Solar PV - Solar PV Inverters - Solar PV Panels
A Solar PV inverter is an electrical device that changes the direct current (DC) electricity , that is produced by Solar PV panels, into alternating current (AC)
Solar PV Inverters - String Inverters
The alternating current produced by the Solar PV panels can be used to reduce the building’s power consumption from the National Grid. At times when the Solar PV panels are producing more electricity than the building requires, the excess can be fed into the National Grid system, earning an income from the UK Government's Feed in Tariffs scheme.
The Solar PV inverter is an important part of the Solar PV system. In a multiple Solar PV panels system, one string inverter will be used to control all the Solar PV panels on the system. It will ensure that the output voltage from the Solar PV panels is slightly higher than the voltage coming in from the National Grid system. This means that the building’s systems and appliances will use the cheaper electricity from the Solar PV system, in preference to electricity from the National Grid system. Additionally, all surplus power from the Solar PV system will be automatically exported back to the Grid.
Solar PV Inverters - Solar PV Micro-Inverters
A solar micro-inverter also converts direct current (DC) from a single Solar PV panel to alternating current (AC). Micro-inverters contrast with the conventional “string inverter” devices which support a large number of solar panels connected to a single inverter.
The key feature of a true micro-inverter is not its small size or power rating but its one-to-one control over a single panel and the fact that it is mounted on or near the panel. Small string inverters like larger ones control multiple panels and are generally mounted remotely, often inside the building.
Solar PV Inverters - Advantages of Micro-Inverters
Micro-inverters have several advantages over conventional string inverters. The principal advantage is that shading of any one solar panel, or a panel failure, does not disproportionately reduce the output of an entire array of panels. Each micro-inverter can act as a maximum power point tracker for the Solar PV panel it is connected to. Their primary disadvantages are that they are generally more expensive per peak watt than the equivalent power in a string inverter and are normally located on the panel, where they are harder to maintain.
Solar PV Inverters - Maximum Power Point Tracking (MPPT)
Maximum power point tracking is a technique that Solar PV inverters use to get the most power possible from each Solar PV panel. Each Solar PV panel or string of panels will have a maximum power point which defines the amount of current that the inverter should draw from the Solar PV panel in order to obtain the most electrical power possible.
Solar PV Inverters may be classified into three broader types:
Solar PV Inverters - Stand-Alone Inverters
Stand–alone inverters are used in isolated systems where the inverter draws its DC energy from batteries that have been charged by the Solar PV panels. Stand-alone inverters are designed to be used without a connection to the National Grid system. They can be run from Solar PV panels and batteries using a charge controller. The charge controller regulates the input from the Solar PV system and batteries, regulates the battery output and controls the charging of the batteries.
Solar PV Inverters - Grid-Tie Inverters
Grid-Tie inverters contain special circuitry to precisely match the voltage and frequency of the National Grid system. They are designed to be connected to the National Grid, and are designed to detect the presence of the National Grid and shut down automatically on occasions when supply is lost. Grid-tie inverters do not provide backup electricity during power cuts.
Solar PV Inverters - Battery Back-Up Inverters
Battery back-up inverters are special inverters that are designed to draw energy from a battery, manage a battery charge via an onboard charger, and export excess energy to the utility grid. These inverters are capable of supplying AC energy to selected loads during a power cut, and are required to have anti-islanding protection.
Solar PV Inverters - Anti-Islanding protection
Normally, grid-tied inverters will switch off if they do not detect the presence of the National Grid. If, however, there are load circuits in the electrical system that happen to resonate at the frequency of the utility grid, the inverter may be fooled into thinking that the grid is still active even after it had been shut down. This is called islanding. An inverter designed for grid-tie operation will have anti-islanding protection built in; it will inject small pulses that are slightly out of phase with the AC electrical system in order to cancel any stray resonances that may be present when the National Grid shuts down.
The Solar PV panels convert sunlight into direct current electricity which is then converted to alternating current by Solar PV inverters. The electricity can be used on-site or exported to the National Grid system
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