System 2 - Green hydrogen
The involvement of electrolytic hydrogen production in renewable energy systems is unique in our conditions. The electrolyser will be powered by photovoltaic and solar-thermal panels located on the roofs of surrounding buildings. The hydrogen will be stored in a gas tank from where it will be pumped to the fuel cells of Systems 1 and 4. The waste heat from the electrolyser and the heat from the solar-thermal collectors will be stored in a shallow underground storage at a maximum depth of 200 m at a temperature level of 15 to 30 °C. In winter, the heat will be pumped from here to a testing low-temperature heat network to simulate the conditions of the modern district heating systems. Later a high-temperature heat pump will be used to produce 90-95 °C hot water that can be used in the existing district heating system. System 2 will therefore not only produce the hydrogen itself for Systems 1 and 4, but will also be one of the heat sources used to heat Litoměřice.
- Photovoltaic panel PV
- Photovoltaic-thermal collector PVT
- Ground source heat pump HP
- Fuel cell FC
- Shallow well field to a depth of 200 m WELL 200
- Electrolyser EL
- Pressure storage of hydrogen H2
- District heating system DHS
- Low-temperature network emulator EM
Photovoltaic panel PV converts sunlight into electricity. Its basic functional element is a photovoltaic cell. The current is proportional to the area of the cell, its efficiency and the intensity of the sun's radiation. For a particular cell, it depends in part on the spectrum of the incident sunlight, which varies throughout the day and year. A photovoltaic panel is usually composed of a number of cells connected in series. Photovoltaic panels commonly available on the market can be divided into crystalline and thin-film.
Photovoltaic-thermal collector PVTis capable of combined production of electricity and heat from solar radiation. Since the efficiency of PV panels decreases with higher temperature, the advantage of the combined system is that the flowing cool water cools the PV cell, thus increasing its efficiency. This heats the flowing liquid and can be used in a similar way to a photothermal collector. The main advantage is the use of the available surface area to obtain both heat and electricity from solar radiation. PVT collectors are suited to plants with limited space for the installation of solar elements.
Ground source heat pump HP removes heat from the ground and converts it to a higher temperature level for heating and hot water. The transfer of heat to a higher temperature level is made possible by compressing the vapours of the working substance (refrigerant) drawn from the evaporator by the compressor, heating them up and then condensing them at a usable temperature. This is using the same mechanism as a compressor refrigerator.
Fuel cell FC is an electrochemical device that converts the chemical energy of hydrogen into electrical and thermal energy. The basic element of a fuel cell is two electrodes separated by a membrane or electrolyte. Hydrogen is supplied to the negative electrode and oxygen to the positive electrode.
A field of shallow wells to a depth of 200 m WELL 200 will be used for interseasonal heat storage. The plan is to build a series of equally deep wells in order to achieve the highest efficiency and capacity of the system. To a depth of c. 170-180 m wells will reach Mesozoic Upper Cretaceous sandstones, under which there is a striking red Protozoan claystone. The rocks in this interval have variable and as yet insufficiently explored properties, which have a direct impact on determining the design of wells. The specific technical solution for heat storage will therefore be chosen based on the results of numerical modeling based on ongoing geological and hydrogeological research.
Electrolyser EL is a device producing hydrogen by the decomposition of water by the action of electricity. Oxygen is produced along with hydrogen. In the case of electricity supply only from renewable sources such as PV panels, green hydrogen is produced.
Pressure storage of hydrogen H2 is used for its seasonal storage. Hydrogen is compressed and stored in specially-designed pressure vessels.
District heating system DHS supplies heat to buildings in Litoměřice. It is operated by ENERGIE Holding a. s. Currently it burns wood chips and coal. From 2027 it should use geothermal energy thanks to the SYNERGYS project.
Low-temperature network emulator EM simulates conditions in modern heat networks. At the same time, it interconnects systems with seasonal storage to supply low-temperature heat to the district heating network via a high-temperature heat pump.
