Batteries or Transmission? The Wrong Question for Renewable Curtailment

When renewable surplus is concentrated in a few states, the answer is a portfolio — not a national battery target

India curtailed 8,133 GWh (8.133 TWh) of solar electricity between April and June 2026. The government attributed this primarily to transmission bottlenecks and grid-security requirements, and to a mismatch between the pace at which renewable energy capacity was commissioned and the pace at which evacuation infrastructure kept up. Monthly curtailment was 2,417 GWh in April, 3,235 GWh in May, and 2,481 GWh in June — disclosed by the Minister of State for New and Renewable Energy in a written reply to Parliament, drawing on Grid-India data.

The immediate policy response to a number like this is predictable: India is curtailing renewable energy, therefore India needs more battery storage. That conclusion is premature. But the opposite instinct — that India should simply build more transmission — is equally simplistic. For India's present situation, where renewable generation and curtailment are heavily concentrated in a limited number of RE-rich states, both BESS and transmission can be expensive solutions if applied indiscriminately, and neither has an inherent claim to being cheaper than the other.

The right question is not:

Should India solve curtailment through transmission or through BESS?

The right question is:

For each location and each type of curtailment, what is the lowest-cost combination of demand flexibility, better grid utilisation, BESS, transmission, generation flexibility and economically acceptable residual curtailment?

That is a materially different policy framework from either a national storage target or a national transmission build-out.

Let Us First, Understand the Nature of India's Curtailment

The 8.133 TWh figure should not be read as a national storage requirement. It is an accumulation of curtailed energy over three months, and India's renewable surplus is not evenly distributed across the country — it is concentrated around specific resource-rich states and specific transmission pockets within them. Further, While 8.1 TWh sounds enormous—and represents roughly one-eighth of potential solar output for the quarter—it was only about 8% of total Variable renewable generation and around 1.6% of India's total electricity generation. Therefore, a detailed Cost-Benefit Analysis with system wide implications is necessary.

Independent data corroborates this concentration. ICRA's analysis found that around a third of India's recently commissioned renewable capacity — roughly 54.8 GW as of May 2026 — was being evacuated through the temporary General Network Access (T-GNA) route rather than firm access, and that curtailment on this route ran as high as 50–60% during solar hours. ICRA identified Rajasthan and Gujarat as the states where solar curtailment was most prominent, while curtailment in the southern region remained comparatively limited even during peak solar hours. Separately, the Rajasthan Solar Association has estimated that the state — India's largest producer of green power — has seen nearly 4 GW of clean energy curtailed, with associated developer losses running into hundreds of crores of rupees.

This changes the economics considerably. If India had a uniform national surplus of electricity at noon, the problem would be primarily temporal — too much electricity now, not enough demand now. But when Rajasthan has a local surplus while another region has simultaneous demand, the problem is partly spatial. If the congestion occurs for only a few hours on selected days, a local battery may be the answer. If the constraint persists for long hours and carries very large volumes of power, transmission reinforcement may be cheaper over its lifetime. If the surplus can be absorbed locally through flexible demand, neither may be required.

There is no universal winner — the answer depends on duration, volume and geography, evaluated case by case.

The Battery Calculation: Useful, but Easily Misread

Take a 1 GW / 4 GWh BESS — a typical 4-hour configuration. If it completes exactly one full cycle every day for the 91 days between April and June, and every cycle is dedicated entirely to curtailed solar, it absorbs:

4 GWh × 91 days = 364 GWh, or 0.364 TWh

Against the quarter's actual curtailment of 8.133 TWh, that is 0.364 ÷ 8.133 ≈ 4.5%.

To theoretically absorb the entire 8.133 TWh over the quarter under these same idealised assumptions of perfect siting and daily cycling, India would need approximately 22.3 GW / 89 GWh of 4-hour BESS — a very large, capital-intensive fleet, deployed for the singular purpose of eliminating curtailment whose underlying causes a battery often cannot fix at all. It is noteworthy that India's current BESS portfolio including pipeline projects is around 1 GW.

