Solar-hour and non-solar-hour access let CTUIL allocate the same scarce ISTS interface more deliberately across the day; they are connectivity and scheduling-right concepts for qualifying ISTS projects, not a new rule for ordinary rooftop or intra-state captive solar.
Key Takeaways
- CERC’s Third Amendment to the Connectivity and GNA Regulations became effective on 9 September 2025 and introduced solar-hour and non-solar-hour access.
- Solar-based and certain hybrid connectivity grantees entered a transition process, while wind projects and energy storage systems can seek qualifying non-solar-hour access.
- CTUIL declared non-solar-hour margins and has been processing right-of-first-refusal and other applications before publishing refreshed hour-specific margins and bay allocations.
- The framework matters most to large ISTS-connected solar, wind, hybrid, storage and bulk-consumer structures; it does not automatically govern behind-the-meter rooftop solar or ordinary intra-state open access.
- Commercial teams should test injection rights, drawal rights, bay sharing, transmission margins and PPA schedules separately. This is general information, not legal advice.
What changed under CERC’s Third Amendment?
CERC’s consolidated Connectivity and GNA Regulations now contain Regulation 5.11 on entities with solar-hour and non-solar-hour access. CERC’s 8 December 2025 transition order records that the Third Amendment became effective on 9 September 2025 and responded to implementation difficulties reported by renewable developers.
Under Regulation 5.11(a), as reproduced in the order, a wind-based renewable generating station, with or without energy storage, or an energy storage system may seek connectivity with non-solar-hour access for 50 MW or more at an ISTS substation terminal bay. It may use a separate dedicated line or a line and bay already allocated to another renewable station or park having solar-hour access, subject to the detailed conditions.
Regulation 5.11(b) addresses conversion of specified existing solar-based renewable generating stations, renewable power park developers and solar-combination hybrid generating stations to solar-hour access. The order states that solar-hour injection scheduling rights correspond to connectivity quantum during solar hours; during non-solar hours, rights correspond to non-solar source capacity, limited by connectivity quantum. The regulation also contained application and conversion timelines and an exception where available non-solar-hour connectivity would be below 50 MW.
Why did CERC need a transition order?
The Third Amendment altered already-granted projects, so developers raised implementation questions. In Petition 14/SM/2025, CERC invoked its powers to remove difficulty and issue implementation directions. It addressed conversion timing, technical compliance, temporary GNA drawal for storage and renewable power park developer applications.
The order is important because reading the amendment alone can miss how CERC directed CTUIL to implement it. For example, the order reproduced the conversion rule and the right to apply for additional capacity during the stipulated period. It also recorded the exception that an entity should remain on full-day access where the non-solar-hour connectivity available for conversion would be less than 50 MW.
The project’s CTUIL grant, conversion communication, agreements and current margin position control; procedural facts do not assure a particular hour-specific right.
How is CTUIL declaring solar and non-solar margins?
CTUIL’s renewable-energy page says ISTS substation injection margins had to be segregated after the Third Amendment. CTUIL declared non-solar-hour margins on 10 September 2025. The page further says the right-of-first-refusal period ended on 21 February 2026 and that CTUIL was processing those and other non-solar applications before declaring updated solar- and non-solar-hour margins and bay-allocation details.
CTUIL’s Detailed Procedure dated 10 April 2026 states that applications are made through the National Single Window System portal, describes applicable formats and requires supporting technical and corporate documents. It also says a requested start date does not itself entitle the applicant to connectivity from that date. Applicants should therefore distinguish the requested date, grant date, effectiveness conditions and actual network readiness in their project schedules, financing documents and formal conditions precedent.
