A MW-scale plant commissioned between 2012 and 2017 now runs on inverters near the end of their service life and modules that have aged for a decade. Some strings are dead, some modules carry hot spots, and the energy meter shows a slow slide toward the floor in the PPA. The obvious fix is to swap parts. The hard part is that nothing you buy today matches what you installed then.
Modern modules are larger, carry more current and sit in a different voltage window. The PPA still fixes the AC capacity you may deliver. So solar plant repowering in India is a redesign problem first and a procurement problem second. This guide is part of our solar engineering hub. It is written for EPC teams and developers who hold an operating ground-mount plant. They need to decide what to replace, what the PPA allows and which approvals follow.
Quick answer. Solar plant repowering in India means replacing modules, inverters or both on an operating plant while the PPA’s contracted AC capacity stays fixed. The SECI standard PPA allows repowering at the developer’s cost and risk, but SECI buys only up to the Contracted Capacity and a CUF ceiling. Redesign strings, current limits, structures and DC/AC ratio together, then confirm CEIG, connectivity and ALMM treatment before ordering.
What triggers solar plant repowering in India?
Four triggers are common. Most plants meet more than one.
Inverter end of life. Central inverters from the early projects lose spare-part support or need repeated board and power-stack repairs. When an overhaul costs more than the energy it protects, replacement is cheaper than repair. This trigger usually sets the timetable, because a failed inverter takes a whole block offline.
Degradation. Field data gives a sense of scale. The NREL review by Jordan and Kurtz assembled nearly 2,000 field degradation rates and found a median of 0.5% per year (OSTI record 1045052, 2013). The later compendium covered more than 11,000 rates from almost 200 studies. It reported a median of 0.5 to 0.6% per year for crystalline silicon but a mean of 0.8 to 0.9% (OSTI record 1400540, 2016). The mean sits above the median because a minority of modules age much faster. Your own plant needs a measured rate, not a literature average. Our glossary entry on degradation rate and the PVsyst degradation modelling guide cover how to estimate it.
Defective modules. Hot spots, glass breakage, potential-induced degradation and delaminated backsheets remove capacity in lumps rather than smoothly. Scattered failures can be handled string by string. Concentrated failures in one block point toward block replacement.
The PPA energy floor. In the SECI standard PPA filed under ISTS-XVIII, SECI is not obliged to buy beyond energy at 110% of the declared CUF. The developer pays a penalty if annual energy falls below 85% of the declared CUF in the first 10 years from the scheduled commencement date. The floor is 80% for the rest of the term. The penalty is 1.5 times the applicable tariff on the shortfall (SECI standard PPA, Article 4.4.1, RfS dated 12 September 2024). At the median rate above, twelve years of degradation leaves a plant near 94% of its year-one output, which clears both floors if it started at its declared CUF. Outages, failed blocks and broken modules are what push energy under them.
Read your own PPA first. The clauses quoted in this guide come from SECI templates dated 2020 to 2025 and the 2017 Ministry of Power guidelines. Plants bid before 2017 sit under earlier documents, which may differ. Pull the signed PPA, the amendments and the connectivity grant before you design anything.
What are your repowering options?
Repowering is a ladder, not a single action. Each rung adds design work and approval exposure.
- Like-for-like inverter replacement. New inverters with the same AC rating and a compatible DC window. The array stays as built.
- Inverter replacement with a changed topology or rating. For example, central inverters replaced by string inverters, or a different block size. DC cabling, AC cabling and protection change.
- Like-for-like or near-match module replacement. Failed modules swapped for the same model, or the closest available model, string by string.
- Block module replacement with a new format. Whole strings or tables get modern modules. Strings, combiner inputs and possibly the structure change.
- Full repowering. New modules and new inverters, with the DC/AC ratio reset inside the PPA corridor.
Two cautions apply across the ladder. First, a string runs at the current of its weakest module, so never mix modules of different current in one string. Second, check whether your original module model is still in production. If it is not, a “like-for-like” swap is really rung 4.
The decision table near the end of this guide maps your situation to a rung.
What does the PPA allow when you repower?
Read three clauses before any design work.
Repowering is permitted, at your cost. The SECI standard PPA lets the developer install the DC field “as per its design of required output”. It also lets the developer “repower the Project from time to time during the term of the PPA”. Article 5.9 adds that components may be reconfigured and repowered at the developer’s own risk and cost. It also says SECI “will be obliged to buy power only upto the Contracted Capacity” (SECI standard PPA, Articles 4.4.2 and 5.9). The same permission appears in SECI RfS ISTS-X (10 April 2020, clause 14.5) and ISTS-XX (12 June 2025, clause 20.7). It is a long-standing template position. The Ministry of Power’s solar bidding guidelines of 3 August 2017 carry it too, in clause 5.2.3 (consolidated text of the 2017 guidelines, 2019).