But this is not an argument against BESS. It is an argument against using an aggregate national number to size a national storage requirement. A battery does not need to absorb every unit of curtailed electricity, and not every curtailed unit needs to be saved. The relevant question is narrower and more local:

At what cost can the marginal curtailed unit, at this specific location, be avoided — and is that cost lower than the value of avoiding the curtailment?

India's Curtailment Problem Has at Least Four Different Forms

Before capital is committed, curtailment should be classified by its underlying character.

1. Short-duration local congestion. Suppose a renewable-rich substation or corridor is overloaded for three or four hours around noon. A new transmission line sized for that peak may sit underutilised for the rest of the year. Here, a strategically located BESS can act as a genuine non-wire alternative — absorbing the surplus during the congested hours and discharging once network capacity frees up. The relevant comparison is not the capital cost of a line versus the capital cost of a battery; it is the lifecycle cost of relieving one MW of congestion for the specific number of hours it actually occurs. For short-duration, intermittent congestion, BESS is often the more economic answer.

2. Persistent, high-volume transmission congestion. Now consider a major corridor experiencing surplus generation for six to eight hours almost every day, with simultaneous demand elsewhere. A battery must charge, store and then discharge; transmission simply transfers and lets the load consume. Here transmission's higher upfront capital expenditure can be justified because it avoids round-trip losses, does not degrade with cycling, can operate for several decades, and can carry electricity from multiple generators to multiple, changing demand centres. High capex does not necessarily mean high lifecycle cost — a transmission asset heavily utilised over 30–40 years can deliver a lower cost per MWh than a battery that requires periodic augmentation or replacement. But this holds only where utilisation is genuinely high; a line built merely to eliminate a handful of curtailment hours a year can be the more expensive option.

3. Local daytime surplus with exploitable flexible demand. This may be India's most underused option. Before routing surplus solar through storage — Solar → Battery → Consumer — the system should ask whether it can instead achieve Solar → Consumer directly, with no storage step at all. Candidate flexible loads include agricultural and municipal water pumping, water treatment, cold storage and commercial cooling, industrial processes, thermal storage, EV charging, and selected data-centre operations. CEEW's 2026 roadmap for a demand-flexibility market in India sets out a five-pillar framework — covering metering and data infrastructure, market design, aggregation, tariff design and governance — for building exactly this kind of capability at scale, drawing on the experience of systems such as Great Britain's, where flexible demand has been used explicitly as a lower-cost alternative to network reinforcement. For RE-rich states, the question is not only "where can this electricity go," but "what productive demand can be created or shifted into these hours, in this location." The cheapest battery is often a consumer who can shift demand to the hours when electricity is abundant.

4. System-wide simultaneous surplus. There will also be periods when the problem is genuinely national — most regions generating abundant solar at once, with insufficient demand anywhere to absorb it. In this case transmission does not solve the problem; it only moves the surplus from one saturated region to another. The remaining options are demand creation, BESS, pumped storage, other storage forms, or accepting the curtailment as an efficient outcome of a renewable-overbuilt system. Storage matters most here — but even in this case, the objective should not necessarily be zero curtailment.

A Least-Cost Decision Framework, Not a Fixed Merit Order

Because the same aggregate number can conceal these four very different situations, India should resist a single fixed technology hierarchy and instead apply a decision matrix that maps the type of constraint to its likely least-cost response.

Nature of curtailment

Likely least-cost response

• Operational or scheduling problem

• Better forecasting, dispatch and scheduling

• Short-duration local congestion

• BESS or grid-enhancing technology

• Local surplus with flexible demand available

• Demand response and demand shifting

• Persistent, high-volume export constraint

• Transmission reinforcement

• Long-duration daily energy surplus

• Pumped storage, transmission or flexible demand

• Thermal plants unable to back down

• Thermal and hydro flexibility

• System-wide simultaneous surplus

• Storage, demand creation or planned curtailment

• Rare, low-volume curtailment

• Accept the curtailment

This is a more realistic starting point for India than declaring, in advance, either "transmission first" or "BESS first."

