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Solar System - Inverters.

From the last page we now have Direct Current (DC) power stored in our batteries but quite a few devices use Alternating Current (AC). To convert our stored DC to AC we need to use an Inverter. While inverters are fairly simple, modern ones have many more functions rather than just changing the current flow. Most of them also up the voltage to a industry standard for the country. When choosing an inverter there are a couple of things we must look at, size and quality.

Waveform


Size
    You will need an inverter that will support the loads you wish to draw through it (current and future loads). Add up what you will be using to work out how many watts at most you will want to use. And the easy bit, you need an inverter than will handle that load. Even if your inverter is not that expensive its a good idea to buy a fuse to protect it. Past that you need to choose one that produces the right voltage and frequency. Most AC devices either use 240V, 50 Hertz or 120V, 60 Hertz, and it's pretty standard across any country, so check one of your devices and the rest should be the same.
It's also worth a not to check if the power output is continuous or surge. When some items like motors are turn on they can require up to 7 times as much power as when they are running. The inverter you get should be rated to handle those those surge loads as well as the continuous loads. And it's always safer to get a larger one than you need just incase.

Quality
    The quality of the electricity is determined by what is called it's waveform. If you are running sensitive devices like TV's and computers then you will need a better quality of power. Lets go through some basics of waveforms.
 
Waveform


    You can see above roughly what AC looks like over time. One moment current is flowing in one direction (12 VDC) and the next minute in the opposite direction (-12 VDC), ie over time current changes directions - aka it alternates. The frequency or cycles over time give your hertz (50 Hertz means 50 cycles per second) and the amplitude the voltage. The waveform, the important thing in determining the quality, is the shape of this wave. The best quality wave is the sine wave (given by the formula Y=sin(x) ) and approximately like the picture above. And the poorest quality wave is a square wave, like below.

    A Square waveform is very cheap to produce and the sine wave is the most expensive. Square waveforms are pretty hard to find as they are such low quality but as you can imagine there are many shapes of waveforms between these, one of the most popular is called the quasi sine or modified wave.

Other choices
Inverters can be driven mechanically (by motors) or electronically. Mechanical inverts deliver a pure sine wave and handle changes in demand easily but the are not great with surges and are not that efficient. There are two types of electronic inverters, high frequency switching units (cheap and light, but have a short life and don't handle surges well) and transformer based (more expensive but last longer). If you have access to grid power there is also a third option of synchronous inverter, that gives and takes power from the grid depending on demand (very expensive).

And that is pretty much a complete solar system. Enjoy and mail me if you have any trouble!


 

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