Landmark Verdict On RE Power Curtailment By APTEL


Appellate Tribunal For Electricity (APTEL) has given a landmark order on unauthorized RE power curtailment (Solar & Wind) by state DISCOM and SLDC in state of Tamilnadu.


Background :

Tamilnadu government vide the Tamilnadu Solar Energy Policy, 2012 proposed to establish large scale solar utility project in the state of Tamilnadu. Based on which several Solar power developers had set up their solar plants in Tamilnadu. Since commissioning of several large scale solar power plant, TNSLDC & TANGEDCO issued several backing down instructions to solar & wind developer without any written communication in context of grid security. For this rampant & arbitrary curtailment of RE power several developer facing huge financial losses.


As per regulation 5.2 of the Indian Electricity Grid Code Regulation, 2010 (IEGC) notified by CERC, system operator (SLDC/RLDC) shall make all efforts to evacuate the available solar & wind power and treat as a Must-Run station without compromising grid security. Still, Tamilnadu state DISCOM & SLDC resort to curtail the must run renewable power in view of grid security.


In this context in 2016, petitioner NSEFI asked TNERC to restrain DISCOM from further unauthorized RE power curtailment and compensation against lost deemed solar generation for curtailed time block. For this as per TNERC order, POSOCO conducted an inquiry for the time period of 01.03.2017 to 30.06.2017.

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The formula applied for assessing of curtailed time-block responsible for grid security is given below.

Sl No.DescriptionFormulaRemarks
1Cases of curtailment
in which negligible
margin was available
for backing down from
conventional energy
Margin available /
(Curtailment + Deviation)
< 20%
Since less margin is
available it is
considered as all
possible actions have
been exhausted
2Cases of curtailment
where 100 % of
curtailment could
have been avoided
with available margins
Margin available >
(Curtailment + Deviation)
Full Curtailment could
have been avoided
since sufficient
margins are available
for backing down in
3Cases of curtailment
where specified % of
curtailment could
have been avoided to
certain extent with
available margins
a. >80% to 100%
b. >50% to 80% and
c. >20% to 50%
a. Margin available /
(Curtailment +
Deviation) > 80% but
less than or equal to
b. Margin available /
(Curtailment +
Deviation) > 50% but
less than or equal to
c. Margin available /
(Curtailment +
Deviation) > 20% but
less than or equal to 50%
Classification done on
remaining time blocks.
Since margin is less
compared to
classification is done to
understand the amount
of Curtailment which
could have been
avoided with the
available margins in
Note : Up to 20% Margin has been considered as negligible margin.
The frequency range of 49.90-50.05 Hz and over drawl/under drawl
permitted is +/- 250 MW is permitted in any given time.

Considering grid frequency and under drawl of Tamilnadu from the grid for time period of 01.03.2017 to 30.06.2017, only 5.26% (60 out of 1140 blocks), appears to be justified for grid security perspective. Thus the percentage of quantum of power responsible for grid disturbance was minimal. In view of the above analysis, TNERC order TNSLDC & TNGEDCO to keep valid proof on reason of RE power curtailment but refrain to conclude the compensation of deemed lost solar power generation.

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APTEL’s Analysis:

For getting the compensation of deemed solar generation petitioner approached APTEL. After observing appellate & respondent’s submission and counter submissions, APTEL given the following orders:

(i) For the period 01.03.2017 to 30.06.2017, the TNGEDCO & INSLDC 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.

(ii) POSOCO shall carryout similar exercise for the period up to 31.10.2020 on the same lines and submit report to Respondent Commission within 3 months. Tamil Nadu SLDC and Appellant are directed to submit details to POSOCO. 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.

(iii) Curtailment quantum shall be considered as per POSOCO report.

(iv) The Respondents shall pay compensation along with interest at 9% for the entire period.

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Way forward, all state DISCOM and SLDC should follow the above order and refrain itself from RE power curtailment in disguise of grid security reason.

Conditions which will not be valid reason for RE power curtailment anymore given below.

(i) For Future, any curtailment of Renewable Energy shall not be considered as meant for grid security if the backing down instruction were given under 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 over loading 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 grid on short-term basis from Power Exchange or other sources simultaneously backing down power from intra-state conventional or non-conventional sources.

(ii) As a deterrent, the curtailment of Renewable Energy for the 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 APTEL would apply till such time the Forum of Regulators or the Central Government formulates guidelines in relation to curtailment of renewable energy.

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