The Critical Variable Is the Duration of Congestion

The economics of transmission versus BESS turn heavily on one variable: how many hours a year is the network actually constrained? A corridor congested for roughly 500 hours a year, served by a large dedicated transmission asset, will likely see that asset sit idle the rest of the time — a battery covering those same 500 hours can be cheaper. A corridor congested for 3,000–4,000 hours a year, with continuous downstream demand, reverses the calculus: the transmission asset's high capital cost is spread across a far larger volume of energy, and its economics improve accordingly.

Short-duration congestion favours flexibility; persistent congestion favours network reinforcement.

The precise crossover point has to be established through system modelling and lifecycle-cost analysis specific to each corridor — it cannot be set by a national rule of thumb or a generic ₹/MW comparison.

Before Building New Assets, Use Existing Ones Better

India should also separate a genuine lack of transmission capacity from inefficient utilisation of capacity that already exists. Before committing to a new line or a new battery, planners should examine dynamic line and transformer ratings, reconductoring, voltage uprating, topology optimisation, advanced power-flow control, flexible or non-firm connection arrangements, and co-location of generation with storage. If latent capacity in the existing network can resolve the constraint, that is cheaper than either a new line or a new battery — and it is particularly relevant given that one of the government's own stated causes of the current curtailment is RE capacity being commissioned faster than the transmission system built to evacuate it.

BESS Should Compete With Transmission, Not Sit in a Separate Silo

This is perhaps the most important institutional implication. India's storage policy and transmission planning should not be developed as parallel, disconnected exercises. For every transmission reinforcement proposed primarily to relieve RE-driven congestion, the planner should size up the alternatives on comparable terms:

Transmission — capital cost, utilisation factor, energy transferred, system-wide benefit, asset life.

Local BESS — MW/MWh sizing, expected cycling, congestion avoided, round-trip losses, degradation and augmentation cost, and additional value from peak shifting and ancillary services.

Demand flexibility — what load can be shifted, at what cost, for how many hours, and whether local consumers can absorb the surplus directly.

A hybrid — a smaller transmission line combined with strategically located BESS and demand response, addressing only the residual structural constraint through the network.

That fourth option — a blend rather than a single technology at 100% — will often be the lowest-cost outcome in practice.

BESS Has a Genuine Advantage in India's RE-Rich States

None of this is an argument against storage. In fact, India's specific situation — concentrated surplus, identifiable locations, identifiable hours — is close to the ideal case for targeted BESS deployment. A battery placed downstream of a constrained corridor can absorb local surplus, defer or avoid transmission reinforcement, discharge into the evening peak once congestion clears, provide frequency response and ancillary services, and support local voltage depending on design. The economics strengthen considerably once a single asset performs several of these functions simultaneously — a markedly different proposition from installing a national fleet of batteries simply because the aggregate curtailment number was large. The former is locational system optimisation; the latter is poor planning dressed up as a target.

That said, a battery installed solely to capture curtailed electricity, with no other revenue stream, will likely see highly seasonal and partial utilisation — its cost recovered from a comparatively small volume of energy, which weakens the economics considerably. The best BESS project is therefore not necessarily the one that captures the most curtailment; it is the one that stacks congestion management, peak capacity, frequency response, ancillary services, resource adequacy and energy arbitrage into a single asset.

