APPEAL NO. 197 of 2019 & IA NO. 1706 of 2019 dated 2 August 2021

National Solar Energy Federation of India

1. Tamil Nadu Electricity Regulatory Commission
2. Tamil Nadu Generation and Distribution Corpn. Ltd. (TANGEDCO)
3. Tamil Nadu State Load Despatch Centre (TNSLDC)
4. Tamil Nadu Transmission Corpn. Ltd (TANTRANSCO)
5. Ministry of New and Renewable Energy (MNRE)

Appellant filed an appeal before Hon'ble APTEL on behalf of its member solar power generators in Tamil Nadu who faced curtailment for their plants many times. The reason for backing down instructions given by TNSLDC to these solar power generators was for grid security purposes.
However, Backingdown instructions were issued by TNSLDC through telephone and no specific reason or data regarding the backing down instructions were communicated in writing.

Based on the appeal, Hon'ble APTEL passed the Judgement dated 26 August 2020 wherein Hon'ble APTEL directed POSOCO to conduct a third-party assessment on the issue raised by the appellant. Accordingly, POSOCO carried out a detailed assessment for the period of 1 March 2017 to 30 June 2017.
POSOCO assessed the following aspects to comply with the directions of Hon'ble APTEL:
a) Detailed verification of the data after considering the contentions raised by the parties
b) Analysis of whether there was intentional curtailment by the Respondents/SLDC or whether these actions were on account of grid safety measures taken by SLDC as contended by the Respondents.
c) Was there any fair and justifiable curtailment of power from all generators, both renewable and non-renewable, the actual generation and injection of energy?

a) Detailed verification of the data after considering the contentions raised by the parties:
- Out of the 56 generators, 16 generators with a total installed capacity of 1052 MW submitted data. Data of 10 generators were complete and data of 6 generators was partial.
- Period and percentage of curtailment actually implemented by the developer and instruction given by TNSLDC was found to be different with varying times of delay in implementation. This could not be verified since all the instructions were oral.
- Curtailment quantum in Energy (MU) terms over a day were found to be in order however there were inconsistencies found in block-wise MW data.
b) Indicate whether there was intentional curtailment by the Respondents/SLDC or whether these actions were on account of grid safety measures taken by SLDC as contended by the Respondents:

-From the detailed analysis of the data it can be concluded that 5.26% (60 out of 1140 blocks where solar was curtailed) of the cases appears to be justified from a grid security perspective.
c) Was there any fair and justifiable curtailment of power from all generators, both Renewable and Non-Renewable, the actual generation and injection of energy?
1. Fairness among Solar Developers
It appears that most of the solar generators with a per unit cost of Rs 7.01 is curtailed more both in terms of percentage generation as compared to other solar generators.
2. Fairness among Solar & Wind Developers
- In terms of Generation (MW): Based on the analysis, it can be concluded that Wind and Solar were curtailed equitably.
- In terms of Energy (MU): Based on the analysis it can be concluded that curtailment among wind and solar is carried out in an equitable manner to a large extent.
3. Among renewable and non-renewable
It was felt that it would not be appropriate to compare curtailment/ backing down of non-renewable plants with renewable energy due to reasons cited in section 4.3.3. (refer Judgement of Aptel) Accordingly, the analysis was not carried out and no attempt is made for arriving at the inference.

(i) For the period 01.03.2017 to 30.06.2017, the Respondents shall pay compensation for 1080 blocks considered by POSOCO, during which curtailment instructions were issued for reasons other than grid security, at the rate of 75% of PPA tariff per unit within 60 days from the date of this order. The computation shall be made separately for individual members of the Appellant Association based on the curtailment period/blocks falling in 1080 blocks.
(ii) POSOCO shall carry out a similar exercise for the period up to 31.10.2020 on the same lines and submit the report to Respondent Commission within 3 months. Tamil Nadu SLDC and Appellant are directed to submit details to POSOCO. Based on the POSOCO report, State Commission shall allow compensation for the backed down energy at the rate of 75% of the PPA tariff per unit.
(iii) Curtailment quantum shall be considered as per the POSOCO report.
(iv) The Respondents shall pay compensation along with interest at 9% for the entire period.

Way forward for curtailment of RE power by State Load Dispatch Centre

(i) For the Future, any curtailment of Renewable Energy shall not be considered as meant for grid security if the backing down instruction were given under the following conditions:
a) System Frequency is in the band of 49.90Hz-50.05Hz
b) Voltages level is between: 380kV to 420kV for 400kV systems & 198kV to 245kV for 220kV systems
c) No network overloading issues or transmission constraints
d) Margins are available for backing down from conventional energy sources
e) State is overdrawing from the grid or State is drawing from the grid on a short-term basis from Power Exchange or other sources simultaneously backing down power from intrastate conventional or non-conventional sources.
(ii) As a deterrent, the curtailment of Renewable Energy for reasons other than grid security shall be compensated at PPA tariff in future. The compensation shall be based on the methodology adopted in the POSOCO report. POSOCO is directed to keep the report on its website.
(iii) The State Load Dispatch Centre (SLDC) shall submit a monthly report to the State Commission with detailed reasons for any backing down instructions issued to solar power plants.
(iv) The above guiding factors stipulated by us would apply till such time the Forum of Regulators or the Central Government formulates guidelines in relation to curtailment of renewable energy.