Gravitricity has partnered with firms in the US and Germany to deploy its gravity energy storage solution while Energy Vault has provided an update on its China project. Contact online >>
Gravitricity has partnered with firms in the US and Germany to deploy its gravity energy storage solution while Energy Vault has provided an update on its China project.
Gravitricity has signed an agreement with US firm IEA Infrastructure Construction to seek funds for projects in the US from the Bipartisan Infrastructure Bill which provided US$450 million for clean energy projects at mining sites. The company plans to fund up to five projects at current and former mines.
Gravitricity has also been contracted to investigate the potential of storing energy at a decommissioned mine in Halle, Germany, by the mine’s owner Geiger Group. Investigative work will start in May and, if successful, Gravitricity will deliver a concept design and project development plan to Geiger Group for it to consider the deployment of a full-scale gravity energy storage plant.
Gravitricity develops below ground gravity energy storage systems and raised £40 million to commercialise projects in January this year, as covered by our sister site Solar Power Portal. The firm’s technology works by raising weights in a deep shaft and releasing them when energy is required.
The technology is similar to that employed by Switzerland-headquartered and NYSE-listed Energy Vault, whose CEO Robert Piconi provided an update to its first commercial gravity energy storage project in Rudong, China, in a shareholder letter.
The letter – “From Rudong to Beijing to Mongolia: My insights from Energy Vault''s recent trip to China and the site of the first EVx gravity energy storage system” – provided an update with pictures (below).
“When fully commissioned later this year, the 25 MW, 100 MWh EVx system will be integrated into China''s national energy grid to provide critical storage and delivery of clean renewable energy generated by the adjacent wind farm. This is a significant milestone that brings us one step closer to realising our mission of decarbonisation through the deployment of sustainable energy solutions in the largest energy consumption market in the world,” Piconi said.
It also revealed that the concrete foundations have been completed for the firm’s first gravity storage project in the US, in Georgia with Enel Green Power.
Energy Vault now provides a range of energy storage solutions including battery storage and green hydrogen and is forecasting for US$325-425 million in revenues this year.
Energy-Storage.news'' publisher Solar Media will host the 1st Energy Storage Summit Asia, 11-12 July 2023 in Singapore. The event will help give clarity on this nascent, yet quickly growing market, bringing together a community of credible independent generators, policymakers, banks, funds, off-takers and technology providers. For more information, go to the website.
Gravity energy storage (GES) is an innovative technology to store electricity as the potential energy of solid weights lifted against the Earth's gravity force. When surplus electricity is available, it is used to lift weights. When electricity demand is high, the weights descend by the force of gravity and potential energy converts back into electricity (Fig. 1). A specific GES configuration that uses pulley systems working in tandem with a motor-generator to move the weights is known as lifted weight storage (LWS).
Technical Characteristics
The energy capacity of LWS is proportional to the cumulative potential energy of weights
where (M) is the total mass of all the weights, (g) is the acceleration due to gravity, and (H) is the height of vertical movement of the gravity center of the weights (Berrada, Loudiyi, and Zorkani, 2017; Franklin, et al., 2022; Morstyn and Botha, 2022; Li et al., 2023). The installed power of LWS is equal to the sum of operating power of all incorporated lifting systems (Kropotin and Marchuk, 2023a). The LWS efficiency depends on the efficiency of the lifting mechanisms. It has been shown that the round-trip efficiency of the LWS can reach 86% (Kropotin and Marchuk, 2023b).
The operational principle of LWS eliminates the fire hazards of lithium-ion batteries and flooding risks specific to pumped-hydro storage (PHS). LWS is virtually free from disadvantages, such as degradation of performance over time or the cycle number limit. The former is due to the absence of leakage currents in the given engineering solution, as occurs in Li-ion batteries, and loss of weight mass, as occurs in PHS. The latter is related to the fact that the number of charge–discharge cycles weakly affects the lifetime of the structure and the equipment degradation is eliminated by repairs, which are classified as operations and maintenance costs (O&M).
The structure with a height of more than 100 meters has an area comparable to that of a Li-ion storage system of the same power and energy capacity (Kropotin, Penkov, and Marchuk, 2023). The majority of the literature on GES highlights its extended service life of about 40–60 years (Berrada, Loudiyi, and Zorkani, 2016; Berrada, 2022), high full-cycle efficiency of about 85% (Emrani et al., 2022; Kropotin and Marchuk, 2023b), and even the high maneuverability in the range of milliseconds (Tong et al., 2023). Thus, LWS can provide: load shifting, renewable energy integration, black start capability, absorbance of reactive power, and even fast-response frequency regulation.
Economic Characteristics
From a technical point of view, LWS is capable of providing at least the same services as Li-ion batteries. Therefore, the revenue stream for LWS is no less than that of Li-ion storage and the main question lies in the comparison of expenses. The total capital expenditures [$] of LWS depend on the energy capacity (E) [MWh] and installed power (P) [MW] (Kropotin and Marchuk, 2023a):
This means that, unlike other energy storage technologies, the capex of the gravity storage system decreases as it scales up, not only due to economies of scale but also due to the design of the LWS itself. Thus, as the LWS capacity increases, we have a double effect of capex drops.
A quantitative assessment without taking into account economies of scale showed that the capex can be reduced to nearly 450 $/kWh (Kropotin and Marchuk, 2023a). The value was calculated using the prices (p_i) that includes the costs of materials, labor, taxes, equipment, subcontractors, overheads as well as construction company profits. Due to the design simplicity, annual O&M costs are quite accurately estimated based on the datasheets of widely used devices and materials of the LWS and accounted for less than 0.5% of CAPEX (Berrada, Loudiyi, and Zorkani, 2016; Berrada, 2022). To summarize the costs and facilitate an economic comparing of an LWS with a Li-ion one, the total cost of ownership has to be calculated as follows:
Startups Gravitricity and GravityPower (; ) propose using abandoned mines for vertical weight movement, which is an innovative closed-cycle economy approach. To increase the total weight mass, Gravitricity's system uses additional weight in the upper-level storage area, as shown in Fig.3. While this solution increases energy capacity of the storage system, it requires horizontal movement of weights, which in turn has a detrimental impact on both the efficiency and operational cost of the system. Seismic activities, a curvilinear path inside a mine shaft, groundwater, and wall maintenance are also major challenges to achieving positive economics for the project.
To make the most of the available space within the cylindrical shell, adjustments to the energy cell sizes are essential, as depicted in Fig.5. Consequently, different cell sizes accommodate varying quantities of weights, leading to energy capacity varying from cell to cell. This complexity adds intricacy to the control of the storage system. Additionally, constructing a thin-walled reinforced concrete shell presents a technically demanding task. In 2021, Energozapas developed the technology of robotic construction for a reinforced concrete load-bearing skeleton of LWS (https://youtu /Vi0BYnK4CBM).
GRAVIENT's energy storage project employs robotic assembly for its load-bearing skeleton. Robotic assembly can reduce construction costs and terms several times, especially in the case of high-rise buildings. While specific project details are currently limited, it can be inferred that the components of the steel load-bearing skeleton are lighter and more compact compared to equivalent reinforced concrete elements with similar load-bearing capacity. Consequently, the cost of robotic construction for the steel skeleton is lower than that for its reinforced concrete counterpart.
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