The HDS technology

The USP of the ReneStor-M hydro-dynamic storage system lies in its efficiency, flexibility and sustainability. The innovative technology of the fully mechanical HDS, its parameters and performance exceed those of the well-established storage technologies, and those that are still in development.

In contrast to a pumped hydro storage facility, ReneStor-M’s HDS is a fully geographically independent unit and which be set up practically anywhere. It is more efficient and is much more compact with its minimum capacity of two megawatt hours. It can be scaled up to several hundred MWh or even to the size of few GWh.

Compared to electrochemical battery storage, HDS is considerably more stable and sustainable. With a lifespan of more than 80 years and at least 85,000 charging cycles without loss in performance, the HDS is times and times more durable and performant than batteries. Another decisive advantage of the HDS is that it produces a fraction of the CO₂ emission compared environmental impact of manufacturing a battery storage system. In addition, 96 percent of the hydro-dynamic storage system can be recycled.

A grid-scale storage system suitable for the energy transition must fulfil strict criteria. Those technologies already in application, but also experimental concepts, only partially meet the substantial requirements of future stable, sustainable and feasible energy supply from renewable sources. An ideal electricity storage in the context of the energy transition is:

environmentally friendly in production, operation and disposal
reliable and has a life-cycle of at least 80 years with
at least 85,000 charge/discharge cycles and minimum maintenance
compact and decentralized, geographically independent
feasible and resource-sparing
efficient, with high energy density
sustainable in production, operation and disposal
black start capable and scalable

The ReneStor-M hydro-dynamic energy storage system fully meets these requirements.

The functionality of the hydro-dynamic storage is based on the most wide-spread, reliable and economical way of storing energy – the principle of PHS. In ReneStor-M’s HDS, like in conventional pumped hydro storage in the mountains, water acts as a storage medium. But ReneStor-M’s self-imposed requirement was to achieve high levels of efficiency and energy density on flat terrain, regardless of location. There was only one solution to achieve this: replace the heights and barrier lakes with artificial vessels and inlet pressure. It was the critical challenge and required a large number of calculations and simulations for several years before the result was certain.

The HDS from ReneStor-M is the state-of-the-art modification of the pumped hydro storage system, a technology which is used to store more than 97 percent of the electricity worldwide. The hydro-dynamic storage system uses gas as propellant which replaces the PHS height and achieves high inlet pressures of the storage medium. Besides, it that makes the HDS system independent of large space requirements. No mechanical energy is transmitted into the gas, high pressures achieve high energy density and short paths of the storage medium increase the efficiency. The HDS works in a closed cycle, as a completely CO2- and emission-free system.

The technology is mature, ReneStor-M relies on components which are used in industry since decades, such as turbines, high pressure pumps as well as electrical and control engineering.

The Chair for Hydraulic Engineering and Water Management at the Technical University of Munich has examined and confirmed the feasibility of the HDS technology in a detailed study:

„The novel energy storage system proposed by ReneStor-M is based on a high-pressure vessel that is filled with water during the charging cycle via a high-pressure pump driven by an electric engine. When discharging, the stored mechanical energy is converted back into electrical energy via an expansion turbine and a synchronous generator with high efficiency. Compared to a compressed air storage, this has the advantage that the hydraulic machines used for energy conversion are very efficient.“

Dr. Ing. Wilfried Knapp, Technical University of Munich, Munich on June 8, 2018

System structure and key data

The modular system structure enables robust and stable operation over a nearly a century. The ReneStor-M HDS system consists of:

Turbine house with all facilities for plant operation
Vessel for the storage medium
Vessel for the propellant
High pressure pump / power in
Pressure maintenance system with applicable software
Feed system with gate valve
Turbines (power out) for 2 and to > 1000 megawatts (MW) depending on requirements and design
Generator suitable for the turbine
Process control system with control and regulation unit

The system has automatic control, monitoring, lubrication and regulation systems for fully autonomous operation with remote operation, and is compliant with the KRITIS (critical infrastructure) requirements.

Due to the architecture and the resource-sparing design, ReneStor-M energy storage system can be planned, approved and implemented in a short time. Since there are no environmental impacts from wastewater, exhaust gases, waste heat or noise emissions, HDS storage system can be easily implemented on a small plot near commercial or industrial areas.

The high overall efficiency of around 85 percent is due to minimal friction losses within the system and the high efficiency of the machines used of (from 90 to 94 percent). The HDS is a closed system with short paths for the storage and propellant media, without foreign objects such as sand or sediments as they occur in a pumped hydro storage system. The efficiency remains stable over the entire operating area despite high flexibility and is independent of the operational sequence. Depending on the grid voltage and structure, transformers for infeed and outfeed can be avoided, which contributes to a further improvement in efficiency.

Due to the fact that it operates independently from external energy, the HDS is ideally suited for black starts – i.e. in the event that a network has to be repaired and stabilized with the help of an energy storage system after a sudden and complete power failure, so called blackout. This option is available with only a few power storage systems.

The turbines used are particularly suitable for high pressures greater than 100 meters of water column (mWS) and work in a control range between 10 and 100 percent with a consistently high level of efficiency. This range can be expanded to zero to 100 percent by additional measures.

A sensitive control and regulation system enables short-term load changes. This also ensures that the power output can be quickly adapted to the grid. With the help of an idling drive, the turbine and the generator are kept rotating so that they can run up to power in seconds, even when waiting.

Technical parameters of HDS

Life span	» 80 years
Cycles	» 85.000 cycles
Overall efficiency	» 85%
Availability	99%
Storage capacity	2 MWh – 400 MWh
Power – in, pump	2 MW – 400 MW
Power out turbine+generator	2 MW – 400 MW
Energy density	4.66 – 6.22 kWh/m³
Response time Pmax	« 15 s
Controllability	0 – 100 % (kW-level possible)
Depth of discharge	100%
Voltage at grid access point	H / M / L
CO2 Print / MW	61t / 1 MW / 80 years
Environmental considerations	none
Recyclablity	94% recycleable
Location	anywhere
Footprint/Dimensions	ca. 2000 m² for 14 MWh plant
Realisation time	1 year
Ambient temperature	from -20°C to +50°C

The HDS technology

System structure and key data

Technical parameters of HDS

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