Long-duration storage – the missing piece of the clean energy puzzle
- Speciale Invest
- Jan 12
- 5 min read
Storage solutions that can hold energy for days and weeks are urgently needed the world over
The arithmetic of the energy transition is increasingly clear. Solar and wind can now generate electricity at prices that rival, and even undercut, fossil fuels. “The business case for renewables is now stronger than ever,” as the International Renewable Energy Agency noted this year.
Yet grids across the world are still curtailing large volumes of clean power because they have nowhere to put it. In this gap between generation and usable supply sits one of the most important missing links of decarbonisation: long-duration energy storage.
Analysts estimate that globally between 50 and 70 terawatt-hours of renewable electricity are wasted each year through curtailment, roughly 5–15 per cent of output in some high-penetration markets. In Europe, grid operators cut back around 11 per cent of renewable generation during the summer of 2025 as transmission and balancing constraints bit.
In India, Rajasthan alone has curtailed 3–4GW of solar capacity since March 2025, with industry estimates pointing to losses of around Rs. 250 crore. Chile curtailed some 11,900GWh of renewables between 2022 and May 2025, equal to millions of tonnes of avoided carbon that never materialised.
This is not simply a matter of a few hours’ mismatch between supply and demand. Regions with strong wind resources, such as northern Europe, often see surpluses in winter nights and deficits in summer lulls. Solar-heavy systems, from Rajasthan to California, produce more power than they can absorb in sunny months and then fall short in monsoon or winter.
The challenge is seasonal as much as it is daily. Once renewables approach 60–70 per cent of a grid’s annual mix, systems need storage that can hold energy not just for four or six hours, but for days or even weeks.
Notes that at very high shares of wind and solar PV (e.g., 70–80%), electricity will need to be stored over days, weeks or months, and stresses the need for long‑term storage to smooth supply over those timescales.
For systems with >70% VRE in annual generation, the IEA finds that flexibility needs extend to seasonal timescales, requiring resources that can provide flexibility throughout the year, including over weeks.
Most of today’s technologies are not built for that job. Lithium-ion batteries, whose costs have fallen by nearly 90 percent since 2010, are well suited to short-duration tasks: shaving peaks, shifting solar output into evening hours and providing fast frequency response. But their economics deteriorate when stretched to multi-day applications.
States that, “even with these cost declines, lithium‑ion battery storage is unlikely to be cost‑effective for multi‑day storage durations,” while alternative LDES technologies can provide such durations at lower system cost.
The capital intensity of adding more storage hours, combined with degradation and safety requirements, makes very long-duration projects expensive. Flow batteries can in principle store energy for longer, but still struggle with efficiency, membrane cost and system complexity, limiting their commercial use mainly to sub-24-hour durations. Pumped hydro can store vast quantities of energy, yet it is bound by geography, heavy civil works and long permitting timelines. Gravity and thermal systems show promise but remain early in deployment and constrained to specific sites.
Against that backdrop, long-duration energy storage (LDES) has moved from engineering curiosity to a defined market category. The global LDES market is projected to grow from about $4.8 billion in 2024 to more than $10.4 billion by 2030, a compound annual growth rate of roughly 13–14 percent.
Within that, systems able to discharge for more than 36 hours are expected to grow fastest, at more than 20 percent per year, as grids seek solutions that can ride through multi-day weather events and extended supply shortfalls. North America is currently in the lead, driven by aggressive renewable targets, coal retirements and grid-modernization plans.
India’s challenge is sharper still. We have pledged 500GW of non-fossil capacity by 2030. To integrate that power without crippling curtailment or instability, the Central Electricity Authority projects the need for around 411GWh of storage by 2031–32, split between roughly 236GWh of battery systems and 175GWh of pumped hydro.
Market researchers estimate that India’s energy storage base will grow from a few hundred megawatt-hours today to more than 6,600MWh by 2033, implying annual growth rates above 40 percent. If these numbers materialise, storage will sit alongside transmission as the main enabling infrastructure for the next phase of the country’s power system.
It is into this structural bottleneck that Sthyr Energy positions itself. The company is developing zinc–air systems designed specifically for long-duration and seasonal storage. Unlike lithium-ion, which relies on globally concentrated supply chains for lithium, cobalt and graphite, Sthyr’s technology is based on zinc, water and air — materials that are widely available in India.
Sthyr’s mechanically rechargeable architecture separates the charging and discharging processes- allowing to store energy directly in metallic zinc, while decoupling power & energy components. In principle, this allows the duration of storage to be extended by adding low-cost zinc-based energy modules, without proportionally increasing the cost of the power conversion hardware.
The focus is not on replacing lithium-ion in its existing niches, but on filling a gap that short-duration batteries and conventional assets do not address well.
For grid operators facing rising curtailment of wind and solar—like CAISO's 3.4M MWh in 2024 (up 29% YoY) a 100-hour battery capable of repeated, deep cycling across seasons turns stranded electrons into dispatchable capacity by avoiding 3–9% renewable waste providing firm power during 5+ day lulls, deferring T&D upgrades and enhancing grid stability slashing curtailment costs up to 80%.
For states and utilities under pressure to retire ageing gas-peaker plants, long-duration batteries offer a cleaner alternative that can still respond when demand spikes for several days, not just a single evening. Studies of peaker replacement in markets such as the United States have already shown that four-hour batteries can compete with new gas units on cost for certain applications; extending duration widens the scope of what storage can displace.
India’s own policy framework is nudging in this direction. Energy-storage obligations, peaking reserve requirements and tenders that explicitly call for six-hour-plus solutions signal that regulators expect storage to play more than a marginal role. Yet the technologies deployed must match the profile of the problem: multi-day, seasonal and increasingly linked to questions of supply-chain resilience.
In that sense, Sthyr’s work is less about a single product and more about where it sits in the energy system. Long-duration storage does not grab attention in the way that vast solar parks and offshore wind farms do. But if clean generation is to move from the margins toward dominance of the power mix and eventually to 100% RE, the infrastructure that allows it to be stored across time will be a central determinant of success. The puzzle pieces for a low-carbon grid are being assembled, and without reliable long-duration storage, the picture will remain incomplete.
