With currently about 65 gigawatts of wind and 3 gigawatts of photovoltaics installed capacity in the United States and continuing if not accelerated growth in renewable energy technologies, grid operators are increasingly challenged to accommodate the growing volatility of generation supply and the growing uncertainties of having sufficient capacity when the customers demand it.
Not only are the uncertainties challenging for grid operators of how much capacity of wind and solar will be available in the next hours, but also how fast the wind will die down or clouds will reduced the output of the PV capacity.
Sharp ramping events have been observed in the Pacific Northwest and are projected in California with the growth of rooftop PV installation. The California ramping problem is usually referred to as the “duck curve” with sharp ramps in the evening when customers come home, turn up their AC, and start preparing for a meal, right at the time when the PV output is sharply decreasing.
What grid operators are increasingly looking for is flexibility in the grid operation to turn up or down the supply in accordance to the new system needs.
There are traditional supply-side solutions that provide the desirable flexibility. Conventional hydropower has been the number one player in the grid operator’s toolbox for accommodating large dispatch swings.
However, with increasing constraints on the hydro-system its flexibility has almost been exhausted. New technologies are being tested to provide the next generation of grid flexibility. Energy storage of all sizes and kinds are being developed at a rapid pace.
While still expensive and not fully proven, large-scale and small scale storage technologies have attracted significant interest in the industry. Chemical energy storage systems – batteries - have many advantages over conventional generation technologies. One is that they can be dispatch almost instantly to go from zero charging to full rate charging almost instantaneously. This new almost instantaneous behavior provides unprecedented agility in the transmission and distribution system that has significant value in grid operations.
California is again on the cusp of driving new storage technologies into the market place with its storage procurement mandate. We will see how California will take advantage of this new technology as Governor Brown requests the Californians to get ready for a 50 percent renewable portfolio standard by 2030.
Michael Kintner-Meyer is staff scientist at the Pacific Northwest National Laboratory.