Data Centre Magazine recently reported that data centres currently account for around 3% of all global electricity consumption. With the growth in demand for data, this figure is predicted to rise to at least 4% within a few years, with the average hyperscale facility consuming between 20 and 50 megawatts of power annuallyi.
This situation is clearly unsustainable if we are to meet carbon emission targets by reducing our reliance on electricity generated by conventional fossil fuel technologies and supplied over a national electricity grid.
For data centres, one of the options being widely considered is the use of hydrogen power. This is not, however, a clear-cut choice! Hydrogen production can take various forms, not all of which resolve the fundamental challenge of minimising or eliminating carbon emissions. For example, so-called grey hydrogen is produced using natural gas or methane in an energy-intensive process. Adding carbon capture and storage to the process results in blue hydrogen, while pink hydrogen is produced using nuclear power. None of these methods are, from an environmental aspect, ideal.
The best option, where it is practical, is to choose green hydrogen, with local renewable wind or solar energy sources being used to power an on-site hydrogen generation plant. This uses an electrolyser, where an electric current is passed through water to separate it into its constituent elements: hydrogen and oxygen.
In simple terms, the process of electrolysis uses an electrolytic cell, containing an electrolyte solution (for example, water with sodium hydroxide added to improve conductivity) plus two electrodes: an anode and a cathode. When an electric current is passed through the electrolyte, water molecules near the anode are oxidized, releasing electrons and forming oxygen. The electrons subsequently flow through an external circuit to the cathode, where they are used to reduce water molecules, generating hydrogen. The hydrogen is normally stored until it is required for use in a hydrogen fuel cell, which produces electricity, with the by-products being heat and water.
This arrangement is simple, efficient and scalable, making it ideal for use in data centres. It does, however, depend for its success on the availability of a reliable supply of purified water.
Purified water is essential
Water for hydrogen production is generally drawn from a mains supply, borehole or surface source. In each case, it will contain varying degrees of impurities, in the form of minerals, salts, chemicals and microorganisms. All of these have the potential to affect the efficient operation of the hydrogen production system, causing corrosion and fouling the electrolyser; this leads to a reduction in efficiency, increased energy consumption and high operating and maintenance costs.
The solution is to introduce a suitable water purification system. The exact configuration will depend on the nature of the source water and the type of electrolyser used. Typically, a system will incorporate pre-treatment to reduce particulate matter and eliminate chlorine, plus high-performance reverse osmosis (RO) membranes to remove up to 99% of minerals and microorganisms, with the output passing through either an ion exchange or continuous electro-deionisation (CEDI) unit for final polishing.
It is important that the water purification system is correctly specified and sized. It should be noted that as the mass of oxygen in water is 16 times greater than that of hydrogen, then it will account for 89% of the molecular weight of each kilogram of water. In other words, 9kg of water will be required to produce 1kg of hydrogen.
Sizing the water purification system also depends on understanding the power rating in MW of the electrolyser and the amount of energy required to convert water to hydrogen. As a rule of thumb, approximately 0.2 m3/hour is required for each MW of electrolyser capacity.
To avoid complications, the easy answer is to work with a supplier such as Purite with the knowledge and experience to understand your exact requirements. We also have the engineering facilities and technical support to help you develop a customised and future-proof water purification system that will deliver the quality and volume of water that you need for the efficient generation of hydrogen.