Hydrogen vs. diesel: The great datacentre backup power debate

In this guest post, Martin Keenan, technical director at IT distributor Avnet Abacus, sets out why hydrogen fuel cells could be on course to replace diesel generators as the datacentre industry’s go-to source of backup power.

Hydrogen fuel cells are a rapidly maturing technology, finding interesting new applications on a regular basis. One particularly promising area is in emergency power situations in datacentres, where traditionally diesel generators were the go-to solution.

Presently diesel power underpins much of the infrastructure used to power our increasingly digital economy. Datacentres and server farms might use the grid or take advantage of local power generators for their everyday operations, but during power outage events, backup generators are required to maintain uptime.

These generators have traditionally been diesel powered – a situation that is beginning to shift in favour of greener, less polluting alternatives, including lithium ion batteries and hydrogen fuel cells.

Driving away from diesel

This swing is occurring for a variety of reasons. Some drivers include the increased investment from colocation and hyperscale datacentre operators. This alone has generated substantial demand, especially as larger capacity facilities (more than 15 MW) require multiple generators at a single location, sometimes just to meet their power requirements.

Other drivers are the broader move towards sustainability and renewable energy by the datacentre industry, as green issues continue to move up their clients’ boardroom agendas.

Many jurisdictions have also introduced stringent regulations regarding the procurement and operation of diesel generators too.

There are also the maintenance and logistical complexities that diesel generators raise. Diesel fuel has a limited shelf life, so stores need to be refreshed regularly, and mechanical generators require regular testing to ensure they are serviceable if needed. These are all specialised duties that require qualified technicians, logistic support and personnel that would otherwise not be required by a datacentre operator.

That said, there is still a substantial market for diesel generators. A recent analyst report predicted the datacentre generator market is expected to grow at a Compound Annual Growth Rate (CAGR) of over 2% between 2019–2025, with the bulk of activity in Europe and the US.

Among the US diesel generator projects implemented in 2019, around 35% had a power capacity of 5–15 MW, 28% had more than 15 MW of capacity, and 35% of the projects had up to 5 MW of power capacity.

Google estimates there are a total of around 20 gigawatts of backup diesel generators distributed globally, during a study published as part of an announcement it made about testing banks of Lithium-Ion batteries as an alternative backup power source within its datacentres.

The internet search giant said it would begin testing the 3MW battery backup solution at its St Ghislain datacentre in Belgium, with an eye to providing load-balancing services to the grid as a potentially valuable side benefit.

Hydrogen fuel cells as an alternative to diesel

The other major competitor in this race are hydrogen fuel cells. Microsoft has been championing these as an alternative source of backup energy for some years, testing solid oxide fuel cells (SOFCs) back in 2013 and proton exchange membrane (PEM) fuel cells more recently.

Microsoft announced in July 2020 that 10 racks of datacentre servers had been powered purely by hydrogen fuel cells for 48 consecutive hours, in a test aimed at replacing Azure datacentre diesel generators with PEM fuel cells.

The company noted that the cost of fuel cells has plummeted, and that the use of an on-site hydrogen storage tank and an electrolyzer enables the datacentre to act as a power grid load balancer.

This works by using excess energy (from renewables such as wind farms) to convert water into hydrogen, then starting up the fuel cells when there is high demand for electricity. In addition, hydrogen-powered commercial vehicles could fill up from the system, creating better return on investment and aiding decarbonisation of the grid.

Hydrogen vs. diesel: The drawbacks

There are of course challenges to overcome: storing hydrogen is more complex and demanding than diesel, and while the cost per unit of a PEM fuel cell is broadly equivalent to the same capacity diesel generator, hydrogen is around three times more expensive as a fuel when all costs are factored in.

One method of offsetting the hydrogen costs is to simply use a small solar array to ‘trickle charge’ larger hydrogen storage tanks when the sun shines – especially relevant for backup scenarios, where running the cells for more than a few hours is unlikely. However, even this ingenuity raises questions around the carbon debt of the solar panels, and that is before getting into the ethics of platinum mining, given platinum is a key component of PEM cells.

While it is clearly still early days to announce the ‘death’ of the diesel generator in a datacentre context, both batteries and fuel cells offer strong potential alternatives. As well as delivering backup power in a cleaner and more sustainable way, the ability to load balance the electricity grid adds an additional layer of value for datacentre operators and utility companies alike.

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