As digitisation steadily increases, so does the energy demand for data centres. Being the backbone of digitisation, these centres offer great sustainability potential, which is increasingly being developed through innovation funding from politics and industry. Concepts for the reuse of server waste heat as useful heat in buildings are of great interest for the energy and heat transition.  

Being the largest data centre location in Europe, Germany is home to more than 53,000 data centres. Their servers enable our daily online communication, ranging from short WhatsApp messages to streamed films on Netflix. Digital transformation indisputably increases our communication at all levels of our society, along with the amount of data that is stored, processed, exchanged, received and sent in computer centres. The amount of data stored in data centres worldwide will increase by an estimated factor of 4.6 to 1.327 Zettabytes between 2016-2021. Cloud computing in particular, which is used by more than one in four companies in the EU, and AI, Big Data and IoT are contributing to the data centre growth and fuelling the digital hunger for energy.

However, data centres also have the important potential to make a decisive contribution to the transition of energy systems. The energy efficiency of the data centre infrastructure has improved by around  60% in the last ten years, making German data centres some of the most energy-efficient in the world. Despite these significant improvements, the demand for data centre services continues to rise. The resulting increase in energy demand is therefore primarily due to IT components such as servers, storage and networks. In 2017, German data centres required 13.2 billion kWh of electricity (see Figure 1), which roughly corresponds to Berlin’s annual electricity consumption. Data centres now already account for more than 2,3% of Germany’s total electricity consumption. Overall, the energy demand of German data centres has increased by more than 25% in the last 10 years and will not decline, even in view of the clear global trend towards ever larger data centres. The worldwide power consumption of data centres has even surged by 70% in the last 10 years. Energy efficiency is of critical importance here, making sustainable concepts in high demand. In addition, data centres can make an important contribution to the energy transition through intelligent integration into electricity and heating networks.

Figure 1: The increasing energy demand of data centres in Germany from 2010 to 2017, surveyed as part of a study on the development of the data centre market in Germany conducted by the network for energy efficient data centres NeRZ. (Source:

Counteracting the digitisation’s thirst for energy

The German data centre industry has already recognised the relevance of energy efficiency when it comes to the sustainable operation of data centres and made innovative technological adjustments. The Power Usage Effectiveness (PUE) parameter states the total energy demand of data centres in relation to the energy requirement of the IT components, and can be used to provide information on a centre’s energy efficiency. Data centre operators aim for a low PUE value – ideally being one. Between 2010 and 2017, the average PUE value of German data centres fell from 1.98 to 1.75.

In recent years, energy savings have been achieved primarily through energy efficiency measures in the data centre infrastructure, which offers great savings potential. Think about cooling, air conditioning and ventilation. However, the more efficient the infrastructure is, the lower the impact of further improvements on energy consumption. Moreover, IT components such as servers and storage account for the majority of the data centre’s power consumption. As a result of the growing data flood, and despite all energy efficiency efforts, Germany’s data centres increasingly need more energy (see Figure 2). While the total energy demand for information and communication technology (ICT) will fall in the medium term (due to the decreasing ICT energy demand in households and at workplaces), the requirements for ICT infrastructure in areas such as computer centres and telecommunications networks are expected to rise. Developing new energy efficiency technologies to optimise the PUE are therefore not sufficient. Further solutions are needed to meet the increasing needs of green data centres.

Figure 2: Forecast of the energy demand for ICT in Germany, carried out as part of a study commissioned by the Federal Ministry of Economics and Energy on the development of ICT-related electricity demand in Germany. (Source:

Data centres as energy suppliers instead of electricity consumers

Not only energy efficiency is crucial to promote sustainable data centre operation. Regenerative energy sources instead of conventional ones should also be considered. And what happens to the consumed electricity? It is very often dissipated from the data centre as waste heat and released into the environment – unused. This waste heat could be used profitably by being converted back into energy and fed into the cycle. Waste heat can, for example, be used for heating buildings or generating hot water. Data centres can thus make a direct contribution to meet heating demands.

To implement this technically, distribution networks are needed to deliver waste heat to buildings. In addition, the temperature of the waste heat, which averages 35 to 40 degrees, must be raised to the conventional heating network level of approx. 95 degrees using heat pumps to be able to use it further. Further possibilities are to lower the temperature of the 4th generation heating networks to 55 degrees and to supply buildings with low-temperature district heating according to modern energy standards.

Figure 3: Waste heat recovery from data centres. (Source:

Rethinking heat is standard in many countries

In Scandinavia, especially in Sweden, waste heat is already being recovered systematically. Data centres are built in such a way that their waste heat is fed into the local district heating network. District heating is more widespread there, and the electricity fee of three to four cents per kWh is significantly cheaper than in Germany, which has one of the highest electricity prices in the world. In autumn 2016, the Swedish government also decided to further reduce the electricity tax for data centres. Stockholm in particular is a pioneer in the use of waste heat. More than 30 data centres are already located here, which feed their waste heat into the 2,800-kilometer district heating network.

