1. What are hybrid energy storage systems?

Hybrid energy storage systems are designed to provide energy independence and serve as backup power sources. Energy generated by sources such as photovoltaic installations or wind turbines can be stored. The energy is stored in a combined manner.

Battery packs are used to accumulate energy on a daily basis. Resources stored in this way guarantee the handling of daily energy demand. Compressed hydrogen gas is used to store energy on an annual time horizon. The fuel is produced in an electrolyzer during seasonal peak production to secure energy demand during periods of reduced generation from renewable sources.

2. How is the energy storage system constructed?

A hybrid energy storage system consists of a main unit and a set of compressed hydrogen tanks. Depending on the connection power of the installation, the main unit will be housed in an enclosure corresponding to the size of a shipping container of 3 meters (15 kW connection power), 6 meters (50 kW), and 12 meters (150 kW, 300 kW, and 500 kW). Integrating the installation in one enclosure means that connection work at the consumer site is limited to preparing the foundation for the generating container and tanks and connecting them.

3. How does it work?

Energy is stored in battery packs and in the form of compressed hydrogen. To meet the user’s daily energy demand, battery packs are used. Their high efficiency and operational flexibility compensate for rapid changes in electricity production and consumption. Their size is chosen to fully serve the customer’s demand for a maximum of 2-3 days.


Hydrogen is used for balancing energy consumption in the longer, especially seasonal, cycle. Its production starts when the batteries are charged, and the consumer has a buffer of energy for at least a day. In this way, the surplus from renewable energy production can be accumulated for several months.

4. What is the efficiency of the energy storage system?

The overall energy efficiency of the device, considering electrical and thermal energy, is over 80%. However, the exact efficiency value can only be determined after familiarizing oneself with the energy profile of the consumer’s installation. Since energy is stored and released in a combined manner, the resulting efficiency depends on the proportion of energy stored in battery packs and hydrogen, and how much heat is absorbed by the consumer.It is possible to provide approximate electrical efficiency values for two types of storage: for a battery pack, it is around 90%, while for a hydrogen installation, it is 30-35%. The overall efficiency of the hydrogen system is influenced by the efficiency of the electrolyzer, compression process, and fuel cell. It is worth noting that Frako-Term installs the latest European-made devices.

Part of the energy that cannot be converted into electricity is captured as heat. This solution results in very high overall device efficiency. The main idea of the designers was to design the system so that, since higher cell and electrolyzer efficiency cannot be achieved due to physical processes, the heat obtained in this way should be transferred to the consumer as efficiently as possible.

This way, an energy storage system was obtained that meets the energy demand of all installations in the building.

5. What is the system's lifespan?

This parameter is also related to the usage profile. The control program will adapt to the user’s needs and decide whether to prioritize achieving the highest efficiency or extending the device’s lifespan. It can be assumed that the entire storage system will function for at least 25 years, and regeneration of membranes in the cell and electrolyzer will be necessary in about 7-9 years. However, this period is approximate and will vary depending on whether the system serves as emergency power or energy storage in an off-grid installation. To achieve the highest storage system lifespan, the designers have provided several solutions, such as additional water supply filtering and softening, filter sets, and service procedures.

6. Is this a safe technology?

Yes, hydrogen is a gas that has been used in the industry for years, and manufacturers have products dedicated to working with this medium (pressure fittings, tanks, or hydrogen leak detectors). Frako-Term uses components exclusively from reputable and proven manufacturers. All the technical solutions provided in the device, including the control algorithm, are dictated by safety considerations, which always come first. The installation must be placed in an open space with a certain separation distance from adjacent elements (e.g., 16 meters from an air intake for ventilation or 8 meters from open flame sources). Hydrogen, as the lightest gas, will always evaporate into the air in the event of a leak, and all enclosed spaces of the installation are continuously ventilated. A certain amount of gas is also regularly released during normal (non-emergency) operation, for which a dedicated discharge system is used (with an outlet at least 3 meters above the ground).

7. Who is the product aimed at?

The solution is aimed at anyone who values independence and reliable power supply. One of the design assumptions was that the main customers for medium-sized storage systems would be consumers with a nonlinear energy consumption pattern.