Solar inverter
It is the purpose of the MPPT system to sample the output of the cells and determine a resistance (load) to obtain maximum power for any given environmental conditions.
In conventional microinverter designs that work with one-phase power, the energy from the panel must be stored during the period where the voltage is passing through zero, which it does twice per cycle (at 50 or 60 Hz).
The reduction in energy storage significantly lowers the price and complexity of the converter hardware, as well as potentially increasing its expected lifetime.
If one uses these inexpensive types of inverters, all of the power generated during the time that the DC side is turned off is simply lost, and this represents a significant amount of each cycle.
The problem with this approach is that the amount of energy storage needed when connected to a typical modern solar panel can only economically be provided through the use of electrolytic capacitors.
This has led to a great debate in the industry over whether or not microinverters are a good idea, because when these capacitors start to fail at the end of their expected life, replacing them will require the panels to be removed, often on the roof.
A microinverter designed specifically for three-phase supply can eliminate much of the required storage by simply selecting which wire is closest to its own operating voltage at any given instant.
In this case, the system only has to store the amount of energy from the peak to the minimum of the cycle as a whole, which is much smaller both in voltage difference and time.
At any given instant two of the three wires will have a positive (or negative) voltage and using the one closer to the DC side will take advantage of slight efficiency improvements in the conversion hardware.
[13] Simplicity in system design, lower amperage wires, simplified stock management, and added safety are other factors introduced with the microinverter solution.
[17] However, this effect is not entirely accurate and ignores the complex interaction between modern string inverter maximum power point tracking and even module bypass diodes.
Shade studies by major microinverter and DC optimizer companies show small yearly gains in light, medium and heavy shaded conditions – 2%, 5% and 8% respectively – over an older string inverter[18] 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.
[19][20] However, as stated above, these yearly yield losses are relatively small and newer technologies allow some string inverters to significantly reduce the effects of partial shading.
This same issue makes it difficult to change array size over time, adding power when funds are available (modularity).
And because cooling fans have moving parts, dirt, dust, and moisture can negatively affect their performance over time.
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 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.
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.
[24] With steadily decreasing prices, the introduction of dual microinverters and the advent of wider[25] model selections to match PV module output more closely, cost is less of an obstacle.
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.
This means that adding one or more panels will just provide more energy, as long as the fused electricity group in a house or building is not exceeding its limits.
[28][29] A three-phase micro using zero-voltage switching can also offer higher circuit density and lower cost components, while improving conversion efficiency to over 98%, better than the typical one-phase peak around 96%.
[33] In 1993 Mastervolt introduced their first grid-tie inverter, the Sunmaster 130S, based on a collaborative effort between Shell Solar, Ecofys and ECN.
In 2000, the 130 was replaced by the Soladin 120, a microinverter in the form of an AC adapter that allows panels to be connected simply by plugging them into any wall socket.
[34] In 1995, OKE-Services designed a new high-frequency version with improved efficiency, which was introduced commercially as the OK4-100 in 1995 by NKF Kabel, and re-branded for US sales as the Trace Microsine.
In 2006 he formed Enphase Energy with another Cerent engineer, Raghu Belur, and they spent the next year applying their telecommunications design expertise to the inverter problem.
[43] In early 2011, they announced that re-branded versions of the new design will be sold by Siemens directly to electrical contractors for widespread distribution.
OKE-Services updated OK4-All product was bought by SMA in 2009 and released as the SunnyBoy 240 after an extended gestation period,[49] while Power-One has introduced the AURORA 250 and 300.
In 2019, the few remaining include Enphase which purchased SolarBridge in 2021, Omnik Solar[54] and Chilicon Power (acquired by Generac in July 2021).
