News
1.PV battery
To develop a solar inverter system, it is important to first understand the different characteristics of solar cells (PV cells). Rp and Rs are parasitic resistances, which are infinite and zero, respectively, under ideal conditions.
Light intensity and temperature can greatly affect the operating characteristics of PV cells. The current is directly proportional to the light intensity, but the change of light has little effect on the working voltage. However, the operating voltage is affected by temperature. An increase in battery temperature reduces the operating voltage but has little effect on the generated current. The figure below illustrates the effect of temperature and light on a PV module.
The impact of light intensity changes on battery output power is greater than the impact of temperature changes. This is true for all commonly used PV materials. The important consequence of the combination of these two effects is that the power of a PV cell decreases with decreasing light intensity and/or increasing temperature.
2. Maximum power point (MPP)
Solar cells can operate over a wide range of voltages and currents. By continuously increasing the resistive load on the irradiated cell from zero (short-circuit event) to very high values (open-circuit event), MPP can be determined. MPP is the operating point at which V x I reaches its maximum value, and at this irradiation intensity Maximum power can be achieved. The output power is zero in the event of a short circuit (PV voltage equal to zero) or an open circuit (PV current equal to zero) event.
A high-quality monocrystalline silicon solar cell produces an open circuit voltage of 0.60 volts at its temperature of 25°C. With full sunlight and an air temperature of 25°C, the temperature of a given cell could be closer to 45°C, which would drop the open circuit voltage to about 0.55V, which continues to drop with increasing temperature until PV Module shorted.
Maximum power at a cell temperature of 45°C is typically produced at 80% open circuit voltage and 90% short circuit current. The short-circuit current of the battery is almost proportional to the illuminance, and the open-circuit voltage may only decrease by 10% when the illuminance is reduced by 80%. The voltage of the lower-quality battery will decrease faster when the current increases, thus reducing the available power. Output dropped from 70% to 50%, or even just 25%.
More energy can be harvested using a maximum power point control loop, also known as a Maximum Power Point Tracker (MPPT). Achieving a high ratio of MPP tracking also requires the PV output voltage ripple to be small enough so that the PV current does not change too much when operating near the maximum power point. The MPP voltage range of PV modules can usually be defined in the range of 25V to 45V, the power generation is about 250W, and the open circuit voltage is lower than 50V. A solar microinverter must ensure that the PV modules are operating at MPP at any given time so that maximum energy can be drawn from the PV modules.
