POSOCO Report Finds Clear Bias Against RE Developers in Tamil Nadu

Following APTEL’s order in August, the Power System Operation Corporation Limited (POSOCO) has submitted a report on renewable energy curtailment in Tamil Nadu. The order, widely welcomed by solar developer bodies like the NSEFI, had asked for verification of claims made by both sides on the issue of curtailment. As it turns out the POSOCO report makes the Tamil Nadu stand even flimsier, with facts belying the state power firms claims. The POSOCO remit was to confirm whether the Tamil Nadu State Load Despatch Center had intentionally curtailed power or was it done to preserve grid safety, as claimed. For the state regulator TNERC, the case has been a poor advertisement for its fairness.

The Tamil Nadu State Load Despatch Center (TNSLDC) and Tamil Nadu Generation and Distribution Corporation (TANGEDCO) will be required to  compensate the solar developers for curtailment of power at 75% of the tariff listed in the power purchase agreement (PPA) along with 9% interest.

POSOCO analyzed the data from March 1, 2017, to June 30, 2017, and reported that 16 out of 56 power generators, comprising approximately 68% of the total installed solar capacity in the state (totaling 1,052 MW), had submitted the data. Of the 16, only ten generators submitted complete data.

Actual generation was deducted from irradiance-based estimated generation to arrive at the proportion of curtailment suffered by generators. “It appears that most of the solar generators with per unit cost of Rs 7.01 is curtailed more both in terms of instances of curtailment as well as in terms of percentage generation as compared to other solar generators.” This line pretty much sums up the approach of the Tamil Nadu discoms.

POSOCO reported the following findings after its studies.

  • Of the 1,140 blocks (total curtailed blocks), 55 blocks (4.82%) had a frequency greater than 50.05 Hz. Grid frequency within 49.90 Hz – 50.05 Hz is considered safe and does not call for security measures.
  • In terms of grid frequency, only 5.26% (60 out of 1,140 blocks) curtailment was justified from a grid security standpoint.
  • Most solar power generators with a tariff of Rs 7.01 /kWh faced more curtailment in terms of instances and percentage generation compared to other solar power generators.
  • Frequency was over 50.00 Hz in 427 blocks (37.45%) of 1,140 blocks. The state was under-drawing in 350 of the 427 blocks. In 60 of the 350 blocks, there was no margin for backing down thermal and hydro generation to absorb renewable energy.
  • Wind and solar energy generation were not curtailed simultaneously (during the same day or month); however, wind and solar power were equitably curtailed to a large extent over the four months.
  • In terms of generation (MW), from the solar generators’ standpoint, 52% of time blocks where wind energy was curtailed were equitable. Meanwhile, from the wind generators’ perspective, 48% of time blocks where solar energy was curtailed were equitable.

This excerpt from the report says it all. “There was no abnormal voltage condition at 400kV level of the grid and no network loading issue which required backing down / curtailment during the said period. Further no Specific constraint is expressed by TNSLDC at State level. Voltage and Transmission Constraints tend to be localised. The Curtailment instruction by TNSLDC was state-wide. There were no constraints/Violation which necessitated the state wide curtailment during the period under consideration”.

With POSOCO carrying out a similar study for the period up to 31.10.2020 and submit report to Respondent Commission within 3 months. Based on POSOCO report, State Commission shall allow compensation for the backed down energy at the rate of 75% of the PPA tariff per unit. That could mean a pretty big bill coming the way of the TN agencies involved.

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