Complementary Optimization of Hydropower with Pumped Hydro Storage–Photovoltaic Plant for All-Day Peak Electricity Demand in Malawi

Solar energy is currently dispatched ahead of other renewable energy sources. For the first time, this study presents a concept of exploiting temporary–periodical runoff discharge in the Shire River. Pumped hydro storage–photovoltaic plant (PHS–PV) was optimized to satisfy the all-day peak electricity demand in Malawi. The effect of varying the net head on the PHS system in both the generation and pumping operation modes was investigated. The bi-objective optimization evaluated the system reliability for day-time and night-time operation together with implied costs of investment for the whole system. The optimized system generated above 53% of added power as contrasted to single-source power generation from the existing hydropower plants. The estimated optimal capacities were 182 MWp (solar PV) and 86 MW (PHS plant). These additional optimal capacities achieved a 99.8% maximum system reliability (Loss of Power Supply Probability—LPSP—of 0.2%) and Levelized Cost of Energy—LCOE—of 0.13 USD/kWh. The overall investment cost of the PHS–PV system was estimated at 671.23 USD for an LPSP of 0.20%. The net head varies from 15.5 to 17.8 m with an impact on electricity generation of the PHS–PV system. More notably, the PHS–PV production matches with daily day-time and night-time peak loads and functions as a peaking plant

Thermal Cracking Analysis of Microbial Cemented Sand under Various Strains Based on the DEM

Microbial-induced calcite precipitation (MICP) is a novel ground improvement method to increase the strength and stiffness of sand. However, the influences of temperature load on the internal microstructure of microbial cemented sand (MCS) material under the experimented strain have always been a key concern for the extensive application. Three kinds of experiments, X-ray diffraction (XRD), X-ray computed tomography (XCT), and scanning electron microscopy (SEM), were conducted to explore the composition, shape, and bonding characteristics of physical assemblies in this paper. A precision DEM modelling of MCS, mainly composed of irregular particle modelling and a mesoparameter calibration algorithm, has been proposed for the thermal cracking analysis under various strains (i.e., 1.0‰–3.0‰). Research results indicate that three kinds of bonding (that is sand-calcite, calcite-calcite, and sand-sand) are present in the MCS material. The application of temperature has a superposition effect on the damage of MCS material with increasing strain. Moreover, as the heating duration gradually increases, the effect of thermal rupture produces a distinct quiet period. The length of thermal cracks in the transverse direction increases throughout the heating process