When most renewable energy advocates talk about energy storage they are referring to relatively short-term storage; everything from 15 minute storage to stabilize the grid and provide bridging power during sudden changes in output (for example the Notrees battery storage facility or the Beacon Power Flywheel facility in Pennsylvania) to 12-14 hours of Thermal Energy Storage which allows the Gemasolar Concentrated Solar Power Plant in Spain to run 7x24x365. But if you examine the PV Solar generation from Germany on an annual basis it becomes obvious that there is also a long-term storage problem that needs to be solved.
Summer PV Solar output is about 5 times greater than winter output. Any attempt to treat PV Solar in Germany as a consistent and reliable source of electricity would involve building out 5x more capacity than is really justified and then dealing with a huge surplus of electricity in the summer. This would be both highly inefficient and horrendously expensive.
There are not a lot of options when it comes to really long-term energy storage that would span many months. However, there is one solution that would work and has been deployed in a limited way in real-world applications. That solution involves powering an electrolyzer to break water down into oxygen and hydrogen, then using the hydrogen in one fashion or another sometime later.
Research and development into the use of hydrogen storage of renewable energy has been going on since 2007 at the National Renewable Energy Laboratory (NREL) in Golden, Colorado. In partnership with Xcel Energy the NREL wind to hydrogen test bed has included a number of different components including different types of electrolyzers, fuel cells, hydrogen powered generators, and various interconnection technologies. Using hydrogen as a way to store energy is complicated with many ways to handle the flow of electricity between the electrolyzers and eventual end users of the hydrogen. The need to flip between AC and DC and to efficiently control the electricity flow within a “smart grid” represent significant challenges and only through tests of multiple configurations and using several different technologies will the optimal design be determined for deployment at scale. Research is ongoing.
In an effort to evaluate some of the challenges that would be encountered in a commercial application of hydrogen storage technology the Basin Electric Power Co-operative entered into a pilot project with the Energy & Environment Research Center at the University of North Dakota. This project used real time dynamic scheduling to draw electricity from the Wilton Wind farm and feed that into an electrolyzer. The output hydrogen was stored in tanks and delivered directly to three pickup trucks and a tractor that were converted to use hydrogen fuel.
As might be expected in a ground-breaking research project many issues were encountered, primarily around the reliability of some of the equipment components. Despite the challenges the project ran successully in a “production” mode from early 2008 until 2011 when the equipment was transferred to the NREL site in Colorado. A great deal of very valuable information was documented through this project regarding the full-cycle costs and practical application of hydrogen storage and use for the transporation sector.
In remote Bella Coola British Columbia, Canada hydrogen storage was used to reduce the amount of diesel fuel burned to generate electricity.
The $7.4 million funding for the project was provided by BC Hydro, Sustainable Development Technology Canada, and General Electric Canada.
Excess hydro electricity was used to power an electrolyzer which extracted hydrogen gas from water. This gas was compressed and stored in tanks for future use. Part of the excess hydro electricity was also stored in a flow battery which provided very fast response both for storage and delivery of electricity.
If peak demand exceeded the capacity of the hydro facility then the compressed hydrogen was fed into fuel cells which generated electricity without combustion making this an emissions-free system. Total hydrogen storage implemented in this project was 3.3 MW-hr which delivered 100 KW for about 16 hours after accounting for energy losses in the fuel cells and associated processes.
Overall end-to-end efficiency of the system was about 25%. That is, for every MW of hydro electricity used to produce the hydrogen gas about 0.25 MW of power was eventually returned to the grid via the fuel cells.
A 75% loss may seem like a lot but the alternative is to let the water pass through the hydro dam spillways without generating electricity at all. That’s a 100% loss.
And according to Sean Allen, chief engineer for Powertech, the prime contractor for the project, there are ways to improve the overall efficiency including using heat generated by the Electrolyzer, Fuel Cells, and compressor as part of a district heating solution.
Even on the relatively small scale of this project construction costs were under $5/watt-hr ($7.4 million for effective delivery of 1.6 MW-Hrs). This compares quite favourably with the Notrees battery complex at $5/watt-hr and the Beacon Power flywheel technology at about $8/watt-hr. The big advantage for hydrogen storage systems is their ability to scale up for large amounts of storage by adding compressed hydrogen tanks. Theoretically weeks or months of excess energy could be stored in this way.
The HARP project was initiated in 200 and abandoned in 2013.
The big disadvantage for this configuration of hydrogen storage system is the overall efficiency compared to batteries or flywheels. That implies that the electricity used to power the system must truly be surplus to any reasonable need and therefore is essentially worthless. Hydro power at night when reservoirs are full represents one viable source that fits this definition. PV Solar at mid-day is reaching that point in some jurisdictions as is wind in places like Texas where wind generators are sometimes offering electricity at negative prices.
At the opposite end of the country another Canadian project has created a “hydrogen village” on the western tip of Prince Edward Island. The goal of this project is to demonstrate that remote communities can be completely self-sufficient in terms of electrical power without resorting to diesel generators. The wind farm produces electricity which is dynamically routed to satisfy both real-time demand as well as fueling an electrolyzer producing hydrogen which is stored in compressed form. When the wind is calm the stored hydrogen is used to fuel a back-up generator. The project started in 2009 and is ongoing.
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18-Oct-2016 Update: I recently came across the Hydrogen House project. Homeowner Mike Strizki decided he wanted to be completely independent of the local electrical grid. By installing a large number of solar panels, an electrolyzer, a number of large hydrogen storage tanks and a fuel cell he has achieved his goal. By storing excess solar energy during the summer months in the form of compressed hydrogen he can power his home all winter. At a latitude of more than 40 degrees North that is an amazing achievement.
17-Apr-2017 Update: Both the project in Bella Coola and the Hydrogen Village in Prince Edward Island have been abandoned with equipment being scrapped or re-purposed. Hcellenergy has not been able to secure either significant funding or any large project although a second Hydrogen House was developed in New Jersey in November, 2015.
