QINOUS interviews Professor Dirk Uwe Sauer

In this interview, Professor Dirk Uwe Sauer offers an insight into the latest developments around energy storage and renewables in Germany.

Professor Sauer, does Germany need new electricity storage facilities?

Prof. Sauer: Storage systems will become essential in relation to the overall market as soon as 40% of total electricity production in Germany is covered by wind power and photovoltaics (PV). This is shown by our detailed computer simulations at RWTH Aachen, but also by various other studies.

Why hasn’t the massive expansion of renewables long since led to power cuts on a broader front?

Prof. Sauer: The entire energy system is surprisingly stable to date, even without significant electricity storage capacities. This is due to the very high flexibility of all system components, including conventional power plants and consistently well-developed networks. That’s the good news. Yet consequently we have had little demand for the development and use of storage systems in Germany to date and therefore have a lot of catching up to do in terms of development and market pervasion.

When will the magic 40 percent share for PV and wind be reached?

Prof. Sauer: In its latest monitoring report on the energy transition in June 2018, the German government confirmed that the renewable share within total electricity consumption is to rise to 65% by 2030. However, this figure includes hydropower and biomass. In this scenario, fluctuating renewable energy, i.e. PV and wind power, should contribute between 52 and 54% of total electricity production in 2030. The 40% limit for PV and wind power should be reached around 2025, if politicians seriously comply with the targets. Then the regulation of excess electricity and the provision of peak load electricity will probably cost us more than short-term storage. Local demand could arise earlier due to network bottlenecks. However, it is only possible to “see” this from grid operations, not through the electricity exchange.

Yet renewable electricity production will continue to grow rapidly after 2025. What are the consequences?

Prof. Sauer: From a fluctuating share of renewables of around 80%, we need additional long-term storage. These include gases such as methane and hydrogen, which are used seasonally with few cycles. Power-to technologies will also be used to generate gas, fuels and primary chemicals from electricity.  It should also be noted at this point that the figures of 40 and 80% respectively refer to direct electricity demand, i.e. approximately 550 to 600 terawatt hours (TWh) produced today. In order to provide a sustainable energy supply to the heat, transport and industrial sectors, much more electricity is needed. Therefore, the percentages can be lower in relation to the total production.

Lithium-ion rechargeable batteries are the preferred choice for short-load energy storage. Will the boom continue or are we currently just experiencing lithium-ion “mania”?

Prof. Sauer: The technical parameters of lithium-ion batteries, especially durability and efficiency, are simply very, very good. Today, the car batteries of the US manufacturer Tesla reach 260-watt hours per kilogram whereas lead or nickel-cadmium batteries only reach 40 to 60-watt hours. Lithium-ion thus reaches five times the capacity of conventional batteries. This is what has made electromobility possible in the first place.

How many lithium-ion batteries will electric transport need in the future?

Prof. Sauer: Let’s take Volkswagen as an example. The Group has announced ambitious targets. On this basis, we have calculated the demand at my institute: VW intends to sell so many electric vehicles in 2025 that it will require 200 gigawatt hours (GWh) plus or minus 50 GWh. Extrapolated to the total vehicle market, this would result in between 700 and 1,000 GWh of lithium-ion storage capacity. In the coming years, this will continue to grow. That’s gigantic. By way of comparison, all German pumped storage facilities in total achieve only 40 gigawatt hours a year. Tesla’s Gigafactory is expected to produce 35 GWh a year when fully operational.

Can this demand for lithiumion be satisfied at all?

Prof. Sauer: For all car manufacturers enormous resources are necessary. Lithium production worldwide would have to triple by 2025. Lithium-ion batteries also require nickel, so global nickel production would have to grow by 40%. These are gigantic growth rates for the mining industry. In addition, the demand for cobalt has doubled. There is still some savings potential for cobalt through further technical development, but not for lithium and nickel.

There is much to be said for exploring additional alternatives to lithium-ion. In the stationary sector, for example, lead-acid batteries or redox-flow technologies could be used, and lithium, which is mined all over the world, could primarily be used to serve the transport sector.

The interview was conducted by Dr. Joachim Müller-Soares