Let me preface this by saying that any off grid system can produce power that is just as "clean" if not "cleaner" than what you get from the power company--IF you choose the right inverter. That's why I'm letting you know about the 'unclean power' option so you don't make the mistake we made.
Background for Newbies
First, a little background for those who are new to off grid systems. If you've never heard of an inverter before, it's a component in a renewable energy system that converts DC power (what is stored in batteries) into AC power (what you use in your home). If you want to learn more about it, I covered this question in my blog post: Renewable Energy Systems Overview. Most quality inverters also have a charger built in. The charger is used when your battery bank may need to be manually charged with a fuel powered generator. There are two main types of inverters--sine wave and modified sine wave.
A quality sine wave inverter will produce power that is just as "clean" if not cleaner than what you get from the power company right now. Hands down, that is the first choice for any off grid system. Then there are modified sine wave inverters, which may produce a varying "quality" of power (i.e. better models may produce decent power, while the cheapest models put out awful electricity). For years, the only reason why someone would consider a modified sine wave inverter was because of price, which was roughly half the cost of a comparable sine wave inverter. This is what I call 'unclean' power.
Why This Could Impact You
But things have changed over the last few years. Now, the cost of sine wave inverters has dropped and the price of a quality modified sine wave inverter has risen to where there is not a large difference between the two. If that is the case, why would anyone even consider buying a modified sine wave inverter? Why am I even writing this article?
If your budget allows buying a brand new sine wave inverter, then there is no point in reading any further. This article is for those who are trying to reduce their budget by cutting corners with their inverter choice.
Because so many people have switched from a modified sine wave to a sine wave inverter, it is quite possible that you may come upon a really "good deal" on Craigslist or eBay for a modified sine wave inverter. It can be very tempting when your budget is tight, but I just want you to be fully aware of what you'll be dealing with.
You may decide that a modified sine wave inverter is perfect for you, and if so, that's great! But I want you to make an informed decision. And I can speak from lots of first hand experience on this issue, having lived for extended periods of time with both a quality sine wave inverter and a well regarded modified sine wave inverter. During the years I have used a modified sine wave inverter, it was only out of necessity, but hopefully it will provide some insights to you.
What Impact Would This Have On Your Lifestyle?
First, you need to decide if you will be operating sensitive electronics that could possible be affected by poor quality electricity. Here is a partial list of items that MAY possibly be negatively affected by a modified sine wave inverter:
- Newer front loading washing machine
- Cordless drill chargers (especially Makita)
- Sewing machine variable speed control
- Blender with variable speed control
- Really, almost anything with variable speed control
- Digital clocks
- Light dimmers
- Laser printers
- Satellite receivers
- Plasma TV
- Among other things
This is not to say that every one of these items will be destroyed or will not function with a modified sine wave inverter. There are many variables. But it means that there is the potential of encountering issues with any of these appliances when using a modified sine wave inverter.
Here's My Experience With Modified Sine Wave...
Theoretically, motor driven appliances and devices with a little black transformer cube should operate just fine. I do have suspicions about the impact that a modified sine wave inverter will have on the lifespan of these appliances and have personally seen some destroyed. There are varying thoughts on this, but one concern is the extra heat that is created as a result of the "dirty" electricity, and some say that could have a negative impact on the lifespan of your appliances.
After having a very nice and relatively new electric toothbrush die, LED lights fade to the point of obscurity, and a handheld massage device die (even producing smoke!), we became more careful with what appliances we would expose to modified sine wave electricity. I suggest you do the same if you find yourself using an inverter of this variety.
But having said that, out of necessity we have used everything from computers to hard drives to simple blenders (not adjustable speed) to hair blow dryers with no noticeable issues. It makes me nervous, but we have done it.
[WARNING: This section gets a little technical, so if I lose you here, just skip to "The Lesser Of Two Evils" below]
Let me give you my experience with a very popular modified sine wave inverter of yester-year. The Trace DR series, which was bought out and became the Xantrex DR series until they changed the name to Xantrex TR series. Then Schneider bought it out and renamed it the Schneider TR series until it was recently discontinued. You are likely to run into one of these inverters on the used market. In a nut shell, don't touch it unless it is free, and even then I would discourage using it for anything but a seldom used power system. I have extensive experience with this inverter, and here is why I say this.
The charger function leaves much to be desired. With the 24 volt model, it will charge at full power until the voltage reaches an arbitrary, non-adjustable 29.0 volts. Then it will hold it there until the charger backs off to 5% of the battery capacity. So if you tell the inverter that your battery bank is 1,000 amp hours, it will hold the voltage at 29.0 until the charger backs off to 5% of 1,000 which is 50 amps. Then the charger thinks your battery is full and ends the charge. In reality, your battery is far from full at this point. Don't believe me? Test the specific gravity and see--I've done it!
In an effort to "trick" the charger into fully charging my battery, I tried programming my battery size as smaller than it was in an effort to force it to charge for a longer period of time. For example, my battery bank is 1,000 amp hours, and the charger turns off after backing off to 5% or 50 amps. So I program in a battery size of 500 amp hours instead. 5% of 500 is 25 amps, which means the charger will have to run longer until it finally trips off at 25 amps. Unfortunately, that didn't do the job either. I would have to restart the charger multiple times before getting close to being charged.
The problem is two-fold. First, the charger will not allow you to adjust it's absorb voltage set point--it is an arbitrary number that will not work for very many batteries. Second, there is no way to adjust the period of time the voltage is held at the absorb set point. Bottom line? Have fun trying to fully charge your batteries with this charger!
Most inverters have a search mode that is akin to "sleep" mode with some appliances. Basically, if it detects that you are not using any power, it goes to sleep in order to save power. But while asleep, it is constantly searching for any hint that you are trying to use power so it can spring to life again. There is an adjustment for the search mode that controls how sensitive the sensor is. That can allow the inverter to go to sleep even if a small amount of power is being used. Personally, I like keeping an inverter at the most sensitive setting, so that even the smallest appliance will "wake it up". Unfortunately it doesn't work that way with this inverter.
Even in the most sensitive position, our CFL or LED lights would not turn it on. The computer would not. Even the blender would not! Only certain motor driven appliances seem to reliably pull it out of search mode. Needless to say, it's a big hassle!
Sorry if it seems like I'm belly-aching. I just want to save you from an unpleasant experience.
The Lesser of Two Evils - Or Neither
If I had to choose a modified sine wave inverter, the only one I would even consider is the Magnum RD series. It has a great charger and is the best you can get in the modified sine wave world.
But I fail to understand why anyone would go that route. Since there is a pretty decent sine wave inverter of similar size, AND it doesn't cost much more (the Schneider Context SW)! So if you could stand a slightly higher budget, both the Magnum MS series and the Outback VFX series are top notch options that I highly recommend. If you are interested in those two, I did a comparison of them here: Inverter Comparison: Magnum MS series vs Outback VFX series.
Just my two pennies worth.