To answer at this question, I use a part of the site http://www.bcp-energia.it/:
"" The inverter is an electronic device for converting direct current generated by solar cells into alternating one. It's connected to the electricity grid to power the main uses of your home. Since the control unit is powered by the photovoltaic modules, the inverter is switched off completely during the night, and so it doesn't consume energy.
These devices extend basic possibilities of generic inverters with other, more advanced, through the use of particular control system to extract maximum power from solar panels. This function is called MPPT, an acronym for Maximum Power Point Tracker.
The photovoltaic modules in fact, have a characteristic curve V / I; there's an optimum working point said maximum power point, where it's possible to extract all the available power. This point of the characteristic curve varies continuously as a function of solar radiation striking the cell surface. It's evident that with an inverter "freezed" at this point,we can always have the maximum power available in any condition. ""
For example :
"" There are several techniques for creating the MPPT function, with differences in dynamic performance and accuracy. Although the MPPT accuracy is extremely important, the settling time is, in some cases, even more. While all inverter manufacturers are able to obtain accurate on MPPT (typically between 99 to 99.6% of the maximum available), only few are able to combine speed with accuracy.
On days with variable cloudiness we have the greatest change of solar power. It's very common to detect variations of 100W / m² to 1000-1200W / m² in less than 2 seconds. Under these conditions, which are very frequent, an inverter with settling times less than 5 seconds can produce up to 15% -20% of energy more than a slower one. [..] ""
To finish the post, I report the news of a product read some days ago:
""[..] Siemens Industry Inc. further strengthens its portfolio of solar inverters with the introduction of its new Sinvert PVM UL inverter, designed for peak efficiency and maximum plant yields to convert solar energy into grid-compliant AC voltage for infeed into conventional power supply networks. The Sinvert PVM UL inverters are available in the range from 12kW to 24kW for small to medium sized plants in the commercial market, and are capable of delivering over 98% peak efficiency. [..] ""
http://www.onlinetes.com/renewable-solar-energy-Siemens-022912.aspx
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