Do you also belong to the »streamers«? Currently in trend: binge-watching. This involves watching through complete seasons of series in one piece. This requires computing power and energy: on the TV screen, smartphone or tablet, on the router and in the provider's data centre. However, the energy suppliers must first generate the energy. But we have hardly any influence on how the electricity is generated. Is the data centre located in an area with many coal-fired power stations? Then the climate balance is much worse than in an area with many Phohovoltaic (PV) plants. It is even more likely to achieve this in your own home: if you generate some of your own electricity using solar modules, this has a positive effect on the energy footprint.
It is not clear to the consumer which method is the best: should he or she watch TV via satellite or cable, stream – via TV, smartphone or tablet – or rather watch a DVD in the old-fashioned way? On top of this comes the power consumption of the data centres for streaming: According to Bitkom, this currently totals more than twelve billion kilowatt hours per year in Germany – that is about as much as Berlin consumes annually.
A Bitkom study deals in detail with the questions about the sustainability of streaming and provides – sometimes surprising – answers.
The most important facts in brief
- The energy requirement depends very much on the end device and on the resolution of the stream.
- Video viewing with Standard Definition (SD) on a smartphone, tablet or notebook requires much less energy than classic television or playing a DVD on a 50-inch flat-screen TV.
- Watching HD-quality videos on a fixed network generates between 100 and 200 g of CO2 per hour with today's energy mix – comparable to a one km drive in a car with a combustion engine. Accordingly, the CO2 emissions from watching videos on the net are low compared to other leisure activities.
- Streaming is continuously becoming more energy efficient: For 2020, it is assumed that the provision and transmission of the same film will require about 25 percent less energy than in 2018. 
One hour of DVD watching on a 50 inch flat screen TV requires between 93 and 100 Wh. The energy requirement is higher for video streaming, however, depending on the selected resolution and device. One hour of video streaming via the landline in High Definition (HD) 720p on a 65-inch TV causes an energy consumption of about 280 Wh (in total about 130 g CO2). More than half of the energy required is used on the television itself. One hour of streaming of 4K video data on the same 65″ TV even requires 1,300 Wh (corresponding to about 610 g CO2). Communication networks and data centres are responsible for 88 percent of the energy demand. In contrast, smartphones or tablets require only about 65 or 75 Wh of energy, respectively, for streaming in SD resolution, which corresponds to about 30 to 35 g CO2. Here again, the largest share is allocated to data centres and networks. All values given here refer to data transmission via the landline network. Under current circumstances, the mobile network has a much higher energy requirement. However, the calculation is very complex due to the different mobile phone generations. 
In summary, the energy requirement increases with the size of the device and the selected resolution. By contrast, the demand in data centres and communication networks remains high – which makes it very intransparent for the user. Streaming via landline is also much more environmentally friendly than via mobile radio.
Is streaming the new flying?
Binge-watching is the trend – flying is out. This raises the question: Are CO2 emissions merely being relocated? The study »Lean ICT: Towards digital sobriety« by the French »The Shift Project« shows that digitalisation is responsible for just over three percent of global greenhouse gas emissions. This is roughly equivalent to the CO2 emissions of global aviation. Moreover, the share is growing rapidly and would be responsible for about eight percent of global greenhouse gases in 2030. However, according to Bitkom, the study is based on a single source, so the results are not always transparent or comprehensible. 
The question of energy requirements for digitalisation in general and streaming in particular is therefore not trivial. Many factors are involved. Even for data centres, estimates of energy requirements differ – they would today be responsible for 200  to 650  TWh of energy consumption worldwide each year. More realistic calculations are roughly in the middle.
For communication networks, calculations are much more complicated, and there are hardly any current studies. Based on realistic assumptions, the authors of the Bitkom study assume a total of approximately 400 to 500 TWh worldwide for 2020. The most difficult thing to estimate is the consumption of mobile devices, as the number is very large and their inventory changes rapidly. After looking at various studies, the experts consider about 350 TWh per year to be realistic here.
The share of streaming in global primary energy consumption is interesting: if the above-mentioned sums are added together, this amounts to around 1,100 to 1,250 TWh worldwide annually for streaming services. This corresponds to around five percent of the global electricity consumption of 26,700 TWh and less than one percent of the global primary energy consumption of 150,000 TWh . All in all, digitalisation as a whole is responsible for about 1.5 percent of global greenhouse gases (484 g CO2 per kWh ).
As the Corona crisis shows, video conferences can be a good substitute for travel. However, despite all the progress in technology, streaming represents an energy requirement that should not be underestimated. In the context of preventing the spread of a pandemic, however, streaming is something like the new way of flying – in a positive sense.
What can each individual do?
First of all, the user can save energy when choosing the transmission method: Landlines – even in combination with WiFi – are better than mobile networks. In addition, a lot can be achieved with the choice of resolution: If possible, choose a lower resolution and reduce the degree of image optimisation. Another point: Do without functions such as Auto-Play to avoid playing advertisements, trailers or follow-up titles. The ideal solution would be to generate the energy used at home with PV power, for example, and to avoid streaming completely when travelling.
 Masanet, Eric et al. »Recalibrating global data center energy-use estimates.« Science 367.6481 (2020): 984-986. doi: 10.1126/science.aba3758.
 Belkhir, Lotfi, and Ahmed Elmeligi. »Assessing ICT global emissions footprint: Trends to 2040 & recommenda-tions.« Journal of Cleaner Production 177 (10. März 2018): 448-463. www.sciencedirect.com/science/article/pii/S095965261733233X.
 Pavarini, Claudia et al. Tracking the decoupling of electricity demand and associated CO2 emissions. Paris: IEA, 2019. www.iea.org/commentaries/tracking-the-decoupling-of-electricity-demand-and-associated-co2-emissions.