The uncertainty of wind/photovoltaics (PV) power generation and load fluctuations highlight the urgent need for flexible yet stable power resources. With the increasing in the share of renewable energy, the fluctuation presents a trend toward the longer periods, larger amplitudes, and more drastic changes. Therefore, research on the long duration flexible resource planning for the scenarios of the ultra high share of renewable power system (UHRPS) has become the focus. In this work, the main structural and operating characteristics of UHRPS are introduced and analyzed, which is followed by the flexibility requirements and flexibility planning challenges of UHRPS scenarios. Then, the current research trends in flexibility planning schemes of renewable energy power systems are reviewed. Finally, the key problems and solutions for research on the long duration flexibility resource planning of UHRPS are proposed.

With the advantage of integrating distributed energy, storage and DC load with high efficiency, the DC distribution network recently attracted wide attention in the field of nearly zero energy buildings. Considering the large number of buildings and the enormous energy-saving potential, the distribution form and the revenue distribution are key factors affecting energy efficiency and operational economy. Aiming at the characteristics of AC and DC distribution topologies in nearly zero energy buildings, an energy efficiency evaluation method is proposed based on time-sequential power flow simulation, where the piecewise linear efficiency function of converters and dynamic line power loss model are established. Based on a DC distribution demonstration project, an AC power distribution system with the same boundary conditions is designed. The results show that the efficiency of DC distribution topology is about 6% higher than the AC system, while the efficiency advantage in office, hotel, commercial, educational and residential buildings in Beijing, Shenzhen and Shanghai varies from 0.6–4.96%, which shows a high correlation with the proportion of a high-power load, with Pearson correlation coefficient of 0.794. With the increase of DC load ratio and distributed power supply access capacity, the efficiency of the system will be improved accordingly. On the basis of this, a method to equalize DC distribution income in the nearly zero energy buildings power market is proposed. In addition, 15 typical scenarios of different cities were selected to evaluate efficiency and influencing factors. Finally, assessing the multi-stakeholder impact of DC retrofitting to balance the revenue generated by the DC distribution model suggests that transport costs should be raised by 8.2–13.1% to balance revenue with the equipment prices decreased by about 0.1 yuan/W.

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