Overview
Redstone Solar Thermal Power (RSTP) is an operational solar power tower facility located in Postmasburg, near Kimberley, in the Northern Cape Region of South Africa. The plant utilizes concentrated solar power technology with molten salt energy storage, enabling it to deliver consistent electricity generation. With an installed capacity of 100 MW, the facility is designed to supply power to approximately 200,000 people. The project was developed under bid window 3.5 of the Renewable Energy Independent Power Producer Procurement Programme (REIPPP) and was awarded in 2015 at a strike price of 122.3 ZAR/KWh, incorporating time-of-day pricing mechanisms.
The development of Redstone Solar Thermal Power involved significant technological and contractual milestones. The project initially relied on technology from Solar Reserve, a company that subsequently faced bankruptcy, leading to delays in the signing of the Power Purchase Agreement (PPA) with Eskom, which was finalized in 2018. After the project was revived, construction proceeded over a four-year period. The plant was officially connected to the grid for the first time in May 2025, marking the culmination of years of engineering and logistical efforts. The technology for the plant is provided by Brightsource and John Cockerill, building on demonstrations from the Noor Energy 1 project in the UAE.
Operated by ACWA Power, Redstone Solar Thermal Power represents a key addition to South Africa’s renewable energy infrastructure. The facility’s operational status as of 2025 underscores its role in diversifying the national energy mix and enhancing grid stability through advanced solar thermal storage capabilities.
Why it matters
Redstone Solar Thermal Power (RSTP) represents a significant milestone for concentrated solar power (CSP) technology in South Africa, marking the successful deployment of a 100 MW solar power tower with molten salt energy storage in the Northern Cape Region. As part of the Renewable Energy Independent Power Producer Procurement Programme (REIPPP), specifically awarded in bid window 3.5 in 2015, RSTP underscores the strategic importance of CSP in diversifying South Africa’s energy mix. The project was initially based on the technology of Solar Reserve, but faced delays due to the late signing of the Power Purchase Agreement (PPA) by Eskom in 2018. Despite these challenges, the plant was revived and constructed over four years, connecting to the grid for the first time in May 2025.
The significance of RSTP extends beyond its capacity to deliver power to approximately 200,000 people. It plays a crucial role in the local solar park alongside other major projects such as Lesedi and Jasper PV. This integration highlights the collaborative effort to enhance renewable energy infrastructure in the region. The technology provided by Brightsource and John Cockerill, as demonstrated in the Noor Energy 1 project in the UAE, further validates the reliability and efficiency of CSP technology in diverse geographical settings.
Project Statistics
| Parameter | Value |
|---|---|
| Entity Type | Solar Farm |
| Primary Fuel/Source | Solar |
| Country | South Africa (ZA) |
| Operational Status | Operational |
| Capacity | 100 MW |
| Operator | ACWA Power |
| Commissioned | 2025 |
| Strike Price | 122.3 ZAR/KWh |
| Location | Postmasburg, near Kimberley, Northern Cape |
| Technology Providers | Brightsource, John Cockerill |
In conclusion, Redstone Solar Thermal Power is not just a testament to the resilience of CSP technology but also a vital component of South Africa’s renewable energy strategy. Its successful commissioning in 2025, after overcoming initial setbacks, demonstrates the potential for large-scale solar projects to contribute significantly to the nation’s energy security and sustainability goals.
How does solar thermal power with molten salt storage work?
Redstone Solar Thermal Power utilizes concentrated solar power (CSP) technology, specifically the solar power tower configuration, to generate electricity. Unlike photovoltaic (PV) systems that convert sunlight directly into electricity using semiconductor cells, CSP systems use mirrors to concentrate solar radiation onto a single receiver. At Redstone, this is achieved through a field of heliostats—large, computer-controlled mirrors that track the sun’s movement across the sky and reflect its rays toward a central tower. The concentrated sunlight heats a working fluid within the receiver located at the top of the tower.
Molten Salt Energy Storage
A defining feature of the Redstone plant is its integration of molten salt energy storage, which allows for dispatchable power generation. The system employs a two-tank direct storage configuration. The molten salt, typically a mixture of sodium nitrate and potassium nitrate, circulates through the receiver where it is heated to high temperatures, often exceeding 400°C to 560°C. The hot salt is then pumped into a hot storage tank, while cooler salt from a cold storage tank is circulated back to the receiver. This thermal energy storage system provides significant operational flexibility. According to the project specifications, the molten salt storage capacity allows for approximately 12 hours of full-load power generation. This means the plant can continue to produce electricity even when the sun is not shining, such as during peak evening demand or on cloudy days, by using the stored thermal energy to generate steam and drive a turbine.
