The application on grid-connected solar cells for DC current electronic equipment

The focus of the discussion in this paper is the development of solar cells on the electricity network connected to solar cell energy, the use of energy is selected based on the current mode which aims to optimize the use of energy generated from solar cells. The development of this system is prioritized for consumers who can manage electrical equipment connected to the electricity grid or from solar cells. The development of this system is adjusted to the required hardware and software. The method used is the application of science into technological design. based on the results obtained, there is an energy saving of dc electronic equipment that is connected directly to the MPPT solar cell system of 7.6% when compared to the use of an inverter.


Introduction
Indonesia, with its vast expanse and relatively high intensity and solar radiation, has enormous potential to develop solar-based energy.The high intensity of sunlight because it is on the equator, an area that has the same duration of day and night and only has summer and rain.Therefore, this will further support the use of solar power plants as an effort to use alternative energy sources [1] [2]. Figure 1 will show the potential of solar energy in Indonesia [3].Fig. 1 Indonesian Photovoltaic Power Potential [3] The potential use of solar energy in Indonesia is very large and is at a high potential level.The potential is very large, namely 4.8 KWh/m 2 which is equivalent to 112,000 GWp, but the utilization of solar energy has not yet reached 1% of the total potential.[4].The potential for solar energy in Indonesia is very large, around 4.8 KWh/m 2 or equivalent to 112,000 GWp, but only about 10 MWp has been utilized.Currently, the government has issued a roadmap for the utilization of solar energy which targets the installed PLTS capacity by 2025 to be 0.87 GW or around 50 MWp/year.This number represents a fairly large market potential in the development of solar energy in the future.Solar cell is a device that can convert solar radiation energy into electrical energy.The ability of solar cells to convert this energy is a very good capital for the use of energy today and in the future [5].Very high energy requirements can be supported by solar energy which is converted through solar cells.
The daily power requirement can be calculated using the what hour (Wh) equation.The daily Wh calculation can be seen from the need for electronic equipment used and the time of use, this can be calculated by a simple equation, namely by multiplying the load power by the time of use [1].If the power used can be determined, it is easy to determine the type of solar cell to be used.The amount of power generated by the solar cell is the product of the current and the output voltage of the solar cell.While the total electrical energy can be calculated by the following equation.

∑ 𝑊ℎ = ∑(𝑃𝑥𝑡)
dimana, ∑ Wh = Total energy of solar cells in hours P = Load Power (Watt) t = Time duration (jam) Solar cells were originally developed with the Off grid system, where solar cells independently generate electricity and are connected to equipment that requires the energy.However, the system requires energy storage if the energy produced exceeds current needs [6].Energy storage in the form of batteries with specifications capable of storing large amounts of power.Batteries with large capacities can also be found at a high price.
In addition, energy generation in solar cells has also been developed with a system without selfstorage, where the excess energy can be channeled to the national electricity company or connected to the grid [7].This system has a lower cost because it does not require a standalone battery, and the remaining unused energy can be channeled which is an advantage in the form of energy sales.By knowing the solar cell energy yield system and the load on the use of electronic equipment, the total value of solar cell power that is able to meet the load in a certain time duration can be calculated, so that the rest becomes storage that can be used again in the electric power grid system.The on-grid topology can be seen in Figure 2 Fig 2 .Topologi on grid In the process, the use of connected and unconnected electricity has the same process for use in all electronic equipment, namely a) converting solar energy into DC electrical energy by solar cells, b) converting DC electricity into AC electricity by the Inverter system, c) energy distribution from the inverter.to electronic equipment and power grids.In the process, the results obtained with the on grid system process will get greater savings when compared to without a network system [8].
Researchers try to continue to develop this on-grid system to get even greater power savings, namely without converting the electrical energy produced by solar cells into AC electricity or remaining on DC electricity.This goal is closely related to the power wasted during the conversion process on the inverter and also on the adapter / power supply [9].The efficiency of the inverter is 92-98% while the efficiency of the power supply is 80-95%.Thus the energy lost in the conversion process is quite large.Besides that, most of the electronic equipment that is often used by users is DC electricity such as television, lighting, computers, smartphones etc.Based on these conditions, the researchers developed a hybrid system based on the need for the use of electrical energy, namely the use of solar cell energy directly for DC electronic equipment and conversion through an inverter for AC electronic equipment and connected to the electricity network.

Research Methods
This study uses experimental research methods.This method is to apply science and technological developments to realize the design and development of equipment to be able to contribute to technological developments.The system design is done by developing the conceptual into the form of a block diagram.The block diagram design can be seen in Figure 3.

