A typical working day in the office often starts by pressing the on button of a computer. The screen lights up, the latest e-mails are loaded and the calendar displays what is coming up that day. In the back­ground, thou­sands of giga­bytes of data are passing unno­ticed through Microsoft’s German data centers. Since April 2024, the power for this has been supplied from Saxony.

Where lignite was once extracted, 1.1 million solar modules are now producing elec­trical power at the Witznitz Energy Park south of Leipzig. Due to its previous use, the land on which the park is located could not be switched to agri­cul­tural use for envi­ron­mental and economic reasons. So why not use the site, which is as large as Hamburg Airport, to generate renew­able energy? That was the idea of MOVE ON Energy, which installed 1.1 million solar modules, 207 trans­former stations and two dedi­cated substa­tions, at the same time rena­turing compen­sa­tion areas covering 160 hectares. The power gener­ated is sold to oil and gas company Shell and then on to Microsoft for its data centers.

Trans­former stations ensure the right voltage

Solar modules

When sunlight falls on solar modules, they generate direct current that is then converted into alter­nating current by the solar park’s more than 3,500 inverters.

Trans­former stations

The inverters at the Witznitz Energy Park deliver a voltage of 600 volts. A total of 207 trans­former stations increase the voltage to 30,000 volts, enabling the current to be trans­ported via the medium-voltage grid to the two substa­tions with as little loss as possible.

Substa­tions

At the Witznitz Energy Park, the dedi­cated 380kV substa­tions and an extra-high voltage tower have been installed on the site. The substa­tions take the medium-voltage current, convert it to extra-high voltage and then transfer the power to the trans­mis­sion grid via the tower. As the substa­tions are located directly in the Energy Park, the medium-voltage current is not trans­ported over longer distances, which reduces trans­port losses.

Cables

Trans­mis­sion losses in the power grid are mainly caused by the resis­tance of the elec­trical cables through which the current flows – known as ohmic resis­tance. Some of the elec­trical power is converted into heat and can there­fore no longer be used. Some is also lost to heat during conver­sion of the voltage in the trans­former stations.

High-voltage tower

A 380 kV high voltage tower is part of the extra-high voltage grid that is used to trans­port elec­trical power over long distances. The cables on this tower are designed for a nominal voltage of 380,000 volts (380 kV) – in Germany, this is the highest voltage level in the trans­mis­sion grid for the long-distance trans­port of elec­trical power. The high voltage is used to reduce the current level and thus mini­mize trans­mis­sion losses. Thanks to high-voltage direct current trans­mis­sion, power losses over long distances can be reduced even further.

(Photo | MOVE ON Energy)

24/7 oper­a­tion

Inside, the trans­former stations are divided into two areas. On the low-voltage side, the current is received from the inverters. At the center is the trans­former that increases the voltage of the current to 30 kV. It then passes to the medium-voltage side and on to the substa­tion. The trans­former stations operate at full capacity every day, gener­ating heat due to conver­sion losses – this is a phys­ical phenom­enon. However, the trans­former stations also contain sensi­tive compo­nents such as sensors, protec­tion devices, circuit breakers and mini elec­tronics. They must not be allowed to get too hot as they could other­wise be damaged and reli­able oper­a­tion of the system could no longer be guar­an­teed. Steffen Montag, managing director MOVE ON Energy, explains: “The fuses espe­cially are sensi­tive to extreme temper­a­ture fluc­tu­a­tions – heat is more harmful than cold.”

That is why the heat gener­ated must be reli­ably dissi­pated from the trans­former stations so that the sensi­tive compo­nents do not over­heat. If this is not done, their service life could be reduced by as much as half. For this reason, MOVE ON Energy was looking for a solu­tion to cool the trans­former stations – and found it in the fans from ebm-papst. 

Compact fan solu­tion

A partic­ular chal­lenge was the limited space avail­able for instal­la­tion because both the trans­formers them­selves and the medium-voltage system in the trans­former station take up a lot of space. To ensure effi­cient cooling, the fans are installed in the door of the trans­former station. This enables the air flow to circu­late unhin­dered between the trans­former and the fan. The fans draw warm air from the inte­rior and trans­port it to the surrounding envi­ron­ment. As it is warmer in the summer, the fans operate at higher speed than in the winter. “Of course, the noise level of 207 trans­former stations also plays a role,” says Sonntag. That is why EC centrifugal fans from the RadiCal range were chosen. Thanks to their compact design, high pres­sure increase and opti­mized air duct design, they are partic­u­larly able to with­stand the high back pres­sures caused by the restricted space. The rounded leading edges of the impeller blades ensure opti­mized noise char­ac­ter­is­tics. 

We were convinced by the repu­ta­tion of ebm-papst as a German manu­fac­turer, its ability to deliver and the reli­a­bility of its product quality.

Steffen Montag, Managing Director MOVE ON Energy

Daniel Krause, a tech­nical sales engi­neer at ebm-papst, was respon­sible for the tech­nical imple­men­ta­tion of the cooling solu­tion at the Witznitz Energy Park. He explains the approach: “MOVE ON Energy knows how much heat the trans­formers generate when oper­ating at full capacity. On this basis, we calcu­lated the neces­sary air flow and proposed the RadiCal as a suit­able solu­tion.”

(Photo | MOVE ON Energy)

Stable temper­a­tures ensure longer service life and reli­a­bility

A total of 207 fans have been installed at the Witznitz Energy Park, one fan for each trans­former station. To ensure that the temper­a­ture can be regu­lated as required, a sensor deter­mines the trans­former, building and ambient temper­a­tures and trans­mits these data to a temper­a­ture control module. Based on this infor­ma­tion, the optimal fan speed is deter­mined and adjusted as required. “In ebm-papst, we have found exactly the right partner to deliver the overall concept of fans, control tech­nology and moni­toring,” says Montag with satis­fac­tion.

By main­taining a stable temper­a­ture, the fans can double the service life of the trans­former compo­nents from seven to as much as 14 years. The Energy Park has now been oper­ating for over a year. “The first summers are behind us and we’re happy,” says Montag.

Where lignite was once mined, 1.1 million solar modules now produce elec­tricity at the Witznitz Energy Park south of Leipzig. (Photo | MOVE ON Energy)

In addi­tion to the energy park, MOVE ON Energy devel­oped 160 hectares of compen­sa­tion areas to protect the envi­ron­ment and nature. (Photo | MOVE ON Energy)