Dual-Layer Optimization for H2-NH3 Integrated Energy System

The world is shifting its energy sources, moving away from burning coal and toward capturing power from the wind and the sun. This transition is essential for a cleaner future, but it brings a difficult puzzle: the wind does not always blow when people need electricity, and the sun does not shine at night. To keep the lights on, power grids often rely on large thermal power plants that burn fuel. These plants are reliable, but they struggle to adjust quickly to the unpredictable nature of renewable energy. When the wind blows too hard or the sun shines too brightly, the grid can become overwhelmed, forcing operators to waste the clean energy they have just generated. For years, engineers have looked for ways to store this excess power so it can be used later, but storing electricity directly is expensive and technically difficult.

A promising solution involves turning that extra electricity into a chemical fuel. One method creates hydrogen, a clean gas, but storing and moving hydrogen is tricky because it is very light and requires extreme pressure or freezing temperatures to handle safely. A newer approach uses a different chemical: ammonia. Ammonia is a liquid at much milder conditions, making it far easier to store and transport than hydrogen. It can also be burned directly in power plants to generate electricity, acting as a bridge between the fluctuating wind and sun and the steady needs of the grid. Researchers in China have now explored how to combine these ideas—using excess wind and solar power to make ammonia, and then burning that ammonia in coal plants—to create a more stable and efficient energy system.

In a study focused on a region in Inner Mongolia, a team of engineers from North China Electric Power University and the China Electric Power Research Institute designed a sophisticated plan to manage this complex mix of energy sources. They did not just look at the equipment; they built a computer model to simulate how a power grid would behave if it included wind turbines, solar panels, traditional coal-fired power plants, and a new facility that converts electricity into ammonia. The researchers wanted to see if they could run this entire system in a way that saved money, reduced pollution, and kept the power plants running safely. To do this, they created a two-step planning process, or a "dual-layer" model, that acts like a smart manager for the grid.

The first step of their plan focuses on how well the different parts of the system work together. The computer checks if the coal plants are changing their output too wildly, which can damage the machinery, and it calculates how much of the wind and solar power is being used versus wasted. The goal here is to find a balance where the renewable energy is absorbed as much as possible without forcing the coal plants to operate in unsafe ways. Once this balance is found, the second step of the plan kicks in to calculate the cost. This layer looks at every expense involved: the fuel for the coal plants, the cost of the ammonia, the wear and tear on the equipment, and the fees for carbon emissions. By running these two steps together, the model finds the single best way to operate the system for any given hour of the day.

The researchers tested their model using real data from a specific area in Ordos, Inner Mongolia, simulating both a typical winter day and a typical summer day. They compared three different scenarios to see which worked best. The first scenario was a baseline where the system tried to use every bit of wind and solar power available, even if it meant the coal plants had to run inefficiently. The second scenario applied their new two-step planning model but without the ammonia facility. The third scenario applied the same planning model but included the ammonia facility, where excess electricity is turned into ammonia and then burned in the coal plants.

The results showed that the new planning model made a significant difference. In the winter simulation, using the two-step model without ammonia already lowered the total operating cost by 4.4 percent compared to the baseline. When the ammonia facility was added into the mix, the cost dropped even further, reaching a total reduction of 0.97 percent in the summer scenario relative to the non-ammonia model. This saving came from several sources. The ammonia facility allowed the system to store excess renewable energy instead of wasting it. Furthermore, the process of making ammonia generates heat as a byproduct, which the system captured and used to warm buildings, reducing the amount of coal needed for heating. The coal plants also benefited because they no longer had to run at dangerously low levels to accommodate the wind and sun; instead, they could burn a mixture of coal and ammonia, which kept their operation smoother and safer.

Beyond the money, the environmental impact was also positive. The study found that carbon emissions decreased noticeably in the summer simulation, where the system with ammonia produced 4.43 percent less carbon dioxide than the system without it. In the winter, however, the system with ammonia produced slightly more emissions than the non-ammonia optimized model, though still less than the baseline scenario where all renewables were forced into the grid. This variation occurred because the trade-offs between fuel substitution, operational efficiency, and the specific mix of renewable generation differed between seasons. The researchers also observed that the amount of wind and solar energy that had to be thrown away dropped dramatically. In the winter, the system without ammonia wasted 17.66 percent of its wind power, but with the ammonia facility, that waste fell to just 2.27 percent. The system was able to absorb almost all the clean energy it generated.

The study also highlighted how the ammonia facility helped the power plants avoid "deep peak regulation," a stressful mode where a plant runs at very low power levels to match the grid's needs. Running at these low levels can cause metal parts inside the plant to crack and wear out faster. By using the ammonia system to soak up excess power, the coal plants were able to stay in a more stable, efficient operating range. The simulation showed that within the scheduling period, the facility produced about 91.2 tons of ammonia, which was enough to replace roughly 23.5 tons of standard coal. Additionally, the heat generated during the ammonia production saved another 9.3 tons of coal that would have been needed for heating.

While the model showed clear benefits, the researchers noted that it is a simulation based on specific data from Inner Mongolia. The results suggest that this approach is highly effective for regions with high amounts of wind and solar power, but the exact savings would depend on local conditions, such as the price of coal and the specific weather patterns. The study did not claim that this solution works everywhere or that it solves every problem in the energy grid, but it provided strong evidence that combining ammonia production with existing power plants is a viable path forward. The dual-layer optimization model proved to be a powerful tool for finding the right balance between cost, safety, and environmental protection.

Ultimately, the work demonstrates that the future of energy does not require choosing between renewable sources and reliable power. By using smart planning and chemical storage like ammonia, it is possible to integrate large amounts of wind and solar power without sacrificing the stability of the grid. The researchers showed that with the right strategy, a system can be cheaper, cleaner, and safer than one that relies on traditional methods alone. The findings offer a concrete example of how engineering can turn the challenges of renewable energy into opportunities for a more efficient and sustainable power supply.