In La Solana in Spain a solar power plant with a peak output of about 6.5 MW is in operation. Solar inverters are used to transform the current into line frequency. To protect the inverters from atmospheric inﬂuence, the inverters are placed in small buildings. During the transformation process there is a power loss, which is released in heat form. To cool down the electric devices sufficiently and ensure a smooth operation, a earth heat exchanger system was constructed and built by TinniT Technologies. This cooling system is using the fact, that the earth temperature in only a few meters (about 2 to 5 m) depth is nearly constant over the whole year. The cooling system is basically composed of a distribution and a collector tube, which are connected with heat exchange tubes. The air from the ambience is guided through the tube system using a fan. During the ﬂow through the heat exchanger tubes the air cools down convectively and the heat is conducted into the soil. Now the cool air is guided into the building and ensures a smooth operation of the solar inverters. For dimensioning and determining the system control of the earth heat exchanger, there were made a couple of different analytical and numerical calculations. Most important in dimensioning the cooling system is the required cooling power and the ambient conditions like ambient and earth temperature. According to these requirements and ambient conditions the dimension and the number of heat exchange tubes can be chosen. After the construction of the cooling system it was assembled with all necessary measurement instruments to control the efficiency and also to evaluate the CFD calculations made before. The numerical calculations during the building process were essentially to work out an efficient operating control. Using the CFD calculations it was also possible to check the constant distribution of the ﬂow through the heat exchanger tubes and calculate the pressure drop of the whole system, what was necessary to choose a qualiﬁed fan.