Stochastic programming based coordinated expansion planning of generation,transmission,demand side resources,and energy storage considering the DC transmission system

With the increasing penetration of wind and solar energies,the accompanying uncertainty that propagates in the system places higher requirements on the expansion planning of power systems.A source-grid-load-storage coordinated expansion planning model based on stochastic programming was proposed to suppress the impact of wind and solar energy fluctuations.Multiple types of system components,including demand response service entities,converter stations,DC transmission systems,cascade hydropower stations,and other traditional components,have been extensively modeled.Moreover,energy storage systems are considered to improve the accommodation level of renewable energy and alleviate the influence of intermittence.Demand-response service entities from the load side are used to reduce and move the demand during peak load periods.The uncertainties in wind,solar energy,and loads were simulated using stochastic programming.Finally,the effectiveness of the proposed model is verified through numerical simulations.

Combined hybrid energy storage system and transmission grid model for peak shaving based on time series operation simulation

This study proposes a combined hybrid energy storage system(HESS) and transmission grid(TG) model, and a corresponding time series operation simulation(TSOS) model is established to relieve the peak-shaving pressure of power systems under the integration of renewable energy. First, a linear model for the optimal operation of the HESS is established, which considers the different power-efficiency characteristics of the pumped storage system, electrochemical storage system, and a new type of liquid compressed air energy storage. Second, a TSOS simulation model for peak shaving is built to maximize the power entering the grid from the wind farms and HESS. Based on the proposed model, this study considers the transmission capacity of a TG. By adding the power-flow constraints of the TG, a TSOS-based HESS and TG combination model for peak shaving is established. Finally, the improved IEEE-39 and IEEE-118 bus systems were considered as examples to verify the effectiveness and feasibility of the proposed model.

Review on global change status and its impacts on the Tibetan Plateau environment

The Tibetan Plateau(TP)holds fundamental ecological and environmental significances to China and Asia.The TP also lies in the core zone of the belt and road initiative.To protect the TP environment,a comprehensive screening on current ecological research status is entailed.The teased out research gap can also be utilized as guidelines for the recently launched major research programs,i.e.the second TP scientific expedition and silk and belt road research plan.The findings showed that the TP has experienced significant temperature increase at a rate of 0.2℃ per decade since 1960s.The most robust warming trend was found in the northern plateau.Precipitation also exhibited an increasing trend but with high spatial heterogeneity.Changing climates have caused a series of environmental consequences,including lake area changes,glacier shrinkage,permafrost degradation and exacerbated desertification.The rising temperature is the main reason behind the glaciers shrinkage,snow melting,permafrost degradation and lake area changes on the TP and neighboring regions.The projected loss of glacial area on the plateau is estimated to be around 43%by 2070 and 75%by the end of the century.Vegetation was responsive to the changed environments,varied climates and intensified human activities by changing phenology and productivity.Future global change study should be more oriented toward integrating various research methods and tools,and synthesizing diverse subjects of water,vegetation,atmosphere and soil.

Longer conserved alpine forests ecosystem exhibits higher stability to climate change on the Tibetan Plateau

Aims Vegetation dynamics are simultaneously regulated by climate change and anthropogenic activities.Since the 1980s,climate has been warming on the Tibetan Plateau(TP)at a rate higher than North Hemisphere average.Anthropogenic activities,including grazing,farming,and urbanization,are also influencing the alpine ecosystem on the TP.Especially,an ensemble of large engineering projects,such as power transported from west to east by State Grid,has been in operation on the TP.While studies disentangling effects of climate and anthropogenic activities interference are still lacking for the forest ecosystems on the TP.The overarching objectives of this study were to separate effects of natural climates and human interferences on forest ecosystem dynamics on the TP.Methods We compared vegetation activities of two typical natural reserves(Gongbu natural reserve,GNR,and Yarlung zangbo river grand canyon natural reserve,YNR)and their surroundings in southeastern Tibet(outside of the natural reserves,ONR)using long-term satel-lite normalized difference vegetation index(NDVI)dataset.Linear regression and partial correlation analyses were constructed for the relationship between vegetation activity and climates to evaluate the distinct climate effects on the two natural reserves.Important Findings The two natural reserves were established at different time,which were related to anthropogenic activities impact durations.The results showed that the annual mean NDVI fluctuated between 0.5 and 0.6 in the relatively longer reserved YNR,which was re-markably higher than those in other regions(with NDVI lower than 0.45).The vegetation vigor in the YNR showed neither a sig-nificant temporal trend nor significant relationship with climate.Nevertheless,vegetation vigor exhibited a significant increasing trend during the last three decades(0.012/decade)at the GNR.The inter-decadal analysis turned out positive relationships between vegetation vigor and annual temperature since late 1990s until early 2000s when the GNR was officially established.This study underlined the importance of considering human interference duration when assessing the relationships between vegetation dy-namics and climates.