Thursday, May 13, 2021

The Energy Cost of Online Living in Lockdown

Readers of his blog will know that one of the many things ethical I worry about is the energy cost of AI. As part of the work I'm doing with Claudia Pagliari and her National Expert Group on Digital Ethics for Scotland I've been looking also into the energy costs of what is - for many of us - everyday digital life in lockdown. I don't yet have a complete set of results but what I have found so far is surprising - and not in a good way.

So far I've looked into the energy costs of (i) uploading to the cloud, (ii) streaming video (i.e. from iPlayer or Netflix), and (iii) video conferencing.

(i) Uploading to the cloud. This 2017 article in the Stanford Magazine explains that when you save a 1 Gbyte file – that’s about 1 hour of video - to your laptop’s disk drive the energy cost is 0.000005 kWh, or 5 milliWatt hours. Save the same file to the Cloud and the energy cost is between 3 and 7 kWh. For comparison your electric kettle burns about 3 kWh. This mean that the energy cost of saving to the cloud is about a million times higher than to your local disk drive. 

The huge difference makes sense when you consider that there is a very complex international network of switches, routers and exchange hubs, plus countless amplifiers maintaining signal strength over long distance transmission lines. All of this consumes energy. Then add a slice of the energy costs of the server farm.

(ii) Streaming video. This article in The Times from May 2019 makes the claim that streaming a 2 hour HD movie from Netflix incurs the same energy cost as boiling 10 kettles (based on the sustainable computing research of Mike Hazas). To estimate  how much energy that equates to we need to guess how full the kettle is. A half full 3kWh kettle will take about 2 minutes to boil, and consume therefore 100 Watts. Do that 10 times and you've burned 1kW. A DVD player typically consumes 8 Watts, so streaming costs 125 times more energy.

Again this makes sense against uploading to the cloud, except that here you are downloading from Netflix servers. A 2 hour HD movie is alot of data, around 10GBytes, so 10 times more than the case for (i) above.

(iii) Video conferencing. This post on David Mytton's excellent blog explores the energy cost of Zoom meetings in some detail. David estimates that a 1 hour video zoom call with 6 participants generates between 5 and 15GB of data and that the data transfer consumes between 0.07 – 0.22kWh of electricity. Using our benchmark of kettles boiled this is pretty modest - at most less than one tenth of the energy cost. 

However this estimate makes 2 assumptions: first that you are connected via cable or fixed line - which here in the UK costs 0.015kWh per GByte. A mobile connection costs about seven times that at 0.1kWh/GB. And second, this estimate measures only the energy costs of data transmission and fails to take account of the energy costs of Zoom's data centres, which - if (i) and (ii) here are anything to go by, could be significant, especially since there aren't any in the UK and the default servers are in the US.

As this article on the Zoom blog explains, Zoom calls are not peer to peer. The video from each participant is streamed first to a zoom server then broadcast to every other person on the call. As David Mytton says Zoom don't release information on the overall energy costs of calls. I strongly suspect that if server energy costs were factored in they would be in line with cases (i) and (ii) above. Even so, I feel sure that David Mytton's overall conclusion remains true: that the energy cost of Zoom meetings is significantly lower than all but local or regional travel.


I would like to see networking services like cloud storage, video on demand and video conferencing publish a meaningful energy cost. When we buy packaged food from the supermarket we expect to read the calorific energy value of each item, broken down into fat, salt and so on.  It would be great if every online transaction, from sending an email, to watching a movie revealed its energy/carbon cost. Not just for energy geeks like me, but to remind all of us that the Digital Economy is *very* energy hungry.

I would welcome any additional data which either adds to the above (especially the energy costs for smaller online transactions like tweets, emails or card payments), or shows that the estimates above are wrong. 

Related blog posts:

On Sustainable Robotics
Energy and Exploitation: AIs dirty secrets
What's wrong with Consumer Electronics? 


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