# A Real Model of a Micro-Grid to Improve Network Stability
## 3 Description of the DC Micro-Grid
### Hydrogen Circuit  
In the presented micro-grid, a hydrogen circuit is applied when all the accumulators are fully charged and the smart grid shows an energy surplus (namely, the related photovoltaic panels, wind power plants, or small hydroelectric plants generate energy on a constant basis). Such a surplus is then used to produce hydrogen, and this product is stored in the metal hydride storage case. Figure 4: The Ovonic(tm) solid hydrogen storage canister, 760 sl (standard liters). In our case, a small hydrogen circuit containing a metal hydride canister is applied; for an effective description, this hydrogen circuit can be subdivided into three main parts. The first of these components is an electrolyzer (a hydrogen generator) with a dryer and a purifier; the second one embodies the storage, or a metal hydride storage tank with a valve system to switch between charging and consumption; and the third one consists of an FC. We opted to use an ACTA EL100c electrolyzer (Crespina, Italy) with a dryer hydrogen generator (Figure 5). The technical specifications of the EL100c are as follows: maximum hydrogen flow rate of @ 20 \({}^{\circ}\)C/1 bar, 100 NI/h; max. pressure of 30 bar; hydrogen purity of 99.95% @ 30 bar; max. power consumption of 700 W; and max. water consumption of 0.1 L/h [35]. The hydrogen laboratory arrangement is outlined within the block diagram and image shown in Figure 6. The entire circuit can be controlled using LabView made by National Instruments (Austin, TX, USA) and CompactRIO, via a signal communicated by the CWP control program. If an energy surplus is detected, the program will send a signal to activate the relevant controlled switch; the electrolyzer and dryer will then start to operate. The electrolyzer is capable of producing very clean (with 99.95% purity) dry hydrogen at 30 bar. Such a high pressure has to be decreased to the value of 10 bar by means of a manual reduction valve; the reduced pressure is applied to fill the hydrogen storage, namely, the metal hydride canister. In the opposite state, a condition when the local accumulators are discharged and only an insufficient amount of energy is available in the network, LabView dispatches a signal to open controlled valve 2; through the open valve, hydrogen will be transported from the metal hydride storage to the FC. The hydrogen pressure, however, has to be maintained at 0.45 bar; otherwise, the cell could be destroyed. Further, it is also possible to utilize a flowmeter to determine the quantity of hydrogen flowing from the metal hydride storage. The FC, too, is switched on by a signal because its actual start needs to be performed in the no-load mode; only after approximately 10 s, the controlled DC/DC converter is connected. The converter regulates the amount of current flowing from the FC, thus facilitating optimal operation of the cell. The resulting efficiency of the hydrogen circuit can therefore be expressed as an amount of approximately 16%. Figure 5: The ACTA EL100c hydrogen generator including a dryer. Communication and Control Elements to Manage the Devices and Instrumentation of the Smart Energy Model  
The physical equivalents of the energy generated through the water and wind power plants are simulated by the RES-controlled power module connected into the SEM via the CB1 module, Figures 1 and 7. The CB1 is a significant module facilitating energy transfer and voltage transformation from 12 V\({}_{\text{DC}}\) to 24 V\({}_{\text{DC}}\) and vice versa. The CB1 and RES are controlled by the CompactRIO system according to the data received from the wireless data logger. Each power control device (the CB1, CB2, and RES) uses its input/output circuits to communicate with the CC physically via wired connections in the laboratory. These low-power control connections are only schematically indicated in Figure 1 for better clarity.