Solar Power Inverters: Do I Need One? [DIY Mini Course 5/6]
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In DIY solar energy, power inverters are an accessory you almost always need, and they are often one of the most intimidating components of any system.
Power inverters, 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 cover the basics of power inverters as well as how to choose and install the right one for your DIY solar energy system.
What Are Power Inverters?
A power inverter is a device that can change or invert electrical current from direct current (DC) to alternating current (AC). They range in size from small devices that you can plug into a car’s cigarette lighterall the way to larger full-home electricity inverters.
It is important to understand that AC is the type of electricity that household outlets and most electronic devices use. On the other hand, DC is most commonly stored in batteries and used in low-voltage situations, like in automotive applications.
What Do Power Inverters Do in a Solar Panel System?
Today, the electricity solar-powered panels generate and then store in solar batteries as DC electricity. Once the energy passes through the inverter, it becomes 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?
You can create a pure DC-powered solar energy system to run a simple off-grid system for devices like well pumps. Systems like these may not require an inverter as they are limited to only powering the devices that they have been specifically designed to run.
But the truth is a majority of DIY solar systems have power inverters. 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 mentioned, power inverters come in a wide range of sizes and capabilities. Here, we 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 typically has an output panel where you can directly plug-in devices. 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 utilize the built-inverter on a portable solar generator.
If you have a grid-tie or grid-tied solar panel system, you can install two kinds of inverters. A grid-tie inverter (GTI) modifies your solar energy to fit the grid power frequency since excess electricity production goes back into the grid.
If you have a grid-tie system with a battery backup (also known as a hybrid system), then you 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 types of inverter technology: pure sine and modified sine wave. By far, the most popular are pure sine wave. Pure sine wave inverters use sophisticated technology to deliver the smoothest possible electric current, like a grid-tied home. For the best overall performance, we highly advise you to look into a pure sine wave inverter.
Modified sine wave inverters are generally the cheaper alternative to pure sine wave. Although you can use modified sine wave inverters 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 more basic technology, making it difficult to power devices with varying current draws, such as smartphones, fridges, air conditioners, power tools, and other appliances.
Another option is a hybrid or all-in-one inverter, which combines a power inverter, battery inverter, and solar PV charge controller. The major benefit to an all-in-one inverter is that you only have to manage and monitor a single piece of equipment. They’re generally easy to use and install, and we truly believe they’re the future of solar.
All-in-one inverters make sense, especially if you’re investing in a system that you hope to grow in the future. You can add them to any system, but wiring and installing them into an existing setup can be a little tricky. So, say your current solar system doesn't have battery backup, but you're planning to add it in the future. When you do, you'll need to add another piece of equipment anyway. Why not start with a hybrid inverter, so you have everything you need from the beginning?
There are some downsides to hybrid converters, the main one being that they’re more expensive than other options. But, remember, with an all-in-one converter, you’re essentially getting a complete solar system in a box, so it’s easy to justify the cost.
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 and volts.
Although the technical aspects may cause first-timers’ eyes to glaze over, selecting the right sized inverter prevents damage, increases efficiency, and allows for the best overall user experience.
Watts measures 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 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. 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 want to prevent possible damage to your inverter by not overloading your system. Allow yourself a bit of wiggle room, and purchase an inverter 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 measure voltage, which is what makes electric charges move as the potential difference across a conductor. You can calculate voltage by dividing watts by amps (V = W/A). So, the lower the voltage system you have, the more current or amps required to power the inverter.
The most common input voltages for off-grid solar power inverters are 12V, 24V, and 48V. Twelve and 24-volt inverters are, by far, the most common and least expensive kinds of inverters for DIY off-grid solar systems. Generally, if you have a 12V battery or a 24V battery, you will want 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 also determines the size of the wire gauge best for your solar power system.
How to Hook Up a Solar Power Inverter
In an off-grid solar energy system, the power inverter hooks up directly to the battery. Most of the time, it is also the last piece of equipment of the system and where you can plug in your appliances.
On your inverter, there should be an input panel with a negative and positive charge port. Here, you 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 add a fuse between the battery and the inverter for added protection.
To select the correct size wire gauge, you need to consider your continuous AC load as well as your inverter voltage. Twelve-volt 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. As in all parts of a solar system, generally, it is best to leave some wiggle room for error. Limiting your wire size because it is cheaper will result in less power being drawn from your battery.
If you want to run your household devices and appliances on solar power, you are probably going to need an inverter. For the best results, choose a pure sine wave inverter rated to deliver more than enough wattage to continuously power your devices. With consistent voltage across your 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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