Battery Storage and Ancillary Services

Ancillary services by definition are services that support the transmission of electricity from its generation site to the customer or helps maintain its usability throughout the system. Many people may not know that the standard 120 volts we are used to receiving from the wall actually varies a tiny amount from second to second. If you were to monitor the power from the wall, the voltage may swing from 118-122 volts. We do not typically think about the mechanisms that take place to keep our power useful and ready for when we flip the switch.

On a larger scale, ancillary services are generators or other service providers that are synchronized to the grid and are able to rapidly increase output in three major categories: contingency, regulation, and flexibility reserves. The contingency reserve requirement is assumed to be constant for all hours of the year and corresponds to a spinning reserve equal to about 3% of peak load and about 4.5% of the average load. Another way to think of “spinning reserves” are the backup or redundancy built into the grid. Basically, we slightly overbuild the total generation needed so the grid can be provided with ancillary services making good quality power possible.

Additionally, regulation and flexibility reserve requirements vary by hour based on the net load and impact of variability and uncertainty of wind and solar. The availability and constraints of individual generators to provide reserves are a major source of the cost of providing reserves. Not all generators are capable of providing certain regulation reserves based on operational practice or lack of necessary equipment to follow a regulation signal.

So, what does the future of ancillary services hold and how can they be more beneficial?

At a residential level, a combination of solar and storage is only worthwhile when specific conditions are met that make the value of storage greater than the cost of installing It. For example, when the renewable energy creates an excess, the extra energy can be stored for later consumption. This would allow the customer to buy less power from the grid and enable them to cut their costs.

However, some customers are now being charged for using power during peak times, which is known as a demand charge. Energy storage can be used to lower peak time energy consumption, or the highest amount of power a customer draws from the grid; therefore, reducing the amount customers spend on demand charges. In North America, the break-even point for most demand charges is $9 per kilowatt. Energy storage can lower that cost to $4 or $5 per kilowatt by as early as 2020. As storage costs decrease, more customers will begin to see economic benefits and existing storage users will see the optimum size of energy storage increase.

Lastly, energy storage will impact electricity grids as a whole because it provides more function than just power on demand. Batteries can provide the grid with ancillary services like frequency regulation and should be compensated to do so. All this is to say, if utilities provide appropriate price signals to the market, customers will respond by installing battery storage where and how they can be compensated.

Currently, grids experience a continuous imbalance between the power they produce and its consumption because of the millions of devices that are turned on and off in an unrelated way. The imbalance can cause frequencies to deviate, which can affect equipment and potentially hurt the stability of the grid. Energy storage is well suited for frequency regulation because of its rapid response time and its ability to charge and discharge efficiently. This storage could significantly reduce the amount and cost of the reserves currently needed to provide such services to the grid.

One reason for the optimistic outlook on battery storage’s role with providing ancillary services is the progress lithium ion batteries have made in recent years. In 2015, lithium-ion batteries were responsible for 95 percent of energy storage at both the residential and grid levels. The reason for the increase in popularity is due to the price dropping, safety improving, and better performance characteristics. All of these qualities are leading to lithium-ion batteries being suitable for stationary energy storage across the grid; ranging from large-scale installations and transmission infrastructure to individual and residential use, even without being appropriately compensated for ancillary services.

The most important aspect is the large-scale deployment of energy storage that could overturn the status quo for many electricity markets. In developed countries, central or bulk generation traditionally has been used to satisfy instantaneous demand, with ancillary services helping to smooth out discrepancies between generation and load; and energy storage is well suited to provide such ancillary services. Eventually, as costs fall, it could move beyond that role, providing more and more power to the grid, displacing plants; however, that time has not yet come although approaching quickly. It is important to recognize that energy storage has the potential to upend the industry structures, both physical and economic, that have defined power markets for the last century or more.

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