Which projects and buyers should pay attention?
| Project or buyer | Likely relevance | Main diligence issue |
|---|---|---|
| Large ISTS solar generator | High | Conversion, daylight rights and non-solar source limit |
| Wind project sharing a solar bay | High | Non-solar margin, shared line and 50 MW threshold |
| Co-located or standalone ESS | High | Injection plus charging/drawal treatment |
| ISTS-connected hybrid | High | Source-wise capacity and scheduling rights |
| Bulk consumer with 50 MW-plus load | Potentially high | GNA drawal and delivery profile |
| Intra-state captive solar | Usually indirect | State open-access rules remain primary |
| Rooftop behind the meter | Low | Net metering or self-consumption regime, not GNA |
CTUIL’s GNA portal states that a distribution licensee or bulk consumer with load of at least 50 MW may seek ISTS connectivity through a GNA application. That is a different threshold and role from the 50 MW non-solar-hour injection provision for specified generators and storage. Teams should not mix generator connectivity, consumer drawal GNA and open-access approvals.
Our open-access solar guide and capex, opex and open-access comparison help establish whether ISTS is part of the route before hour-specific GNA analysis begins.
Why do captive, hybrid and storage buyers care?
A large captive buyer may contract for solar, wind and storage to shape delivery around factory demand. Hour-specific connectivity can affect how much of each source may be scheduled through a shared interface. If a commercial model assumes wind injection all day or battery discharge during evening peaks, the model must match the rights actually granted.
The same applies to charging. Storage at an ISTS injection point can need drawal study, metering, scheduling and settlement arrangements. The transition order discussed temporary-GNA drawal by ESS pending a CTUIL drawal study; buyers should verify project-specific communications.
How should a procurement team model the change?
What should the hourly model contain?
Use at least hourly, and preferably 15-minute, source profiles; factory load; granted injection rights; losses; curtailment; storage charging and discharging constraints; and state delivery charges. Run summer, monsoon and winter cases. A single annual capacity-utilisation factor cannot reveal a connection-right bottleneck.
What should the bid documents require?
Require bidders to identify the ISTS substation, bay, dedicated or shared line, source-wise installed capacity, connectivity quantum, solar-hour status, non-solar-hour application status and evidence date. The bidder should distinguish confirmed grants from pending applications and published indicative margins.
Which contract clauses need alignment?
The PPA should allocate risks for delayed connectivity, restricted scheduling rights, augmentation, shared-facility outages and change in law. Minimum supply or shape guarantees should be conditional on network rights that the generator can actually exercise. Avoid drafting “24x7 connectivity” as shorthand when the grant is hour-specific.
What is the practical decision rule?
First decide whether the project is ISTS-connected. If not, this framework is background rather than the governing rule. If it is, map each source and storage action to injection or drawal rights by hour, using the solar-wind hybrid comparison where relevant. Then verify the latest CTUIL declaration and the project’s grant. Finally, reconcile those rights with the PPA schedule and the buyer’s load.
A good investment memo lists unresolved applications as conditions precedent rather than assumptions. It addresses smaller-than-expected non-solar margin, a delayed shared bay and constrained storage drawal.
Frequently Asked Questions
Are solar hours fixed clock times for every project?
The applicable regulatory definition and CTUIL implementation should be checked in documents. Commercial teams should not invent their own daylight window.
Does solar-hour access reduce a plant’s installed capacity?
Not necessarily. It defines network access and scheduling rights; installed generation capacity and permitted injection are related but distinct concepts.
Can a battery automatically use a solar project’s bay at night?
No. Sharing depends on eligibility, application, studies, agreements, margins and CTUIL’s grant. Physical availability alone is insufficient.
Is this rule relevant to a factory rooftop system?
Ordinarily no. A behind-the-meter rooftop system is generally governed by state distribution, metering and safety rules rather than ISTS GNA.
Does hour-specific access guarantee open-access approval in the receiving state?
No. ISTS connectivity does not replace state approvals, scheduling, metering or surcharge analysis at the consumption point.
Where should buyers verify available margins?
Use CTUIL’s renewable-energy publications for current indications, then verify project-specific grants and communications. Published margins are not substitutes for approval.
Sources
Ready to Go Solar?
Get a free consultation and custom quote for your industrial or commercial facility. Start saving on energy costs today.
Get Free Quote