sReg, dReg, E-dReg: What are the differences?

On December 22, 2021, Taipower held the fifth orientation for its electricity trading platform, further illustrating the purpose, procedures, and qualification of the E-dReg. But what exactly are the sReg, dReg, and E-dReg?
 

Electricity ancillary service

In addition to raising self-consumption of renewables, reducing wind, solar curtailment, and energy arbitrage, electricity ancillary service is one of the most discussed benefits of installing ESS. Electricity ancillary service includes Fast Response Reserve Service, Regulation Reserve, Spinning Reserve Service, and Supplement Reserve Service, which all play unique roles in the entire process of power distribution.

Fast Response Reserve Service and Regulation Reserve Service function to cope with the high volatility of renewable energy and to respond within seconds and operates for more than 15 minutes upon the occurrence of accidents. Spinning Reserve Service and Supplement Reserve Service tackle circuit trips on power supply units that result from discordant power supply and demand. Units with these services have lower ramp rates but are capable of longer terms of power supply, and which of Supplement Reserve Service lasts longer than that of Spinning Reserve Service.  

Regulation Reserve

During the process of charging and discharging, high volatility of the grid results in unstable frequency. This is where regulation reserve comes in, producing power to stabilize the grid. There are two types of Regulation Reserve, namely Static Regulation Reserve (sReg) and Dynamic Regulation Reserve (dReg).

The sReg is a one-way, upward regulation reserve service. When frequency of the grid drops too low, the sReg system should detect this change within a second and boost to reach 100% of power output in ten seconds, preventing the frequency from declining further. 

The dReg is a two-way regulation reserve service, which, in accordance with the situation the grid is in, completes charging and discharging within a second. There are two modes of dReg, dReg 0.25 and dReg 0.5, with the suffixing numbers indicating the range during which the frequency will be maintained (±0.25, ±0.5). For instance, power systems in Taiwan have 60Hz of frequency; therefore, the dReg 0.5 system will keep the frequency between 60Hz±5Hz. This means when the frequency is lower than 59.5 Hz, the system will feed 100% of charted capacity to the grid, until the frequency returns to 60 Hz for grid stability.

Generally, dReg does not operate at full capacity, with deReg 0.5 runs at less than 50%, and dReg 0.25 at 75%. In most cases, the dReg 0.25 already satisfies Taipower’s need for regulation. Therefore, Taipower launched the E-dReg in the hope to make the best use of ancillary services and optimize the usage effectiveness of dReg 0.5.  

Enhancement dynamic Regulation, E-dReg

As aforementioned, dReg 0.5 usually runs at less than 50% of capacity. Therefore, the E-dReg primarily combines high power and higher energy batteries to form a composite-battery ESS. This way, the ESS can provide dReg 0.5 regulation reserve service and peak shaving service, simultaneously, making the most out of the dReg 0.5 service.

As one of the ancillary services on the Taiwanese market, the E-dReg competes with all other regulation reserve services in auctions, which only grid-connected ESS with a capacity larger than 5 MW/12.5 MWh is eligible to participate. In 2022, the E-dReg is officially launched in Taiwan, with a P/E ratio 50% higher than that of dReg and sReg. However, as grid-connected battery storage systems have not participated in any electricity trading, but only paid by Taipower for service fees, specific management mechanism is still on the drawing board. A comprehensive policy framework and regulations are expected in the future to improve efficiency and safety of power supply and provide guarantees for investors.

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