Section 6: Long-term energy storage
Compressed air energy storage & pumped hydro-storage
The Secretary General of the United Nations, António Guterres, this year told the COP26 Roundtable of Clean Power Transition, “To achieve net zero emissions by 2050, we need an urgent transition from fossil fuels to renewable energy.” However, renewable energy generates electricity less reliably than traditional, fossil fuel technology. Therefore, energy storage solutions are needed to help counteract large fluctuations in energy production from renewable sources, and fluctuations in energy demand. Writing in Envirotec Magazine, VINCI Energies notes the challenge of renewable energy generated by wind and solar power: “The weather cannot simply be switched on when everyone wants to boil water…in the way a power station can be activated to cope with additional demand.” Long duration energy storage is the key to solving this issue. The definition of ‘long-term’ is industry specific. One definition is applied to technologies that offer between ten to one thousand+ hours of consistent energy discharge. These technologies should be able to store large amounts of energy in a cost-effective manner, effectively competing with lithium-ion battery technology. We will use ‘long-term’ here to mean suitable to provide a baseload of renewably generated power, from potentially intermittent sources.
Global patent activity In this section, we investigate the innovation relating to compressed air energy storage systems (CAES) and pumped hydro-storage. These technologies have been a staple of energy storage for decades, but the patent data indicates considerable on-going innovation in these fields.
Compressed Air Energy Storage (CAES)
The graph in Figure 1.1 below represents the number of applications filed with priorities in each year since 1997: Figure 6.1 Priority filing trend - CAES Click graph to enlarge
Note: Due to an 18-month lag between patent application and full publication of patent data, data from 2021 has not been reported, and data from 2020 includes data through May 2020.
The growth in innovation with this technology area is perhaps surprising, given that compressed air energy storage sites have been in operation since the 1970s. Recent innovation is focused on improving efficiency in the process of compression, storage, and the subsequent expansion of air. In particular, there has been interesting patent activity relating to adiabatic compression and expansion; air inside a chamber is compressed and generates heat, which is then removed via heat exchangers and stored as thermal energy. The compressed air is stored under high pressure. The stored thermal energy is subsequently used to expand the air and drive turbines. This process has the potential to offer low-cost energy storage at scale. For example, Hydrostor’s patent application, WO2020/146938A1, discloses a combined compressed gas storage system, gas compressor/expander system and a thermal storage system. This application details a method to store heat generated during gas compression, and to re-use it later to aid with its expansion, reducing energy wasted across the process. The data shows most priority applications are being filed in Japan and the U.S.
Figure 6.2 Priority filing trend - top ten filing jurisdictions - CAES Click graph to enlarge
In recent years, one applicant – Japan’s Kobe Steel – has led the way in patent filings for CAES. Since filing its first patent in this area in 2015, Kobe Steel has invested significantly in building its portfolio of CAES-related patents.
Figure 6.3 Priority filing trend - top filing assignees - CAES Click graph to enlarge
Note: Due to an 18-month lag between patent application and full publication of patent data, data from 2021 has not been reported, and data from 2020 includes data through May 2020.
Whilst many other companies are showing moderate innovation in this area, Kobe Steel continues to make significant filings across territories – perhaps an indication that Japanese companies are looking to invest heavily in this market. As with the Hydrostor patent application, innovations patented by Kobe focus on harvesting energy losses in the compression process, improving efficiency by minimising energy losses from the system during energy storage. A good example of this is patent US10655505B2, which sets out the use of various heat exchangers in the compression process along with a controller, sensors, and a flow rate adjuster, to control the extraction of heat from gas during compression. It is clear that a lot of innovation in this technology area is about efficiency and how energy loss can be reduced during the process of compressing, and subsequently expanding, air. It will be interesting to see how other companies in this field respond to Kobe’s dramatic increase in filings.
Pumped hydro-storage
Having been around for decades, the British Hydropower Association calls pumped storage “the oldest kind of large-scale energy storage”. Underlying this technology are two reservoirs situated at different altitudes. When water travels from the higher reservoir to the lower reservoir, the downflow generates energy which – via a turbine and generator – creates electricity. The International Hydropower Association (IHA) predicts pumped storage capacity will double in the coming years, though this is insufficient storage capacity for electricity grids relying on solar and wind power. Even though this technology has a long history, patent filings are on an upwards trend.
Figure 6.4 Priority filing trend - pumped hydro-storage Click graph to enlarge
Note: Due to an 18-month lag between patent application and full publication of patent data, data from 2021 has not been reported, and data from 2020 includes data through May 2020.
The patent data shows that in recent years, most applications have been filed in China. The charts below show filing activity among the five jurisdictions with the most priority filings. Note that the full dataset for 2020 is not yet available, so it is unclear whether China’s upwards trend will continue.
Figure 6.5 Priority filing trend - top five filing jurisdictions - CAES Click graph to enlarge
Note: Due to an 18-month lag between patent application and full publication of patent data, data from 2021 has not been reported, and data from 2020 includes data through May 2020.
Pumped hydro-storage plants require large spaces. Interestingly, the patent data highlights innovation around converting existing underground mine space (perhaps coal mines that were used in the fossil fuel industry) for uses related to green technology. This idea has been mooted in recent years, but China University of Mining & Technology has recently made several related filings, for example, WO2020087882A1, WO2020087880A1 and WO2020087883A1. Therefore, converting fossil-fuel technology into green/renewable technology could be of significant interest to those countries with a history of coal mining.
Implications for innovation and future patent filings What’s clear from the patent data is that despite being long-established technologies, innovation remains valuable in compressed air energy storage and pumped hydro-storage. The prospects of providing a sustainable, long-term energy storage system and legislation from governments is driving innovation in these traditional, long-term energy storage solutions. As with all energy solutions, efficiency is everything, and the patent data in these two technology areas shows that the drive towards more efficient energy storage solutions is on-going. The challenge for innovators is often to identify incremental improvements that can – ultimately – create a commercial advantage for the patent holder.
The challenge for innovators is often to identify incremental improvements that can – ultimately – create a commercial advantage for the patent holder.
Paul Beynon Senior Associate MEng, CPA, EPA
Rory Brown Trainee Patent Attorney, MPhys, PhD