The Pure Sine Wave Inverter

A pure sine wave inverter, also known as true sine wave inverter, is one of the solar inverters types. A solar inverter is a necessary component for any solar power generating system. Inverters and solar panels complement each other and are designed to match each other in voltage, current and power ratings.

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Why are solar inverters needed?

What are the types of solar inverters?

What is a pure sine wave inverter?

What are the important specifications of solar inverters?

Why are solar inverters needed?

Solar panels generate DC electric power. Our home appliances and lighting bulbs need AC power for their normal operation. The utility grid carries AC power with precise characteristics into our homes (115V 60 Hz in the US). The solar inverter is an a smart electronic device that converts the DC power generated by the solar panels into standard AC power. Our appliances lighting bulbs and entertainment electronic devices “can’t tell the difference” between the utility supplied power and the inverter supplied power.
A piece of history; in the late years of the 19th century, there was a fierce battle between Edison who supported DC generators and Tesla who supported AC generators. In the Chicago 1893 exposition, Tesla proved the superiority of AC power generation and AC power distribution. In those days, electronic engineering was still in very early stage to provide the engineering solutions we have today

What are the types of solar inverters?

Different application areas call for different types of solar inverters. The three most important application area are:

  • Grid-tied inverters: 
solar inverters that are connected to the utility grid and to the home supply line. A grid tied inverter must have an automatic shut-down mechanism (anti-islanding protection) during power outages. Since 1999, the standard for anti-islanding protection in the United States has been UL 1741. Similar standards exist in other regions of the world

  • Stand-alone (off-grid) inverters:
off-grid solar inverters are not connected directly to the solar panels. They are connected to a bank of deep cycle batteries. The batteries are charged through a charge controller by the solar panels. The batteries can be charged also by a small wind turbine or by a micro-hydro (water stream) dam-less turbine. The higher power versions of these inverters are used for off-grid homes (homes not connected to the grid). Medium size and small size inverters are used to complement the RV solar panel, and for small boat solar systems.

  • Battery backup inverters: a less ubiquitous application in which the inverter is designed to pull charge from deep cycle batteries (controlled by a charge monitor) and supply the surplus electrical energy to critical loads. These inverters are the replacement of traditional diesel emergency back-up generators that provide power to selected loads (such as elevators and emergency lighting) during utility power shutdown. These inverters are required to have anti-islanding protection per UL 1741
  • What is a pure sine wave inverter?

    The utility supplies a well regulated AC power, 115V 60 Hz in the US. The voltage follows an almost perfect sinusoidal waveform. Electrical appliances, especially those that have electrical motors (refrigerators, washing machines, dish washers, etc.) require for their optimal performance that the supplied voltage will be a pure sine wave. The pure sine wave inverter is an electronic masterpiece that supply an almost perfect sine waveform electrical power at the right voltage (115V in the US) and right frequency (60 Hz in the US).
    There are other inverters on the market that are not pure sine inverters; a cheaper inverter provide a square waveform power, it is more efficient, however only a limited types of home electrical loads can be supplied from these inverters. There is also a type called modified sine wave inverter, the Total Harmonic Distortion (THD) exceeds the 5% limit most appliances could stand, therefore I don't recommend to use the modified sine wave inverter to feed power to home appliances.

    The important specifications of solar pure sine wave inverters

    What are the main specifications for a pure sine wave inverter you want to look into?

  • DC voltage rating and the tolerance; you want a nominal 12V (9-17VDC) inverter for 12V operation

  • Rated maximum input current

  • Output AC Power: 120VAC, 60Hz (plus or minus 0.4%) for the US; for most other countries, 230V 50Hz

  • Power capability in Watts (AC side) to fit your home consumption

  • Power Surge capability in Watts – to accommodate for source (batteries or solar panels) voltage changes and load current changes (when heavy load such as a washing machines starts, a transition to a higher current consumption causes a transient that the inverter must cope with)

  • Efficiency - What percentage of DC power is actually converted to useful AC power? Look for numbers around 92% or even exceeding 92%

  • Over-current protection, over-temperature protection and other protections

  • Heat removal method (usually a fan)

  • AC and DC circuit breakers, remote control (dry contacts) is a desired feature

  • A smart controller and remote monitoring

  • Compliance to UL 1741

  • For pure sine wave inverter the purity is measured by the harmonics; look for low harmonics content measured by THD (Total Harmonics Distortion), less than 5%. (rings a bell? HiFi systems also have a distortion limit. With musical ear you can actually hear the higher harmonics of the 60Hz sound)

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