How can renewable energy be integrated at a high level in the power system? What is the path to achieving a large share of renewable energy applications? The requirements for inverters differ at each stage. Currently, the main approach is combining distributed energy with storage to form microgrids, and the automation inverters used at different stages are completely different.
The application of high-penetration renewable energy is mainly divided into four stages: distributed photovoltaic development, distributed plus energy storage, multi-energy complementary microgrids, and regional energy management platforms. In the past two years, distributed PV has developed rapidly. The relationship between distributed generation and the grid helps reduce losses from long-distance transmission. However, the distributed scale is small, the number is large, geographically dispersed, invisible, and hard to schedule, making management challenging. Instant delivery is rigid and not grid-friendly. Some areas face over-generation, but regulations limit it. In many regions, only 25% of the park’s power grid communication is allowed, and when clusters are connected to the grid, only 10% of the grid is exchanged.
Distributed PV must be used in high proportion, so adding energy storage is essential. But how much storage is needed? Can we just add storage arbitrarily? A key issue with adding storage is that volatility must be addressed. The variability of wind and solar is real. Now, new energy is replacing traditional energy, and solving this volatility requires traditional methods. You need to prepare a plan. As the percentage increases, it becomes harder to break through technologically. Energy storage costs are still high, and reducing electricity costs is crucial. System cost reduction is important. The biggest problem is lowering the cost of power supply. How to improve system efficiency? In the same system, an energy storage system can achieve 85% efficiency, while lithium batteries reach 90%. Electricity costs are significant. Many batteries don’t change much after running for a while, but they float. Online adjustments and replacements are necessary, requiring technological breakthroughs.
In the Shanghai project, fixed costs have dropped to about 0.5 yuan, and the peak-to-valley electricity price difference is 0.91 yuan. In Tibet, a pure energy storage system uses lead-carbon and lithium batteries, reducing electricity costs to 0.45 yuan. However, the conditions from the Tibet Power Bureau are favorable. The on-grid PV price is 1.15 yuan, but Tibet PV has 30%, which gives us a few cents. For an energy storage system to be profitable, focusing on electricity costs is key. If this is achieved, the market potential is vast. Battery manufacturers believe that battery costs will drop below 50% in the next three years, leading to electricity costs of just three cents, creating infinite opportunities.
A high penetration of renewable energy requires solving the issue of volatility. Don’t expect the power plant to solve it. We use distributed systems, and the entire grid is still centralized. The development of electric power is moving towards fragmentation and integration. Security and stability are now key concerns. Beyond energy storage, the next step is to address multi-energy complementarity and microgrids. Photovoltaics plus storage may work for a year, but without effective monitoring, battery issues can arise if one fails.
Multi-energy complementary systems are complex. What problems does the energy management system solve? These include photovoltaic generation, energy storage, wind power, gas development, voltage and current sources, power electronic converters, and synchronous generators. Fluctuations in power generation, load changes, and differences in energy storage all require careful management. The inverter requirements for pure photovoltaic systems are one-way, but more complementary systems demand more advanced inverters.
In Qinghai, a 7.2 MW photovoltaic system with 28 MWh of energy storage was completed in 2013. It operated smoothly for three consecutive years. We used some lithium batteries and lead-acid batteries as backup. The inverters had to operate in parallel, and we used eight inverters to create a 4 MW inverter system. We have done three projects in Qinghai, including 4 MW photovoltaics and 40 MWh of energy storage. Economics is essential; without it, these projects won’t work. We are preparing to acquire a California energy storage project, which serves the grid. However, we encountered a major issue: PCS 5 only allows the battery to charge at 0.25C. When the grid needs adjustments, the capacity isn’t enough. Grid energy storage, peaking, and frequency modulation require different capabilities. Solving this issue improves the system's economics significantly. If the system is purely for peaking, the return rate is less than 6% globally, but with frequency modulation, it can reach 10%.
In Tibet, we have 18 devices operating in parallel with 20 MWh of storage. I’ve always said that high-penetration renewable energy replaces traditional sources and complements them. When a community can support itself and rely less on the grid, dependence drops to 25%, then to 10%. This model can be scaled up, and when it becomes economical, the energy transition will naturally occur.
The trend of replacing traditional energy with renewables is unstoppable. In California, they focus on photovoltaics to create a cleaner future. In Canada, gas-fired power plants use energy storage for frequency modulation and peak shaving. Technological advancements in energy storage and peak shaving are critical. We’ve already achieved millisecond-level response times, and further breakthroughs are needed.
The key to large-scale renewable energy adoption today is energy storage. Energy storage isn’t lacking in technology, but improving its cost-performance is essential. Intelligent inverters allow multiple inverters to run in parallel and perform parallel conversion. Without online conversion, the system can’t keep up with fluctuations. Controlling large-scale storage stations is also important. We need to transform distributed energy storage into centralized storage. With technological breakthroughs and falling lithium and lead-carbon battery costs, this future is within reach.
We’ve piloted projects in the U.S., Canada, and Australia, and also implemented several in China. Beijing has set up a department, and investment in this area is booming. Within two months, over 5 billion yuan was invested by interested companies. Research into this technology must continue to ensure its success.
Multi-energy complementary microgrid solutions involve reducing costs, optimizing portfolios, combining various power sources, and developing effective management and control strategies. Mixed energy storage is possible, and in Tibet, we use both lithium and lead-carbon batteries. Why use lithium? Because it allows quick charging and discharging during fluctuations, while lead-carbon batteries handle longer cycles. Mixing technologies enhances system flexibility and fine-tunes storage and discharge characteristics. Fault tolerance and online improvements are crucial for system stability.
Traditional energy storage systems are too volatile for conventional models. The supply side must evolve. Many microgrid issues stem from energy storage. The cost of energy storage is 0.51 yuan, while lead-carbon batteries are 0.31 yuan. The core of multi-energy complementarity lies in the energy management system. Stability is minute-based, economy is hourly, and optimization spans weeks, months, and years. Initially, microgrids need stable and economical operation strategies, with learning functions to adapt and optimize based on user behavior and data.
Regional energy management platforms help manage multiple microgrids. Single microgrids may have stability issues, so managing groups of microgrids is better. Each home or building can have its own microgrid, enabling peer-to-peer energy trading. As more microgrids form, power transactions become automatic. Multiple microgrids offer better stability and reduce reliance on the main grid. If the main grid only exchanges 25% of energy, the system remains stable. Distributed + microgrid control is the way forward, gradually reducing grid dependence.
These systems place high demands on inverters, especially virtual synchronous generator testing. Certification platforms provide four public simulation networks. The system is cloud-based. Only with technological breakthroughs can the market be captured.
High-penetration renewable energy, combined with energy storage, microgrids, and microgrid groups, is the future. Demand-side response policies are crucial. In Australia, electricity prices adjust every five minutes, while in California, every 15 minutes. Price differences can be threefold. Demand response doesn’t force users to consume less; instead, it creates opportunities for charging and discharging when prices are low. In Germany, daily electricity prices vary widely. China’s pricing mechanism is controlled by the big grid. Transitioning from centralized to distributed power generation is essential. Renewable energy replacing traditional energy is no longer a market competition issue but a matter of human survival. We must work harder in the field of new energy. I believe high-penetration renewable energy is achievable.
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