In 2008, the city of Beijing hosted the Summer Olympics, incidentally drawing global attention to the region's air pollution issues. Several weeks prior to the games, authorities closed nearby factories and placed restrictions on vehicles in and around Beijing—even going so far as to seed the clouds to encourage a cleansing rainfall—in an effort to improve the air quality for the athletes and spectators. The temporary restrictions did the job but not long after the closing ceremony, the pollution returned.
As China's capital prepares to host the 2022 Winter Olympics, the powers-that-be aren't satisfied with another short-term fix. They signed a deal to have Siemens build a facility that turns surplus wind power into emission-free fuel. The company will install a megawatt-scale electrolyzer, powered by a nearby wind farm, to extract hydrogen from water. The city's public transportation systems will use the resulting "green hydrogen" during and after the Olympics. The facility is part of China's efforts to curtail climate change by decarbonizing its power and transportation systems.
The same gas that propels hydrogen vehicles can also power emission-free backup generators, be combined with conventional fuels to reduce greenhouse gas emissions and provide an energy storage medium for renewable energy systems. Engineers are also developing gas turbines that burn pure hydrogen, which will deliver carbon-free combustion. Let's look at a few ways in which hydrogen can reduce or eliminate carbon emissions.
Transportation
Despite the less-than-stellar efficiency of water electrolysis, the fact that it produces clean fuel with a wide range of applications makes it a reasonable tradeoff. When the hydrogen is produced by electrolysis using electricity from renewable sources, the vehicles are truly emission-free.
Batteries are fine for small electric vehicles with relatively short range, but fast-charging technology leaves much to be desired, making long trips inconvenient. When it comes to large vehicles, such as ships, jet aircraft and locomotives, a battery’s low energy-to-weight ratio makes it incapable of delivering adequate power and range.
Hydrogen, on the other hand, is lightweight and scalable. Fuel cells operate near 70 percent efficiency, which is two to three times better than internal combustion engines, and emit nothing except water vapor. Increasing the range of a fuel cell electric vehicle (FCEV) only requires a larger tank, which can be refilled as quickly as that of a petroleum-powered vehicle.
Industry
Ninety percent of the hydrogen produced today is used by industry. Hydrogen is an ingredient in many synthetic fuels, fertilizers and polymers. It's also mixed with natural gas to reduce the carbon footprint of the steel industry, which is currently responsible for 7 percent of all man-made CO2 emissions. Unfortunately, most industrial hydrogen is extracted from fossil fuels in a process that releases some CO2 but not as much as burning fossil fuels. As PEM electrolyzers driven by renewable energy sources become more commonplace, water, not petroleum, can become the primary source of industrial hydrogen.
Renewable Energy Support
Because of its intermittent nature, renewable energy is still considered an auxiliary power source on the grid, not a source of baseload generation. For solar and wind to become the primary source of electric power, we need ways to store excess energy during high-generation, low-demand periods so we can use it when the renewable resources are low, which can be weeks or even months at a time. Grid-level energy storage must deliver high-quality power, low-energy consumption during standby operation, quick response times, large storage capacity and efficiency when operated intermittently.
From a cost and materials standpoint, batteries simply aren't up to the task of long-duration storage. The National Renewable Energy Laboratory (NREL) determined that batteries aren’t cost-effective if they have to provide for more than 12 hours at a stretch. When it comes to long-duration storage and generation, two very mature technologies—compressed air and pumped hydro—outperform batteries but both, especially pumped hydro, are dependent on geography. Among all storage technologies, hydrogen provides the best discharge duration, the highest capacity and the most versatility.
Energiepark Mainz
The Beijing plant will be Siemens' first electrolyzer in China, but the company already established the "power to gas" precedent in Germany, where Energiepark Mainz has been making hydrogen from renewable energy since 2015. Germany has a goal of 80 percent renewable generation by 2050, most of which will come from wind turbines. Energiepark Mainz is located near a wind farm and serves as not only an energy storage facility but also a research laboratory, providing insights into decentralized storage, hydrogen compression and storage technology, optimized local load management, hydrogen injection into natural gas pipelines and renewable energy grid integration. Here's a short video about Energiepark Mainz:
Efficiency Isn't Everything
For more than a century, we've accepted that the internal combustion engine is only 25 to 30 percent efficient, so let's not get hung up on the efficiency of electrolysis—which is still improving, by the way—especially when the power comes from a green source.
Grid operators often shut down wind turbines when power generation exceeds demand because it's easier to put the brakes on a turbine than it is to reduce production from a baseload generator. Although electrolysis is only about 70 percent efficient, a wind turbine that's not spinning on a windy day is 0 percent efficient. So, why not use that excess energy to split water molecules and produce clean fuel?