Power Optimiser
A small DC-to-DC converter fitted to each module that performs maximum power point tracking at module level and conditions the module's output before it joins the string. The string then feeds a simplified central inverter that handles only the DC-to-AC conversion.
Optimisers address the weakest-module problem of a series string: a shaded or soiled panel no longer limits its neighbours, and each module reports its own production for monitoring. They also provide module-level shutdown, which satisfies rapid shutdown rules. The trade-offs are more electronics on the roof, more connections to fail, added cost, and a system that is usually tied to one manufacturer's matching inverter. On an unshaded, single-orientation roof the energy gain over a good string inverter is often modest.