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Introduction of Solar Inverters

published: 2011-07-07 14:34

Solar inverter is a critical component in a solar energy system. It converts DC power output into AC current that can be fed into the grid and directly influences the efficiency and reliability of a solar energy system. In most occasions, 220VAC and 110VAC are needed for power supply. Because direct output from solar energy is usually 12VDC, 24VDC, or 48VDC, it is necessary to use DC-AC inverter in order to be able to supply power to 220VAC electronic devices. Inverters are generally rated by the amount of AC power they can supply continuously. In general, manufacturers provide 5 second and 1/2 hour surge figures which give an indication of how much power is supplied by the inverter.

1. Solar inverters require a high efficiency rating. Since use of solar cells remains relatively costly, it is paramount to adopt high efficiency inverter to optimize the performance of solar energy system.
2. High reliability helps keep maintenance cost low. Since most solar power stations are built in rural areas without any monitoring manpower, it requires that inverters have competent circuit structure, strict selection of components and protective functions such as internal short circuit protection, overheating protection and overcharge protection.

3. Wider tolerance to DC input current plays an important role since the terminal voltage varies depending on the load and sunlight. Though energy storage batteries are significant in providing consistent power supply, variation in voltage increases as the battery’s remaining capacity and internal resistance condition changes especially when the battery is ageing, widening its terminal voltage variation range.

4. In mid-to-large capacity solar energy systems, inverters’ power output should be in the form of sine waves which attain less distortion in energy transmission. Many solar energy power stations are equipped with gadgets that require higher quality of electricity grid which, when connected to the solar systems, requires sine waves to avoid electric harmonic pollution from the public power supply network.

How Inverters Work
There are three major functions an inverter provides to ensure the operation of a solar system

The inversion process converts DC power generated by the PV array to AC power. Except for the use in small off-grid systems, directly using DC power from PV array is not practical. Although many home appliances use DC power, large loads and the electrical network use AC power to allow long distance power distribution and minimizes energy loss.

Maximum Power Point Tracking:
Maximum power point tracking is a technique solar inverters use to allow modules to produce all the power they are capable of. Sunlight intensity varies significantly depending on the time and location, and therefore variation in cell temperature and solar irradiation, temperature and total resistance all affect the design of inverter as well as system.

Grid Disconnection:
As required by the safety standard UL 1741 and system intersection standard IEEE 1547, all inverters used in systems tied to grid must disconnect from the grid if the AC line voltage or frequency reaches above or below stated limits in the standards. The inverter must also activate and execute a shutdown protocol on the system when the grid is no longer present. These protections eliminate a hazard caused by continuous injection of voltage into the disconnected wire or switch gear.

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