Renewable energies are all well and good – but where do electricity and heat come from when there is no wind and it is dark? A new method of energy storage should provide a remedy.
If we want to avoid extreme weather phenomena such as the flood disaster in summer in Germany * in the future, we have to minimize global warming as far as possible. To do this, in turn, greenhouse gas emissions must fall – also in the energy sector. There one speaks of decarbonization through the use of low-carbon energy sources. Instead of electricity from coal-fired power plants, electricity from wind or solar energy should be used. It can only become problematic if there is no breeze or the sun goes down. This is where energy storage systems come into play, in which supplies are collected. They become more and more important the more we depend on renewable energies.
Batteries are often used for this. “So far, lead-acid batteries have mainly been used. In the meantime, the lithium-ion batteries known from cell phones and laptops are increasingly being used, among other things because they have a high overall efficiency of around 85 percent, ”writes the Federal Ministry of Economics. The latter are popular because of their high energy density. However, they are still quite expensive for large-scale use, and cost reductions are only expected in the next few years. Lithium-ion batteries are also controversial, as the extraction of raw materials brings with it ecological and socio-economic challenges, as the Öko-Institut describes in a short study.
Renewable energies: sand as a storage medium for bad times
However, researchers from the USA are now working on an energy storage device that consists of a material that is actually found in abundance on earth: sand. They want to pack the sediment in large silos for this. Scientists at the National Renewable Energy Laboratory (NREL) in Colorado are currently testing a prototype. In a press release they describe the approach that their project called “ENDURING” is taking as “a reliable, cost-effective and scalable solution that can be located anywhere”. Storable, electrically heated sand can thus deliver electricity on demand.
According to the announcement, the system uses excess energy from the sun or wind to heat the storage material, quartz sand – to 1200 degrees Celsius. Imagine pouring the sand through a huge toaster. The heated particles are then fed into insulated concrete silos. The researchers designed the basic system for storage of up to 26,000 megawatt hours. The capacity can, however, simply be scaled up or down.
“When energy is required, the hot particles are passed through a heat exchanger that heats and pressurizes a working gas to drive the turbo machines and rotary generators that generate electricity for the grid,” the researchers write. At times when there is a high demand for electricity – for example in the morning or in the evening, while cooking or watching TV – and when only limited electricity from wind or solar systems is available, the system discharges. The used, cold particles are then fed back into a silo.
Sand as an energy store could drive the expansion of renewable energies
According to its developers, the “ENDURING” system offers several advantages over other types of storage: Quartz sand is relatively cheap, according to the researchers, between 30 and 50 US dollars per ton and has a far weaker ecological impact than lithium-ion batteries, for example. Although their energy density is higher – they can transport more electricity in a smaller space, which makes them well suited for sectors such as transport – the value chain has its price. The system presented is safe through the use of quartz sand as a storage medium, “which makes it the ideal candidate for massive, long-term energy storage”.
Another advantage is the local independence, the system can be set up anywhere in the country. You can even use the existing infrastructure, for example from former coal or gas power plants. “ENDURING technology can support the expansion of a generation of renewable energies across the country. The construction of these low-cost thermal particle storage systems in the US could help utility companies keep using solar and wind power without the risk of destabilizing the grid or the need to restrict renewable energy production, ”the scientists write. The systems also provided energy reserves so that communities could navigate more relaxed through ongoing weather events, such as a week-long cold front or a heat wave in summer.
Germany: volcanic rock as energy storage in Hamburg
The US is planning to phase out coal by 2035 and aim to achieve a net zero emissions economy by 2050. In Germany they want to say goodbye to coal * in 2038 and be climate-neutral by 2045. The NREL researchers see great potential in the “ENDURING” project or in thermal particle energy storage for achieving the climate goals. “While decarbonizing electricity has a clear path, decarbonizing the entire economy – which includes things like building heating and industrial processes – is more of a challenge, as natural gas is very cheap and therefore difficult to replace,” says lead researcher Zhiwen Ma. “Decarbonising industrial processes and building up heat is very difficult.” The conversion of renewable electricity into heat is one way of decarbonising these sectors.
The prototypes of the heaters and heat exchangers are currently being tested under high temperature conditions. If the prototype tasks are successful this fall, Ma is confident that the technology has great potential to support renewable integration for future carbon-free energy supply.
In addition to batteries, pumped storage power plants are widespread in Germany, but research is already being carried out into alternative electricity storage systems in Germany. In Hamburg, a storage facility with volcanic rock is already a reality. According to the Federal Ministry of Economics, the system can store up to 130 megawatt hours of thermal energy for around a week – or supply 1,500 households with electricity for 24 hours. (ial) * fr.de is an offer from IPPEN.MEDIA.