The capacity is AC. The PPA defines Installed Capacity as the rated AC capacity and requires it to match the capacity for which connectivity was granted. CUF is computed on the Contracted Capacity as metered energy divided by contracted MW times 8,766 hours. A higher DC field therefore raises CUF without changing the denominator.
Excess energy is not assured revenue. Above the 110% ceiling, SECI may buy the excess at the PPA tariff only if the Buying Entity consents. The developer must give 60 days’ notice before excess generation begins. If the peak output exceeds the Contracted Capacity and disturbs the system, the developer must cut the output and may owe charges. The 2017 guidelines treat excess energy differently. Excess generation may be sold to others, subject to the procurer’s right of first refusal. The procurer may buy it at 75% of the PPA tariff (clause 5.2.1(b)). Which regime your PPA follows depends on its vintage.
The RfS for ISTS-XX also allows higher DC capacity arrays to reach the AC limit at the delivery point. It adds that generation above the maximum AC capacity at the delivery point is not considered under the PPA (SECI RfS ISTS-XX, Annexure, clause 9).
We found no MNRE guideline dedicated to solar repowering. The MNRE policies and guidelines index we could open lists the tariff-based bidding guidelines but no repowering document. Treat the PPA and the regulators below as the rulebook, and confirm with your procurer in writing.
How do you set the DC/AC ratio under a fixed AC capacity?
Under a fixed AC contract, extra DC meets four ceilings. They are the AC limit at the delivery point, the 110% CUF ceiling, the DC current limit of the inverters and the cost per added kWh. Our DC-to-AC ratio guide covers the clipping economics, and the glossary has entries for the inverter loading ratio and inverter clipping. Here the question is narrower: what does a new ILR do to the rest of the plant?
Take an illustrative plant. All figures below are assumptions for the arithmetic, not data from any real project.
- Contracted and installed capacity: 10 MW AC, four 2.5 MW central inverters.
- As built: 33,333 modules of 330 Wp, which is 11.0 MWp DC (ILR 1.10), in strings of 19 on a 1,000 V DC system.
- Declared CUF: 25%.
The PPA energy corridor in that example, using the 8,766-hour definition, is:
| Limit | Basis | Annual energy (MWh) |
|---|---|---|
| Declared | 10 MW x 8,766 h x 25% | 21,915 |
| Ceiling | 110% of declared CUF | 24,107 |
| Floor, first 10 years | 85% of declared CUF | 18,628 |
| Floor, after year 10 | 80% of declared CUF | 17,532 |
Repowering can move the plant up toward the ceiling. It cannot move it past the ceiling at the same tariff. If your plant already runs near 110%, more DC buys nothing.
Now size the new array with a 575 Wp module. Module and string data come from two manufacturer datasheets. One is a 2016-era Jinko 330 Wp polycrystalline module. The other is a 2024 Jinko 575 Wp bifacial module. Both stand in as typical of their eras.
| Case | DC (MWp) | Strings of 17 | Modules | Module area (m²) | MPP current per 2.5 MW block (A) |
|---|---|---|---|---|---|
| As built, 330 Wp, ILR 1.10 | 11.00 | 1,754 (of 19) | 33,333 | 64,678 | 3,833 |
| Repowered, ILR 1.10 | 11.01 | 1,126 | 19,142 | 49,449 | 3,699 |
| Repowered, ILR 1.20 | 12.00 | 1,228 | 20,876 | 53,928 | 4,036 |
| Repowered, ILR 1.30 | 13.00 | 1,330 | 22,610 | 58,407 | 4,372 |
Three results matter. The new array needs 32% to 43% fewer modules for the same or higher DC. The module area falls by 10% to 24%, so land is not the constraint. And at ILR 1.30 each 2.5 MW block carries about 14% more MPP current than the original design did. A 1,000 V plant can raise power only by raising current. The inverter’s maximum DC input current becomes the gate, not the array.
A high ILR is not automatically better. Clipping loss, the CUF ceiling and inverter current all push back. Model the candidates in PVsyst with measured degradation and your site’s irradiance, then pick the ILR where the marginal energy no longer pays for the marginal module.
Will larger modules fit your strings, current limits and tables?
