Explainer: peak and average electricity demand in data centres

7 October 2021 

Well, data centres have had quite a media run of it the past couple of weeks – and most recently they’ve been up for discussion at the Joint Oireachtas Committee on Climate Action (JOCCA). 

However, it turns out when it comes to their electricity demand, there are important elements in here for us to understand. 

We checked in with Professor Barry McMullin on the matter – and he gave us the lowdown. 

Quick recap: what are data centres? 

They physically house our online world. Everything we put online needs to be stored somewhere – so it’s like the hard drive for your computer but on a massive scale. 

Dublin is currently the largest data centre hub in Europe – we’ve got 70 operational ones to date. 

The argument typically made is that Ireland has the right climate for these centres – they can’t overheat and our average temperatures prevent that from happening. 

As we said above, data centres essentially power the internet – and with that much going on, it’s going to need a lot of power and electricity behind them. 

To give you an example, it’s been reported that a data centre with a 60 megawatt load alone could use the same amount of electricity as Kilkenny. 

So what is the electricity demand picture like then? 

This is where things get a bit trickier. 

There’s two important things (and there are a lot more of course) to understand here with demand when it comes to data centres: there’s average demand and then there’s peak demand. 

Average demand is the total amount of demand from data centres in the course of a year. For example, EirGrid have projected that data centres could take up 23 per cent of average electricity demand by 2030 based on their latest assessment

This figure is crucial for emissions, Prof Barry McMullin stressed to The Green News. 

Both EirGrid and the Electricity Association of Ireland (EAI) have made it clear that gas will be a necessary component of the electricity generation mix until the end of the decade – which means that the emissions from its use will be with us, too. 

So if we’re seeing data centres account for 23 percent of that demand, that will translate into them accounting for 23 percent of total electricity emissions. 

Or, Prof McMullin pointed out, “there will be 23 percent more emissions than there would have been if those data centres weren’t connected.” 

Of course, this depends on how much of this electricity is being produced by renewable sources. Theoretically, if it’s all zero-carbon sources, then the emissions aren’t a problem. 

But, as we said earlier, it looks like gas will be with us for at least another decade so we can imagine that a portion of this demand will result in greenhouse gas emissions. 

Still with us? Good. Just checking. 

Now – onto the issue of peak demand, which is all to do with the risk of grid instability.  Demand for electricity fluctuates seasonally (with more demand coming in colder months) and day-to-day (as there is generally less demand on the weekends).

EirGrid has to keep the amount of generation essentially equal around the clock in order to meet this varying demand. This challenge is made even more complicated due to the different levels of wind and solar-generated electricity depending on weather patterns and the time and day.

If demand peaks to a point where we physically can’t meet the demand with the supply of electricity – even over just minutes – we’ll have a blackout. 

So peak demand refers to the highest amount of electricity demanded over a relatively short period of time (15 minutes) as experienced over a longer period, like a whole year.

When we find ourselves at a peak or near-peak demand, that’s when we have the greatest risk of a blackout – and this is what ultimately dictates how much total generation capacity EirGrid, and the Commission for the Regulation of Utilities, need to plan to have available (with some extra too, just to be safe).

According to EirGrid’s testimony at the Joint Oireachtas Committee on Climate Action earlier this week, if the risk of a blackout does present itself, they’re going to direct data centres to switch to their own back-up generation of electricity in order to prevent one from happening.

So just to recap: average electricity demand is all to do with emissions, while peak demand is critical for understanding the risk of blackouts. 

And while data centres should be able to power their own sites with back-up generators if they need to, the problem still remains around the potential emissions increase data centres could create depending on how the next decade unfolds. 

Are you curious to know more about data centres? Let us know what you want us to dig into by either sending us a message on Twitter or by emailing us at editor@greennews.ie 

About the Author

Kayle Crosson