Leading Chinese electric utility China Huaneng Group formally initiated operation of the first direct current (DC)-side energy storage upgrade and renovation of its solar photovoltaic (PV) plants recently, on the heels of a successful commissioning of the project.
The project was launched as part of the fourth phase of Huaneng’s 180 MW central PV plant in Golmud, Qinghai province, China. The 3.5 MWH first-phase of the energy storage demonstration facility selected lead carbon and lithium iron phosphate batteries as the energy storage solution. With Sineng Electric’s DC/DC converter designed specially for PV energy storage on the DC-side in combination with China Huaneng Clean Energy Research Institute (CERI)’s proprietary DC-side PV energy storage management system, the energy storage system is connected to the DC input side of the solar inverters at the PV plant in operation, helping transform a traditional PV set-up to a PV energy storage station. The system will work with any brand of solar inverters. Once construction is finished, the facility will be able to address the curtailment and other limitations when it comes to connecting PV systems to the power grid, as well as vastly reduce the volatility in output associated with solar power as well as improve the accuracy when forecasting and controlling anticipated available output. The facility is expected to become a model for upgrading existing ground PV plants with the energy storage system as well as new PV installations.
As the new energy industry continues to evolve rapidly, the level of curtailment and types of limitations that have been observed when connecting PV-originated power to the grid varies widely across the most affected regions in China, mainly in the northwestern, northeastern and northern parts of the country, leading to wasted electricity and reduced income from power generation, while having had, overall, a negative impact on the healthy development of the PV sector.
In addition, with the increasing share of PV power connected to the grid, the power fluctuations and difficulties in predicting output have been increasing. As a result, the issues are having an impact that cannot be ignored as they interfere with the safe and stable operation of the grid.
The application of energy storage technology to PV plants will not only help effectively resolve the curtailment issue and boost the absorption of renewable energy, but also vastly reduce the volatility in the output, narrowing the gap between peaks and valleys as well as their frequency and the need to constantly adjust the voltage. The technology also deals with the issue of scalability when in comes to connecting large suppliers of renewable energy to the grid.
On October 11, 2017, the National Development and Reform Commission, the Ministry of Finance, the Ministry of Science and Technology, the Ministry of Industry and Information Technology and the National Energy Administration jointly issued the circular Instructions on Boosting the Development of Energy Storage Technology and Industry in China, confirming the importance of applying energy storage technology across various components of the power grid, including the smart power grid, renewable energy feed-ins, prevailing energy systems and the energy internet.
With the ongoing improvements in electrochemistry energy storage technology, the cost of energy storage batteries and their cycle life, among other performance indicators, the commercial value of using the energy storage system as the basis for upgrading and renovating a large number of ground PV plants, especially facilities that date back to the introduction into China of solar as a power source, has been proven. The system has the potential of addressing the curtailment issue, leveling out the output curve and controlling the accuracy of energy forecasting, especially given the relatively high feed-in tariffs. It needs to be noted that the installation of a traditional central energy storage system connected on the alternating current (AC)-side of a PV plant already in operation faces several challenges, including difficulties in renovation of the connection to the grid, a large investment in additional equipment, need for a large space where the energy storage units need to be placed (given that they must be placed alongside each other) as well as multiple energy transfer steps and poor system efficiency.
With years of experience in the PV sector and a deep understanding of PV systems, continuous development of technologies for PV and energy storage systems and the support of CERI’s DC-side energy storage management system, Sineng Electric has the experience and the know-how to incorporate the energy storage system into the PV set-up seamlessly. The efficient charging of energy storage batteries with PV modules and the discharging of energy storage batteries to inverters are made possible by simply connecting the DC/DC converters and energy storage batteries specially designed for PV energy storage to the DC input side of any brand of central solar inverters, without compromising the operation of the original PV facility. The PV energy storage system boasts a transparent architecture, requires a small investment in equipment and delivers a high stored energy conversion rate, paving the way for upgrading the traditional PV plants with energy storage systems in the future.