The typical size of this microinverter is: 22x16.4x5.2 cm / 8.66x6.46x2.05". As said, microinverters produce grid-matching power directly at the back of the panel (i.e. 220 V). Arrays of panels are connected in parallel to each other, and then to the grid. This has the major advantage that a single failing panel or inverter cannot take the entire string offline. Combined with the lower power and heat loads, and improved MTBF, some suggest that overall array reliability of a microinverter-based system is significantly greater than a string inverter-based one. This assertion is supported by longer warranties, typically 15 to 25 years, compared with 5 or 10-year warranties that are more typical for string inverters. Additionally, when faults occur, they are identifiable to a single point, as opposed to an entire string. This not only makes fault isolation easier, but unmasks minor problems that might not otherwise become visible – a single under-performing panel may not affect a long string's output enough to be noticed. 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 simply 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.