Gravity-based electricity storage - Bulk storage
The complexity of electricity storage technologies and different requirements in applications represent a challenge for adequate cost assessment of electricity storage solutions. Therefore, cost assessments of electricity storage solutions must be based on their levelised cost of storage (LCOS), an application-specific quantification of a technology’s discounted cost of electricity per unit of discharged electricity. The figure below shows the LCOS for Heindl Energy's Gravity Storage concept and the four most common deployed storage technologies for bulk electricity storage.
Figure - LCOS in US$/MWh discharged electricity for investigated bulk storage technologies of 5 GWh system size, 8 hours discharge duration, 330 full equivalent charge cycles per year, electricity price of 20 US$/MWh and 8% discount rate. Values are compared to results from studies by Lazard. Only lithium-ion among technologies considered in 2017 Lazard study.
Based on the given data, Gravity Storage is the most cost-effective bulk electricity storage technology for systems larger than 1 GWh, followed by compressed air and pumped hydro. Low specific energy investment costs represent the key advantage for these technologies at the required discharge duration of 8 hours. Gravity Storage further benefits from moderate specific power investment costs and more significant scale effects with increasing system size.
Schmidt, O. Levelised Cost of Storage - Gravity Storage. Imperial College Consultants and Storage Lab. 2018. (Report)
Gravity-based electricity storage - Frequency response
LCOS can be expressed in power terms as $/kW-year, also called annuitised capacity cost. This metric represents the minimum payment required for each “kW” that is made available for power provision for an entire year to achieve a net present value of zero. It is used for applications that require electric power like frequency response services. The figure below shows the power LCOS for four technologies providing frequency response compared to the gravity-based concept by Gravitricity.
Figure - Gravitricity concept and comparison of its LCOS in a frequency response application (US$/kW-year) to other suitable electricity storage technologies.
Low specific power cost and high cyclability represent the key advantages of Gravitricity over the comparison technologies. These characteristics match best with the power-to-energy ratio and cycle requirements in the given application.
Schmidt, O. Levelised Cost of Storage for Gravitricity storage systems. Imperial College Consultants and Storage Lab. 2018.
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