String inverter, microinverter or power optimiser: which is the best option?

When researching solar energy you will come across the terms string inverter, microinverter and optimiser. All of them are involved in turning the energy produced by the modules into usable electricity, but each works differently and affects the performance and cost of the system.

String inverter

The most traditional model: several modules are connected in series (a string) and one central inverter converts the energy of all of them at once. Advantages: lower cost, simple installation and the best fit for large plants. On the downside, it suffers more from shading — a drop in one panel affects the whole string — and offers less flexibility on roofs with different tilts and orientations.

Microinverter

The microinverter is installed behind each panel (or each pair) and works individually. It delivers good efficiency where there is partial shading, allows module-level monitoring and improves electrical safety, because there is no high-voltage DC running across the roof. The trade-offs are a higher upfront cost and more complex maintenance, since the electronics sit on the roof.

Power optimiser

The optimiser is a middle ground: a DC-DC device installed on each panel, still working with a central string inverter. It reduces losses from shade or soiling and offers module-level monitoring at an intermediate cost — but it still requires the main inverter, so it costs more than a string inverter alone.

How to choose

The choice depends on the budget, the roof conditions and the efficiency you want. As a rule: the string inverter suits large systems on unshaded sites; the microinverter best serves residential roofs with several pitches or shading; and the optimiser balances efficiency and cost in medium projects with partial shading. Sizing the inverter correctly matters as much as the choice of technology — see how to calculate the DC/AC ratio safely.

String vs micro vs optimiser