A shock absorber for the grid to enhance efficiency, reliability, and security
In their July 16th piece on solar energy technology in The New York Times, Andrew Revkin and Matthew Wald wrote that, “With more research, the solar thermal method might allow for storing energy. Currently, all solar power is hampered by a lack of storage capability.” They are certainly right. In fact, a lack of storage capacity hampers a lot of things.
While there’s been a lot of talk about coupling energy storage to solar (and wind) power, there are additional reasons for addressing our lack of storage capability. In fact, storage technologies can act as a “shock absorber” for the whole grid and can help address some of the key challenges facing the industry, including efficiency, reliability, and security. Simply put, energy storage is good for the grid.
The current electric power system is built around a central tenet: electricity must be produced when it is needed and used once it is produced. Bulk energy storage technologies break this antiquated linkage by allowing operators to produce and store electricity for later use — as one would in other commodity markets.
Bulk energy storage also benefits all of us by creating a reserve that could be tapped in case of national emergency, much like the petroleum reserve. After all, our entire economy — including our national defense capability — runs on electricity. If key parts of the grid are taken out, and there is no electricity reserve at the ready, what happens then?
Emergency back-up power more often than not means diesel generators, and as we saw during the blackout of 2003, many diesel generators either couldn’t get up and running or ran out of fuel before the lights came back on.
More specifically, however, storage benefits the energy consumer by providing a risk-management strategy, and it benefits the energy generator by making its assets more productive and efficient. As electricity demand continues to increase over time, existing generation assets must achieve greater efficiencies — for both market and environmental reasons.
The amount of electricity flowing through the grid at any one point is determined not only by consumer demand but by physics as well. The grid itself requires a certain level of electricity flow in order to maintain its integrity. Ramping power up or down without taking grid requirements into consideration risks destabilizing the grid and costs money. So, during off-peak hours, coal facilities ramp down their utilization rate while nuclear facilities provide the baseload power needed to stabilize the grid. As additional power is needed, coal facilities are instructed to increase generation to meet demand. (Whether you like coal or not, by capacity coal-fired plants represent the largest fleet of power facilities). This process is called load following.
Coal plants follow the load requirements of the grid by ramping up or down as needed. The problem with this is that it wreaks havoc on coal plant systems, lowers overall efficiency, increases O&M budgets with additional maintenance, and results in shorter life spans of critical equipment.
However, if coal plants were not required to ramp down during off-peak periods — nighttime — but could instead continue to generate power and store it for release during the day, these facilities would not be required to perform as much of the load-following role as they currently do. Instead, power generators can provide power in long-duration (and more efficient) discharges and then use stored energy to provide low-cost ancillary services such as load following and spinning reserves. This would increase a plant’s capacity factor, a measure of asset productivity, and reduce systemic stress and the costs required to address that stress. Utilized in this manner, large-scale storage helps offset the need for some additional peaking capacity, but is focused more as a system optimizer than generation replacement.
Coupled with storage, a generation facility can also gain much-needed flexibility during the critical scheduled “outage” seasons (when units are taken out of service for planned maintenance) of the spring and fall to avoid spot make-up purchases.
Other optimizing roles for storage include improving the economic and environmental profiles of fossil assets by reducing regular dispatch and cycling costs. Storage lowers the fixed-cost-per-unit output, improves the economics of these capital-intensive facilities, and helps them to run in a more efficient — both operationally and environmentally — manner that lowers overall per-unit production cost.
And, of course, coal facilities must also deal with their impact on the environment. Because emission limits (NOx restrictions, etc.) can constrain a power facility from operating maximally during peak times such as summer, they are often forced to operate at partial power. Unfortunately, when operating at partial power, plants are less efficient and have higher emissions per unit of heat input. Storage could help these facilities reduce their total emission per unit of output by shifting some production to the evening when the facility could run at its rated — instead of partial — generating capacity. And, by producing more power at night, air quality near the coal facility is improved since ozone-induced haze, a by-product of NOx, O2, and sunlight, is less likely to develop.