Microinverters have several advantages over conventional inverters. The main advantage is that small amounts of shading, debris or snow lines on any inverter circuit diagram pdf solar module, or even a complete module failure, do not disproportionately reduce the output of the entire array.
This also makes them harder to maintain and more costly to remove and replace. Some manufacturers have addressed these issues with panels with built-in microinverters. A type of technology similar to a microinverter is a power optimizer which also does panel-level maximum power point tracking, but does not convert to AC per module. Solar panels produce direct current at a voltage that depends on module design and lighting conditions. Modern modules using 6-inch cells typically contain 60 cells and produce a nominal 30 V. For conversion into AC, panels may be connected in series to produce an array that is effectively a single large panel with a nominal rating of 300 to 600 VDC.
The main problem with the “string inverter” approach is the string of panels acts as if it were a single larger panel with a max current rating equivalent to the poorest performer in the string. Additionally, the efficiency of a panel’s output is strongly affected by the load the inverter places on it. To maximize production, inverters use a technique called maximum power point tracking to ensure optimal energy harvest by adjusting the applied load. However, the same issues that cause output to vary from panel to panel, affect the proper load that the MPPT system should apply. Another issue, though minor, is that string inverters are available in a limited selection of power ratings. This means that a given array normally up-sizes the inverter to the next-largest model over the rating of the panel array.
For instance, a 10-panel array of 2300 W might have to use a 2500 or even 3000 W inverter, paying for conversion capability it cannot use. This same issue makes it difficult to change array size over time, adding power when funds are available. Other challenges associated with centralized inverters include the space required to locate the device, as well as heat dissipation requirements. Large central inverters are typically actively cooled. Cooling fans make noise, so location of the inverter relative to offices and occupied areas must be considered.
And because cooling fans have moving parts, dirt, dust, and moisture can negatively affect their performance over time. Microinverters are small inverters rated to handle the output of a single panel. Modern grid-tie panels are normally rated between 225 and 275W, but rarely produce this in practice, so microinverters are typically rated between 190 and 220 W. More importantly, a microinverter attached to a single panel allows it to isolate and tune the output of that panel. For example, in the same 10-panel array used as an example above, with microinverters any panel that is under-performing has no effect on panels around it. Microinverters produce grid-matching power directly at the back of the panel. Arrays of panels are connected in parallel to each other, and then to the grid.
For conversion into AC — hi Sat the ampere hour capacity is given on the battery by the manuacturer. The main disadvantage of the microinverter concept has — tips Description Here is a 100 Watt inverter circuit using a minimum number of components. In the aftermath of the 2001 Telecoms crash, a Review of the Single Phase Photovoltaic Module Integrated Converter Topologies with Three Different DC Link Configurations”. Some suggest that overall array reliability of a microinverter – monitoring and maintenance is also easier as many microinverter producers provide apps or websites to monitor the power output of their units.
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. 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. 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. With microinverters, each one has to have its own set of inputs and outputs, in its own box. Because that box is on the roof, it has to be sealed and weatherproofed. This can represent a significant portion of the overall price-per-watt. To further reduce costs, some models control two or three panels from a single box, 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. Some have suggested that this approach will make microinverters comparable in cost with those using string inverters. Microinverters have become common where array sizes are small and maximizing performance from every panel is a concern. In these cases, 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. An often overlooked disadvantage of micro inverters is the future operation and maintenance costs associated with them.
While the technology has improved over the years the fact remains that the devices will eventually either fail or wear out. In a string configuration, when a panel on a string is shaded, the output of the entire string of panels is reduced to the output of the lowest producing panel. This is not the case with micro inverters. A further advantage is found in the panel output quality. This is mitigated with a string configuration but not so in a microinverter configuration. The result is maximum power harvesting from a microinverter array. Monitoring and maintenance is also easier as many microinverter producers provide apps or websites to monitor the power output of their units.