Storage Wars: Can Wind and Solar Afford Grid Energy Storage?

US wind and solar electricity generation has grown substantially over the past decade. This trend is expected to continue, with the US Energy Information Administration projecting a nearly 200 percent increase in wind and a 1000 percent increase in solar generating capacity between 2011 and 2040. The trajectory of these renewable industries is promising given their low carbon footprint, but they both face a major hurdle to widespread adoption – grid energy storage. Solar and wind are weather-dependent, so they can only generate when the sun is shining or the wind is blowing. Without energy storage technologies, higher demand will not be met during lulls in generation. Conversely, if demand is low during periods of high production, grid energy storage technologies could be used to store that excess production for future use.

Currently the wind and solar industries produce a net energy surplus, in that they produce more energy than is used in their manufacturing and production process, but the development of grid-scale storage technologies requires a large upfront energy cost in order to manufacture, build, and operate the systems. A 2014 Energy and Environmental Science article by Stanford researchers Michael Carbajales-Dale, Charles J. Barnhart, and Sally M. Benson investigates whether wind and solar generation can take on the energy costs associated with developing storage technologies and still remain net energy producers. They find that wind generation can easily support up to three days of uninterrupted storage before operating at an energy deficit, while the more energy intensive solar generation can support about 24 hours of storage. These findings illustrate the importance of continuing to lower energy costs for both generation and storage, which could be further incentivized by policymakers.

Battery and geologic storage are the two general categories for large-scale storage technologies. Many grid battery technologies exist, but they are conceptually similar, allowing a battery system to store excess energy until needed. The most common type of geologic storage is pumped-hydroelectric storage, which pumps water uphill during periods of excess generation. When energy is needed, the water is then released downhill through a generator. Citing research from previous studies, the authors looked at the net energy costs of on-shore and off-shore wind generators, as well as several different solar technologies and compared them to the net energy costs of different combinations of battery and geologic storage technologies.

When compared to wind turbines, all of the solar technologies have a much higher energetic cost given their more involved manufacturing process. Similarly, battery storage technologies are over ten times more energy intensive than geologic storage, for the same reasons. Given these differences in energetic costs, it is not surprising that wind technologies were found to afford more storage than solar, and geologic storage was found to be energetically ‘cheaper’ than battery storage.

The study found that wind technologies could easily support 72 hours of storage from either battery or geologic storage. Affording that 72-hour window is crucial, since it is common for many weather patterns to have lulls of that magnitude. On-shore wind utilizing only geologic storage is the energetically cheapest combination, and the study found it could support the same 72 hours of storage but also maintain a 100 percent annual growth rate. The results for solar were less striking. Certain solar technologies such as single crystal silicon cells are growing too rapidly and currently produce at an energy deficit, so they cannot support any form of storage. Most solar technologies could afford 24 hours of an equal mix of geologic and battery storage, which would still allow for the overnight storage that solar requires.

Despite their appealing low carbon footprint, the variability of wind and solar generation will eventually limit their penetration into the electricity grid. Policy measures such as curtailment and demand-side management offer some solutions to grid flexibility, but the long-term solution will inevitably come down to grid energy storage. Realizing this, the Department of Energy has published a long-term strategic plan for energy storage deployment over the next decade, and California was the first state to impose a mandate requiring that the three major utility companies procure 1,325 megawatts of energy storage by 2020. The results of this study highlight the benefits from storage and generation technologies with low energetic costs, which should be considered as energy storage advancements are made. Policymakers could accelerate the reaping of these benefits by incentivizing manufacturers, especially from the solar and battery industries, to reduce these costs.

Article Source: Michael Carbajales-Dale, Charles J. Barnhart, and Sally M. Benson, “Can we afford storage? A dynamic net energy analysis of renewable electricity generation supported by energy storage,” Energy and Environmental Science 7 (2014): 1538-44.

Feature photo: cc/(renew my energy)