Energy storage charging piles lose power quickly in cold weather. Battery makers claim peak performances in temperature ranges from 50° F to 110° F (10 o C to 43 o C) but the optimum performance for.
Ma and Wang proposed using energy piles to store solar thermal energy underground in summer, which can be retrieved later to meet the heat demands in winter, as schematically illustrated in Fig. 1. A mathematical model of the coupled energy pile-solar collector system was developed, and a parametric study was carried out.
The heat-carrying fluid particle transports heat from the solar collector to the energy pile-soil system continuously. The rate of charging and discharging depends on the flowrate, the intensity of radiation, and the condition of the energy pile-soil system.
How much energy is stored per unit pile?
Quantitatively, the daily average rate of energy storage per unit pile length reaches about 200 W/m for the case in saturated soil with turbulent flowrate and high-level radiation. This is almost 4 times that in the dry soil. Under low-level radiation, it is about 60 W/m.
Does flow rate affect energy storage during the first charging phase?
By the end of the first charging phase, the rate of energy storage per unit pile length in saturated soil is about 150 W/m higher than that in dry soil. The flowrate seems to have no significant effect on the evolution of the rate of energy storage during the first charging phase, except for cases in saturated soil.
How many cycles of energy storage are maintained in a pile-soil system?
In addition, the model domain of the energy pile-soil system has limited dimensions and thus only five cycles of energy storage were maintained for each test. These factors affect the results quantitatively, while they should not invalidate the fair comparison between different tests.
It indicates that both the inlet and outlet temperature of the energy pile undergo a rapid increase during the first hour. Then they increase quite slowly as the underground storage of solar thermal energy continues. The maximum inlet temperature is about 60 °C.