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Apr 7

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Power Inverters—Ask Questions Before You Buy

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If you know even a bit about power inverters, you realize that there are a lot of considerations that should go into purchasing one since not all inverters are created equally—and that is as it should be since some applications will do fine with lower-cost inverters while other applications should use only top-quality inverters.  You might be asking:   “Should I get a modified sine wave inverter or a pure sine wave inverter?”  “Should I buy an inverter with a built-in battery charger or no built-in battery charger?”   “Will I need a DC conduit box or not need one?”  The list of questions could go on and on; but here are a few more questions to hopefully help you narrow your choice when it comes time to buy:

1: Should I Buy A Lower-Priced Inverter?

If you’re planning to power a limited number of small AC appliances, a 1500-watt modified sine wave inverter should serve you well.   The cost of this type of power inverter is quite affordable and is designed for mobile applications.  Size-wise, a 1500-watt modified sine wave inverter is about the smallest-sized inverter that can still power the likes of a small refrigerator or microwave oven.  These inverters are typically 12-volt input inverters but are available in an array of different outputs.

As would be expected, lower-cost inverters do not have the kind of robust overload and control features the more expensive models have.  One would need to be very aware of possible system overloads which could result in battery or inverter damage with lower-wattage models.  Each inverter has its pro’s and con’s; and what you end up with will boil down to the type of equipment you want to power.   An electrically-sensitive laser-printer would require a more expensive pure sine wave inverter as opposed to a less expensive modified sine wave inverter.

2: Do I Need A Battery Bank?

You might be considering using a power inverter to reduce your utility bill and are not concerned or interested in powering your lights and appliances once it gets dark or during a power outage.   If this fits your agenda, you might not need a battery bank.   This will allow you to use a lower-cost, ‘grid-tie’ inverter which would permit the use of a much higher voltage solar array.  This, in turn, can result in reduced solar array wire size and accompanying installation costs.

However, if installing a battery bank is part of the plan and if your loads will include delicate, power-sensitive devices such as computers or audio/video equipment, pure sine-wave inverters would be the safe option powered from a 24 or 48-volt DC battery bank.

3:  How Do I Determine The Size Of A Power Inverter For A Single Device?

This is a great, proactive question; and simply put, you’ll need to look at how much wattage your piece of equipment needs to normally function.  If you have an appliance that needs to be supplied with 500 watts, then a 750 watt inverter should be used.  You’ll definitely want to purchase an inverter that is rated a bit higher than the wattage for your appliance or device.  This will take into consideration voltage spikes that can and do occur when an appliance is turned on.

4: Can I Use A Power Inverter To Sell Power To The Utility Company?

Yes, one can sell power back to one’s utility company; and one can use a small-scale grid-tie inverter (under 25kW) to do it.   This would have to be done, legally, however, and one’s utility company can provide all the details one would need to know, such as the installation of a special electric meter that would tally the electric flow in both directions.  State regulations can vary and some states are definitely more strict than others.

In a nutshell, when it comes to selling power back to the utility company, a grid-tie inverter power system connects solar panels to the electrical grid.   The solar panels generate electricity and any unused electricity can be sold to the power company.   The basic components of a grid-tie solar system include the solar panels, the inverter and the meter which has the ability to spin backwards.    During those times when it is overcast, electricity from the grid is available in the usual manner.  The solar panels will not be useable during cloudy days since there is no battery backup with the grid-tie system.

Again though, the cool thing is, excess electricity will cause the meter to spin in reverse, reflecting a credit to the home owner.    Pretty cool!

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