Comparison to Photovoltaic Technology
The choice of solar thermal power with molten salt storage offers distinct advantages over traditional photovoltaic (PV) systems, particularly in terms of grid stability and dispatchability. PV panels generate electricity only when sunlight is directly hitting the cells, requiring battery storage (typically lithium-ion) to smooth out production. In contrast, the thermal inertia of molten salt provides a cost-effective and durable storage medium for large-scale plants like Redstone. The 100 MW capacity of Redstone, operated by ACWA Power, demonstrates how CSP can deliver consistent power output, complementing the variable nature of solar PV. The technology, provided by Brightsource and John Cockerill, leverages proven engineering from projects such as Noor Energy 1 in the UAE, ensuring reliable performance in the Northern Cape region. This approach addresses one of the primary challenges of solar energy: matching generation with consumption patterns, thereby enhancing the reliability of the South African power grid.
History
Redstone Solar Thermal Power (RSTP) was awarded in bid window 3.5 of the Renewable Energy Independent Power Producer Procurement Programme (REIPPP) in 2015. The project was initially developed using technology from SolarReserve, with a strike price of 122.3 ZAR/KWh including time-of-day pricing. Despite the early award, the project faced significant delays because the Power Purchase Agreement (PPA) with Eskom was not signed until 2018. SolarReserve subsequently went bankrupt, further complicating the development timeline.
Following the bankruptcy of the original technology provider, the project was revived under the operation of ACWA Power. The technology for the solar power tower with molten salt energy storage was provided by Brightsource and John Cockerill, similar to the Noor Energy 1 project in the UAE. Construction began after the revival, lasting four years. In May 2025, the plant was connected to the grid for the first time, marking the operational start of the 100 MW facility located in Postmasburg, near Kimberley in the Northern Cape Region of South Africa.
Timeline of Development
| Year | Event |
|---|---|
| 2015 | Awarded in REIPPP bid window 3.5; initial technology based on SolarReserve. |
| 2018 | Power Purchase Agreement (PPA) signed by Eskom. |
| Post-2018 | SolarReserve bankruptcy; project revived by ACWA Power. |
| 2021-2025 | Construction phase lasting four years. |
| May 2025 | First connection to the grid; operational status achieved. |
What caused the delays in the Redstone project?
The development of the Redstone Solar Thermal Power (RSTP) plant was characterized by significant temporal gaps between its initial award and final grid connection. Despite this early selection, the project faced immediate administrative hurdles. The Power Purchase Agreement (PPA) with Eskom, the national grid operator, was not signed until 2018, resulting in a three-year delay that pushed the project into a period of financial uncertainty.
Technological and Financial Instability
A critical factor in the project's stagnation was the reliance on technology from SolarReserve, a company that subsequently declared bankruptcy. The project was initially based on SolarReserve’s technology, but the developer’s insolvency in 2020 further complicated the development timeline. This bankruptcy necessitated a strategic pivot in technology providers. The transition from a bankrupt original technology provider to new international partners required significant renegotiation and engineering adjustments.
Construction and Commissioning
Following the resolution of financing and technology issues, the project moved into the construction phase. Financing was completed in 2019, setting the stage for physical development. The construction period lasted four years, reflecting the complexity of deploying a 100 MW solar power tower with molten salt storage in the Northern Cape Region. The plant was finally connected to the grid for the first time in May 2025, marking the end of a decade-long development cycle that began with its 2015 bid award. The delays highlight the risks associated with relying on single-technology providers in large-scale renewable energy projects and the importance of timely PPA execution in the South African energy market.
Construction and technical specifications
The project was initially based on the technology of Solar Reserve, a company that subsequently became bankrupt. Development faced significant delays as the power purchase agreement (PPA) was not signed by Eskom until 2018, despite the project being awarded in bid window 3.5 of the Renewable Energy Independent Power Producer Procurement Programme (REIPPP) in 2015. The plant was awarded at a strike price of 122.3 ZAR/KWh, which included time of day pricing.