Compare the two datasheets before touching a drawing. The string maths drives most of the redesign.
| Parameter | 2016-era 330 Wp | 2024 575 Wp |
|---|---|---|
| Size (mm) | 1,956 x 992 x 40 | 2,278 x 1,134 x 30 |
| Area (m²) | 1.94 | 2.58 |
| Weight (kg) | 26.5 | 31.0 |
| Weight per m² (kg) | 13.7 | 12.0 |
| Power per m² (W) | 170 | 223 |
| Voc / Isc at STC | 46.9 V / 9.14 A | 52.30 V / 13.89 A |
| Voc temperature coefficient | -0.30%/°C | -0.25%/°C |
| Voc at 0 °C (assumed site minimum) | 50.4 V | 55.6 V |
| Modules per string at 1,000 V | 19 | 17 |
| String Voc at 0 °C | 958 V | 945 V |
| String Vmp at STC | 718 V | 743 V |
| Maximum system voltage | 1,000 V DC | 1,500 V DC |
| Maximum series fuse | 15 A | 30 A |
| Mechanical load rating | 2,400 Pa wind, 5,400 Pa snow | 5,400 Pa front, 2,400 Pa rear |
Sources: Jinko JKM330PP-72 datasheet and Jinko JKM575N-72HL4-BDV datasheet, 2024. The 0 °C minimum is an assumption for the arithmetic; use your site’s design minimum.
Strings and current
The new module has a higher open-circuit voltage but a lower voltage temperature coefficient. The string length on a 1,000 V plant drops from 19 to 17. Eighteen new modules would reach about 1,000.2 V at 0 °C, which is over the limit. Our string sizing maths guide shows the full method.
The bigger change is current. Isc rises from 9.14 A to 13.89 A, up 52%. Re-check every part in the current path: string fuses and connectors, combiner busbars, DC cable ampacity, and the inverter’s maximum DC input current. A 15 A fuse that suited the old module can fail the new one. The new modules are rated to 1,500 V. Your combiners, cables and inverters may only be rated to 1,000 V. A 1,500 V string is therefore a full DC-side rebuild and a separate decision.
Structures and clamps
Start with the geometry. A two-portrait table has a chord of 3.91 m with old modules and 4.56 m with new ones, which is 16.5% deeper. At the same row pitch, the ground coverage ratio rises by the same 16.5% and inter-row shading follows. Our ground coverage ratio guide covers the trade-off.
Weight is not the problem. The new module is heavier per piece but lighter per square metre, 12.0 kg against 13.7 kg. Wind is the problem. Wind force scales with exposed area, so a deeper table collects more load and a larger overturning moment on the same piles. Recalculate the loads with IS 875 (Part 3) 2015 using the as-built tilt and height, as set out in our wind load guide. Then check the foundations against the as-built pile test or geotechnical records. Measure the remaining zinc coating on sampled members before you load a ten-year-old structure harder.
Clamp zones decide whether the old rails can be reused. Take the 2,278 mm module. The manufacturer’s manual puts long-side clamps at A/4 plus or minus 50 mm from the short edge. A is the long side. This position carries the +5,400/-2,400 Pa rating. Short-side and corner clamping are rated at only plus or minus 1,600 Pa. The manual calls for at least four clamps per module (Jinko installation manual, Tiger Neo 72HL4-BDV, Table 4). That puts the clamp line 519.5 to 619.5 mm from each short edge, so the rails must sit 1,039 to 1,239 mm apart. Measure your as-built rail spacing against that window. Frame height also changes from 40 mm to 30 mm, so old clamps may not grip. These figures are for one manufacturer’s module and manual revision. Use the manual for the exact model you buy.
CEA’s Safety Regulations also touch the layout. Regulation 121 requires walkways between rows for cleaning and maintenance. It requires fencing at least 1.8 m high around ground-mounted installations. It also requires earthing of each array structure and mounting structure, with welded earth strip joints (CEA Safety Regulations 2023, Regulation 121). New tables or changed table spacing mean new earth connections and a fresh check of the clear walkways.
If your tables cannot take the new format, a fixed AC cap gives you options that a greenfield design does not. You need fewer modules, so you can retire the worst-shaded or most-soiled tables and keep the rest. Table, foundation and DC layout engineering is the work covered by our ground-mount design service.
Which approvals apply when the plant changes?
