This involves the use of the existing natural gas (methane) grid as the store. In this case, the carbon dioxide is given economic value as a component of an energy carrier. This "solar fuel" cycle uses the excess electrical renewable energy that cannot be used instantaneously in the grid, which otherwise would be wasted to create hydrogen via electrolysis of water. The hydrogen is then combined with CO2 to create synthetic or substitute natural gas SNG and stored in the natural gas network. The natural gas is used to create electrical energy (and the heat used as well in CHP) on demand when there is not enough sun (photovoltaic, CSP...) or wind (turbines) or water (hydro, ocean current, waves...). The German natural gas grid, for example, has two months of storage, more than enough to outlast renewable energy low production points.