Most solar sites in India fail on the grid long before they fail on irradiance. A developer can lock land, finish a yield study and sign an offtaker, then find the nearest substation has no bay or no margin until a line that is still only a plan gets built.
Knowing who plans that line, and on what calendar, is the cheapest risk check you can run.
Quick answer. In India, the Central Transmission Utility (CTUIL) plans the inter-state transmission system (ISTS) through a five-year rolling plan, issued as an interim report in September and a final report in March. Each State Transmission Utility (STU) plans its intra-state network on an annual cycle, with a draft due by 15 August and a final plan by 30 September. Both work from CEA plans. Your project’s evacuation risk depends on which plan contains your substation.
TL;DR
- CTUIL plans the ISTS. Each STU plans its own state network. CEA sets the criteria and the long-range plans both follow.
- The ISTS rolling plan covers five years and is reissued twice a year. The current final report covers 2030-31 and was published in March 2026.
- Under the CEA planning manual (Amendment-I, 2025), STUs publish a draft plan by 15 August and a final plan by 30 September each year.
- A line in a plan is not a line in service. New lines and substations take about four to five years from concept to commissioning, per CEA.
- Check the right plan, then the substation margin, before you pay for land or a detailed design.
This guide is for developers and EPC teams picking sites for utility-scale or open access solar. It explains planning, not the connectivity application. For the application route itself, see our CTU vs STU glossary entry, which covers who you apply to and why voltage alone does not decide it.
Who plans transmission in India: CTU, STU or CEA?
Three bodies share the job. Each owns a different layer, and their documents feed into each other.
| Body | Plans what | Main document | Cycle |
|---|---|---|---|
| CEA (Central Electricity Authority) | National short-term and perspective transmission plans | Short-term plan and perspective plan | Short term yearly, up to 5 years ahead; perspective every other year, 10 years ahead |
| CTUIL (acting as CTU) | Inter-state transmission system | ISTS Rolling Plan | Twice a year: interim in September, final in March |
| STU (one per state) | Intra-state transmission system | State transmission plan | Yearly: draft by 15 August, final by 30 September |
The split comes from sections 38 and 39 of the Electricity Act, 2003. Section 38 gives the CTU planning and coordination of the ISTS. Section 39 gives each STU the same duty for its state network.
CEA sets the rules both use. The Manual on Transmission Planning Criteria (with Amendment-I), 2025 has applied since 1 April 2023. It covers the ISTS, intra-state systems and dedicated lines down to 66 kV.
How does the CTUIL ISTS rolling plan work?
CTUIL draws up a plan for the ISTS covering the next five years, refreshed every year. It does this under the Electricity (Transmission System Planning, Development and Recovery of Inter-State Transmission Charges) Rules, 2021, according to the ISTS Rolling Plan 2030-31 (CTUIL, March 2026).
Each year has two cycles:
- April to September. Data collection and studies, ending in the interim report.
- October to March. Updated data and studies, ending in the final report.
CTUIL’s rolling plan updates page shows this in practice. It lists the data request for the final 2030-31 plan on 6 October 2025 and the request for the interim 2031-32 plan on 9 April 2026.
Schemes from the plan go to monthly consultation meetings. They then go to the National Committee on Transmission (NCT), the Regional Power Committees and the Ministry of Power. Approved schemes are built by transmission service providers under tariff-based competitive bidding (TBCB) or the regulated tariff mechanism (RTM).
What the 2030-31 plan says about solar-rich states
The final 2030-31 report has numbers that matter for site selection in the two biggest solar states:
- Rajasthan. MNRE has declared 223 GW of ISTS renewable potential. About 205 GW of it sits in Jaisalmer, Jodhpur, Barmer and Bikaner. Connectivity applications reached about 150 GW by February 2026.
- Gujarat. Against 96.2 GW of declared ISTS potential, transmission for about 65 GW is existing or in implementation. About 54.7 GW of that is in Kutch and Banaskantha.
- Both. The report says transmission for about 70 GW in Rajasthan and 35 GW in Gujarat “could not be finalized” because nearby load centres were already covered.
That last point changes how you read a map. A district with strong irradiance and cheap land can still have no planned evacuation path for new capacity.
How does an STU plan the intra-state network?
The STU is the nodal agency for intra-state planning, working with DISCOMs and generators in the state. The CEA manual also makes the STU the single point of contact for ISTS planning on behalf of all intra-state entities.
Amendment-I to the manual sets a yearly STU calendar:
| Step | Owner | Deadline |
|---|---|---|
| Collect CEA and CTU plan inputs, open access and GNA requests | STU | 1 to 30 April |
| Validate data and prepare state load-generation balances | STU, with DISCOMs, generators, SLDC | 30 June |
| Publish draft plan and assumptions for comments | STU | 15 August |
| Stakeholder comments on the draft | Stakeholders | 31 August |
| Final plan uploaded to the STU website | STU | 30 September |
Source: CEA Manual on Transmission Planning Criteria (with Amendment-I), 2025, section 7.4.4.
STU inputs also feed the national plan. The CTUIL Procedure for Planning of ISTS (December 2021) requires each STU to send network, generation and demand data to CTUIL twice a year.
