Meg Cichon, Associate Editor, Renewable Energy World
As increasing amounts of variable renewable energy penetrate the grid, utility operators are scrambling to figure out how to balance power loads. Sources like wind and solar cannot be controlled, so when the sun is out or the wind is blowing, power ramps up and has the potential to overload the grid — when it is cloudy or still, there is a potential lack of power as grid operators struggle to engage other sources.
Wind alone has rapidly grown in the past 10 years, and now represents 62.3 gigawatts (GW) of capacity in the U.S. alone, with another 13 GW under construction. Though this only represents about 5 percent of total U.S. capacity, “it is still causing significant impact on the grid,” said Aaron Anderson and panelist on the Fossil and Renewable Energy Partnerships session at the Renewable Energy World, North America Conference and Expo. This impact is especially relevant in the central U.S., which is home to a significant amount of the nation’s wind capacity.
“This causes several issues,” said Anderson. “For one, if most wind resources are in middle of the U.S., and heavy load demands are more towards the coasts, how do we move energy towards the demand? Also, what about really windy or still days where we see rapid increases and decreases in production?”
In order to find ways to solve these intermittency issues, Anderson conducted a study on the possibility of co-locating wind with natural gas. Since many natural gas resources are located in the same high-wind regions, it would be a logical fit, said Anderson.
The study looked at a 200-MW wind farm that runs at an average 42.8 percent net capacity factor (NCF). It was co-located with 105-MW natural gas plant with Wartsilla engines that are able to quickly ramp up and down while also maintaining efficiency. The study prioritized the wind turbines as the main energy source, and intermittent gaps were filled using either the natural gas plant or conventional grid power — whichever was cheaper.
Even though gas prices were very low at the time of the study, Anderson found that energy was purchased from the grid three times as often as the natural gas plant. Therefore, large-scale co-located plants are typically not an economically viable option. “We have some cases where it makes sense, but more often than not it doesn't make a ton of economic sense.”
Anderson said that it would make more sense to address wind variability via the total market area — utilities should look at all viable power sources in the region instead one a single resource. It also may be more economical on a smaller scale — distributed resources could be a perfect fit for this type of hybrid solution.
Storage could also provide an economical solution for some projects, but it is still not financially feasible for larger projects, explained Anderson.
“We have done wind projects with battery backup. It has bother very good and very bad aspects,” said Anderson. “The very bad is that it is expensive. The very good is that batteries offer a lot of flexibility, such as frequency voltage and reactive power. But there are still a lot of parts of the country where it is not crucial to meet renewable energy and carbon requirements, so the cost benefit it not there yet.”