Sarawak Energy is Malaysia’s largest renewable energy developer and a vertically integrated utility responsible for generation, transmission, retail, and electricity exports across the Malaysian state of Sarawak. Serving approximately 3 million people and around 800,000 account holders, the organization plays a central role in supporting economic growth and long-term energy security across the region.
With a system already heavily supported by hydropower, Sarawak Energy is now planning for the next stage of its energy transition. The utility has committed to phasing out coal and diesel generation over the next five to 10 years, while targeting net-zero emissions by 2050. At the same time, it is pursuing an aggressive renewable energy roadmap centered around large-scale solar expansion.
That growth introduces a new layer of complexity. Sarawak Energy currently operates around 50 MW of solar capacity but plans to increase that to 7,500 MW over the next 10 to 15 years. While the expansion supports decarbonization goals, it also creates operational challenges tied to solar variability and forecast uncertainty, surplus generation, curtailment risk, and increasingly volatile system dynamics.
To evaluate how different generation technologies could support this transition, Sarawak Energy used PLEXOS® long-term planning capabilities to assess the role of battery energy storage systems (BESS) in future capacity expansion planning.
As renewable penetration increases, long-term planning becomes significantly more complex. Utilities must balance cost, reliability, operational flexibility, fuel exposure, and future uncertainty, all while maintaining secure system operations.
For Sarawak Energy, one of the key questions was how to support large-scale solar growth without overbuilding thermal generation or increasing system inefficiencies.
The utility evaluated two primary candidate generation technologies as part of its long-term planning framework:
Each option presented tradeoffs.
CCGT capacity offered relatively fast construction timelines and lower upfront capital costs, but relied on liquefied natural gas (LNG), which was assumed to be roughly twice as expensive as fuel used in Sarawak Energy’s existing gas fleet.
CPS generation, meanwhile, benefited from low operating costs because it relied on water resources, but required significantly higher capital investment and longer development timelines.
At the same time, Sarawak Energy needed to understand whether adding battery storage to the system could improve flexibility, reduce curtailment, and lower overall system costs as solar penetration increased.
The challenge was not simply identifying which technologies to build. It was determining the optimal timing, scale, and mix of future investments while maintaining reliability targets and minimizing total system cost over the long term.
Sarawak Energy used the PLEXOS® Long-Term (LT) planning phase to model and compare long-term generation expansion scenarios.
PLEXOS® LT is designed to identify the least-cost expansion pathway by optimizing investment decisions over time. The platform minimizes total net present value (NPV) across system costs, including:
The study focused on two scenarios:
Both scenarios maintained the same solar assumptions and reliability targets. The key difference was whether PLEXOS® could economically justify battery storage within the system.
Sarawak Energy then used the LT results as inputs into short-term production cost modeling to validate operational outcomes and better understand dispatch behavior across both scenarios.
The modeling highlighted clear differences in investment decisions over time.
In both scenarios, PLEXOS® selected 1,000 MW of new CCGT capacity in 2031. However, the pathways diverged quickly after that.
In the scenario without battery storage, the model continued building additional CCGT capacity to meet system requirements. By 2040, the system added approximately 4,500 MW of CCGT generation.
In the scenario with battery storage, PLEXOS® selected approximately 2,000 MW of 4-hour BESS capacity while reducing total CCGT builds to roughly 3,000 MW.
The model also showed that CPS generation entered the system earlier in the BESS scenario, beginning around 2034 instead of after 2036.
Operationally, the differences became even more significant.
Without BESS, the system relied heavily on newly built CCGT units operating at a technical minimum of 60%. This created a more inflexible system structure and resulted in higher energy surplus levels.
With BESS included, the system was able to use existing generation assets more effectively, including existing gas, coal, hydro, and earlier CPS generation. Battery storage improved system flexibility and reduced the need to build additional thermal generation simply to satisfy capacity requirements.
The study also incorporated assumptions around battery round-trip efficiency, modeled at approximately 85%, alongside unit commitment constraints for CCGT generation.
The modeling results showed that adding battery storage created measurable economic and operational benefits for Sarawak Energy’s future system.
Most notably, the scenario with BESS delivered a lower overall system cost.
Over the 10-year study period, the battery-enabled scenario reduced total net present system cost by approximately $4 billion compared to the scenario without storage.
Although the BESS scenario required slightly higher upfront capital expenditure, those investments were offset by significantly lower operating costs over time.
The inclusion of storage also reduced the system’s dependence on LNG-fueled CCGT generation, helping mitigate exposure to higher fuel costs.
Beyond economics, the study showed that battery storage improved overall system flexibility.
In the non-BESS scenario, surplus energy across the system reached approximately 3,000 GWh over the study period. That surplus largely reflected solar curtailment and hydro spilling caused by inflexible thermal generation.
In contrast, the BESS scenario drastically reduced surplus energy levels by allowing the system to better absorb and shift renewable generation.
The results also demonstrated how storage can unlock greater value from existing generation assets rather than relying primarily on new thermal builds.
As solar penetration increased, the combination of battery storage and existing generation resources enabled more balanced dispatch outcomes and improved utilization across the system.
Sarawak Energy also identified several areas for future modeling development, including:
The utility noted that future studies will continue refining assumptions and validating reliability outcomes through iterative long-term and short-term modeling workflows within PLEXOS®.
Sarawak Energy’s study demonstrates how long-term capacity expansion planning is evolving as utilities manage growing renewable penetration, changing load patterns, and decarbonization targets.
Using PLEXOS®, the utility was able to evaluate how battery energy storage could support system flexibility, reduce thermal generation dependence, and lower overall system costs in a future grid with significantly higher solar penetration.
The results showed that storage was not simply an add-on technology. Within the modeled system, battery storage materially changed investment pathways, improved utilization of existing resources, accelerated the adoption of additional renewable generation, and reduced surplus energy across the network.
As Sarawak Energy continues progressing toward its net-zero goals and large-scale solar expansion plans, PLEXOS® provides a framework for testing future scenarios, validating operational outcomes, and making more informed long-term planning decisions.
For utilities managing increasingly dynamic power systems, the study offers a practical example of how integrated long-term and short-term energy modeling can help balance reliability, affordability, and decarbonization in a rapidly changing energy landscape.