A Modular Power Plant Is Steaming Up Kenya's Geothermal Efficiency

Sosian Menengai Geothermal Power, Kenya’s newest geothermal power plant, is powered by modular technology that maximizes efficiency, reduces costs, and enhances scalability.

Kenya’s scenic Rift Valley region is a literal hotbed of geothermal potential. Part of the vast East African Rift Valley System (EARS), a 6,400-kilometer (km) tectonic divergence that is cleaving the African continent into two plates, Kenya’s Rift Valley forms a vertical corridor of intensive faulting and volcanic activity, hot springs, fumaroles, and sulfur-oozing fissures. But while the country began geothermal exploration for power development in the 1950s, most of its investments have been focused on the Olkaria region situated within Hell’s Gate National Park near the flamingo-flecked Lake Naivasha in Nakuru County. Five of six geothermal power stations in Olkaria are owned by KenGen (with a combined capacity of 799 MW), while Nevada-based Ormat Technologies owns a 150-MW plant. Olkaria plants in 2023 provided nearly 45% of Kenya’s total generation, a sizeable contribution to the East African powerhouse’s meager 3.3-GW installed capacity.

In 2008, the Geothermal Development Co. (GDC), a state-owned special-purpose vehicle tasked with accelerating the nation’s geothermal resource development, expanded its focus to the Menengai region just north of Olkaria, at the site of a massive shield volcano with one of the biggest calderas in the world. While GDC says the Menengai complex harbors a potential of 1,600 MW, its long-term goal is to develop 465 MW of geothermal steam equivalent.

In 2013, it took the first step to competitively award the first three initial 35-MW power projects at the complex to three independent power producers (IPPs): Orpower 22 (a former subsidiary of New York firm Symbion now owned by China’s Kaishan Group), South African-based Quantum Power East Africa (now majority owned by UK firm Globeleq), and Nairobi-headquartered Sosian Energy. In August 2023, the first of these projects—Menengai III, now formally known as the Sosian Menengai Geothermal Power—wrapped up a 16-month construction timeframe and began delivering first power to the grid.

A Technology Breakthrough

Sosian’s condensed timeframe is especially stunning given that traditional geothermal development can exceed seven years. This is owing in part to a complex process that involves drilling and testing multiple wells, selecting a centralized power plant location, ordering steam turbines, and constructing extensive steam collection and reinjection systems. The traditional approach is also ridden with risks, including significant delays and inefficiencies, such as energy losses from steam pressure drops, thermal losses over long distances, and the underutilization of wells with varying pressures.

Sosian, to some measure, had the benefit of the GDC’s public-private partnership model for developing Menengai, under which the GDC assumes upfront risks of geothermal development. The state company has also notably set out to develop the field in five phases, starting with a 105-MW “steam sales” model, where it supplies steam from drilled wells to the power plants via a 25-km steam gathering and piping system. As of 2023, GDC had drilled 53 wells with a potential of 169 MW.

However, the power plant’s success can also be attributed to a distinctive new geothermal development process introduced by China’s Kaishan Group. Dr. Tang Yan, general manager of Kaishan Group, recalled realizing the need for a dramatic shift at a 2015 geothermal conference in Melbourne, Australia, where experts discussed the pitfalls of conventional methods. “I said, ‘Why don’t you put a power plant on the wellhead and do it phase by phase?’ ” he recounted.

Overcoming Traditional Challenges

While the approach proposed to support incremental power production from the start while providing revenue to support future project expansion, Yan learned no technology to support the approach was commercially available. Kaishan, which had then already begun its transition from a giant Shanghai-headquartered air compressor maker to a diversified global company, jumped into action to leverage its 2012-developed Organic Rankine Cycle (ORC) expander and screw steam expander technologies.

