Battery Participation in PFC in Türkiye

Read Before You Start!

For a better understanding of what PFC (Primary Frequency Control) is and how the mechanism works, we recommend reading our article: “What Are Ancillary Services, Really? – Primary Frequency Control.”

Battery Participation in PFC in Türkiye

This article has been prepared by Ratio Energy experts to explain key concepts and technical requirements for organizations aiming to provide PFC services using battery energy storage systems (BESS) in Türkiye. The information here is for general understanding and should not be interpreted as legal or regulatory advice. Due to the evolving nature of the Turkish electricity market and frequent regulatory updates, we recommend seeking professional consultation before taking any action.

The example discussed here assumes a standalone battery energy storage system participating only in the PFC market within a given hour. In cases where the battery is integrated into a wind or solar power plant, or when it simultaneously participates in both Spot Markets and Ancillary Services, the situation becomes more complex. For more in-depth guidance, please visit ratiosim.com or reach out to our team at contact@ratioenergy.co.

Battery Participation in PFC in Türkiye

According to the “Procedures, Principles and Technical Criteria for Electrical Storage Facilities” published on 30 December 2024, battery energy storage systems (BESS) can provide Primary Frequency Control (PFC) services only if they meet the following conditions:

• Article 7 - (1)
  • g) The BESS must have available energy reserves that can meet the committed reserve capacity in both positive and negative directions throughout the supply period.
  • i) For each hour of PFC service, the energy capacity must be at least 1.25 times the committed power capacity.

Based on consultations with TEİAŞ and global ancillary services practices, an example scenario illustrating the required reserve capacity for PFC participation is outlined below.

Example Scenario

Let’s assume the offered PFC capacity = 30 MW.

(Note: In frequency markets, bids and settlements are based on power capacity (MW), not energy (MWh).)

1. Effect of Output Power on PFC Offer

A 30 MW PFC offer necessitates that the battery energy storage system must be capable of:

• Providing up to +30 MW in discharge (when frequency drops, acting to increase frequency — technically called Load Taking)
• Providing up to –30 MW in charge (when frequency rises, acting to decrease frequency — technically called Load Shedding)

Going into more detail: a 200 mHz frequency deviation requires a 30 MW response; a 100 mHz deviation requires a 15 MW response. The response ratio determined by frequency deviation is called the droop rate, which is explained in detail in our PFC article.

Therefore, for a 30 MW bid, the storage unit must support a minimum instantaneous output of +30 MW and –30 MW. In this case, for any storage system:

Max PFC Offer ≤ Facility Power Capacity (PCS Effective Output)

2. Effect of the 1.25 Multiplier in the Legislation on the PFC Bid

According to Article 7-(1)-i), the reserve energy must be 25% greater than the offered capacity. Based on discussions with TEİAŞ, this corresponds to:

Required Minimum Reserve Energy (MWh) = Offered Amount (MW) × 1.25
= 30 × 1.25 = 37.5 MWh

This 37.5 MWh must be available in both directions under Article 7-(1)-g). Thus, within the energy storage unit, both of the following must be available at the same time:

• Enough stored energy to discharge and provide the required reserve to the grid when frequency drops
• Enough free capacity to charge and absorb the reserve from the grid when frequency rises

A common point of confusion arises here: should 37.5 MWh be held in both directions or just 18.75 MWh in each direction?

Interpretation 1: A full 37.5 MWh is required in both directions — meaning the system must hold +37.5 MWh for discharge and –37.5 MWh for charging.

Interpretation 2: The 37.5 MWh represents the total reserve band. Therefore, it is sufficient to have 18.75 MWh stored energy and 18.75 MWh of charging capacity.

Following discussions with the Dispatch Center, Interpretation 2 was confirmed as correct. We proceed with our calculations based on this.

Thus, on paper, providing 18.75 MWh charge level and 18.75 MWh free capacity is enough to submit a 30 MW PFC bid. However, in practice, battery efficiency and DoD constraints may slightly change this 18.75 MWh requirement.

3. Effect of Charging and Discharging Efficiency on the PFC Bid

Her elektriksel sistemde olduğu gibi batarya enerji depolama sistemlerinde de bir miktar enerji verimsizlikler nedeni ile teknik kayba dönüşmektedir.

