This article is Part 2 of a series featuring solutions for always-on mission-critical microgrid applications. The last installment discussed battery energy storage systems (BESSs) using lithium-ion (Li-ion) batteries for managing hybrid energy sources.
While still considered an emerging technology in some industries, fuel cells have been used in various applications for more than 50 years. Due to their high costs, fuel cells were primarily used by the U.S. government for aerospace applications — most famously the Apollo 11 mission, which first landed humans on the moon. However, the cost of hydrogen fuel cells has dropped significantly in recent years, making them an increasingly viable option for mission-critical organizations looking for more carbon-neutral, always-on power sources for local generation.
An introduction to fuel cells
Fuel cells operate differently than other energy storage devices, such as batteries, but the process is rather straightforward. They generate electrical energy from chemical reactions created by a fuel source and oxygen. For example, a fuel cell will split the natural gas molecule, essentially peel off the hydrogen, and use that hydrogen as its fuel to convert to electricity. When hydrogen is used as a fuel source, the only byproducts are water and heat.
The most common fuel sources for fuel cells include hydrogen and natural gas. Compared to traditional diesel generators, natural gas-powered fuel cells are relatively clean but do generate some greenhouse gas emissions. Hydrogen can be produced from renewable energy through the electrolysis of water — referred to as “green hydrogen” because it does not generate greenhouse gas emissions during the production process. Since hydrogen fuel cells do not generate emissions, using green hydrogen to power fuel cells helps enable zero-carbon, on-site energy generation.
The hydrogen distribution network is early in its maturity curve. Hydrogen used to power fuel cells in stationary power applications needs to be transported by truck from where it’s produced to where it’s being used and stored. An alternative is a hydrolyzer on-site that is run from local photovoltaic (PV) or wind sustainable sources. There are storage options to support 24, 48, or even 72 hours of continuous operation. This makes hydrogen fuel cells an emerging option for microgrid solutions that toggle between primary power sources (the grid) and secondary or tertiary sources, including renewable sources of energy, to deliver necessary backup power and optimized energy use.
Potential microgrid fuel cell applications
Fuel cells are typically powered by the underground natural gas pipeline if they are a solid oxide fuel cells (SOFCs) or hydrogen if they are polymer electrolyte membranes (PEMs). They can provide long-term backup as long as there is a hydrogen source. Fuel cells also can be connected on the primary source side of a mission critical distributed energy system (DES). This allows mission critical businesses to perform critical elements of their business even during grid outages.
Connecting a fuel cell microgrid in the primary source configuration can help mission critical businesses save on energy costs, guard against a loss of revenue due to short or long outages, and provide resiliency and reliability. Here are a few examples of these applications.
Pairing fuel cells with a UPS — Fuel cells are relatively slow to respond to load changes, creating transients, and therefore, they need a way to dissipate the excess energy. This can be accomplished through UPS systems. By configuring the fuel cells and the UPS systems' lithium-ion batteries in parallel, the fuel cells can dissipate excess energy resulting from load changes by storing energy in the battery system. Using this configuration, the system does not even have to transfer the load to the backup power source, but rather, the system transfers the load to the batteries when an outage occurs. Therefore, the batteries are continuously charged by the fuel cells until stored hydrogen is depleted. UPS energy management capabilities will also be used to increase fuel cell value by enabling peak shaving and other grid services. Fuel cells can be spongey, so UPS lithium-ion batteries help stiffen up the fuel cell on load step and help absorb energy on load drops.
Proposed microgrid point of electrical service as a primary source — Fuel cell microgrids can be incorporated in the primary source capacity of a mission critical electric systems alongside the utility grid. When outages occur, fuel cell microgrids can carry the load. While backup power must still be available, this reduces the need to run on backup generators in the case of a grid outage. It also helps mitigate the risk of diesel supply issues in the event of longer outages, which can be difficult to restore in extreme weather emergencies.
Integrating additional distributed energy resources (DER)s with fuel cells — Additional on-site generation resources can be integrated into a fuel cell microgrid. For example, if a facility has on-site interconnected solar power systems with anti-islanding, when the grid goes down, the solar system is disconnected. In this scenario, the solar system cannot power the facility during the outage and becomes a dead asset. However, with the right power architecture that includes fuel cells, this solar system can be converted to an active resource during outage conditions by providing solar energy to a BESS and can be utilized to its maximum capacity. Similarly, on-site batteries and engine generators also can be integrated, during which the fuel cell system will be the base power and the other sources will be dispatched to cover variability in the load.
Utility grids in most regions are unlikely to provide 100% renewable power to all customers for the foreseeable future, so the responsibility is on operators to work with partners to develop solutions that enable carbon-free operation. Local energy generation using solar or wind power isn’t practical for most mission-critical sites, and the intermittency of alternative energy creates challenges for always-on applications. As they become more cost-friendly, we could see hydrogen fuel cells deployed in conjunction with a microgrid to produce a viable solution for on-site energy generation at a wide range of mission-critical applications.
