Technology

The conventional PV-solar architecture

Conventional solar module installations “string” solar panels in series before connecting to a central inverter that converts the direct current (DC) from the solar modules to alternating current (AC) for connection to the power grid.

Installation is complex and expensive, requiring specialist skills and safety procedures due to the high DC voltages and currents that are developed. These can reach up to 900V at 5A – lethal if touched. In systems using DC strings, energy harvesting is reduced every time a PV module, or even a few cells within a module, have their performance compromised due to shadows caused by clouds or other obstacles, or the build up of dust, leaves or other contaminants on its surface. Worse still, the poorest performing module then drags down the performance of the whole system and, because you can only monitor the complete system, not individual modules, it is very difficult and expensive to determine the precise location of any problems.

Installing individual DC-DC converters behind each module, then feeding a lower DC voltage to a central inverter, overcomes these problems. However, it’s not a magic solution because, as in the conventional system, you need a large central inverter which is expensive, large, heavy, generates fan noise, requires regular maintenance and is rarely guaranteed for more than 12 to 15 years – just half the life of the PV modules themselves.

Micro-inverter system architecture

The micro-inverter system architecture eliminates all of the above problems.

The micro-inverter architecture uses one DC to AC converter, or micro-inverter, per solar module. The inverter outputs a grid-level AC voltage, locked in phase to the grid.

This approach has a number of distinct advantages:

• It eliminates the single most common cause of failure in PV solar systems – the central inverter.
• It maximises the power harvested from every module by enabling per-module maximum power point tracking (MPPT). This delivers between 5% and 15% more power from the installation.
• Any degradation in the performance of a module, due to clouds, shadows or other obstructions, does not affect the performance of other modules and has minimal affect on the power harvested from the system as a whole.
• Installers don’t need to match adjacent panels for best output and modules can be installed on any available roof space – the modules don’t need to be on a single plane, as they do with a conventional DC string installation. This makes installation faster, easier and cheaper.
• The system is intrinsically safer requiring no specialist, high voltage DC installation equipment or practices.
• The system can be monitored on a per-module basis, making it very easy to identify the exact location of any problems that might occur over the life of the installation.