Inverters & Power Control Equipment
Inverters are a critical balance of system component in PV systems
A solar inverter converts the DC current output of a photo-voltaic array, into alternating AC current that can be fed into a commercial electrical grid or used by a customer in an Off Grid installation for powering ordinary AC powered equipment.
Solar inverters are classified into three broad types: Stand-alone inverters, used in isolated systems where the inverter draws its DC power from batteries charged by photovoltaic arrays. Many stand-alone inverters also incorporate integral battery chargers to replenish the battery from an AC source, when available. Normally these do not interface in any way with the utility grid, and as such, are not required to have anti-islanding protection.
Grid-tie inverters, which match phase with a utility-supplied sine wave, are designed to shut down automatically upon loss of utility supply, for safety reasons. They do not provide backup power during utility outages. Battery backup inverters are special inverters which are designed to draw energy from a battery, manage the battery charge via an on-board charger, and export excess energy to the utility grid. These inverters are capable of supplying AC energy to selected loads during a utility outage, and are required to have anti-islanding protection. Solar inverters use maximum power point tracking (MPPT) to get the maximum possible power from the PV array. Solar cells have a complex relationship between solar irradiation, temperature and total resistance that produces a non-linear output efficiency known as the I-V curve. It is the purpose of the MPPT system to sample the output of the cells and determine a resistance (load) to obtain maximum power for any given environmental conditions.
Advanced solar pumping inverters convert DC current from the solar array into AC current to drive submersible pumps directly without the need for batteries or other energy storage devices. By utilizing MPPT solar pumping inverters regulate output frequency to control the speed of the pumps in order to save the pump motor from damage.