Figure 4: The 5 MW Multigrid data centre operated in Kista Science City in Stockholm since 2018. This is part of the long-term “Stockholm Data Parks” initiative launched by the City of Stockholm, the district heating provider Fortum Värme and the electricity grid operator Ellevio to establish Stockholm as a location for the systematic use of waste heat. (Source:

Other European countries have also recognised the contribution of waste heat recovery at an early stage. Telehouse Europe offers companies and providers of telecommunications, Internet and cloud services highly available data centre space. 10 years ago, they began to use the waste heat from their first data centre, Telehouse West in London, to heat neighbouring residential and commercial buildings. This enables them to deliver up to 9 megawatts (MW) of heating capacity to external customers and avoid up to 1,100 tons of CO₂ emissions annually.

Figure 5: The Condorcet data centre operated by Telecity in Paris. (Source:

Another innovative concept for waste heat recovery was implemented in Paris a few years ago. The waste heat generated by the Condorcet data centre is used to heat a connected arboretum . In this arboretum, the Société Forestière and the French National Institute for Agricultural Research (INRA) investigate the effects of climate change on plants under extreme climatic conditions. According to the operator, this waste heat recovery model could save 28 million kWh of electricity per year and 2,500 tonnes of CO₂.

Combining digitisation and heat recovery in Germany

In Germany, the potential of waste heat recovery has not yet been fully exploited. A survey by the network for energy efficient data centres NeRZ shows that only 1% of data centre operators use more than 50% of their generated waste heat, while 18% use 10 to 50% of it. According to NeRZ, the reasons for this limited waste heat recovery are mainly the low economic efficiency and the lack of customers interested in waste heat. This is particularly the case for providers of colocation centres who rent out their space as operators to different customers. By 2020, the share of colocation centres in the total IT area of German data centres is expected to rise to 40%. Here, the systematic use of waste heat is countered by the high German electricity prices, which lead to relatively high costs for heat pump electricity. At 29 cents per kilowatt hour, electricity prices in Germany have currently reached an all-time high. Waste heat recovery in German data centres must therefore be promoted even more specifically.

Figure 6: Results of a survey conducted by the network for energy efficient data centres (NeRZ) on existing obstructions to the use of waste heat in data centres (2017).

Clear political support should especially increase the economical attractiveness of waste heat recovery. This calls for innovative business models that actively involve property developers, energy suppliers and municipalities. The first framework conditions for investments have already been created, e.g. the Municipal Directive of the Federal Ministry for the Environment, Nature Conservation and Nuclear Safety (BMU), which grants subsidies to municipalities investing in energy-efficient data centres. The current development of the Blue Angel environmental quality label for energy-efficient data centres established by the Federal Environment Agency also creates the necessary incentives for the use of waste heat. Further beneficial objectives were also formulated in the key points for an environmental digital agenda published at the beginning of May 2019. Relevant actors on this final agenda are to work out these points by the end of the year in a joint dialogue. These points will, among other things, further enhance the energy and resource efficiency of ICT and computer centres with new standards for industry and public authorities.

Germany’s strong research landscape could support a more targeted political promotion of waste heat recovery. A leading programme here is ReUseHeat, in which nine European countries are carrying out demo projects over the period 2017-2021. The projects recover waste heat at various locations in Europe, not only from data centres, but also from other energy sources close to cities. Germany is participating with a demo project in Braunschweig. The project, which is funded by the European Union as part of the Horizon 2020 programme, aims to draw attention to the large amounts of heat that are currently being wasted in Europe and to the existence of innovative urban waste heat recovery solutions that are both technically and economically viable. According to the research team, the amount of heat currently wasted from energy installations in Europe could be used to heat the entire European building stock.

The German start-up scene is also setting important innovation impulses for the recovery of waste heat in data centres. Cloud & Heat Technologies GmbH, a former start-up from Dresden, has made its name by developing a special concept for server waste heat recovery using a hot water cooling system. By providing decentralised, modular server containers, public authorities and companies that have both a Cloud and heat requirement can make use of Cloud solutions within their own company and use the waste heat for their own business and office premises.

Another interesting approach is that of the young start-up Windcloud from Schleswig-Holstein. Located on the Greentech Campus of a former German Armed Forces site, it builds its data centres in the immediate vicinity of existing wind energy facilities and uses their waste heat for greenhouses. Together with partner companies, the waste heat is thus refined for innovative industrial projects such as fish and algae farming and indoor farming.

Data centres play a central role in our digital society. That is why developing the energy and resource-saving potential of data centres through politics, research and industry is so important. The use of waste heat from data centres and the associated recognition of waste heat as a valuable commodity will play a central role when it comes to making digitisation ecologically compatible.