to contribute to these ancillary services.
Yet there is a light at the end of the tunnel. Solutions available today can help alleviate these impacts of variable generation and give back utilities the power to control energy.
In AC electrical grids, there are two kinds of power; real and reactive power. Real power is what actually does the useful work whereas reactive power is what’s needed to maintain sufficient levels of voltage that help transport the power. As wind and solar become more of a significant portion of our generation portfolio, enabling these facilities to be a reliable and useful contributor to the systems’ reactive power supply is the first step to integrating renewables. By adding reactive power compensation devices such as Static Synchronous Compensators (STATCOMs), which are voltage source converters (VSC), can help regulate the voltage at the point of common coupling by instantly injecting or absorbing reactive power. With instant and continuous voltage regulation and power factor control, renewable generation facilities can support the grid and be a source for ancillary services such as voltage supply. Reactive power compensation provided by statcoms can also mitigate power quality issues caused by rapid fluctuations in voltage levels, preventing the wind or solar plant from tripping offline or disrupting the surrounding network.
Not only do we have the technologies to control the reactive power, but we can also control real power through energy storage technologies. Electricity is a unique commodity in that once it is produced it must be instantly consumed. Renewables can be a cheap, domestic, and a clean source of power, however dictating when these facilities produce power is not feasible. Controlling the power output with energy storage will facilitate better alignment of supply and demand by having the storage device absorb real power when demand is low, store it for later use and instantly dispatch power when demand increases. This energy time-shift approach can increase the profitability of the wind or solar plant and help lower costs of the electricity, making the adoption of renewables technically possible and commercially viable.
Through capacity firming, energy storage can smooth the power output, allowing for a constant and stable supply of energy, significantly minimizing the rapid fluctuation in power output. Storage can also provide several of the ancillary services such as voltage and frequency control. When appropriately sized, the energy storage device with an advanced power conversion system can also provide reactive power support locally, regulating the voltage and power factor. In addition to voltage regulation, storage can maintain frequency levels which deviates at times when there is a misalignment of power supply and demand. By instantly injecting or absorbing real power in milliseconds, the energy storage device can quickly realign frequency levels to meet the operational requirements to maintain stability.
With states expanding their renewables targets, the proliferationof variable generation will continue to pose challenges for the way we operate and maintain the grid. Giving system operators the ability to control real and reactive power through advanced grid technology solutions will not only remove significant barriers to further adoption of renewable energy, but will give grid operators the ability to better control their networks so we can have the benefit of more sustainable energy without compromising the integrity of the grid.