Off grid: the 'string boards' handle parallel connection between photovoltaic strings, usually composed of 3 or 4 panels connected in series. Each string must have voltage from 90 to 160 V (120 V is recommended for optimal efficiency of the MPPT) and current no higher than 10 A (12 A with appropriate fuses). The strings must be inserted through the dedicated holes in the ZHERO case and screwed to the board terminal block, paying attention to the connection sequence. On grid: the 'string boards' handle parallel connection between the solar panel strings, usually composed of 7 to 15 panels connected in series. Each string must have voltage between 200 and 600 V (300 - 400 V recommended for optimal MPPT performance) and current of no more than 10 A (12 A with appropriate fuses). The strings must be plugged in via dedicated connectors inside the ZHERO unit