Technical Specifications
The technology provided for the plant is supplied by Brightsource and John Cockerill. This specific technological configuration was previously demonstrated in the Noor Energy 1 project in the UAE. The plant features a tower height of 248 meters and utilizes 40,000 heliostats to concentrate solar radiation. The use of molten salt allows for energy storage, enhancing the plant's ability to deliver power beyond immediate solar irradiance.
Construction and Grid Connection
Following the revival of the project after the initial delays, construction proceeded over a period of four years. In May 2025, the plant was connected to the grid for the first time, marking the end of the construction phase. The operator of the facility is ACWA Power. The plant is currently operational, having been commissioned in 2025. The successful grid connection in May 2025 followed the four-year construction timeline initiated after the PPA signing in 2018.
Economic and operational details
The winning bid established a strike price of 122.3 ZAR/KWh, a tariff structure that included time-of-day pricing mechanisms to optimize energy delivery relative to peak demand periods. Despite the initial award in 2015, the financial closure and contractual stability were delayed because the Power Purchase Agreement (PPA) was not signed by Eskom, the national utility, until 2018. This three-year gap between the bid award and PPA signing represents a significant period of financial holding for the project stakeholders.
Financial and Operational Metrics
| Metric | Value | Context |
|---|---|---|
| Strike Price | 122.3 ZAR/KWh | REIPPP Bid Window 3.5 (2015) |
| PPA Signing Year | 2018 | Agreement with Eskom |
| Grid Connection | May 2025 | First connection after construction |
| Construction Duration | 4 years | Post-revival construction phase |
| Target Beneficiaries | 200,000 people | Estimated power delivery reach |
The project's operational timeline was significantly impacted by the initial technology provider, Solar Reserve, which became bankrupt. This corporate failure necessitated a revival of the project, leading to a change in technology providers to Brightsource and John Cockerill. The construction phase, following this revival, lasted for 4 years, culminating in the plant's first connection to the grid in May 2025. The operational status is now listed as operational, with a commissioned year of 2025.
The economic model relies on the 100 MW capacity to deliver power to an estimated 200,000 people, leveraging the molten salt energy storage technology to provide dispatchable solar power. The involvement of Brightsource and John Cockerill brings technology demonstrated in the Noor Energy 1 project in the UAE, suggesting a reliance on proven international engineering standards to mitigate risk after the initial Solar Reserve failure. The 122.3 ZAR/KWh strike price remains a key financial benchmark for the project's revenue generation over its operational life, although specific details regarding the total operational lifespan or job creation numbers are not explicitly detailed in the provided grounding snippets beyond the beneficiary count.
Location and surrounding infrastructure
The Redstone Solar Thermal Power plant is situated in Postmasburg, a town located in the Northern Cape province of South Africa. This region is characterized by its arid climate and high solar irradiance, making it a strategic location for solar energy infrastructure. The facility is positioned near Kimberley, serving as a key node in the growing renewable energy landscape of the Northern Cape. According to the project documentation, the plant is designed to deliver power to approximately 200,000 people, integrating into the local grid to support regional energy demands.
Regional Solar Clusters
Postmasburg has emerged as a significant hub for solar power generation in South Africa. The Redstone project is not an isolated installation but is part of a broader concentration of solar infrastructure in the area. The region hosts other major solar facilities, including the Lesedi and Jasper photovoltaic (PV) projects. These installations contribute to a combined solar park capacity of 271 MW in the vicinity, creating a synergistic effect on the local transmission grid and land use planning.
The proximity of these projects allows for shared infrastructure benefits and optimized grid connections. The Lesedi and Jasper PV projects, alongside Redstone, illustrate the strategic clustering of renewable energy assets in the Northern Cape. This concentration supports the South African government's Renewable Energy Independent Power Producer Procurement Programme (REIPPP), specifically under bid window 3.5, where Redstone was awarded. The strike price for Redstone was set at 122.3 ZAR/KWh, reflecting the competitive nature of the regional solar market.
The development of these solar parks has transformed the local economic and infrastructural landscape of Postmasburg. The area has seen increased investment in transmission lines and grid stability measures to accommodate the influx of solar power. The presence of multiple large-scale solar facilities, including the 100 MW Redstone plant, underscores the Northern Cape's role as a primary driver of South Africa's solar energy expansion. The region's ability to host such a dense cluster of solar projects highlights its potential for further renewable energy development and grid integration.