India Should Aim for Optimal Curtailment, Not Zero Curtailment

India should not set itself the objective of eliminating renewable curtailment altogether. Doing so risks over-investment in transmission, BESS, pumped storage and flexible capacity alike, chasing units of electricity whose recovery costs more than their value. The governing optimisation is:

Total System Cost = Generation + Transmission + Storage + Flexibility + Backup + Demand Response + Cost of Residual Curtailment

Beyond a certain point, the cost of capturing the next curtailed MWh exceeds its value, and at that point curtailment is the economically rational outcome, not a policy failure. The relevant question is not whether India should curtail 0%, 1%, 5% or 10% of renewable output nationally — that figure has no single correct answer. The question is what level of curtailment minimises total system cost at each location, and that will differ by state, corridor, season, hour, technology mix and demand pattern.

From a National Capacity Target to Locational Planning

A national target of a given number of GW of BESS does not, by itself, say where the battery should sit, what congestion it should relieve, how often it will actually cycle, whether local demand exists to be tapped instead, whether transmission would be cheaper on that specific corridor, or whether the asset carries capacity value beyond curtailment absorption. The same limitation applies to a national transmission target: a line should not be sanctioned merely because RE capacity has been added somewhere upstream of it.

What India needs instead is a locational flexibility and curtailment map — for every major RE zone, Grid-India, the Central Electricity Authority and the relevant state transmission utility identifying hourly curtailment, its cause, the specific constrained network element, its duration and frequency, alternative demand centres, available flexible demand, BESS and pumped-storage alternatives, and the estimated cost of reinforcement. Only with that granularity can a genuine least-cost comparison be made corridor by corridor, rather than assumed at the national level. ICRA's finding that a third of recently commissioned capacity is already running on temporary access arrangements — with the practical curtailment consequences that implies — suggests the underlying data to start this exercise substantially exists within Grid-India and the transmission utilities already; it needs to be organised and published at the level of granularity the decision requires.

The Real Lesson From India's 8.1 TWh Curtailment

India's 8.133 TWh of curtailed solar power should not trigger a reflexive conclusion that the country needs tens of gigawatt-hours of batteries, and it should not trigger an equally reflexive nationwide transmission build-out either. The least-cost solution depends on the specific nature of the constraint, corridor by corridor.

For India's RE-rich states, the likely answer is a portfolio, applied in roughly this order of first resort: improve forecasting, scheduling and utilisation of the network that already exists; create and shift flexible demand into the hours and locations of RE surplus; deploy BESS where congestion is local, intermittent and short-duration, and where the asset can be designed to stack multiple system services; reinforce transmission where congestion is persistent, high-volume, and there is sustained simultaneous demand elsewhere to justify the utilisation; turn to pumped storage or other longer-duration solutions where the surplus itself extends across many hours each day; and finally, accept the residual curtailment once eliminating it would cost more than the electricity it would save.

Curtailment should not be treated as a storage problem. It is a locational system-optimisation problem, and the answer cannot be found by setting a single national target for either gigawatts of transmission or gigawatt-hours of batteries.

The real question India's planners now face is:

For every renewable-rich location, what is the least-cost combination of flexible demand, existing-grid optimisation, BESS, transmission reinforcement, generation flexibility and residual curtailment?

The objective of the energy transition was never to save every possible unit of renewable electricity. It is to deliver reliable electricity at the lowest full system cost — and in a country where renewable surplus is as geographically concentrated as India's currently is, that cost is minimised corridor by corridor, not by a single national verdict on storage versus transmission.

Curtailment and peak-demand figures (8,133 GWh, April–June 2026; monthly breakdown) are drawn from the Minister of State for New and Renewable Energy's written reply to Parliament, reported by Reuters (28 July 2026) and citing Grid-India data. The T-GNA curtailment and state-concentration findings are drawn from ICRA's analysis as reported by pv magazine India (July 2026). The Rajasthan curtailment and loss estimates are attributed to the Rajasthan Solar Association as reported by Reuters. The CEEW reference is to "How can India Create a Demand Flexibility Market? A Roadmap for a Flexible Power System" (CEEW, June 2026). The decision-matrix classifications, the duration-crossover argument and the illustrative BESS-sizing calculations are original analytical constructs for this piece, not official figures.