Is Liquid Air Energy Storage The Key To Making Data Centres Green?

Energy is a big issue, and the problem is not just using it, but storing it too. I’ve recently been looking at an approach to energy storage that could double up to provide backup power to data centres.

The big difficulty with running an electric grid is in storing the energy. It’s costly and not usually very efficient to store electricity, and the demand from consumers varies very rapidly, so the grid has to respond, more or less immediately to any peaks and troughs.

Energy storage blues

Add to this the fact that renewable energy sources such as wind and solar power cannot be switched on and off at will, and it is clearly going to be very difficult to get rid of the fossil fueled power stations that we rely on and are capable of meeting peak demands at a moment’s notice.

Increasing the amount of energy storage would decrease our dependence on fossil fuels, however. But how can we increase the amount of storage on the grid?  Pumped hydro-electric stations like Dinorwig in Wales are a help, but they can’t do it all.

One suggestion to provide more storage is to use batteries that are connected to the grid – such as electric vehicles during their charge cycle. Add up all the batteries and you can draw power from them as needed, as if from a large virtual battery.

But there are logistical problems there – these batteries are relatively small, and how do you make sure that enough of them are charged when the grid needs them? Other storage technologies are needed, preferably with high capacity and the ability to remain charged for long periods.

Data centres run from the mains, but they all have a need for energy back-up systems. Typically, these are diesel generators which take over from UPS (uninterruptible power supplies) when there is a problem with the grid supply. Other backup energy sources are being considered, including fuel cells, but how about if they adopted an energy storage system which could save off-peak energy from the mains, and give some back when required?

Last month, I heard about a possible technology that might fit the bill, at an ecoConnect Green in the City event in London.

Liquid air engineering

If air is cooled, using a conventional refrigeration system, it condenses, and the liquid air can be kept in pressurised cylinders. When electricity is needed, the air is allowed to evaporate, driving turbines to generate electricity. This “cryogenic” storage is in use in prototype form, in Slough, operated by a company called Highview Power Storage.

Like all energy storage, this isn’t 100 percent efficient. The basic level of efficiency is around 50 percent, but this can be increased to around 70 percent if there is a source of waste heat which can be used to warm the gas up and help evaporate it when energy is needed.

That maximum-efficiency level may not sound that great, but apparently it is roughly what is achieved in Dinorwig, where water is pumped uphill during offpeak times, to generate hydroelectric power at peak hours.

All we need is a good source of waste heat – and who do we know with a load of waste heat, and a whole industry trying to reduce the energy associated with getting rid of it? That’s right, the data centre industry!

Cryogenic storage can be switched on very quickly – it’s literally as easy as turning on a tap. So the specs are probably as good as diesel generators, but without any on-site pollution.

The way it would work is as follows: the data centre invests in some more backup cryogenic storage than it would need in a power cut, and charges the system up during off-peak hours. Hours of peak demand for electricity probably coincide with peak demand for data centre services (in business and leisure hours, people do a lot of Facebook and social media).

The servers are busy, they are producing waste heat, and the data centre owner uses some of that heat to regenerate energy from the cryo storage – being sure to leave enough for its disaster recovery needs. If there is an outage, the cryo system kicks in and services the data centre exclusively.

At the EcoConnect event, Highview CEO Gareth Brett agreed with my suggestion, but said he’s not had much enthusiasm yet from data centres.

Anyone care to tell me what I am missing? What’s the drawback to cryogenic backup power in data centres?

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