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Solar Power Inverters: Do I Need One? [DIY Mini Course 5/6]

DIY Solar Mini Course [Lesson 5]: Solar Power Inverters - Do I Need One? 

In DIY solar energy, power inverters are an almost always necessary, and often intimidating component of any system.  Power inverters, which are often also referred to as solar inverters (or simply, inverters) make it possible to run household devices with the energy harnessed by your solar panels.  So yes, you are probably going to need one.  In this lesson, we are going to cover the basics of power inverters as well as how to choose and hook up the right one for your DIY solar energy system.  

What are Power Inverters? 

A power inverter is a device that can change (or, invert) electricity current from Direct Current (DC) to Alternating Current (AC).  Power inverters can range in size from small devices that can be plugged into a car’s cigarette lighter all the way to larger full-home electricity inverters.  

Here, it is important to understand that AC current is the type of electricity that household outlets, and most electronic devices, use.  DC current, on the other hand, is the type of electricity that is most commonly stored in batteries and used in low voltage instances, such as automotive applications.  

What do Power Inverters Do (In a Solar Panel System)?

Today, all of the electricity that is generated by solar panels and stored in solar batteries is in the form of DC electricity.  Once the energy passes through the inverter, it turns into the usable, alternating current (AC).  In small, DIY systems, the inverter generally has one or more AC power outlets to plug-in and power electric devices.  

Why Do I Need a Power Inverter? 

On one hand, it is true that you can create a pure DC powered solar energy system to run a simple off-grid system for devices like well pumps.  Whereas systems such as these may not require an inverter, they are limited to only powering the devices that they have been specifically designed to run.  

The truth is, that the majority of DIY solar systems are built with power inverters.  This is because in a solar energy system, power inverters make it possible to run AC-powered devices such as televisions, electronics, tools, medical devices, and anything else that plugs into a traditional wall outlet.  

Types of Solar Power Inverters For Solar

As we’ve mentioned above, power inverters come in a wide range of sizes and capabilities.  Here, we are going to explore the different types of inverters as they apply to DIY solar power systems. 

Off Grid vs Grid Tied Power Inverters For Solar

Perhaps the most important distinction in choosing the right solar inverter comes down to the type of solar energy system that you are running.  In an off grid solar system, an inverter will typically have an output panel in which devices can be plugged directly into.  Off grid inverters make it possible to use AC electricity in a cabin, van, RV, or other remote location.  Many DIY systems include a standalone off grid inverter, or else utilize the built-inverter on a portable solar generator.  

If you have a grid tie (also known as grid-tied) solar panel system, then there are two different kinds of inverter you can install.  A “grid tie inverter” (GTI) is specifically designed to modify your solar energy to fit the frequency of grid power, as excess electricity production is sent back into the grid.  If you have a grid tie system with a battery backup (also known as a hybrid system), then you will need an even more specific piece of equipment.  Hybrid systems are more expensive, but have the greatest ROI in combating utility bills with self-produced solar energy. 

Pure Sine vs Modified Sine Wave Inverters For Solar

Getting technical, there are two main types of inverter technology:  Pure Sine and Modified Sine Wave.  By far, the most popular kind of inverters are Pure Sine Wave.  Pure Sine Wave inverters use sophisticated technology to deliver the smoothest possible electric current like that of a grid-tied home.  For the best overall performance, a Pure Sine Wave inverter is heavily advised. 

Modified Sine Wave inverters are generally seen as the cheaper alternative to Pure Sine Wave.  Although it is true that Modified Sine Wave inverters can be used to power simple electronics, most DIYers choose to use a Pure Sine Wave inverter because they are more efficient and generally less noisy.  Modified Sine Wave inverters use a more basic form of technology which make it difficult to power devices with variant current draws such as smartphones, fridges, air conditioners, power tools, and other appliances.  

How to Choose the Right Size Power Inverter for Solar 

So how large of an inverter do you need for your solar energy system?  The answer comes down to watts & volts.  Although the technical aspects may cause first timers’ eyes to glaze over, selecting the right sized inverter will prevent damage, increase efficiency, and allow for the best overall user experience.  

Inverter Wattage

Watts are a measure of how much electricity is being used.  Smaller devices, such as cell phones may only require 6 watts to fully charge, whereas a microwave may need upwards of 1000 watts of continuous power to run.  For a good idea of how much power most household appliances use, you can check out our solar load calculator.  

When you are looking at inverters, you will notice that each device is rated for a certain number of watts for continuous and surge usage.  Surge refers to the amount of power an inverter can supply for ten to fifteen minutes of peak demand, whereas a continuous rating is used as a guideline for safe, normal use. In order to calculate the right size inverter for your electricity needs, simply add together the wattages of all of the devices you plan to run simultaneously.  

In general, you will want to prevent possible damage to your inverter by not overloading your system.  Allow yourself a bit of wiggle room, and purchase an inverter that is rated to power more than enough continuous watts of AC power for all of your daily use devices such as lighting, fans, electronics, and kitchen appliances.  

Power Inverter Voltage

Volts are the measure of voltage, which is what makes electric charges move, as the potential difference across a conductor.  Voltage can be calculated by Watts by Amps (V = W/A).  Therefore, the lower voltage system you have, the more current (amps) will be required to power the inverter.

The most common input voltages for off grid solar power inverters are 12V, 24V, and 48V.  12 and 24 volt inverters are by far the most common, as well as least expensive kinds of inverters for DIY off grid solar systems.  In general, if you have a 12V battery or a 24V battery, you will want to have the same voltage inverter, as it draws power directly from the storage.  The voltage should also match that of your solar charge controller.  Your inverter’s voltage will also determine the size of wire gauge to best run your solar power system. 

How to Hook Up a Solar Power Inverter

In an off grid solar energy system, the power inverter is hooked up directly to the battery.  In most cases, it is also the last piece of equipment of the system in which you can plug in your appliances.  

On your inverter, there should be an input panel which has a negative and positive charge port.  Here, you will want to connect these ports to their corresponding counterparts on the battery (i.e. negative to negative & positive to positive).  We recommend using black and red wires to separate the positive and negative charges.  If you have electrical experience, you can choose to add a fuse between the battery and the inverter for added protection.

In order to select the correct size wire gauge, you will need to consider your continuous AC load as well as your inverter voltage.  12V systems with low usage (i.e. <1000 continuous watts) can generally use an AWG wire size of 2/0, whereas higher demanding systems can use 4/0.  Like in all parts of a solar system, in general, it is always better to leave some wiggle room for error.  Limiting your wire size because it is cheaper will result in less power able to be drawn from your battery.  

Solar Power Inverters Conclusion

In conclusion, if you are looking to run your household devices and appliance on solar power, you are probably going to need an inverter.  For the best results, you will want to choosing a pure sine wave inverter that is rated to deliver more than enough wattage to continuously power your devices.  With consistent voltage across you entire system, hooking up and using your inverter is as easy as connecting the right wires and plugging in your electronics.  

 


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