• Energy Research

Abstract The complementary operating rules of hydro-photovoltaic (PV) hybrid power plants have been explored fully to operate reservoirs for complementing the PV output. However, prevailing operating rules were constant, which is incapable to be dynamically updated based on new observations. To address this issue, adaptive complementary operating rules were developed to deal with the future uncertainties of reservoir inflow and solar radiation using ensemble Kalman filter (EnKF). First, a long-term complementary optimization model was developed to derive the initial parameters of linear operating rules. Then, the optimal decisions under historical condition were used as the observation. Finally, six assimilation schemes were proposed, according to the two state transition equations (the same period of the previous year, the previous period) and three observations (the same period of the previous year, the previous period and their joint). China’s Longyangxia hydro-PV hybrid power plant was chosen as a case study. Results show that (1) the two state transition equations have comparative effects on operation results, (2) the choice of observation plays a decisive role. The assimilation scheme, in which the optimal operation decision of the same period in previous year is as observation, outperforms the stationary operating rules. Specifically, the total power generation and guaranteed rate are improved by 7.14% and 5.33%, respectively, (3) the deriving framework works effectively under the synthetic nonstationary reservoir inflow and solar radiation, and ensures the stability and security of energy system in the changing environment.

Wetlands play a critical role in global hydrological and biogeochemical cycles. Regulating the regional climate is one of the most important ecosystem services of natural wetlands. However, the impact of wetlands on local temperature on the global scale and the attribution is still unclear. This study utilizes the satellite-based products (land surface temperature (LST), albedo, and evapotranspiration (ET)) to evaluate the difference in LST between wetlands and their adjacent landcover types and the possible drivers. Here we show that on average for the whole year, wetlands have a cooling effect in tropical regions, but have a warming effect in boreal regions. The impacts of wetlands on LST show great seasonality in the boreal regions; i.e., the wetlands have a warming effect in winter but a cooling effect in summer. The difference in albedo and ET between wetlands and the other landcover types only interprets 30% of temporal variation of the difference in LST. Due to the large water storage in wetlands, the ground heat flux (G) may interpret the rest of the impact, absorbing energy in summer and releasing energy in winter in wetlands, which has often been neglected in previous studies. Our results indicate that it is critical to comprehensively consider the effects of wetland restoration in different regions to realize potential climatic benefits in the future.

Abstract The variability of photovoltaic (PV) power challenges its integration into power grids at the utility-scale. Operating PV power complementarily with hydropower is a promising way for the grid to accommodate more PV energy. This study optimizes the size of a utility-scale PV plant for integration into a hydro plant using cost–benefit analysis and considering variations in downstream water level (VDWL). A nesting model that incorporates both long- and short-term operating decisions is developed to estimate the delivered PV energy. This includes a multi-objective optimization model that provides long-term decisions for the joint operation of the plants. These factors are then incorporated into a short-term simulation model, which produces successive decisions relating to power curtailment and water levels. Finally, the expected net revenue of the PV plant over its lifespan is calculated while constraining the VDWL to protect downstream water users. China’s Longyangxia hydro–PV plant was selected for a case study. The results indicate that: (1) the optimal size of the PV plant is 950 MW with a maximum net revenue of 5.2 billion CNY over its lifespan; (2) the optimal PV size is sensitive to financial factors (the feed-in tariff, the initial investment, and the operation & maintenance costs); and (3) a larger reservoir storage capacity tends to be integrated with a larger PV plant. The combination of the cost-benefit analysis and the nesting model appears an effective approach to optimize the size of the PV plant being integrated with hydro plant and could equally apply to integrating other renewable energy sources.