The wind doesn’t always blow, and the sun doesn’t always shine—and not always equally or consistently. Even in the sunniest of places, like deserts, “the amount of sunlight can vary from minute to minute.” (The Economist, 2014) On the flipside, demand itself is also irregular, and times of highest demand won’t always match with highest production. This has long been the ultimate downside of renewable energies like wind and solar. Several contingencies have been suggested, or even implemented, to overcome these discrepancies. One such is the use of so-called “peaker stations which fire up quickly when needed, but are expensive to run.” (The Economist, 2014)
Contingencies aside, there is one solution which would solve these problems outright: better battery storage. The ability to store vast amounts of energy eliminates the need for “peaker” station and solves issues of demand and inconsistency. Companies like Alevo reckon “that if a grid as big as America’s Western interconnection (which supplies the west of the United States and Canada) were to use 18GW-worth of its batteries the grid could save $12 billion a year.” (The Economist, 2014)
And as these technologies advance, they become cheaper. An increase in scale to support a grid will revolutionize the industry. Renewables are already approaching cost-competitiveness with nonrenewables. Further advancement in energy storage technologies will close that gap even further.
Currently, pumped hydro dominates available grid-scale storage at a global capacity of 1.4TWhr. It first came onto the scene in “the 1930s and remains the most economical and practical method for large-scale energy storage.” (Dunlap, 2019, 571) The trick is, for this to work, you need geography on your side. Pumped hydro requires “two reservoirs separated by a good gap of altitude.” (The Economist, 2014) Once linked with pipes and using turbines, falling water will generate electricity that, and if fed electricity, they will “turn the other way to pump that water whence it came.” (The Economist, 2014) That cycle can be timed with demand and costs to keep things efficient. Problem is, “pumped storage takes a long time, and a lot of money, to build.” (The Economist, 2014)
The trick is, whatever technology you use, start small and scale up as needed. Batteries can answer that call. Alevo is one company on the cutting edge, but so is Toshiba, and Tesla who has built factories in places like Reno, Nevada to produce batteries designed to be paired with their vehicles, as well as supporting local and grid storage.
The list, and capacities, goes on. In fact, there are a number of grid-scale battery technologies available—some better or with more benefits than others. In those based on the use of solid electrodes, the downside is that they’ll eventually succumb to the wear and tear of constant charging and discharging. Even still, companies like Alevo “claim that its batteries can undergo more than 40,000 cycles of charging and discharging without noticeable loss of function”. (The Economist, 2014)
Another approach is to use electrolytes in what is known as a flow battery to store energy, and their capacity is only limited by the size of the tank used. Granted, these are much less developed than electrode based batteries, but developments have been promising.
Even pumped storage is undergoing a makeover of sorts, thanks to Gravity Power. Their method doesn’t rely on two reservoirs at different altitudes. Instead, Gravity Power proposes using “two water-filled cylindrical shafts—one wider than the other—dug into the ground.” (The Economist, 2014) The two are then linked together to form a circuit while still employing a pump-turbine. The bigger shaft contains a rock or concrete cylinder which serves as a piston.
When the piston sinks, it displaces the water, forcing it up around the circuit and through the turbine, causing it to spin, and in turn generates power. As with any energy endeavour there are some risks, dowsnides, and associated costs. The necessary depth alone generates a hefty pricetag. “A unit 700 metres deep, with a main shaft 26 metres across and a return shaft (or penstock) of about a tenth of that, would cost $170m.” (The Economist, 2014) However, such a shaft could also store 200MWhr’s of energy, and put out 50MW. Even still, this approach would be existentially reliant on friendly geology.
Within a similar, subterranean, realm, another methodology is to fill a hermetically sealed underground salt dome cavern with compressed air. It operates similarly to classical pumped storage, but this uses a gas instead. Problem is, for it to work effectively, natural gas must be used as a part of the process to heat released air which makes the whole process inherently efficient—”one reason there are only two grid-scale examples of it in the world (one in Germany, the other in Alabama).” (The Economist, 2014) A California based firm, LightSail Energy, has high hopes of fixing that inefficiency. They have “developed a small, but still grid-scale, compressed-air system that sprays water into the compression chamber, to cool the air as its volume shrinks.” (The Economist, 2014) Ultimately, their setup can store 700kWhr of energy. Currently, there are “two commercial facilities of this type in operation: one in Huntorf, Germany, and one in Alabama.” (Dunlap, 2019, 576)
All of this, of course, is in an effort to eliminate reliance on nonrenewable energy and to close the gap between night, day, fluctuating rays, cloudy days, and demand, especially in a way that can be scaled up to the grid-level. Solar Ponds have provided one possible solution by relying on artificially constructed ponds with a “large thermal mass” (Dunlap, 2019, 302), a methodology which has been an attractive solution in developing countries due to their low operating costs. Wind, while an attractive solution, comes with its own share of disadvantages. Their efficiency is strongly correlated to relative air velocity as well as tip speed ratio. The “maximum theoretical efficiency that can ever be achieved by a wind turbine, referred to as the Betz limit, is 59%.” (Dunlap, 2019, 338)
Of course, solar is the only “single-energy resource that has the capability to provide enough energy to fulfill all of our needs and that is indefinitely renewable (Dunlap, 2019, 326), but indefinite renewability doesn’t guarantee constant availability. Increasing grid-scale storage capacity and enhancing their design is the next, crucial, step. The good news is that increase in capacity is happening. The NREL is reporting that grid-scale storage capacity in the US is on-trend to increase five-fold by 2050. “Across all scenarios in the study, utility-scale diurnal energy storage deployment grows significantly through 2050, totaling over 125 gigawatts of installed capacity in the modest cost and performance assumptions—a more than five-fold increase from today’s total.” (NREL, 2021) If costs, among other variables, continue to decrease, its estimated capacity could reach 680 gigawatts over the next 25 years.
References
The Economist. (2014, December 6). Smooth Operators. The Economist.
Dunlap, R. A. (2019). Sustainable Energy, SI Edition (Second ed.). Cengage Learning.
NREL. (2021, June 1). Grid-Scale U.S. Storage Capacity Could Grow Five-Fold by 2050. nrel.gov. https://www.nrel.gov/news/program/2021/grid-scale-storage-us-storage-capacity-could-grow-five-fold-by-2050.html
