Utilisation of Ambient Air and Shallow Geothermal Energy - Renewable Energy: Technology, Economics and Environment - page 383

9 Utilisation of Ambient Air and Shallow
Geothermal Energy

A typical characteristic of ambient air and near-surface heat it is the very low
temperature level. The heat is mainly generated by solar radiation (Chapter 2).
Only a small part of the energy in the soil (i.e. shallow geothermal energy) is not
produced by the sun, but by the geothermal energy flow caused by the heat poten-
tial available within the earth (i.e. deep geothermal energy). The share of
geothermal energy normally increases proportionally with an increasing depth un-
derneath the surface of the earth (Chapter 2). Nevertheless, this type of energy is
defined as geothermal energy - independent of the origin of energy in the near-
surface ground (i.e. whether or not it results from solar radiation and/or geother-
mal energy stored in the deep underground, Chapter 2) (Fig. 9.1).

1,000

Solar radiation

100

10

Energy of
ambient air

Atmosphere

1

Water above
surface

Surface of the earth

Influenced by solar
radiation

-1

Shallow
geothermal
heat

-10

Soil with groundwater

-100

-1,000

Deep geo-
thermal
heat

Geothermal heat

-10,000

Fig. 9.1 Terminology definitions

In line with this terminology it has been agreed that utilisation of geothermal
energy in general, and shallow geothermal energy in particular, starts at the sur-
face of the earth (Fig. 9.1). The difference between the use of shallow geothermal
energy and of geothermal energy from deeper layers (Chapter 10) is arbitrary and
goes back to an administrative regulation originally set up in Switzerland. Accord-