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Issue #216 July 2008
Intelligent Energy Solutions
Living And Working Off The Grid
Part 1: Planning And Design
by George Martin
Start | Power Usage | Estimating Solar Radiation | Equipment | Solar Panels | Inverters | Charge Controller | Battery | Miscellaneous Items | System Cost | Sources & PDF
INVERTERS
I must confess that I find inverters boring. They are not as exciting as solar panels, charge controllers, or even batteries. I thought I would not find much difference in available inverters and that probably was due to my lack of enthusiasm. I selected inverters from OutBack Power Systems. I wanted the inverter/charge controller combination to be from one manufacturer. As I looked at the literature, OutBack seemed to have covered all of the issues for my installation. I ended up with two OutBack VFX3648 inverters (see Photo 2). They are 3.6 kW (continuous) with connections for a 48-V battery and vented. You will find vented and sealed inverters. I selected vented because they typically have a larger power rating and I’m not in a harsh environment. Also, the inverters are located in an area that is protected from the elements. Another option is a fan on the inverter. The fan also gives you more capacity, but what will you do when the fan fails, and you know it will? Our system is a normal 220-V home application. So, there are two inverters, one for each phase. OutBack has a neat option that includes a transformer to supply the second phase so the second inverter can remain in a low-power operating mode. When the power requirements become large enough, the main inverter will signal the second (slave) inverter to start up and handle the increased load. This is a good setup for our application. We can install a normal commercial heating/cooling system and power up only the second inverter when the load is calling for it.
Let me also add here that OutBack has great installation diagrams on its web site. Figure 3 is the diagram that I used to configure our system.
a) b)  c)  |
| Photo 2a—This is where it all began: the placement of the Outback System next to the feed into the normal house distribution panel. b—This was a truly do-it-myself project. Here I’m hoisting up inverters to mount. c—I was very pleased when the AC side was wired. From left to right: AC box, inverters, DC box. |
The other feature I was looking for in selecting an inverter was the ability to work seamlessly with a back-up generator. Again, OutBack looked good. The system controller has the ability to start the generator when the batteries get low, warming up the generator under no load, then charging the batteries, and finally letting the generator cool down under no load before shutting off. Also, the amount of current drawn from the generator is programmable. And finally a generator bypass switch is convenient so we can bypass the system and run the workshop from the generator in emergencies or during scheduled maintenance periods.
The more I looked into the inverter, the more I became impressed with all that was available in such a boring device. Inverters just don’t get no respect.
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