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.

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 are energy piles?

One is the primary geotechnical function, and the other is a heat exchanger. Compared to other energy geo-structures, energy piles have been most-widely investigated and adopted in practical engineering to replace the traditional boreholes of the GSHP systems , , .

How to build a model energy pile?

When the soil surface reached 300 mm high, the model energy pile, with dimensions of diameter 60 mm × length 600 mm, was installed. It was constructed by fixing the copper spiral loop with an overall outside diameter of 45 mm in position followed by grouting with a water to cement ratio of 0.3.

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.