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Functional principle of the energy storage device with compressed air

   working scheme          flowchart

The compressed air energy storage is based on the physical principles of hydraulics and pneumatics. The disadvantages of pneumatics (heat and cold losses) can be largely compensated in connection with hydraulics. Hydraulic systems have a very high efficiency of up to 90%.

The storage and provision of energy are based on the same working principle. During the storage process (compression), the hydraulic oil is pumped into several high-pressure cylinders by means of a hydraulic pump (hydraulic motor) using electrical energy. The pistons of the high-pressure cylinders press and compress the air in the storage tanks up to a pressure of 300 bar. During unloading (decompression), the high-pressure cylinders filled with oil are charged with the pneumatic pressure from the storage pressure tanks. Here, too, the oil drives a hydraulic motor, which in turn drives an electricity generator and delivers the generated electrical energy to the consumer. In order to achieve continuous operation, several high-pressure cylinders are used in parallel and one behind the other. The parallel arrangement of the cylinders in connection with a corresponding control can compensate for the damaging heat development in compressors during charging and the cold development leading to icing during unloading.

The physical heat generated when air is compressed is transferred to the cooling water tank of the system and is therefore not lost in terms of energy. The heat stored in it can be used e.g. via a heat exchanger for the heat requirement (domestic water, heating support) outside the system. Likewise, the physical cold that occurs when the compressed air tanks are unloaded can be used for cooling outside the system via a cold exchanger.

The efficiency of electrical energy (electricity) and thermal energy (heating and cooling) can be optimized and controlled within limits as required in the system.

By including and using the thermal energy generated during compression and the cold energy generated during decompression of compressed air, a very high overall efficiency can be achieved for the storage system. Efficiency levels are shown in this overview (link).

Commercially available 80 liter compressed air cylinders, in which the air is compressed up to 300 bar, serve as storage containers. The compression of the air by the hydraulic pump can be done with the appropriate power (max. 20 kW for the pilot) from an external power source. Power sources can be PV, wind generator or any other power generator. When discharging the storage tank to generate electricity, a power of 10 kW can be continuously called up by the consumer. Charging and withdrawal capacities are independent of the amount of energy stored.

The compressed air generated during charging can also be used and fed in as an energy carrier for use in companies' compressed air networks (e.g. 10 bar low pressure). It is also possible to operate the system only as an efficient compressor of compressed air with 50-60% efficiency.

Another field of application is the compression of gases, in particular biogas, which is generated in agricultural biogas plants and has to be stored until the appropriate time of use. In addition, the highly compressed gas can also be reused to generate electricity, which can result in multiple uses. Digester gases in sewage treatment plants can also be compressed and converted into electricity using this principle. The purely hydraulic-pneumatic mode of operation eliminates the risk of explosion.

The stored energy can be called up at any time and without delay.

By providing additional compressed air cylinders, the energy storage capacity of the system can be scaled as required.

The entire storage system consists of or is based on commercially available components. The space requirement of the storage system is approx. 3 square meters.

A pilot system with the functionality described above has been created and is available for demonstration purposes.

Utility model protection and patents have been applied for for the compressed air storage system designed here.

In a test facility (not isolated or optimized) corresponding to our pilots, the following values were determined:
Separate representation of the degree of efficiency (Link)

Efficiencies calculated values
35% electrical (measured) up to 48%
36% heat (measured) up to 26%
16% cold (estimated) up to 14%
The pilot development did not focus on high efficiencies, but rather the testing of functionality. Measurement and optimization of the degree of efficiency are the subject of further development.

We are currently unable to provide any further technical details for reasons of patent law.