Conventional solar PV systems using string or central inverters

Today, most solar PV installations use conventional string or central inverters. Solar panels are wired in series, creating a PV array, which is then connected to a string or central inverter that converts the direct current (DC) from the PV array into alternating current (AC) for connection to the electricity grid. Conventional PV systems with string or central inverters have a number of disadvantages:

• Sub-optimal energy harvest – they dramatically compromise energy harvest from a PV array. Every time the performance of a solar module is compromised, the poorest performing module drags down the performance of the entire solar PV system. The performance of solar modules, either individually or in groups, is often negatively affected by numerous factors. These include shadows from clouds, trees, chimneys, equipment, or other structures, the build-up of dust, leaves or other debris on module surfaces or by quality issues related to the modules themselves. String or central inverters cannot provide Maximum Power Point Tracking (MPPT) for each module, so the highest possible output is not extracted from the PV array.
• Safety concerns – DC wiring emanating from the solar modules in the PV array to string or central inverter represent a safety concern. They also require expensive specialist skills and safety procedures for system installation.
• Reliability issues – high power, string and central inverters usually last about 10 years. That is just half the life of a typical solar module.
• Limited monitoring capability – they monitor the performance of the entire PV array and not each individual solar module. It is therefore difficult to determine the precise location of performance problems.
• Complex PV array design and installation – the design and installation of the PV array and its wiring is made complex and expensive.