RENEWABLE ENERGY: THE HYDROGEN SOLUTION
August 2, 2020 § 12 Comments
The two principal sources of renewable energy share a serious shortcoming. As has been discussed in these pages over the years, wind and solar do not generate electricity when the wind does not blow, and the sun does not shine. Germany gets 40% of its power from renewable sources. But on certain days, that percentage jumped up to 75% and on other days it plummeted to 15%. The (literally) rainy days had electricity augmented from a variety of sources, including batteries. But the days of surplus sometimes required idling of the generation.
Great advances have been made in lowering the cost per unit in both wind and solar. But the need to level the load has never been more important because those very advances have increased the footprint. Some have rushed to use natural gas generators to fill the intermittency gap. This has caused consternation, with some positing the notion that renewables perpetuate fossil fuels because of this dependency. This concern ignores the fact that storage is being investigated at many levels.
Electrochemical storage is the only reasonable option for devices that are carried or move. In many cases, the options are even more limited to light weight batteries. But stationary applications have other options. One that has been in use, where feasible, is pumped water storage. Excess electricity is used to pump water to a high storage site, such as at a dam. When needed, it flows back down to generate electricity. Danish windmills utilize Norwegian hydroelectric sites for this purpose.
The flavor of the day is hydrogen. Excess electricity is used to electrolyze water, producing hydrogen and benign oxygen. The hydrogen may be stored on location to be used to power turbines to produce electricity when needed. In this it serves a similar purpose as does natural gas for the back up generators. As in the case of natural gas, the relatively low duty cycle stretches the pay back period of the capital equipment. Efforts are under way to reduce capital and operating costs. In the former area, expensive platinum electrodes are being replaced with base metal with novel coatings. Operating efficiency improvements are also being targeted. By its very nature, the method is conducive to small scale distribution. Electrolysis to produce hydrogen may be here to stay.
Produced hydrogen could find applications other than for generating electricity. An interesting variant has been piloted for over a year in Cappelle-la-Grande, a town in northern France, by the energy firm Engie, where the hydrogen is blended into existing natural gas pipelines. Hydrogen is a very small molecule and initially there were concerns regarding leakage. But a 25% blend was found to be retained and did not materially corrode the pipes. Furthermore, household burners were found to operate efficiently with that mix. In fact, the mix produced a cleaner burn. Most European countries permit the blend. Some are considering repurposing natural gas lines to exclusively distribute hydrogen.
Hydrogen is an important reagent used in all refineries. Hydrogenation of edible oils is another application. But the workhorse application for this source may well be the admixture into natural gas lines for domestic and industrial use. Because of the low volumetric energy density of hydrogen, storage of hydrogen in the form of ammonia is also being considered. The liquid is easily stored and transported under conditions similar to those for propane. The conversion to ammonia, using nitrogen from air, is straightforward. Utilization can be directly as a fuel in an internal combustion engine, or by catalytic dissociation back to hydrogen for use in that form in a fuel cell for an electric vehicle or any other purpose. Research is under way for improvements in this space, including ammonia production at lower temperatures.
Pipeline transport of hydrogen is feasible but expensive, especially for small volumes. Ammonia, on the other hand, can be transported in pipelines at a cost of about USD 0.20 per kg hydrogen per 1000 miles. This is less than 5% of the expected cost to produce renewable hydrogen at solar and wind installations. The US currently has nearly 3000 miles of ammonia pipelines. Ammonia is a leading candidate for renewable hydrogen storage and distribution.
The main takeaway from this discussion is that renewable energy requires storage, and that storage in fluid form is likely to lead the way. An alternative to using the stored fluid to generate electricity is to use it for a different purpose. This solution for monetizing electricity from periods of excess supply would require the supply troughs to be augmented from another grid source. Hydrogen and ammonia will be important players in the renewable energy world. Alas, silver bullets went out with the Lone Ranger.
August 2, 2020