Can Data Centres Ever be Carbon Neutral? Truth vs Green Wash
Author: Prof. Ian Bitterlin
The 'efficiency' of nearly all data centres is zero unless you define them as heaters. They are 100% efficient as heaters, as they turn all the incoming energy to heat and >99% of them reject that into the environment. That is why the most common metric of PUE (ISO/IEC 30134) uses the term 'effectiveness', not 'efficiency'. Very few offer low-grade waste heat to adjacent use/processes, but it can be difficult to engineer unless you have a district cooling/heating system passing your door, especially if your facility runs at partial load. There is not enough heat generated to pay for the recovery and make a profit.
The question refers to 'carbon neutrality' and 'greenwash', which are inextricably linked, but we are trying to achieve Sustainability, so I will start there. By definition, Sustainability is achieved in three steps that must be taken in order:
Improve the process
Use renewable energy
The data centre industry has turned this on its head. Today, it goes straight for renewable energy, even from other countries and continents, and claims that the data centre is 100% green, sustainable, or zero-carbon. In terms of greenwashing, this claim, in isolation, is a perfect example, mainly because all forms of energy production (including hydro, wind, solar, and nuclear) has a carbon content, and IPCC 2014 sets down the internationally agreed kgCO2/kWh. Luckily wind and nuclear (one each of intermittent and continuous) are the lowest carbon sources at ~14gCO2/kWh. If you are unsure why wind has a carbon expenditure, consider the energy used to manufacture turbine blades, masts, foundations, installation, connection, service, substations etc. The life is 15 years, and a high proportion of the turbine cannot be recycled; hence the embodied carbon is amortised over the service life. So, 'zero' or 'neutral' isn't possible, but don't get me wrong, low-carbon sources must supplant fossil fuels as soon as possible to check the rate of climate change.
Step 1: Reduce Demand.
Data centres have grown exponentially in response to data traffic growth, despite the exponential increase in ICT hardware capacity per watt. Data traffic in Europe has been increasing at an exponential rate of 4% per month for more than 20 years. This is in the order of 60%CAGR, whilst ICT hardware has been improving at 40-50%CAGR. Thus, data centre power has been growing at a net -15%CAGR. Of course, the detailed growth and capacity curve have been step-functions over time, but the trend line has been inexorably steady. Currently, personal use such as HD video streaming and social networking is the dominant driver of that growth. Even through the pandemic with the correlative move to remote working, daily traffic continued to peak at 10 pm, unlikely caused by work meetings on Zoom.
The improvement in ICT capacity/watt has largely exceeded that forecast by Gordon Moore's law. Still, we are just on the cusp of graphene replacing silicon and reaching 1.5nm. That could be the last gasp of Moore's Law when we will have no choice but to constrain data traffic growth. We probably can't get the lid back on Pandora's Box, so if we want to talk about 'sustainable' data centres, we must dislocate demand and view the data centre in isolation. I disagree with doing that, as it is sweeping the environmental problem under the carpet. Still, if we don't do so, then ICT is not sustainable in any form as demand will continue to grow unfettered. Let's not forget that more than 40% of the global population doesn't have an internet connection, but in the future, they could be streaming 4K movies to their mobile phones whilst the floodwater passes their chins. I regret that I am not optimistic about us solving this problem until well after the 11th hour.
Step 2: Improve Process
Here we have three opportunities to reduce energy demand, manage the ICT hardware, the PUE, and reuse waste heat. Managing the ICT hardware is both behavioural and practical. First, we need to purchase hardware with capacity/watt as the main factor for the application. Then, we need to utilise the hardware to the maximum possible extent (including virtualisation if applicable and at >60%), ending our long-term under-utilisation in colocation and enterprise facilities (even today at 10-15%). Finally, whilst the effect of Moore's Law et al. are available to us, we then need to refresh hardware regularly to take full advantage of increasing capacity/watt.
An argument can be made to shift all load to hyperscale facilities – what you may call the cloud, but I would not – where utilisation is maximised, but that must not come with lower availability, reducing attractiveness to the user. Cloud, just another data centre, should be viewed with the energy used in data transport, not just in the data centre - the advantage of 'Edge'. There is a stronger argument for regulating the demand for social networking via taxation and restricting the video definition to save energy, particularly on mobile devices. In the face of climate change, anything that saves energy that is nice to have but not essential should be regulated, most probably by taxation, as was recommended in 1865 by WS Jevons and his Paradox.
In Step 2, we must include reducing PUE to improve the process, but here we run into a problem highlighting some of our dirty washing. Reducing the PUE in new facilities is easy. However, it usually requires the client to agree to take increased risks to his availability of ICT service by reducing M&E redundancy and investigating various ways to manage the ICT hardware thermally. In climates like those of London, Frankfurt, Amsterdam, and Paris, reaching a PUE of 1.30 without water consumption and 1.20 with is not hard.
So, why has the reported PUE (EU CoC Participants Scheme) hardly reduced in the last five years and is still higher than 1.75? The reason is that data centres are built to serve a purpose in a location to suit the business plan. They are rarely fully loaded, and only a very few use evaporative or adiabatic cooling, and PUE largely depends on climate, cooling efficiency and load. The high PUE reflects the preference of most data centres to achieve high availability before low energy. Even the innovative Google (1.12) and Facebook (1.07) don't shout about their PUE anymore.
The greatest opportunity to reuse waste heat will be 'edge' single cabinets in city centres, local hotels that can use 15-20kW of low-grade hot water 24/7.
Step 3: Renewable energy
Operators can buy any blend of power they want where the data centre is in the same grid network in an acceptable Power Purchase Agreement (PPA). The grid then has to balance supply and demand when the fuel/source mix varies. That is why places like Dublin, Frankfurt and Amsterdam have occasionally placed moratoriums on new data centres - because their grid emissions rise when the wind doesn't blow hard enough. But Virtual PPAs should be better explained. Plenty of large operators have data centres located in 100% fossil-fuelled grids that claim to be '100% green' (renewably powered) by purchasing the Renewable Certificates in distant grids with no power connection.
In sum, energy efficiency and carbon neutrality is a big subject that can only be addressed when the audience is fully aware of what is really happening at this time – First-Class Greenwash!
This article was originally published in DCM magazine, click here to find it