Watching movies the green way

In 2019-2020, there was a lot of alarmist nonsense circulating on the Internet, that claimed one hour of watching Netflix translates into 6 kW·h of electricity. This figure has been debunked since then by World Economic Forum (link) and International Energy Agency (link). That said, the original point of Shift Project is still valid: most internet traffic today is video traffic, and we might want to rethink our consumer behavior.

The WEF article linked above points out that "one hour of Netflix" was assumed to correspond to 10.8 GB, i.e. 4K content. Since then Netflix improved their encoding so much that some users complain about low bitrate, similarly to the controversy around SoundCloud in 2018, when they announced switching from 128Kbps MP3 to 64Kbps Opus.

What caused me to write this post is going over Electronics Goes Green 2020 proceedings (33MB .pdf) and seeing this figure on p.98:

The WLAN energy consumption quoted here is simply absurd, a home router transmitter and a set-top box receiver won't ever consume more than 1W together, if only because of government-mandated limits. The "Fixed Network" figure is more defensible: for example, Telefonica's 2020 report claims energy consumption of "78 MWh/PB", translating into 0.7 kWh / 9GB. Like Netflix, Telefonica improved this to 54 MWh/PB (the latest figure) in just one year. Oh, forgot to tell: the majority of their customers are mobile, not fiber/cable. Improvements on ISP side are so massive that LTE today is more efficient than cable 5 years ago.

There are two ways of looking at this. One is to do what we just did: take the global energy consumption by telecoms, divide it by the global amount of traffic, and then multiply by the file size. This can be justified as follows: a reduction in video traffic would reduce the peak demand and eventually translate into telecoms retiring their old inefficient equipment earlier than planned.

The other way is to recognize that every ISP subscriber requires a certain minimum amount of power just in order to be online, and the only way to reduce that energy consumption is to unsubscribe (and who wants to go fully offline?).

This is what Jens Malmodin from Ericsson Research did in his paper, coming up with the following "power model" (p.94 of EGG 2020 Proceedings):

Let's do a reality check here as well. Telefonica has 272 million mobile customers (let's simply ignore the rest and assume fiber contribution is not much), which implies the idle energy consumption of 272 * 10^6 * 1.2W * 24h * 365 = 2.9 TWh per year, according to this model. Their actual total energy consumption in 2021 is 6.1 TWh, or roughly 2.5 W / customer. Each customer gets on average 6.1 [TWh] / 54 [MWh/PB] / 272 * 10^6 / 12 = 35 GB / month; sounds reasonable for a mostly mobile customer base. If we plug in 1.5 W/Mbps, i.e. 12 J / MB, i.e. 12*3.6 = 43.2 Wh / GB, we arrive to 43.2 * 35 * 12 / 1000 = 18 kWh per customer per year, or 18 * 272 * 10^6 / 10^9 = 4.9 TWh. In other words, the model gives 2.9 + 4.9 = 7.8 TWh, which is fairly close to actual 6.1 TWh: for modern equipment, the coefficients should rather be 0.9 and 1.2 instead of 1.2 and 1.5 (keeping proportion the same).

Heck, let's ignore this further improvement, imagine that mobile traffic is dirt cheap, and everyone streams Netflix at 12 Mbps for four hours every day: 12 * 1.5 * 4 = 60 Wh, which averages to extra 60 / 24 = 2.5 W, meaning that the total jumps from 2.5 W to 5 W. This is still twice as low as an average modem+router (aka customer-premises equipment) consumes.

The real issue here is that there is no incentive to upgrade inefficient home routers. ISPs are interested in using them for as long as possible, and the free market is of no help either, because savings on the order of 1-2 euro/month don't justify investing 200-300 euro in a new router. Smartphones, on the other hand, are upgraded more often, if only because of wear and tear, and come with ever more battery-friendly chips. Hence, if you want to minimize your climate impact, just keep the home router turned off as much as you can (even Netflix has the offline download feature), and prefer tethering.

In case you want to learn more, this 100-page long whitepaper named "Carbon impact of video streaming" from June 2021 has more information on the topic than you ever wanted to know.