Catching Sunlight in a Bottle, a Big Step for Renewables
German scientists can now store the Sun’s energy in a jar and release it when needed as clean-burning hydrogen gas.
Solar energy has a big problem: we can’t control the Sun. It obviously doesn’t shine at night and the amount of its energy reaching the Earth’s surface is affected by the weather and time of year. So energy generated through solar farms, residential solar installations, etc. is unable to provide a consistent, reliable stream of electricity to power the grid. The solution is to store excess solar energy and release it as needed, but current battery technology is woefully inadequate to do so on a meaningful scale.
Fortunately, a team of German scientists from the Institute of Inorganic Chemistry at Ulm University developed a solution using the rare metal ruthenium.
Dunkelflaute and the Duck Curve
A German word meaning “dark wind lull,” Dunkelflaute is a well-known term in the energy sector, referring to a time period in which little or no energy is generated by solar or wind. For regions that have invested heavily in these forms of renewable energy, such a lull can pose a problem if other forms of energy creation aren’t present. For example, in recent years, Germany has emerged as a renewable energy leader, with over 45% of their energy being created through clean methods in 2020, yet they have a growing fear of “the winter problem.” This refers to the fact that energy demand is higher during the winter, yet solar energy production is at a minimum, coupled with the threat of extreme cold weather putting wind and solar out of commission, such as what happened to Texas in February 2021. If Germany were to find itself in such conditions, they might have trouble powering their electrical grid.
Two solutions to dunkelflaute are storing excess energy and keeping more traditional forms of energy generation around, but both of these come with problems of their own. First of all, our batteries don’t scale well enough to be used in grid-level storage. While much better designs exist in the research lab, virtually the only battery option is lithium-ion. These work well in most consumer electronics, but the size needed to store meaningful amounts requires them to be so big that they’re inefficient, don’t have a long life, and are at risk of overheating. And this is what happened to the Moss Landing Energy Storage Facility in California, the biggest utility-level energy storage facility in the world. It came online in December 2020, consists of 4,500 battery stacks, is capable of holding enough power for 225,000 homes, and was temporarily shut down in September 2021 due to overheating issues.
When it comes to keeping more traditional forms of energy generation like burning hydrocarbons, besides them being a detriment to the environment, they conflict with renewables, especially financially. This is because a coal plant, for example, can’t simply be turned on and off as needed, meaning it needs to be running well before its energy is needed. Grid managers often dump this excess energy to avoid overloading the grid. So its an awful waste of money and resources to generate energy nobody is going to use. Likewise, during peak solar hours, the grid could be overwhelmed and solar farms might be curtailed or have their energy dumped. So if you’re looking for investors to build a new solar farm, it’s not a great investment pitch to say that the facility will likely be offline and not making money for part its life.
The best example of the conflict between renewables and more traditional forms of energy creation is in California. They’ve invested so much into solar energy that they have trouble efficiently balancing solar with other forms of energy creation. In the graph below, known as the Duck Curve, the grey line at the bottom shows solar energy’s output, and as expected, it peaks during the day and bottoms out at night. However, energy demand gets a bump in the morning when people are waking up and the Sun begins to heat the Earth’s surface and in late afternoon, the hottest part of the day and when people are returning from their day. The problem here is that peak solar production doesn’t match up with peak demand, forcing other power plants to fill the gaps.
Sunshine in a Bottle
In a paper published in Nature Chemistry, Ulm University scientists unveiled a unique solar storage method using a combination of ruthenium, metal oxides, and sodium ascorbate. They described this mixture as an “electron-storage site and hydrogen-evolving catalyst,” which means that the Sun’s energy is stored in the mixture’s electrons and can be released as pure hydrogen gas when an acid, a proton donor, is added. With this method, solar cells aren’t needed, as the sunlight is absorbed directly.
Hydrogen gas is a highly sought after fuel because its only byproduct when burned is water and under the right conditions has a high energy per mass output. In a flame of pure hydrogen gas, burning in air, the hydrogen (H2) reacts with oxygen (O2) to form water (H2O) and releases energy [2H2 (g) + O2 (g) → 2H2O (g) + energy]. The problem, though, is that producing pure hydrogen is an energy intensive process. The most common method is steam-methane reforming, accounting for 95% of US hydrogen production. This method combines super-heated steam (1000 degrees Celsius) and the methane produced from natural gas extraction. With the help of a catalyst, the result is hydrogen and carbon monoxide [CH4 + H2O (+ heat) → CO + 3H2].
The team from Germany hopes their unique solar-storage and hydrogen production method will be the solution the renewable energy sector has been looking for. However, the main drawbacks are that ruthenium is expensive and their mixture can’t be used indefinitely. Despite these problems, they’re confident in their method, as they claimed that “The system is a minimal molecular model for artificial photosynthesis and enables the spatial and temporal separation of light absorption, fuel storage and hydrogen release.”
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