Intermittent renewable electricity output is not the only problem. Something will also have to be done with all the excess power generated by giant wind and solar parks at times when demand is low. This surplus energy needs to be stored so that it can be made available during peak periods. If we want 100 percent of the electricity generated in Austria to come from renewable sources, we will need storage with capacity over 100 times greater than the potential offered by pumped storage. (Source: Vienna University of Technology, ESEA/EA (ed.): ‘Super-4-Micro-Grid’, research project final report, Vienna 2011). The combined capacity of pumped storage plants and battery storage used to date is far from sufficient. Additionally, such facilities can only release electricity. The answer is gas. Besides power generation, it can also be used for heating, in vehicles and as a raw material. The gas transportation and storage infrastructure in place has all the makings of a storage system for green power.
This will make it possible to economically transport and store the renewable solar and wind energy in large quantities and thus to have it available at all times.
The principle behind this new, environmentally friendly technology could hardly be simpler. Surplus solar and wind power is used to split water into oxygen and hydrogen by means of electrolysis. The hydrogen can then be stored for later use, for example as primary energy in fuel cells. But a further step is also possible: in methanation, the hydrogen is reacted with carbon dioxide (CO2). Preferably, the CO2 comes from CO2-rich gas streams (e.g. biogas or industrial plants). The product of the process is renewable synthetic natural gas.
Today the efficiency of the conversion process is already about approx. 60 % – a big step forward in view of the fact that surplus electricity is often not used at all owing to the lack of storage capacity, and instead wind turbines are idled or whole wind farms taken off the grid. If the hydrogen can be used directly, the efficiency rate is even higher.
Thanks to electrolysis and methanation, electricity can be converted into hydrogen and into natural gas, making large-scale power storage possible for the first time.
The process solves one of the biggest problems posed by electricity storage – shortage of space. It means we can simply turn to existing natural gas infrastructure, in the shape of the pipeline grid and large storage facilities. Instead of developing and rolling out expensive and elaborate new storage technologies, the power would
be transformed into synthetic natural gas and stored in depleted gas reservoirs.
In simple terms, gas is stored in summer and removed in winter. The storage has an annual cycle, as can be seen from the graph below. This involves very large amounts of energy – in the case of RAG Austria AG by up to 66 TWh. This service ensures that the energy supply is provided at all times of the year and even during supply interruptions (security of supply). The importance of the seasonal balance between supply and demand will increase significantly in the future if we gradually switch to solar and wind energy.