Fig 3. Block diagram of the system instrument
Based on Figure 3.It can be explained that the energy harvesting system in solar cells will produce DC electricity with a voltage configuration of 17 to 21 Volts.The power from these solar cells can be maximized by using the MPPT system that has been developed in previous research [10] [11].The output of the MPPT system is the input of the inverter as well as the input of DC electronic equipment, and the output of the inverter can also be divided into AC electrical equipment and to the power grid.
Control is done by using a microcontroller system as the center of the control system.Microcontroller works based on input and provides input in accordance with the given conditions.The sensors include current sensors, voltage sensors, power sensors, while the output of the microcontroller is connected to the switch system, and the inverter system.The results of the design can be seen in Figure 4. Making this system is able to manage the power generated by solar cells optimally.Where, power can be used directly without going through the conversion process into AC electricity.This experiment is able to shorten the system and provide power consumption savings.For comparison, it has also been done through the system on a regular basis, namely through the conversion process.Any electronic equipment with DC electricity that is connected to the MPPT solar cell will have a DC DC converter to change the voltage level required by the equipment.If the working voltage of electronic equipment is 12 Volts, then there is no need for a dc dc converter.The dc dc converter is directly integrated and controlled via a microcontroller.
Realizing the system based on the designed model is carried out in the physics laboratory.From the realization of the design, the system can be tested by direct experimentation, if the experimental results are not in accordance with the mechanism, then re-analysis and design changes are carried out.System optimization is carried out to get results according to the initial modeling.The development of this system topology aims to control the transfer of electrical energy from the load to the load in every condition.This system is equipped with stages of control with information and data from sensors.The data obtained is then analyzed to measure the performance and efficiency of the system.The results of the analysis will also get the level of power saving generated by the system .The system that has been designed in this study uses a control system based on a microcontroller, a communication system and programming based on a graphical user interface.This control system will make it easier to regulate the use and distribution of electrical energy from solar cells to DC loads and to the inverter.Data processing and controlling system activities are recorded with a database on a personal computer in the form of text that can be processed into other forms as needed.The monitoring system is carried out in real time.The data generated in this system can make it easier to evaluate the efficiency and control the power output of solar cells.

Results and Discussions
The design of the grid system has been carried out using a system that is connected directly and connected indirectly.The direct link is a combination of converting solar cell energy into a form of energy equal to or equivalent to the electricity produced by the state electricity provider.That is by converting from dc electricity generated by the MPPT solar cell system into ac electricity and by phase adjustment.The indirect connection is with a switching system, namely the transfer of electrical energy from solar cells to electronic equipment directly without going through an inverter conversion.
Experiments using the power generated by solar cells only for DC electrical equipment have been carried out.The voltage and current generated from the solar cell MPPT system are made and regulated according to the needs of electronic equipment.Electronic equipment connected to this system includes a computer with a working voltage of 12 Volts, LED lights with a working voltage of 18 Volts, an adapter for charging smartphones with a working voltage of 5.4 Volts, and others.Based on the data in table 1.It can be explained that the experiment was carried out during the day when the sun was at its peak irradiation at 11.00 WIB, ignoring the influence of reducing radiation levels due to cloud formation.This experiment resulted in the absorption and use of the average power of the electronic equipment which can be seen in Figure 5.In figure 5.The power produced by solar cells for 20 minutes is an average of 77.3 Watts, while each E1, E2 and E3 electronic equipment has a total power consumption that is less than the power generated by solar cells.Thus there is excess power that can be transferred to the inverter and the power grid.Experiments using solar cell power directly without going through an inverter provide better added value than using an inverter, because it goes through an energy conversion process which will result in wasted energy.To get a comparison of the difference in power absorption used by electronic equipment, measurements are also made on the same equipment but through the conversion of electrical energy through an inverter into AC electricity and then converted again into DC electricity using a current rectifier.Comparison of the results of the use of the two methods can be seen in Figure 6.From this experiment, it can be seen that the conversion of electrical energy through conversion through an inverter is more stable but produces an average of 7.6% of wasted energy.When compared with the use of power from the solar cell system directly.This advantage is obtained from the use of three (3) types of DC electrical equipment that have a working voltage of 18 Volt, 12 Volt and 5 Volt respectively.Thus direct use can provide electricity savings.
This system has the advantage that the inverter used does not need to be greater than the need for the resulting electronic equipment.The inverter capacity only needs to consider the residual power generated from the solar cell system to be transmitted to the electricity grid and which will be used by AC electrical equipment.
This system still needs to be developed because it has obstacles that need to be overcome, namely, in the process of switching the use of energy from solar cells to the electricity grid and vice versa, it is necessary to go through the shutdown process of the equipment because if the switching process is carried out directly it can produce fluctuations in electrical voltage that can harm electrical equipment.

Conclusion
Grid systems on solar cells can provide convenience and benefits for users.Users do not need to provide batteries as energy storage but only channel the remaining energy from solar cells to the electricity grid and can be used again if the need is excessive and or without energy harvesting in solar cells such as at night.Controlling the use of DC electricity directly from the solar cell system can provide benefits in the form of reducing power loss from the conversion system in the inverter and power supply system.The results presented show that the performance of the system is able to improve the performance of a solar cell-based renewable energy system.

Fig 4 .
Fig 4. Plan of system grid connection.

Fig 5 .
Fig 5. Power absorption and use of DC electronic equipment

Fig 6 .
Fig 6.Comparison of direct and indirect electrical energy absorption.

Table 1 .
Measurement of the Power of Solar Cells, Electronic Equipment and to the Inverter