What are the best off-grid solar inverters in 2019?

Posted by ai on January 3rd, 2020

If you’ve spent any time researching solar energy, by now you’ve heard of an inverter.

The inverter is like your solar system’s brain. It manages your power flow, controlling two kinds of power.

DC—or direct current—power is the kind stored in batteries. It’s also the kind produced by solar panels.

But you can’t use DC power (directly) to power anything in your home. That’s where your inverter comes in.

Everything in your home uses AC—or alternating current—power. And an inverter takes DC power from your panels (or from batteries) and turns it into AC so it can be used for your fridge, lights, TV, and other household appliances.

How is an off-grid inverter different from a grid-tied inverter?

A grid-tied inverter takes DC power from solar panels, turns it into AC, and sends it into the grid for credit.

Grid-tied inverters are simpler and easier to wire since there are usually only two main components—the inverter itself and your solar panels. (Some grid-tied systems are starting to incorporate energy storage, but most don’t have any batteries at all.)

But an off-grid inverter needs a battery bank to function.

Here’s how it works: your solar panels feed DC power into the batteries. Then your inverter takes that power and “inverts” it, creating AC power for your home. This works essentially like a miniature power grid.

As you might imagine, off-grid systems are more complicated, thanks to additional components like the charge controller, battery monitor, and additional AC and DC circuit breakers. All of these things tend to make off-grid systems more difficult to wire and install.

It can also be a challenge to buy off-grid equipment because there are a lot of associated accessories: remote controls, battery monitor, breakers and enclosures, surge suppressors, and so on.

Picking the right parts can be confusing enough—but there’s no more critical decision than buying the right inverter.

How to Pick the Best Off-Grid Inverter

Think About Size

The first thing to think about is how much power you need.

Fortunately, sizing off-grid inverters is straightforward if you know what appliances you’re going to use.

Add up the wattage of all your lights and appliances to calculate the number of watts you’d need if everything was used all at once. 

Don’t forget to consider the voltage—although most appliances run on 120Vac, some appliances, such as well pumps, require 240Vac. Example: Let’s say you need 1,000 watts for your fridge, 500 watts for lights, and 200 watts for your phone & TV. That adds up to 1,700 watts. In this case, we’d suggest a minimum inverter size of at least 2,000 watts to give you a little extra headroom. (After all, you may add appliances in the future.)

What’s the most popular size we sell? 4kW followed by 8kW. Different models and brands are available in various sizes and most of them can be stacked together for higher power output.

Consider Pure Sine Wave Instead of Modified Sine Wave

You may hear some manufacturers talk about pure sine wave inverters. You don’t need to understand exactly how these work—it’s enough to know that the power that’s put out by a pure sine wave inverter is “cleaner” than what you’d get from a modified sine wave inverter.

Pure sine wave inverters deliver higher quality power output, similar to (or better than) our power grid. Modified sine wave inverters are cheaper, but they deliver lower-quality power output.

For this reason, modified sine wave inverters can cause issues with certain appliances. Motors, pumps and compressors run hotter and wear out more quickly. Certain sensitive appliances like computers can be damaged, or they may not work at all. These inverters also typically cause background noise on a stereo, and reduced video and audio quality for certain TVs.

That’s why we don’t recommend modified sine wave inverters for most applications; most of our off-grid customers are use pure sine wave inverters to avoid these potential issues.

Need a quick way to tell the difference? Look at your inverter’s total harmonic distortion (THD) rating. THD is an indicator of power quality output and will be listed on the spec sheet of any decent inverter.Rule of ThumbTo avoid running into trouble, choose a pure sign wave inverter with THD of 5% or less.

Look at the Technical Specs

Here are some other technical specs to consider:

Efficiency. This is a measure of how much power from the batteries your inverter delivers to your home when it’s operating in perfect conditions. A good peak efficiency rating is around 94% to 96%.

Self-consumption, or no-load current draw. How much power will your inverter consume just sitting there? Obviously you want this to be as low as possible.

Surge capacity. How much short-term overload can the inverter handle before it “trips?” Some appliances, like pumps or fridges, need as much as 2x–3x their running power to start up.

Battery charger output. Many off-grid inverters include a battery charger, which is used to recharge your batteries during the winter months with a backup generator. The battery charger will have a rating, usually measured in amps. Most decent off-grid inverters will have a battery charger in the range of 50-100 amps DC.

Temperature range. Inverters are sensitive to extreme heat. Pay careful attention to the temperature range if you plan on installing your system in your garage or anywhere it could be exposed to temperature extremes.

Warranty. Warranties start at 1 year and typically range from 3-5 years, with a few manufacturers offering a 10 year warranty extension option.

You can normally find information on all these features on the product spec sheets. Check with your solar tech for help comparing and picking the right inverter.

Research Features

Your inverter may need special features. Look into these ones:

Battery charger. A charger allows your system to be charged from a backup AC generator. Most bigger inverters include this; these are called “inverter/chargers.”

Grid-tied capability. Some off-grid inverters have the added capability of feeding power into the grid.