a long string's output enough to be noticed. Disadvantages The main disadvantage of the microinverter concept has, until recently, been cost. Because each microinverter has to duplicate much of the complexity of a string inverter but spread that out over a smaller power rating, costs on a per-watt basis are greater. This offsets any advantage in terms of simplification of individual components. As of February 2018, a central inverter costs approximately $0.13 per watt, whereas a microinverter costs approximately $0.34 per watt. Like string inverters, economic considerations force manufacturers to limit the number of models they produce. Most produce a single model that may be over or undersize when matched with a specific panel. In many cases the packaging can have a significant effect on price. With a central inverter you may have only one set of panel connections for dozens of panels, a single AC output, and one box. Microinverter installations larger than about 15 panels may require a roof mounted "combiner" breaker box as well. This can add to the overall price-per-watt. To further reduce costs, some models control two or three panels from an inverter, reducing the packaging and associated costs. Some systems place two entire micros in a single box, while others duplicate only the MPPT section of the system and use a single DC-to-AC stage for further cost reductions. Some have suggested that this approach will make microinverters comparable in cost with those using string inverters. With steadily decreasing prices, the introduction of dual microinverters and the advent of wider model selections to match PV module output more closely, cost is less of an obstacle. Microinverters have become common where array sizes are small and maximizing performance from every panel is a concern. In these cases, the differential in price-per-watt is minimized due to the small number of panels, and has little effect on overall system cost. The improvement in energy harvest given a fixed size array can offset this difference in cost. For this reason, microinverters have been most successful in the residential market, where limited space for panels constrains array size, and shading from nearby trees or other objects is often an issue. Microinverter manufacturers list many installations, some as small as a single panel and the majority under 50. An often overlooked disadvantage of micro inverters is the future operation and maintenance costs associated with them. While the technology has improved over