Huge subsurface storage potential for excess energy already available in Germany
Authors: Kühn Michael , Nakaten Natalie, Christine , Kempka Thomas 
Published: March 2020

&lt;p&gt;&lt;span&gt;T&lt;/span&gt;&lt;span&gt;he energy supply in Germany is subject to a profound change. The present &lt;/span&gt;&lt;span&gt;paper&lt;/span&gt;&lt;span&gt; addresses the &lt;/span&gt;&lt;span&gt;German &lt;/span&gt;&lt;span&gt;potential &lt;/span&gt;&lt;span&gt;for the innovative idea &lt;/span&gt;&lt;span&gt;o&lt;/span&gt;&lt;span&gt;f &lt;/span&gt;&lt;span&gt;storing excess energy from renewable power sources in the form of hydrocarbons, which can be used in a closed c&lt;/span&gt;&lt;span&gt;ycle&lt;/span&gt;&lt;span&gt; to produce electricity in an environmentally friendly manner &lt;/span&gt;&lt;span&gt;[1]&lt;/span&gt;&lt;span&gt;.&lt;/span&gt;&lt;/p&gt;&lt;p&gt;&lt;span&gt;Excess electricity from wind and sun can be transformed into hydrogen, and with carbon dioxide subsequently into methane &lt;/span&gt;&lt;span&gt;u&lt;/span&gt;&lt;span&gt;ntil &lt;/span&gt;&lt;span&gt;large hydrogen storage capacities b&lt;/span&gt;&lt;span&gt;ecome &lt;/span&gt;&lt;span&gt;available&lt;/span&gt;&lt;span&gt;. When needed, electricity is regained in a combined cycle plant c&lt;/span&gt;&lt;span&gt;ombusting &lt;/span&gt;&lt;span&gt;the methane. To close the carbon cycle, carbon dioxide is captured on site. Two subsurface storage formations for both gases are required for the technology &lt;/span&gt;&lt;span&gt;[2]&lt;/span&gt;&lt;span&gt;. &lt;/span&gt;&lt;span&gt;We studied &lt;/span&gt;&lt;span&gt;a regional show case for the &lt;/span&gt;&lt;span&gt;city&lt;/span&gt;&lt;span&gt; of Potsdam &lt;/span&gt;&lt;span&gt;and worked out &lt;/span&gt;&lt;span&gt;the overall energy and cost efficiency &lt;/span&gt;&lt;span&gt;[3].&lt;/span&gt;&lt;span&gt; Our results demonstrate &lt;/span&gt;&lt;span&gt;that this extended way of power-to-gas &lt;/span&gt;&lt;span&gt;is not only technically, but also economically feasible compared to other state-of-the-art excess energy storage technologies [4].&lt;/span&gt;&lt;/p&gt;&lt;p&gt;&lt;span&gt;Here, we are t&lt;/span&gt;&lt;span&gt;aking into account the actual German storage capacity for &lt;/span&gt;&lt;span&gt;natural gas. &lt;/span&gt;&lt;span&gt;The most recent development is characterised by stagnation of the &lt;/span&gt;&lt;span&gt;available &lt;/span&gt;&lt;span&gt;total &lt;/span&gt;&lt;span&gt;working gas volume &lt;/span&gt;&lt;span&gt;and an increase i&lt;/span&gt;&lt;span&gt;n&lt;/span&gt;&lt;span&gt; the &lt;/span&gt;&lt;span&gt;significance of cavern storage at the expense of porous reservoirs. &lt;/span&gt;&lt;span&gt;This resulted in the decommissioning &lt;/span&gt;&lt;span&gt;of a couple of storage sites within the last years. &lt;/span&gt;&lt;span&gt;In view of the fact that &lt;/span&gt;&lt;span&gt;natural gas &lt;/span&gt;&lt;span&gt;is &lt;/span&gt;&lt;span&gt;still second &lt;/span&gt;&lt;span&gt;most important for &lt;/span&gt;&lt;span&gt;Germany&amp;#8217;s primary energy &lt;/span&gt;&lt;span&gt;provision&lt;/span&gt;&lt;span&gt;, &lt;/span&gt;&lt;span&gt;those sites should better be used to s&lt;/span&gt;&lt;span&gt;tore &lt;/span&gt;&lt;span&gt;excess energy from renewables instead of their abandonment. We show that t&lt;/span&gt;&lt;span&gt;he technology to store excess energy in form of methane via &lt;/span&gt;&lt;span&gt;power-to-gas &lt;/span&gt;&lt;span&gt;is available and ready for operation and &lt;/span&gt;&lt;span&gt;that &lt;/span&gt;&lt;span&gt;the potential within the German subsurface &lt;/span&gt;&lt;span&gt;is &lt;/span&gt;&lt;span&gt;e&lt;/span&gt;&lt;span&gt;normous&lt;/span&gt;&lt;span&gt;. &lt;/span&gt;&lt;span&gt;This provides an &lt;/span&gt;&lt;span&gt;intermediate option to reduce &lt;/span&gt;&lt;span&gt;greenhouse gas&lt;/span&gt;&lt;span&gt; emissions w&lt;/span&gt;&lt;span&gt;hile &lt;/span&gt;&lt;span&gt;hydrogen storage is still under research and development.&lt;/span&gt;&lt;/p&gt;&lt;p&gt;[1] K&amp;#252;hn M. (2013): System and method for ecologically generating and storing electricity. - Patent WO 2013156611 A1&lt;/p&gt;&lt;p&gt;[2] Streibel M., Nakaten N.C., Kempka T., K&amp;#252;hn M. (2013): Analysis of an Integrated Carbon Cycle for Storage of renewables. - Energy Procedia, 40, pp. 202-211&lt;/p&gt;&lt;p&gt;[3] K&amp;#252;hn M., Nakaten N.C., Streibel M., Kempka T. (2014): CO&lt;sub&gt;2&lt;/sub&gt; Geological Storage and Utilization for a Carbon Neutral &amp;#8220;Power-to-gas-to-power&amp;#8221; Cycle to Even Out Fluctuations of Renewable Energy Provision. - Energy Procedia, 63, pp. 8044-8049&lt;/p&gt;&lt;p&gt;&lt;span&gt;[4] Nakaten N.C., Chabab E., Kempka T., K&amp;#252;hn M. (2019): An Updated Classification of the Enhanced Power-to-Gas-to-Power Competitiveness Based on Integrated Geological Storage. - 14&lt;/span&gt;&lt;sup&gt;&lt;span&gt;th&lt;/span&gt;&lt;/sup&gt;&lt;span&gt; Greenhouse Gas Control Technologies Conference Melbourne 21-26 October 2018 (GHGT-14)&lt;/span&gt;&lt;/p&gt;