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A major drawback of renewable energy sources such as wind, solar, and tidal power is the limitations of effective storage for later use and integration to the power grid. For instance, when winds blow powerfully wind turbines generate more electricity than a power grid can absorb. This situation either forces many wind turbines to shut down and remain underutilized or results in negative electricity prices for the renewables operator as they pay to get their power onto the grid.
German and Austrian researchers from the Center for Solar Energy and Hydrogen Research at Baden-Württemberg (ZSW) and the Fraunhofer Institute for Wind Energy and Energy System Technology (IWES) are on the verge of a path breaking invention that makes possible storage of excess energy generated by renewable sources such as wind turbines and solar panels. The process aims at producing synthetic methane from water using the surplus energy. Methane is a carbon neutral gas that fits in with the existing natural gas network.
Image Credit: geograph.org.uk/bluespacecat
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The process of storing wind and solar power as synthetic natural gas combines the technology for electrolysis with methanisation.
Passing the surplus energy generated by wind turbines or solar panels through water decomposes the water into oxygen and hydrogen.
2H2O → 2H2 + O2
One option after the electrolysis is to store the hydrogen for use in fuel cells. The storage, transportation, and combustion of hydrogen however raise several technical challenges and remain a costly option. The new technology follows a different approach of using a simple chemical reaction to produce methane out of hydrogen.
The pure oxygen generated out of the electrolysis is stored for combustion of the to-be-generated methane, to produce electricity at a later stage.
2. Sabatier Process:
The hydrogen resultant from the electrolysis process is subject to the sabatier process. Sabatier process is the reaction of hydrogen with carbon dioxide using a nickel catalyst at high temperature and pressure to methane and water.
CO2 + 4H2 → CH4 + 2H2O
The water resultant from the Sabatier process is recycled for further electrolysis, making the sourcing of pure water for this process a one-time affair.
A prototype of this system is already operational at Stuttgart, and a substantially larger system capable of processing 10 megawatts is poised to become operational by 2012.
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The combustion of methane for producing electricity generates carbon dioxide and water.
CH4 + 2O2 → CO2 + 2H2O
The carbon dioxide is recycled back to boost the Sabatier process. In the absence of recycling, the Sabaiter process pulls back from the atmosphere the carbon dioxide emitted to the air. The water is recycled back to the electrolysis stage. This cycle of methane to carbon dioxide to methane makes this a carbon neutral process, producing no greenhouse gases.
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The efficiency of the process aimed at storing wind and solar power as synthetic natural gas is presently more than sixty percent. Pumped storage of natural gas supply presently has a better efficiency ratio of seventy percent. The net potential loss owing to non-utilization of excess power available from renewable energy sources however from far exceeds the marginal efficiency loss of this new process.
The storing of pure oxygen resultant from electrolysis eliminates the need of nitrous oxides while burning methane to produce electricity.
Image Credit: Wikimedia Commons/Fernando Tomas
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The primary advantage of this new process is the stocking of green energy for future use. The storage of renewable energy at synthetic natural gas as a backup option contributes to the robustness of the smart grid technology.
Synthetic methane is compatible with the existing storage facilities, pipelines and supply network of natural gas network grid, and countries like Germany and UK that already have such robust infrastructure can readily store enough renewable energy in gas form to last through extended days of midwinter calm in volumes that pumped storage could probably never cope with.
The application of this process also contributes to energy self-sufficiency in a big way, and allows doing away with unstable imports of natural gas.
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While the synthetic methane produced through this process integrates with the existing storage facilities, pipelines, and supply network for natural gas supply, the primary challenge is identifying storage systems with sufficient capacity for large-scale storage based on fluctuating renewable energy production trends. Countries without adequate gas network grid would have to set up such infrastructure from scratch.
A secondary challenge is physical infrastructure. Expanding the prototype to real-life conditions would invariably create several challenges in setting up a facility to perform the electrolysis and the sabatier process.
The primary challenge is however on the cost front. The cost-efficiency of this process vis-à-vis piped distribution of natural gas could make or break this innovation in the coming years.
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- Fraunhofer-Gesellschaft (2010, May 5). Storing green electricity as natural gas. ScienceDaily. Retrieved July 19, 2010, from http://www.sciencedaily.com/releases/2010/05/100505113227.htm
- Dillow, Clay. System Stores Wind and Solar Power in the Form of Natural Gas, to Fit Neatly Into Existing Infrastructure. Retrieved from http://www.popsci.com/science/article/2010-05/carbon-neutral-natural-gas-made-wind-and-solar-could-power-existing-infrastructures
- Page, Lewis. Germans plan to make 'synthetic natural' gas from CO2. Retrieved from http://www.theregister.co.uk/2010/05/06/german_synthetic_natural_gas/