Can energy piles store solar thermal energy underground?

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.

What is a coupled energy pile-solar collector system?

For a coupled energy pile-solar collector system in practical engineering, the solar collectors will be mounted on the exterior walls and roofs of buildings to minimise additional land use. To avoid oversizing the solar collector area, it is important to maximise the efficiency of the solar collector through optimal design.

What is the maximum temperature of a solar energy pile?

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.

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.

How does a solar energy pile-soil system work?

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.

What is the irradiance of a solar energy pile-soil system?

The two levels of radiation represent abundant and deficient availability of solar energy with respect to the size of the model energy pile-soil system, respectively. The irradiance was measured using a pyranometer with a precision of 0.2 W/m 2.