California’s zero-carbon future leads the charge for energy storage!
On August 28, 2018, California’s State Assembly passed Senate Bill 100 that establishes a statewide planning goal of 100% fossil fuel free electricity by the year 2045. Such zero-emissions power can be sourced from the state’s Renewable Portfolio Standard (RPS) eligible renewables resources such as wind, solar, geothermal, etc. as well as hydro-power and other carbon-free resources that do not count towards the RPS mandate. It is important to note that the 100% zero emission goal is a planning target and not a strict mandate.
Researchers at NREL had predicted more than a decade ago, what California Independent System Operator (CA ISO) confirmed in 2013 by publishing its now infamous duck-curve. While the duck curve demonstrates the ill-effects of increased solar generation on the grid, high penetration of wind resources has caused extremely low, sometimes even negative locational marginal prices during off-peak load periods when wind is the strongest. Grid operators throughout the world are grappling with such issues caused by renewable penetration of only 20 – 30%. In the face of such challenges, is a 100% renewable energy system even feasible? How is CA going to accomplish its SB 100 goal?
The answer lies, to a large extent, in energy storage and possibly also in demand response. Energy storage has the ability to firm up the inherently variable renewable generation supply and can also time-shift the renewable output availability from off-peak periods (when it is produced but not needed) to peak periods (when it is needed but not often produced). Energy storage technologies, including pumped hydro, battery, thermal, and electro-mechanical to name a few, hold the key to mitigating this supply-demand mismatch. These technologies are already operating in the US today with a total cumulative installed capacity exceeding 24,000 MW.
Source: US Department of Energy (DoE) Global Energy Storage Database as of September 2018
It should be noted that the x-axis of the cumulative installed capacity chart is on a logarithmic scale so it may not be readily evident that the pumped hydro installed capacity outstrips the capacity of other storage technologies by several orders of magnitude. According to the National Hydropower Association (NHA), pumped hydro storage has all the attributes needed to support larger integration of wind and solar. It can do so by soaking up excess renewable generation during periods of low off-peak demand, and being ready to produce power during low wind and solar generation periods. It also has the ability to quickly ramp up the electricity generation in response to periods of peak demand. The $3 billion proposal by Los Angeles Department of Water and Power (LADWP) to add pumped storage to one of America’s most iconic power plants, the Hoover Dam, if implemented, will definitely prove to be a shot in the arm for California’s zero carbon future!
Having said that, it is the battery storage, especially Lithium-ion (Li-ion), which has experienced the highest growth among all the energy storage technologies out there. Li-ion technology has enjoyed a lot of attention, and will continue to do so in the foreseeable future, primarily because of its high energy density that makes it the technology of choice for Electric Vehicles (EVs). Consequently in recent years, Li-ion technology has experienced tremendous growth and rapid cost declines as the battery vendors like Panasonic, Samsung, LG Chem, and Tesla invest heavily to advance research, development, and manufacturing capacity. The attention garnered by the transportation use case for Li-ion has significantly benefited the stationary applications of the battery as well, including integrating large amounts of variable and non-controllable renewable resources into the power grid.
Li-ion technology does have limitations when it comes to stationary storage applications including the issue of limited cycling ability, cell degradation reducing the useful life of the battery, and its unsuitability for longer duration applications (> 4 hours). There is an often-overlooked and relatively lesser known battery technology, the flow battery, that can overcome Li-ion’s limitations and is very well suited for stationary storage applications, where high energy density is not as critical as in EV applications. Currently, the widespread adoption of flow batteries is being hampered by its higher installed system costs relative to Li-ion, but this may rapidly change if the markets start demanding longer duration battery technologies with long useful lives without any noticeable degradation. This will certainly be the case as and when places like California move to a 100% fossil-fuel free grid.
While battery storage can solve the operational challenges of integrating 100% fossil-fuel free resources, some policy changes needed to tackle issues such as the Zero Price Paradox remain to be addressed.