As India accelerates its transition toward renewable energy, one challenge has become increasingly apparent: energy storage. Generating electricity through solar, wind, and other renewable sources is only one part of the equation; efficiently storing that energy for use when the sun isn’t shining or the wind isn’t blowing is equally crucial. Addressing this challenge is Tharam-Thiran Green Energy Flow, a Pune-based startup incubated at Venture Center Pune, which is developing long-duration, sustainable battery energy storage systems (BESS) tailored for the renewable energy sector.

Founded in 2020 by Dr. Umesh Vasu, 37, a mechanical engineer with a doctorate from IIT Madras, along with electrochemist Kaleeshkumar M and product developer Vaisakh V, the startup aims to provide cost-effective, scalable, and environmentally friendly solutions for energy storage. “As India rapidly increases its share of renewable energy and moves toward net-zero goals, the demand for robust BESS has become more urgent than ever,” says Umesh. “We observed that a one-size-fits-all battery solution cannot address the unique challenges of a renewable-dominated grid. In particular, long-duration storage spanning 10 hours or more remains technologically underdeveloped in India, yet it is critical to grid stability and energy security.”

The Problem: Limits of Conventional Batteries

Current battery technologies, Umesh explains, are largely limited to short-to-medium duration storage. Lithium-ion batteries, widely used for grid-scale energy storage, can efficiently discharge energy for only two to four hours. Extending their duration requires adding more battery cells, which increases cost, occupies more space, and can introduce safety concerns.

Vanadium flow batteries, another option for long-duration storage, face their own challenges. “Vanadium salts are expensive and subject to supply chain risks due to geopolitical factors,” says Umesh. “This makes scaling long-duration solutions financially prohibitive.” Moreover, the increasing mismatch between variable renewable generation and consumer demand amplifies the risk of energy curtailment and grid instability, creating an urgent need for affordable, scalable, and safe long-duration energy storage solutions in India.

Exploring a Solution: Sulfur-Iron Flow Batteries

In 2020, Umesh returned to his alma mater, IIITDM Kanchipuram, to focus on developing flow battery technology. Unlike conventional batteries, flow batteries separate energy storage from the cell itself. Energy is stored in liquid electrolytes in external tanks, which are pumped through a cell where chemical reactions charge or discharge electricity. This design allows the energy capacity to scale easily: “If you want the battery to last longer, you simply increase the volume of electrolytes in the tanks, without changing the cell hardware,” explains Umesh.

After evaluating various chemistries, the team chose sulfur-iron redox flow batteries. Sulfur and iron salts are abundant, inexpensive, and safe, offering a sustainable alternative to costly vanadium-based systems. “The electrolyte cost constitutes a major portion of long-duration storage systems,” Umesh notes. “Switching to iron-based chemistries dramatically reduces costs while maintaining performance and safety.”

The startup’s lab-scale prototypes initially achieved a current density of 10–40 mA/cm², whereas commercial viability requires 80–100 mA/cm². By experimenting with metal oxide coatings on electrodes and testing different materials, the team has now reached 80 mA/cm², marking a significant milestone on the path to commercialization.

Scaling Up: From Lab to Pilot

Despite progress at the lab scale, scaling up remains a challenge. “Our lab-scale battery produces 100W. To reach a 100 kW system suitable for industrial applications, we must first demonstrate technology viability to potential customers,” says Umesh. Their plan is phased: pilot testing a 5 kW system within the next 18 months, followed by the deployment of 100 kW commercial-scale batteries. Each stage is designed to validate performance, optimize manufacturing, and build confidence among solar power producers and other stakeholders.

Funding and Team Growth

Over the past five years, Tharam-Thiran Green Energy Flow has raised ₹1.5 crore (~$180,000) for R&D, prototyping, and testing. These funds have primarily gone toward materials, laboratory infrastructure, stack manufacturing, and validation studies.

Looking ahead, the startup plans to raise ₹2.5 crore over the next two years to finalize their Minimum Viable Product (MVP), secure intellectual property, complete certification processes, and implement pilot projects. For commercial-scale deployment, an additional ₹10 crore is projected over the subsequent two years to expand manufacturing, strengthen supply chains, enhance marketing, and forge strategic partnerships with utilities and industrial customers.

Currently, the core team consists of four members, but the company plans to expand to 20 professionals within two years, bringing together expertise in electrochemistry, mechanical engineering, and product development to accelerate the commercialization process.

Competitive Landscape

Globally, ZH Energy and Lucas Energy are among the leading players in long-duration energy storage, giving them first-mover advantages. However, Tharam-Thiran Green Energy Flow differentiates itself with its focus on 10–20-hour storage durations and systems above 50 kW, designed specifically for India’s renewable energy needs. “Our solution combines low-cost materials, safety, scalability, and local adaptability, making it ideal for India’s energy ecosystem,” says Umesh.

The Path Forward

The immediate goal is to complete pilot projects using the 5 kW system, providing real-world validation for performance, efficiency, and reliability. Within the next two years, the startup aims to scale to 100 kW systems, targeting commercial deployments with solar power companies, microgrids, and industrial energy consumers. This phased approach allows them to refine technology, optimize manufacturing, and establish a strong market presence before scaling further.

Impact on India’s Renewable Energy Future

By offering long-duration, cost-effective, and safe energy storage solutions, Tharam-Thiran Green Energy Flow addresses a critical bottleneck in India’s renewable energy transition. Effective energy storage ensures grid stability, reduces dependence on fossil fuels, and allows renewable energy producers to supply electricity consistently, even during periods of low generation.

As India moves toward ambitious net-zero targets and higher renewable energy integration, startups like Tharam-Thiran Green Energy Flow are poised to play a transformational role. Their innovation promises not only to enhance energy security but also to create sustainable, locally manufactured solutions that reduce costs and environmental impact.

In the words of Umesh Vasu, “Developing affordable, scalable, and long-duration batteries is no longer a luxury—it is a necessity for India’s renewable energy future. Our mission is to ensure that every kilowatt generated from sustainable sources can be effectively stored and reliably delivered when needed, making green energy a practical reality for all.”

---