German researchers have evaluated the performance of balcony solar modules connected to an e-bike battery and found that this combination provides stable and continuous operation for three days. They tested two system architectures based on passive and active hybridization and said that both system designs provide satisfactory results.
Their approach consisted of plugging the battery into the system with a minimal amount of additional components and no modifications, which they said kept the cost of the system low. They also specified that in the proposed system configuration, the microinverter does not “know” that it is connected to the battery, forcing the researchers to investigate the use of passive or active measures to avoid maximum power point (MPP) tracking. battery.
For this reason, the research team proposed two different system architectures, which it called passive hybridization or direct connection and active hybridization or active switching.
In the first one, the battery is connected to the panel without a microinverter or charging controller in between. “It is based on the corresponding current and voltage behavior of PV and battery,” the researchers said, noting that the system is self-regulating and does not require a battery management system. “During battery charging, the system voltage increases and drives the PV towards zero current when the battery is fully charged. During discharge, the diode protects the PV from too low voltage levels.
Active architecture means connecting a microinverter and a controller between the battery and the photovoltaic systems, which enables the active control of voltages and currents while regulating the interaction between the components. “Here, one side of the controller is placed in the parallel connection between the PV modules and the inverter,” the researchers said. “The battery is connected to the other side of the controller.”
The passive design is cheaper than the active one, but it is also less efficient than MPP-tracked setups, the team noted.
Academics used real weather data and high-resolution synthetic load profiles to run a series of simulations Via Simulink (MATLAB) to evaluate the performance of the two systems over a period of one year. They assumed that the system consists of three PV modules connected in series, each with a power of 100 W, a 36 V E-Bicycle lithium-ion battery with a rated energy of 555 Wh and a rated capacity of 15.5 Ah, and a 250 W microinverter with an MPP tracker.
They compared the performance of the two architectures with a balcony PV system with the same characteristics but without storage. “The three systems were tested on different days under different weather conditions,” they also explained. “For both AC and DC measurements, data was recorded every one second. Weather data was recorded every ten minutes.”
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Through their analysis, the German team concluded that both active and passive systems are technically viable, as they can provide continuous and stable operation for three days. “The passive hybrid system is conceptually simple and allows continuous use of the inverter, which is advantageous for covering the base load of the household,” it stated. “An active system shows intermittent inverter operation, but has a higher system efficiency.”
The researchers said that the financial viability of both project plans should be further investigated, as the cost of the battery may still be an obstacle that could eventually be removed by increasing the size of the balcony solar system. “Wide applicability requires that system settings be adapted to increase flexibility, which likely requires communication with the battery,” they concluded.
Their findings were presented in the journal “Li-ion battery integration in a micro-photovoltaic system: Passive vs. active switching architecture, published Solar energy.