Bataryalar ile spot piyasada yapılan işlemlerde ve basit fizibilite analizlerinde bu kayıp genel olarak ‘Round-Trip Efficiency’ yani döngüsel enerji kaybı olarak ele alınmaktadır. Örnek olarak şebekeden 10MWh enerji çeken bir batarya, şebekeye 9MWh’lik bir enerji verebiliyorsa round-trip efficiency değeri %90 demektir.

Ancak konu frekans tepkisi nedenli çıkış gücü değişimleri ve reserv kapasitesi olduğunda döngüsel enerji yerine, şarj yönündeki verimlilik ve deşarj yönündeki verimliliğin ayrı ayrı ele alınması daha doğrudur. %90 round-trip efficiency’e sahip bir bataryanın şebekeden çektiği 10MWh’lik enerji sonrasında state-of-charge değerinin ne kadar yükseldiğini bilmek için şarj yönündeki verimliliğe ihtiyacımız vardır.

Like all electrical systems, battery energy storage systems experience technical energy losses.

In spot market operations and simple feasibility analyses, this loss is expressed as Round‑Trip Efficiency — e.g., if a BESS draws 10 MWh from the grid and returns 9 MWh, the round-trip efficiency is 90%.

However, for frequency response and reserve capacity, it is more accurate to consider charging efficiency and discharging efficiency separately. For a battery with 90% round-trip efficiency, we must know how much the state of charge increases from an initial 10 MWh draw — therefore, charging efficiency matters.

Returning to our example:

• 30 MW PFC bid allocates 18.75 MWh for charging and 18.75 MWh for discharging reserves.
• Assume round-trip efficiency of 90%, broken down into:
  • Charge efficiency = 96%
  • Discharge efficiency = 93.75%

An important point: TEİAŞ measures at the connection point. This means the 18.75 MWh refers to actual energy drawn from or provided to the grid.

• When the battery draws 18.75 MWh from the grid:

Energy stored = 18.75 × 0.96(charging efficiency) = 18 MWh

• To discharge 18.75 MWh to the grid:

Stored energy required = 18.75 ÷ 0.9375(discharging efficiency) = 20 MWh

4. Effect of Depth of Discharge (DoD) on the PFC Bid

In lithium-ion (Li-Ion) based battery systems, minimum and maximum State of Charge (SoC) limits are generally set to protect the battery cells’ lifespan and ensure safe operation. For example, if a battery’s datasheet specifies operation within a 5% to 95% SoC range, only 90% of the battery’s total nominal capacity can be effectively utilized. This difference causes the usable energy capacity to be lower than the factory-rated total capacity.

When considered together with efficiency calculations, this creates a critical situation for determining the minimum and maximum SoC levels to be used when submitting a PFC offer.

Returning to our example:

• PFK teklif miktarı = 30MW
• On paper, the required reserve amounts are 18.75 MWh for charging and 18.75 MWh for discharging.
• However, in practice, the maximum reserve and free capacity needed in our energy storage system are:
• Maximum required stored energy = 20 MWh
• Maximum required available empty capacity = 18 MWh
• The minimum SoC level the battery capacity can drop to at factory settings is 5%.
• The maximum SoC level the battery capacity can reach at factory settings is 95%.
• Above the 5% SoC minimum, we need at least 20 MWh of additional energy.
• From the battery’s allowed maximum fullness limit of 95% SoC, we need to be at a point at least 18 MWh lower.

Therefore, we can calculate the minimum required installed battery capacity as follows:

%5 SoC + 20MWh + 18MWh = %95 SoC

38MWh = %90 SoC

%100 SoC = 42.2MWh

5. Alternative Examples

In the previous example, we considered a battery wanting to offer 30 MW — we calculated the minimum battery capacity and reserve. However, you might want to offer part of your battery’s capacity instead of the full 100 MWh for PFC. Consider a 100 MWh battery offering 30 MW:

Example Scenario 2:

• PFC bid = 30 MW
• Battery capacity = 100 MWh
• SoC limits = 5% min, 95% max
• Charge efficiency = 96%, discharge efficiency = 93.75%

Since bid amount, efficiency, and DoD same as Example 1, the required charge capacity of 18 MWh and discharge energy of 20 MWh remains. Now:

• Min SoC (5%) = 5 MWh
• Max SoC (95%) = 95 MWh

25MWh ≤ e ≤ 77MWh
Within this SoC band, you can offer a 30 MW PFC bid.