Solar inverter
A solar inverter or PV inverter, is a type of electrical converter which converts the variable direct current (DC) output of a photovoltaic (PV) solar panel into a utility frequency alternating current (AC) that can be fed into a commercial electrical grid or used by a local, off-grid electrical network. It is a critical balance of system (BOS)–component in a photovoltaic system, allowing the use of ordinary AC-powered equipment. Solar power inverters have special functions adapted for use with photovoltaic arrays, including maximum power point tracking and anti-islanding protection. Classification. Solar inverters may be classified  into four broad types: Maximum power point tracking. Solar inverters use "maximum power point tracking" (MPPT) to get the maximum possible power from the PV array. Solar cells have a complex relationship between solar irradiation, temperature and total resistance that produces a non-linear output efficiency known as the "I-V curve". 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. The fill factor, more commonly known by its abbreviation "FF", is a parameter which, in conjunction with the open  circuit voltage (V) and short circuit current (I) of the panel, determines the maximum power from a solar cell. Fill factor is defined as the ratio of the maximum power from the solar cell to the product of V and I. There are three main types of MPPT algorithms: perturb-and-observe, incremental conductance and constant voltage. The first two methods are often referred to as "hill climbing" methods; they rely on the curve of power plotted against voltage rising to the left of the maximum power point, and falling on the right. Solar micro-inverters. Solar micro-inverter is  an inverter designed to operate with a single PV module. The micro-inverter converts the direct current output from each panel into alternating current. Its design allows parallel connection of multiple, independent units in a modular way. Micro-inverter advantages include single panel power optimization, independent operation of each panel, plug-and play installation, improved installation and fire safety, minimized costs with system design and stock minimization. A 2011 study at Appalachian State University reports that individual integrated inverter setup yielded about 20% more power in unshaded conditions and 27% more power in shaded conditions compared to string connected setup  using one inverter. Both setups used identical solar panels. Grid tied solar inverters. The key role of the grid-interactive or synchronous inverters or simply the grid-tie inverter (GTI) is to synchronize the phase, voltage, and frequency of the power line with that of the grid. Solar grid-tie inverters are designed to quickly disconnect from the grid if the utility grid goes down. This is an NEC requirement that ensures that in the event of a blackout, the grid tie inverter will shut down to prevent the energy it produces from harming any line workers who are sent  to fix the power grid. Grid-tie inverters that are available on the market today use a number of different technologies. The inverters may use the newer high-frequency transformers, conventional low-frequency transformers, or no transformer. Instead of converting direct current directly to 120 or 240 volts AC, high-frequency transformers employ a computerized multi-step process that involves converting the power to high-frequency AC and then back to DC and then to the final AC output voltage. Historically, there have been concerns about having transformerless electrical systems feed into the public utility grid. The concerns stem from  the fact that there is a lack of galvanic isolation between the DC and AC circuits, which could allow the passage of dangerous DC faults to the AC side. Since 2005, the NFPA's NEC allows transformer-less (or non-galvanically) inverters. The VDE 0126-1-1 and IEC 6210 also have been amended to allow and define the safety mechanisms needed for such systems. Primarily, residual or ground current detection is used to detect possible fault conditions. Also isolation tests are performed to ensure DC to AC separation. Many solar inverters are designed to be connected to a utility  grid, and will not operate when they do not detect the presence of the grid. They contain special circuitry to precisely match the voltage, frequency and phase of the grid. Solar pumping inverters. Advanced solar pumping inverters convert DC voltage from the solar array into AC voltage to drive submersible pumps directly without the need for batteries or other energy storage devices. By utilizing MPPT (maximum power point tracking), solar pumping inverters regulate output frequency to control the speed of the pumps in order to save the pump motor from damage. Solar pumping inverters usually have multiple ports to allow  the input of DC current generated by PV arrays, one port to allow the output of AC voltage, and a further port for input from a water-level sensor. Market. As of 2019, conversion efficiency for state-of-the-art solar converters reached more than 98 percent. While string inverters are used in residential to medium-sized commercial PV systems, central inverters cover the large commercial and utility-scale market. Market-share for central and string inverters are about 36 percent and 61 percent, respectively, leaving less than 2 percent to micro-inverters.