(325e) Self-Controlled Electric Power Supply System from Solar Cells Using Hydrogen Storage

Energy source changing from fossil fuels to renewable energies is an urgent problem to solve for human beings. Renewable energy sources like solar power and wind are fluctuated and do not have the same trend as the demand of society. However, energy must be supplied as the same amount of energy as the requirement of society even using renewable energy. Since electricity cannot be stored, the surplus and deficit of renewable energies are compensated by storage or generation from the conventional way currently. Energy compensation like charge and discharge within renewable energy must be established when whole energy supplies from renewable energies. To satisfy this requirement, electricity is required to change its form from electrical to chemical energies and is needed to be controlled along with the surplus or deficit.

This control is not easy because the reasons are as follows.

1) The control system is required rapid change of electricity input/output and a large amount of storage.

2) The storage devices like rechargeable batteries, water electrolyzers, and fuel cells for hydrogen storage, need to control their power to change their storage amount. Otherwise, the voltage and current supplied by the devices change with their supplying power.

3) The system has the merging points of electricity. The merging is not easy considering Kirchhoff's circuit laws.

Therefore, several control methods were proposed like central processing control and DC signaling control. The control methods, however, have problems like very heavy signal traffic and/or abrupt power change.

The control method called “modified DC-bus signaling control”, which we proposed, solves these problems. The control is as follows.

1) Each energy device is connected to the DC-bus line with DC/DC converter. A fast response device like a rechargeable battery which is called a main voltage controller (MVC) absorbs/desorbs the rapidly changing power first.

2) The DC/DC converter controls the voltage of the DC-bus line as a signal proportional to the time integral of the power input to / output from MVC.

3) The power control of the sub voltage controller (SVC) for a large amount of energy storage like hydrogen via water electrolyzers and fuel cells is defined by the deviance from real DC-bus voltage and the standard voltage which is defined for each device.

4) The DC-bus voltage changing from MVC and the power controlling of SVC continues to the power flow for the MVC becoming zero.

This control is performed by each device independently; thus, energy management is not needed to control its homeostatic condition.

The real system with about 2 kW electric power supply was installed and was evaluated under the conditions of step-like input/output change and real solar cell input. The results were the same as expected. These results show that this controlling method can be used as a real energy system with renewable energy. The results of local installing estimation of system size were, however, that each device size is affected by the local weather condition so much. The unitarization of each device is suitable to localize the system. The unitization of each MVC and SVC is also available using this proposed system control method. These considerations show that this controlling method is one of the suitable methods for renewable energy supply systems.

References

27542. Yamashita, et al., Int. J. Hydrogen Energy 44 (2019) 27542.

https://doi.org/10.1016/j.ijhydene.2019.08.234

45. Fujii, et al., J. Jpn. Inst. Energy 100 (2021) 45.

https://doi.org/10.3775/jie.100.45