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What is ISTS Solar Projects | ISTS Charges | ISTS Losses

Updated: Oct 3, 2020

Topics covered

Definition of ISTS and its full form

What is ISTS Charges and Losses

ISTS Charges and Losses on Solar projects in India

How POSCO compute ISTS Charges and Losses

You may heard or read the news ISTS solar projects. But did you know what is ISTS stand for and what are Solar projects? So, I did some research on the same and this is what I found.

ISTS Full Form

ISTS is stand for "Inter State Transmission system".

What is ISTS ?

Any system for the conveyance of electricity by means of a main transmission

line from the territory of one State to another State is called ISTS [the definition is given by POSOCO]

What is ISTS based solar project ?

In ISTS-based Solar project, power generated from one state can be transmitted to other states. ISTS, the developers can bid for their choice of project and location anywhere in India. After getting Developers setting up a solar power plant (or park) at the place allocated to them and build electricity transmission lines to the nearest grid network. The voltage at PV inverter’s output point is low, which needs to be stepped up through a pooling substation. And the development of the same is also in developer’s scope. Customers of developers, can purchase power through gird transmission lines.

Most of the PV energy generators did not have to worry about transmission costs or the cost of scheduling.

  • Wind or early solar projects, selling power under feed-in tariff (FIT) to distribution companies (DISCOMs), need only to connect to the grid. Additional transmission costs are not charged from either the generators or the consumers.

  • Open-access consumers buying power using the state grid pay transmission and wheeling charges in INR/ kWh and may see direct benefit of transmission capacity optimization.

  • Most states offer banking facility, and the banked power can be used up to a year. Generator does not need to optimize generation schedule to match demand with supply

Did you know what is Zero Export Device? [click here to know more]

As per data available on the site of Power System Operation Corporation Limited, inter-state transmission of energy is chargeable (but what about solar? keep reading), and this consist two type of charges transmission charges or ISTS charges and ISTS losses.

The method of computing charges is called Point of Connection (PoC) Charging Method. And the same is developed by POSOCO (Power System Operation Corporation Limited) in compliance of Central Electricity Regulatory Commission.

“Point of connection Charging Method shall mean the methodology of computation of sharing of ISTS charges and losses amongst Designated ISTS Customers, which depends on the location of the node in the grid and is calculated in accordance with Regulation “

What are the ISTS charges and losses for Solar projects?

As per the Central Electricity Regulatory Commission notification on 06.11.2019,

"No transmission charges and losses for the use of ISTS network shall be payable for the generation based on solar and wind power resources for a period of 25 years from the date of commercial operation of such generation projects if they fulfill the following


  1. Such generation capacity has been awarded through competitive bidding;

  2. Such generation capacity has been declared under commercial operation between 13.02.2018 till 31.12.2022;

  3. Power Purchase Agreement(s) have been executed for sale of such generation capacity to all entities including Distribution Companies, for compliance of their renewable purchase obligations


Further more about ISTS charges and losses (not for solar and wind power)

Now here are some terminologies used by POSOCO

Developers = Injecting DIC (or Injecting Designated ISTS Customers).

And Developer’s customers = Drawee DIC (or Drawee Designated ISTS Customers).

ISTS Charges

ISTS tariff is determined as per the CERC (Terms and Conditions of Tariff), Regulations, 2009. ISTS licensee submits tariff petition for approval by CERC.

ISTS Losses

The procedure for sharing of Inter-State transmission system losses is developed by POSOCO (Power System Operation Corporation Limited) in compliance of Central Electricity Regulatory Commission.

Let the Injecting DIC is located in Region-1 and the power is wheeled through Region-2 and the Drawee DIC is located in Region-3.

Also let the contracted quantum power be P.

Let Effective PoC Loss percentage of the injecting DIC in Region-1 be ‘a’ and that of drawee DIC in Region-3 be ‘b’ then the Injecting DIC has to inject P/(1-a/100)

The schedule at the inter-regional boundary between Region-1 and Region-2 shall be P and that between Region-2 and Region-3 shall also be P.

The schedule of drawee DIC shall be = P*(1-b/100).

For the easy of your understanding about ISTS losses, I made following calculator.

Waving off ISTS charges and losses on ISTS solar projects, will helpful for all Solar industrialist or it will be beneficial to Big players only? Leave a comment below.


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