Approvals follow what you touch. A like-for-like inverter swap and a full repowering do not need the same set.
| Approval | Source | What applies | Who confirms |
|---|---|---|---|
| PPA and procurer | PPA Articles 3.1, 4.4, 5.9 | Contracted Capacity stays fixed; DC change at developer’s risk; excess energy needs consent | Procurer, in writing |
| Connectivity | CERC GNA Regulations 2022, First Amendment, Regulation 5.2 | With prior CTU approval, capacity may be added within the granted quantum; net injection cannot exceed total Connectivity | CTU (ISTS); STU or DISCOM for state-connected plants |
| Electrical inspection | CEA Safety Regulations 2023, Regulations 34 and 45 | Alteration or addition needs the Electrical Inspector’s written approval or owner self-certification | State Electrical Inspectorate (CEIG) |
| Grid code and inverter capability | CEA Connectivity Regulations as amended 2019; Grid Code | Harmonics, DC injection, flicker, reactive power and ride-through requirements | Load dispatch centre and CTU or STU |
| Module sourcing | MNRE ALMM orders | See next section | Procurer and MNRE order text |
Sources: CERC GNA First Amendment, 1 April 2023, CEA Technical Standards for Connectivity, consolidated with the 6 February 2019 amendment.
Four points sharpen the table.
CEIG. Regulation 45(6) bars an owner from connecting any addition or alteration to supply. The Electrical Inspector must first approve it in writing, or the owner must self-certify it, as the case may be. Regulation 45(3) requires inspection and testing of generating units above the capacity specified under Regulation 34 before commencement or recommencement of supply. Each state notifies those thresholds. Whether a like-for-like module swap counts as an alteration is a question for your state office, so ask before work starts and keep the answer. Our CEIG approval guide covers the drawings and the process.
Connectivity. The GNA amendment lets an existing connectivity holder add capacity within the quantum it already holds, with CTU approval. That holder stays responsible for Grid Code compliance on the added capacity. It also bars net injection above the total Connectivity. Because the SECI template ties installed AC capacity to the connectivity grant, an AC increase is a different project, not a repowering.
Inverter standards. The CEA connectivity regulations treat each inverter with its associated modules as a separate generating unit. Part II(B), added by the 2019 amendment, sets limits for harmonic current (IEEE 519), DC injection (0.5% of rated output) and flicker (IEC 61000). For stations connected six months or more after publication, it adds three more requirements. They are reactive capability from 0.95 lagging to 0.95 leading, operation from 47.5 to 52 Hz and low-voltage ride-through. Those requirements are written for new connections. Whether the load dispatch centre treats a repowered plant as a new connection is a question to put to them. Specify inverters that meet them, and ask whether re-testing is expected. BIS also lists a Solar System, Devices and Components Goods Order, 2025 (S.O. 3597(E), 5 August 2025) described for solar inverters above 200 kW. Check its scope and dates when you buy (BIS Scheme II page).
Lenders and the owner’s engineer. If the plant carries debt, the financing documents may require lender consent for a change of this size. An owner’s engineer can review the redesign for the owner. After the work, a performance ratio and capacity test gives a measured before-and-after record.
Do replacement modules need to be on the ALMM list?
The honest answer is that the MNRE orders we could open do not say, for a PPA plant bid before 2021, so do not assume either way.
What the orders do say. The MNRE office memorandum of 10 March 2021 limits the ALMM List-I requirement to three groups. They are Government and Government-assisted projects, projects under Government schemes, and projects selling electricity to Government under the Section 63 bidding guidelines. It applies to bids whose last date of submission was on or after 10 April 2021 (MNRE O.M. of 10 March 2021). A plant bid in 2012 to 2017 falls outside that bid-date test as written. The orders do not address module replacement on such a plant, and we found no MNRE text that does.
What changed for cells. MNRE’s O.M. 283/59/2024 of 9 December 2024 provides that from 1 June 2026 only modules using ALMM List-II cells remain in List-I. A separate List-I(a) serves projects exempt from the cell requirement (MNRE O.M. of 9 December 2024). The FAQ memorandum of 23 September 2025 sets the bid-date cut-off for the cell requirement at 31 August 2025. It also answers one repowering-shaped question for a different category. Take net-metering and open-access projects commissioned before 1 June 2026. Any modification or addition to commissioned capacity after the cut-off must follow List-II cells for that modification or addition (MNRE O.M. 283/64/2025, FAQ 9).
So the decision depends on the plant’s category:
- Section 63 PPA plant bid before April 2021: the MNRE orders do not clearly cover replacement modules. Get the procurer’s position in writing, and check for any state scheme conditions.