The technologies—originally developed for waste heat recovery from refineries and steel mills—allowed Kaishan to optimize geothermal power generation by maximizing energy output from varying well conditions, reducing inefficiencies, and enabling the development of four types of decentralized, modular power plants that are quicker to deploy and more adaptable to different geothermal fields, Yan told POWER. “These modular power plants include the steam screw expander modular power plants, the steam ORC modular power plants, the brine ORC modular power plants, and the steam and brine dual resource modular power plants,” he explained.

Steam screw expanders are specifically designed to handle wet or saturated steam, which is common in geothermal wells, effectively extracting energy from a wider range of well conditions, including wells with high non-condensable gas (NCG) content that may not be suitable for traditional turbines. ORC systems, meanwhile, are adept at converting lower-temperature steam and brine—byproducts that would otherwise go to waste—into additional electricity, Yan said.

In addition, Kaishan’s modular plants can be used to form hybrid cycles or thermal systems to meet any production well conditions, maximize their power output, and eliminate low-head pressure (WHP) wasted wells or idling wells. Because the technologies can be adapted to specific geothermal resource conditions at different project sites, they can be tailored to provide stellar efficiency, he said. “We can improve the well thermal efficiency of, for example, medium enthalpy wells, to up to 18% and 19%,” he said. That compares to only 8% to 12% for traditional centralized power plants that only use single-flash steam, he noted.

A Competitive Edge for New Geothermal Power

Kaishan quickly expanded the niche technology into a lucrative business. Since it put online the first of four phases of the 240-MW Sorik Marapi Geothermal Project in Indonesia in 2018, it has built the 10-MW Sokoria Geothermal, also in Indonesia, alongside projects in Turkey, the U.S., and Hungary. At Sosian, Kaishan’s first project in Kenya, the company served as the engineering, procurement, and construction (EPC) contractor.

According to Yan, Kaishan’s cost-effective price point proved a crucial selection advantage. Kaishan’s EPC contract is valued at $65 million, compared to a $108 million EPC contract recently awarded for Menengai II, one of the region’s three equally sized IPP projects. The price difference is rooted in the technology selection, Yan explained. While Sosian’s 35-MW project was designed as a centralized power plant, it is powered by two steam screw expanders and three wet steam ORC modular power plants.

However, GDC’s steam contains 3.3% NCG—which represents a “huge percentage,” he said. If Sosian used traditional steam turbines, they would need to expand steam at 6 bar absolute and then consume more then 30 tons of steam per hour to remove NCG using steam injectors and vacuum pumps. Instead, Sosian employs steam screw expanders and a bottom cycle to handle the saturated steam discharge, reducing the steam to atmospheric levels throughout the entire process while eliminating the parasitic power typically consumed by vacuum systems.

“The overall efficiency compared to a traditional steam turbine is a huge game changer for this site,” Yan said. “The project only needed a guarantee of 33.25 MW, and the target was 35 MW, but we’re actually generating 37 MW.” At the same time, the project doesn’t need to purchase the extra 10% of steam for a steam injector, putting less of a burden on the GDC, he said.

A Solution for Idled Wells

The modularity of the system also proved beneficial to speed up construction and, crucially, to overcome supply chain and project management challenges posed by the COVID pandemic, Yan said. Kaishan typically assembles the modules and conducts component testing in a factory setting over six to nine months, he said. “And then, when we ship to the site, usually it takes a very short time to put them together, and you don’t need to do any welding on the power modules,” he added. “That’s sometimes where quality control can be a challenge,” he noted.

The success of the Sosian Menegai project has so far sparked significant interest in Kenya’s geothermal industry, Yan said. A key reason is that Kenya has a lot of wells, and an estimated 25% to 30% of those wells may not be supported by a steam collection system, which is needed by centralized steam turbines. “They call them idled wells or wasted wells, and they sit there and do nothing,” even if it was costly to drill them, he said. “But our technology doesn’t have that limitation because we can use any good pressure, whether they can produce brine or steam.”

—Sonal Patel is a POWER senior editor (@sonalcpatel, @POWERmagazine).