Electricity

Chapter 9: Power Inverters & 120v Off-Grid

Producing 120v Off the Grid 

The “simplest” solution is to run a generator. I know your first thought is YUCK! And I would tend to agree. Generators are often noisy and smelly; but, they are not all created equal. A Honda Inverter Generator for example, supplies less total wattage then a lower priced generator, but is significantly quieter. As in, could nap near the Honda, while you wouldn’t able to stand comfortably anywhere near the lower priced type.

Honda 2200 Watt $1100
WEN 4750 Watt $450

Personally, we only use our inverter generator when absolutely necessary. For boondocking, it’s always a good idea to have a secondary way to recharge your battery bank.

The truly off-grid solution would be to take the power produced by your solar panels and stored in your battery bank; and, using a power inverter, convert your DC battery power to 120v AC power. When not connected to “the grid”, 120v AC loads require an “inverter” to convert DC voltage (usually in the form of 12v deep-cycle batteries) to 120v AC.

For example, Let’s say you want to power a small 120v Television in your car for the kids on a long trip. You could use a ”small” 300 Watt 12v Power Inverter.

300W Power Inverter w/ Cig Lighter Plug

If you wanted to power more than a single TV or a few very low power appliances in your RV, Skoolie, or home, from your solar array and/or battery bank,  you wold need a larger inverter to supply 120v to the various appliances all at once. Typically, something in the 1000-2000w range is recommended for medium off-grid use, like the Renogy 2000w Pure Sine Wave Inverter. This sized inverter needs to be wired directly to the battery bank or battery bus bars.

Renogy 2000w Pure Sine Wave Inverter

Modified vs. Pure Sine Wave Inverters

So we don’t have to get too technical, I’ve found this great visual explanation of the primary difference between modified and pure sine wave inverters. As you can see, the blue line is smooth, while the orange line is blocky. Pure sine wave inverters produce AC electricity that looks like the blue line, while Modified sine wave inverters produce AC electricity that looks like the orange line.

It is important to be away of your needs with regard to modified vs. pure sine wave inverters. There are some devices that just don’t like modified sine waves and could either not function properly, or be be damaged. Electric motors for example, such as a fan, typically run hotter, and up to 30% less efficient. Pure sine waves are generally needed for items with microcontrollers such as modern TVs, and other appliances.

Unfortunately, just like with PWM vs MPPT Charge Controllers, and like the generators above, the pure sine wave inverters are significantly more expensive than modified sine wave inverters when considering cost as dollars per watt ($/w).

Amp Draw On Battery Bank

The reason we recommend typical off-grid users look for a suitable 1000-2000w inverter is because of the significant power draw on the battery bank at these wattages and greater. A good rule of thumb when considering the amp draw of AC inverted appliances is to multiply the amps required for 120v, by 10.

You read that right, Typically if an appliance needs 1 Amp AC, the inverter will draw 10 Amps DC from our 12v battery bank. Therefore, if you have a 100 Amp Hour battery bank, you could safely run the 1 amp appliance for 5 hours; assuming there is no other load on the battery bank.

Let’s say it’s noon and you have a solar setup putting more than 10 Amps into the battery bank, in this case, in theory, you could run the appliance without any draw on the battery bank, as long as you could keep the solar panels facing the sun! Not only would the solar panels power the appliance, but any additional energy gathered is used to charge the battery bank!

MSH 3000 Watt Hybrid Inverter

Conclusion

Our plan is to take solar energy stored in the battery bank, and using an inverter, supply 120v electricity to a fuse panel, supplying 120v electrical outlets throughout the bus. It is important to oversize your inverter needs; since our goal is to be as sustainable as possible we want to ensure we’ll be prepared for whatever we may need or want.

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