Gravity-Based Power: Eskom and Energy Vault Forge Strategic Alliance to Reshape South African Grid

In a landmark move for the African energy landscape, South Africa’s national public utility and transmission system operator (TSO), Eskom, has entered into a strategic development agreement with Energy Vault, a leader in sustainable, gravity-based energy storage technology. This partnership marks a pivotal step in South Africa’s "Just Energy Transition" (JETP), aiming to modernize a grid long plagued by reliability issues and chronic load shedding while pivoting the nation toward a renewable-heavy future.

The collaboration centers on the deployment of Energy Vault’s proprietary gravity energy storage systems (GESS), with an initial pilot project earmarked for the Hindrina Power Station in Mpumalanga province. This agreement is not merely a pilot; it represents a scalable roadmap that could eventually see up to 4GWh of long-duration energy storage (LDES) deployed across the 16 member states of the Southern African Development Community (SADC).

The Core Technology: Turning Gravity into Stability

Energy Vault’s gravity-based storage technology functions on a principle similar to traditional pumped hydro—a proven method for grid balancing—but utilizes mechanical rather than hydraulic potential energy. The system works by lifting heavy composite blocks using renewable energy during periods of excess generation. When the grid requires power, these blocks are lowered, driving turbines to convert the potential energy back into electricity.

A unique feature of this design is the composition of the blocks. Rather than utilizing materials that require intensive resource extraction, Energy Vault’s systems are designed to incorporate industrial waste and byproducts, specifically coal ash. Given that South Africa’s energy sector has been historically dependent on coal, this creates a circular economic model: the infrastructure that once powered the nation’s coal-fired plants will be repurposed to store renewable energy using the very byproduct of those plants’ historical operation.

Chronology and Strategic Milestones

The agreement follows a period of intense scrutiny and diversification for Energy Vault. Since the company’s first successful commissioning of an operational gravity energy storage system in Rudong, China, the technology has remained a focal point of industry discussion.

• Early Development: Energy Vault established its foothold in China through strategic partnerships, proving that the gravity-based mechanism could function at scale within a national grid.
• The 2023 Pivot: Facing market skepticism regarding the viability of gravity storage, CEO Rob Piconi steered the company toward a multi-technology approach. This included integrating short-duration battery energy storage systems (BESS) and green hydrogen into the company’s portfolio, positioning Energy Vault as an owner-operator of diverse energy assets.
• Expansion and Testing: Throughout 2024 and 2025, the company navigated the challenges of a maturing energy market. Despite the high-profile closure of UK-based competitor Gravitricity, Energy Vault continued to refine its EVx 2.0 architecture.
• The South African Deal (2026): The formalization of the partnership with Eskom marks the first major international deployment of the EVx 2.0 platform, specifically tailored for the unique challenges of the South African grid.

Supporting Data and Technical Specifications

The initial project at the Hindrina Power Station is slated for 25MW/100MWh. While this serves as a foundation, the technical design allows for rapid scalability. According to the development agreement, the system can be scaled to reach up to 4GW of total capacity.

Energy Vault’s role extends beyond the mere delivery of hardware. The firm is providing:

1. On-site Engineering: Full-service deployment of the EVx 2.0 system.
2. Project Management: Integrated logistics and construction management to ensure adherence to local regulations.
3. Capacity Building: Specialized training programs for the local workforce, a critical requirement for the socio-economic mandates of the JETP.

The scale of the SADC-wide ambition—up to 4GWh—is particularly significant. By focusing on LDES, the project addresses the "intermittency gap" inherent in solar and wind power, allowing the grid to hold energy for extended periods, far beyond the capabilities of standard lithium-ion battery arrays currently being deployed in other South African schemes.

Official Responses and Industry Context

Energy Vault has framed this partnership as a solution to two of the most pressing issues in Southern Africa: energy security and sustainable industrial transition.

"This partnership is in direct alignment with our Just Energy Transition initiative," a representative for the project noted. By ensuring that the transition away from coal does not lead to job losses or the abandonment of industrial sites, the project serves as a model for how emerging economies can leverage new technologies to revitalize existing infrastructure.

However, the technology remains a subject of debate. Critics have long questioned the efficiency losses inherent in mechanical storage compared to electrochemical alternatives. In response, Energy Vault has consistently emphasized the "total system cost" advantage. By using onsite coal ash, the company significantly reduces the cost of raw materials for the blocks, while the modularity of the design allows for deployments in regions where traditional hydro or large-scale battery farms might be geographically or economically unfeasible.

The broader market context is also shifting. With Energy Vault reaffirming its 2026 revenue guidance of US$225–300 million, investors are keeping a close watch on how these international partnerships influence the company’s bottom line. The success of the South African project could serve as the definitive "proof of concept" required to silence remaining doubts regarding the viability of gravity-based storage in Western and African markets.

The Implications for the South African Grid

Eskom has faced a tumultuous decade, defined by the "load shedding" crisis—a series of planned blackouts necessitated by the failure of aging coal-fired assets to keep pace with demand. While recent efforts have seen the grid run for over 300 days without such measures, the stability remains fragile.

The introduction of 4GWh of LDES capacity is expected to act as a buffer for the grid as more intermittent solar and wind capacity is brought online. Unlike lithium-ion, which is typically optimized for short-duration frequency regulation (1–4 hours), gravity-based systems are theoretically capable of longer discharge durations, making them an ideal partner for stabilizing the grid during long periods of low renewable output.

Furthermore, the social dimension cannot be overstated. Mpumalanga has been the heart of South Africa’s coal mining industry for generations. The conversion of the Hindrina Power Station into a hub for advanced energy technology represents a tangible effort to preserve the economic vitality of the region. By repurposing coal ash—a waste product—into the storage medium for future-proofed, green energy, the project symbolically closes the loop on the coal era.

Challenges Ahead

Despite the optimism, the project faces significant hurdles:

• Infrastructure Integration: Retrofitting an existing coal-fired power station for a new technology requires complex engineering to ensure the grid interconnection remains stable during the transition.
• Capital and Financing: While the partnership is "strategic," the sheer scale of a 4GW deployment requires massive capital expenditure. The ability to secure funding, likely through a mix of international climate finance and private equity, will be the true test of the partnership’s sustainability.
• Corruption Allegations: Eskom has historically battled internal corruption, which has hampered past infrastructure projects. The transparency of this new partnership will be closely scrutinized by international observers and stakeholders to ensure that the project delivers on its promises without being derailed by bureaucratic or financial mismanagement.

Conclusion

The collaboration between Eskom and Energy Vault is an ambitious undertaking that sits at the intersection of climate action, economic development, and grid engineering. By moving beyond the reliance on lithium-ion batteries and embracing mechanical, gravity-based storage, South Africa is attempting to leapfrog traditional energy limitations.

If the Hindrina pilot proves successful, it will not only solidify Energy Vault’s position as a global leader in LDES but will also provide a blueprint for other developing nations seeking to decarbonize while maintaining grid stability. As the world watches, the transformation of coal ash into the building blocks of a cleaner future may well prove to be one of the most innovative chapters in the history of the Just Energy Transition.