by Jeff Clark
Although hydrogen generally doesn’t come up in a discussion of alternative energy sources, it is a topic relevant to cleaner energy use. So, what’s the difference, and what is hydrogen’s potential role in the data center? Apple, for instance—in addition to building a 20 megawatt solar farm—is also planning a large hydrogen fuel cell project at its Maiden, North Carolina, facility. Can hydrogen sate the data center industry’s ever growing power appetite?
Hydrogen: A Storage Medium
To get a good idea of the basic properties of hydrogen, just think of the Hindenburg: the giant German airship (dirigible) that plunged to the Earth in flames in 1937. The airship gained its lift from hydrogen gas: a very light (i.e., not dense), inflammable gas. Although hydrogen is plentiful (think water, hydrocarbons and so on), it is seldom found in its diatomic elemental form (H2). So, unlike coal, for example, hydrogen is not a readily obtainable fuel source. It can, however, be used as a means of storing or transporting energy—and this is its primary use. As a DatacenterDynamics interview with Siemens (“Using hydrogen to store energy”) notes, “Hydrogen is a multi-purpose energy carrier… Also, hydrogen as a storage medium is a concept that has already been tested in several domains.”
Hydrogen is thus in some ways like gasoline: it is simply a chemical that certain types of equipment can convert into energy and various byproducts. But it’s the nature of these byproducts that makes hydrogen appealing.
Under ideal conditions, the burning of hydrogen (think Hindenburg) produces water and heat as its only products, making its use in internal combustion engines preferable (in this sense, at least) to fossil fuels. But even more useful would be a process that converts hydrogen more directly into energy and water—enter the fuel cell. A fuel cell splits hydrogen into protons and electrons, creating an electrical current. The protons combine with oxygen in a catalytic environment to yield water. What more could a data center ask for? (For a simple animation depicting the operating principles of a fuel cell, see the YouTube video Hydrogen Fuel Cell.)
The fuel cell produces electricity as long as hydrogen fuel is supplied to it. Its characteristics from a physical standpoint are nearly ideal: electricity on demand with virtually no production of carbon compounds or other emissions. Because hydrogen can be stored, it represents energy that can be consumed as needed, not necessarily right away (as in the case of solar or wind power). Sounds great—but as always, there are some caveats.
Getting Your Hands on Hydrogen
As mentioned above, hydrogen does not exist naturally in a manner that makes it readily available as a fuel. Practically speaking, it must be produced from other materials, such as water or fossil fuels. The two main processes are electrolysis of water, whereby an electric current splits water molecules into elemental oxygen (O2) and hydrogen (H2), and steam reforming of hydrocarbons. In each case, energy input of some kind is required, either in the form of electrical energy to electrolyze water or in the form of stored chemical energy in the form of a hydrocarbon. Electrolysis is one means of storing energy from renewable resources like solar or wind, avoiding entirely the need for mined resources like natural gas or coal. Naturally, the efficiency of these processes varies depending on the particulars of the process, the equipment used and so forth.
Alternative processes for generating hydrogen are under investigation—such as biomass production—but these processes do not yet generate hydrogen practically on large scales. Whatever the generation approach, however, the gas must then be stored for transport or for later use.
Storing Hydrogen—A Slight Problem
Hydrogen is an inflammable gas (again, think Hindenburg), but it is not necessarily more dangerous than, say, gasoline vapors. The main problem with storing hydrogen is that compared with other fuels—such as gasoline—it contains much less energy per unit volume (even though it contains more energy per unit mass). Practical (in terms of size) storage requires that the hydrogen be compressed, preferably into liquid form for maximum density. And herein lies the main difference relative to liquid fossil fuels: the container not only holds an inflammable material, but it is also pressurized, creating its own unique challenges and dangers. Fuel leakage into the atmosphere is more problematic, and some environmentalists even claim that this leakage, were hydrogen used on a large scale, could have harmful repercussions on the environment.
Even in liquid form, hydrogen still lags other fuels in energy stored per unit volume. Thus, when implemented in automobiles, for instance, fuel-cell-powered automobiles lack the range of conventional gasoline-powered vehicles. And then there’s the cost of fuel cell technology, which is currently prohibitive. Claims of falling fuel cell prices are dubious, given the unsustainable subsidies from the federal government and some states (like California).
Hydrogen for Data Centers
Apple’s Maiden data center is the highest-profile facility implementing fuel cell technology. According to NewsObserver.com (“Apple plans nation’s biggest private fuel cell energy project at N.C. data center”), Apple will generate hydrogen from natural gas and will employ 24 fuel cell modules. The project is slated for an output of 4.8 megawatts—much less than the data center’s total power consumption, but still a sizable output.
The use of natural gas to generate hydrogen still creates carbon emissions, so this project won’t satisfy everyone (although whether carbon dioxide is as bad as its current politicized reputation would suggest is hardly certain). Nevertheless, like Apple’s large solar farm at the same site, this hydrogen fuel cell project will be a good test of the practicability of hydrogen in the context of data centers.
Hydrogen: Will Most Companies Care?
Jumping into the power generation arena is not something most companies (particularly small and midsize companies) can afford to do—let alone have an interest in doing. So, pending availability of some affordable, prepackaged hydrogen fuel cell system, don’t expect most companies to deploy such a project at their data center sites. Currently, large companies like Apple and Google are among the few dabbling in energy in addition to their primary business. Most companies will, no doubt, prefer to simply plug their data centers into the local utility and let someone else worry about where the energy comes from—these companies wish to focus on their primary business interests.
Conclusion: What Exactly Does Hydrogen Mean for the Data Center?
Hydrogen fuel cells offer some major improvements in controlling emissions, and hydrogen delivers some benefits as a means of storing and transporting energy. But fuel cell technology lacks the economic efficiency of other, traditional power sources, so it has a ways to go before it can attain the status of coal or nuclear, or even smaller-scale sources like solar. Furthermore, the applicability of hydrogen (as such) to data centers is unclear. Power backup seems the most likely present candidate for application of hydrogen and fuel cells. In time, Apple’s project may demonstrate the practicality of electricity via natural gas as another possibility. Until then, however, the industry must wait to see whether this technology matures—and becomes economically feasible.
Photo courtesy of Zero Emission Resource Organisation