- Captive or open-access plant: the 2025 FAQ treats modified or added capacity after the cut-off as subject to List-II cells. Treat a repowered block as ALMM-bound unless the authority confirms that pure replacement is outside the rule.
- Any plant with a loan or a procurer clause that names ALMM: the contract may bind you even where the MNRE order does not.
Even where ALMM does not bind you, the list is a useful screen for supplier quality. For BOQ mechanics, see our ALMM list explainer. List status changes monthly, so verify the live list on the day you order.
Which repowering route fits your plant?
Use this table as a first sort. It maps the situation to a rung on the ladder and to the approvals that route is likely to trigger.
| Your situation | Route | What changes | Approvals to expect |
|---|---|---|---|
| Inverters failing, modules healthy, energy inside the PPA corridor | Like-for-like inverter replacement | Inverters only; keep the DC window | Electrical Inspector (alteration); grid code and BIS checks on the new inverters |
| Inverters at end of life, energy near the floor | Inverter replacement plus a modest ILR rise | New inverters; strings stay if current limits allow | Same as above; procurer notice if energy may exceed the ceiling |
| Scattered module failures, original model still available | Like-for-like module replacement by string | Modules only | Check state view on alteration; ALMM position per your category |
| Original model discontinued or failures concentrated in blocks | Block module replacement with a new format | Strings, combiners, fusing, possibly rails and clamps | Electrical Inspector; ALMM position; structure calculation on file |
| Fixed AC, goal is more energy and a healthier CUF | Full repowering with ILR reset | Modules, inverters, strings, structure checks | All of the above, plus the connectivity check |
| Goal is more MW of AC | Not repowering | A new project in effect | New connectivity, PPA discussion, separate approvals |
What should you do first?
Run the work in this order. It limits the money spent before the unknowns are closed.
- Pull the documents. Signed PPA and amendments, the connectivity grant, the Electrical Inspector approval, the as-built drawings and the structure calculation.
- Measure the plant. Annual energy against the CUF corridor, string-level current checks, thermography for hot spots, and a measured degradation rate.
- Test the structure. Sample the zinc coating, record pile and foundation condition, and measure the rail spacing.
- Model the options. Run PVsyst for each ILR with the new string layout and the inverter’s current limit.
- Ask the authorities in writing. Procurer, CTU or STU, state Electrical Inspectorate, load dispatch centre. Put the same question to each and keep the replies.
If you want a second pair of eyes on the string, table and structure redesign, talk to our ground-mount design team. Send the as-built pack and the PPA corridor through our contact page, and our team will review whether the redesign fits our ground-mount design scope. Turnaround is agreed at scoping.
FAQ
Is there an MNRE policy for repowering solar plants?
We found none. MNRE’s policies and guidelines index lists the tariff-based bidding guidelines but no solar repowering guideline. The permission to repower sits in the PPA and bidding documents. Examples are SECI PPA Articles 4.4.2 and 5.9 and clause 5.2.3 of the 2017 Ministry of Power guidelines.
Can I add DC capacity without changing the inverters?
Only inside the inverter’s current and power limits, and only while energy stays inside the PPA corridor. In a 1,000 V plant, added power means added current, so check the inverter’s maximum DC input current, string fuses and combiner ratings first. Model clipping loss before you buy modules.
Does repowering restart the PPA term or change the tariff?
The SECI templates quoted here do not say so. They keep the Contracted Capacity and tariff as they are and allow repowering at the developer’s risk and cost. Confirm any term or tariff consequence with your procurer in writing, because older PPAs differ.
Can I replace modules with higher-wattage ones on the same structure?
Sometimes. Check the module size against the table, the clamp zone against the rail spacing, and the wind load on the larger face against the as-built piles. Frame height also matters, because old clamps may not fit a 30 mm frame. The structure calculation must be redone, not assumed.
Do I need CEIG approval for a module or inverter replacement?
CEA Regulation 45(6) requires written Electrical Inspector approval or owner self-certification for an addition or alteration before the altered part is connected to supply. States set the thresholds. Ask your state Electrical Inspectorate whether your specific change counts, and keep the reply.
How do I prove the repowering worked?
Record a baseline before the work and repeat the same test after. A capacity and performance ratio test under an agreed procedure gives you a before-and-after figure that the owner, lender and procurer can read in the same way.
This guide was reviewed against the cited sources on 31 October 2026. ALMM lists, BIS orders and PPA templates change, so recheck them before ordering. It is engineering guidance, not legal advice, and no authority has agreed that any design described here will be accepted.