Power Inverter Features

Power inverters take DC voltages and convert them to AC voltages.  This is their basic function.  Batteries and solar panels output DC voltage.  So an inverter placed between the battery array and the main load center will convert to the standard AC voltage used in your house.

There are many options available with power inverters.  I will explain some of them here.

Wave Type

Sine Wave (Pure Sine Wave)

Pure Sine Wave inverters are the best you can buy.  They produce power that is closest to the power provided by the power company.  This is important because as you get further and further away from pure sine wave power, the efficiency of your load appliances gets lower and lower.  

Loads run at their maximum efficiency with pure sine wave power.  Unless you have money to burn on larger battery arrays and more solar panels, only use a pure sine wave inverter.

Additionally, pure sine wave inverters have the highest possible compatibility with loads of all kinds.

Modified Sine Wave

These are the second best inverters you can get.  but realize the modified sine wave introduces inefficiency at every load.  electric motors consume around 20% more power on a modified sine wave inverter.  Any money you save on the inverter by choosing a modified sine wave inverter will be consumed multiple times by the large battery array and solar array you will need.  Modified sine wave inverters are not a good choice for solar energy systems.

Modified sine wave inverters are mostly compatible with a wide range of loads, however some types of loads may not work with them.  Virtually all load types will take a hit in efficiency using these types of inverters.

Square Wave

Square Wave inverters are virtually extinct.  They suffered from compatibility issues and would decrease efficiencies as much as 90%.  It would be very rare to see this in production these days.

Surge Rating

The surge rating is basically how much overload current the inverter will take. Surge current is important because inductive loads create a demand surge when they start.  If you are running an inverter near its surge limit, starting an inductive load can cause a host of power issues; including brown outs, complete power loss etc.  There are two basic types of inverters:

Transformer-based or Low-Frequency

These are big and heavy, but enjoy surge ratings in excess of 250% of nominal load values.  Some have surge values that are 10 times the nominal load values.

Non-Transformer-based or High-Frequency

These are lighter, and cheaper, but have lower surge ratings, typically on the order of 20-25%

It is important to make sure you do not exceed the surge rating of your inverter.  If you used a non-transformer-based inverter, you can mitigate this by putting in a larger inverter to help cover some of the loss of surge capabilities.

Input Voltage

Inverters can be found with several different input voltage ranges.  This is important for a few reasons.

Smaller Cable

Since a power inverter converts one form of power to another, the input power is equal to the output power (if the inverter is 100% efficient)  if the input voltage is 12 V, the input current will be some amount. If the input voltage is 24 V, the input current will be cut in half.  This is important because these parts of the system can have currents of hundreds of amps.  

Using a 12 V battery in this system (240 V at 100 A) would require cable capable of handling 2000 amps between the battery array and the inverter.  That cable is prohibitively large.  Simply by switching to 48 V input to the inverter, we can reduce the cable to 500 amps.

Less Work for the Inverter

The inverter will have to do less work raising the voltage from 48 V than it has to do lifting it from 12 V.  This translated to better efficiency.

Less Demand on the Batteries

The higher amperage is being drawn from the battery array.  Drawing more current will cause the batteries to heat up faster. 

Current Detection

Inverters consume a certain amount of energy when they are idle.  One that I reviewed consumes 250 W while idling.  To put this in perspective, the inverter would need about 3 solar panels just to keep the inverter idling.  This is assuming you are getting 6 hours of Sun per day.  

To cut this energy loss, some inverters monitor when something is demanding power.  When an appliance is turned on, the Inverter comes to life and starts providing power. 

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