The weak link: state plans lag
The manual tells STUs to build downstream networks in the same time frame as the ISTS, “to avoid bottling up of power.” In practice, the 2030-31 rolling plan lists STU lines and transformers that fail the N-1 test, along with STU buses above their design fault level, in several regions.
So an ISTS pooling station can be ready while the state network around it is not. For a project that connects to the state grid, the STU plan is the document that decides your timeline.
STU vs CTU planning: what changes for a solar developer?
The planning body that matters depends on where your project will inject power. This table shows how that changes the work.
| Question | ISTS-connected project | Intra-state project |
|---|---|---|
| Plan to read | CTUIL ISTS Rolling Plan (interim and final) | Current STU transmission plan |
| Typical size | 50 MW and above under the CERC GNA Regulations, with some exceptions | Any size the state route allows |
| Where capacity data sits | CTUIL bay allocation and margin status | STU substation data, if published |
| Who builds new lines | TSPs under TBCB or RTM, after NCT and MoP approval | STU or state-approved licensee |
| Main delay risk | Scheme approved but not yet bid or built | State network not keeping pace with the ISTS |
The 50 MW threshold and its exceptions come from the CERC Connectivity and GNA Regulations, 2022. The glossary entry linked above lists the categories in more detail. If you are bidding ISTS capacity, pair this check with our SECI tender calendar.
How do you check transmission before locking a site?
Run this check before you pay for land or a detailed ground-mount design. It takes a few days of desk work and can save a year of waiting.
- Name the likely substation. Note its owner, voltage and whether it is part of the ISTS or the state system.
- Find it in the right plan. Search the latest CTUIL rolling plan or the current STU plan for that substation and any planned lines into it.
- Check the status. Is the scheme existing, under construction, out for bidding, approved but not bid, or only studied? Each step adds time.
- Check bay and margin data. For ISTS substations, CTUIL publishes a “Status of Bay Allocation & Margin” list on its renewable energy page. For state substations, ask the STU.
- Match dates. Compare the scheme’s planned date with your target commercial operation date. CEA’s manual says new lines or substations take about four to five years from concept to commissioning.
- Record it. Put the substation, plan version and access date in the design basis so the team can recheck it later.
Plan status and what it means for your schedule
| Status in the plan | What it tells you | Design decision |
|---|---|---|
| Existing, with margin | Capacity may be available now | Apply for connectivity, then start detailed design |
| Under construction | Physical progress is under way | Align COD with the scheme date, plus a buffer |
| Bidding or approved | Funded on paper, not yet built | Treat the date as a target, not a commitment |
| Studied or “could not be finalized” | No firm evacuation path | Do not lock land on this basis |
This table is our reading of the plan stages, not a CTUIL classification. Confirm your project’s position with CTUIL or the STU before you act on it.
Where curtailment and storage fit in
Transmission plans now assume storage. The 2030-31 report counts about 95 GW of extra battery storage near renewable plants. CTUIL describes this as an interim step to avoid curtailment in solar-maximum scenarios.
The same report notes more than 100 GW of battery storage applications for ISTS connectivity. If your site sits in a congested pocket, plan the layout so a battery can be added later. Our guide to solar curtailment and grid limits in India covers the generation side, and our BESS sizing guide covers the storage design.
The CERC GNA Regulations also allow connectivity based on solar hours and non-solar hours. That lets two projects share one connection at different times of day.
What should the engineering design basis record?
A transmission planning check only helps if the design team can see it. Put these items in the design basis document:
- the substation name, owner and voltage;
- the ISTS or intra-state route, with the reason;
- the plan version you checked, such as “ISTS Rolling Plan 2030-31, final, March 2026”;
- the scheme status and planned date;
- bay and margin data, with the access date;
- the assumption on storage or curtailment, if any.
This record feeds the high-voltage interconnection design and the technical rules in the CEA connectivity regulations. It also gives lenders a clear trail when they review grid risk.
FAQ
Is CTUIL the same as PGCIL?
No. CTUIL took over CTU functions from POWERGRID (PGCIL) in April 2021. POWERGRID is CTUIL’s parent and still owns large transmission assets. See the PGCIL glossary entry.
How often is the ISTS rolling plan updated?
Twice a year. CTUIL issues an interim report in September and a final report in March. Each covers the next five years.
Where can I find my state’s transmission plan?
On the STU’s website. Under the CEA manual, the draft should appear by 15 August and the final by 30 September. Some states publish late or not at all, so ask the STU directly if you cannot find it. In Gujarat, the STU is GETCO.
Does a planned line mean my project can connect on time?
No. A plan shows intent, not a commitment. Check the scheme status and build time, and keep a buffer in your COD.
Get the grid check into your design basis
Heaven Designs is a solar design and engineering firm. We can carry the transmission findings into your feasibility work, layout and MW-scale project management. CTUIL, the STU and other authorities still decide connectivity and access.
If you have a site shortlist, send us the project details. We reply within 1 business day.
Sources accessed 6 October 2026: CTUIL ISTS Rolling Plan 2030-31 (final, March 2026), CTUIL Procedure for Planning of ISTS (December 2021), and CEA Manual on Transmission Planning Criteria with Amendment-I (2025). Recheck by April 2027, after the final 2031-32 rolling plan.