Inverter Selection for a Roof Top System
The DC power produced is fed to inverter for conversion into AC. In a grid tied roof top system AC power is fed to the grid at 11 KV three phase systems or to a 415V three phases or 220/240 V single phase system line depending on the system installed at institution/commercial establishment or residential complex or single house consumer and load requirement. Power generated from the solar system during the daytime is utilized fully by powering the captive loads and feeding excess power to the grid as long as grid is available. In cases, where solar power is not sufficient due to cloud cover etc. the captive loads are served by drawing power from the grid. The inverter should always give preference to the Solar Power and will use Grid/DG power only when the Solar Power is insufficient to meet the load requirement.
The output of the inverter must synchronize automatically its AC output to the exact AC voltage and frequency of the grid. In a solar PV system without battery or with battery the inverter continuously monitors the condition of the grid and in the event of grid failure; the inverter automatically switches to off-grid supply within 20-50 milliseconds. The solar system is resynchronized with the grid within two minutes after the restoration of grid. Grid voltage is continuously monitored and in the event of voltage going below a preset value and above a preset value, the solar system shall be disconnected from the grid within the set time. Both over voltage and under voltage relays shall have adjustable voltage (50% to 130%) and time settings (0 to 5 seconds).
Over-voltage protection shall be provided by using Metal Oxide Varistors
(MOVs) on DC and AC side the inverter. The inverter shall be so designed so as to operate the PV system near its maximum Power Point (MPP), the operating point where the combined values.
of the current and voltage of the solar modules result in a maximum power
vi. The inverter shall be a true sine way inverter for a grid interactive PV
vii. In case of system with battery, inverter also monitors the, state of Battery
Voltage, and performs switching operations to ensure that battery is charged
viii. The degree of protection of the indoor