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Solar + Storage 101: Basic Battery Backup Parts (and their functions) explained!

Hello again - and here we are, talking about what DPI Solar is seeing lately in the industry and how it works or impacts your choices to adopt some (or all of this tech).

Let's chat about Batteries with solar power - and what it REALLY means for most of our adopters here in Oregon.

First things first - Battery Backup with solar - what is it and how does it work?

Well folks, I've spent a fair amount of time trying to de-tangle and easily explain this tech to our customers, and this is where I landed:

Solar with Battery Backup is very similar to having a generator (like what you'd buy from the store - that runs on gas).

So, how's it similar you ask?

Well, some of you already own a portable generator. Maybe you purchased it for your home in the event of a power outage? Maybe you purchased it to travel with and camp with? Maybe you use it when you're tail-gating at your favorite college football game? Who knows WHY you purchased it, but nonetheless, SOME of you folks already own one.

It's VERY likely that when you went out to buy a generator, the FIRST thing you looked for was its output - and this is a number that is represented in WATTS. Typically, a generator is listed by it's PEAK output (as opposed to continuous output). So... a 10,000 watt generator is capable of providing 10,000 watts (for a short period of time).

Next - that same generator has a listed CONTINUOUS output rating (this is a smaller number than the advertised size of the generator). Typically, a generator can provide about 80% (of it's PEAK) output, continuously. So a 10,000 watt generator can usually offer the user 8,000 watts continuously - until the gas tank runs out.

Finally, this same generator will have listed "run-times" for various levels of use: Typically, one tank of fuel will offer 8 hours of run-time at 50% continuous load (so if you're still with me, that generator will run for 8 hours will be providing 4,000 watts of output). This same label usually indicates how long the fuel will last if it's under "full continuous load" - and for our generator, that is 4 hours total run-time at 8,000 watts.

Still with me? GOOD! Because what I'm about to do is take something you know (and might even already own) and use it to explain and help you understand how a solar array with a backup battery system works!


OK. First - let's just forget about the solar portion of the "Solar with battery backup" - because I'll later explain what the "solar" piece is (in relation to our generator we just discussed above).

Now we are talking about JUST the battery backup components for your project (which Solar DOES attach to!)

So... what do we have first? Well, most systems on the market are comprised of three basic components:

1) Hybrid Inverter (with automatic transfer switch)

2) Auto-Transformer (depending on the brand, this is sometimes integral to the hybrid inverter - and other times, it's a separate component)

3) Battery bank

So, looking at #1 above, what is it and how is it similar to a generator? The hybrid inverter is the piece that will determine the output of your system (in watts). Much like a generator, there are several brands and each is listed for its CONTINUOUS output. So just like a 10,000 watt generator (with an 8000 watt continuous output rating), our hybrid inverters are listed in the same way - but pay attention! Because THESE inverters typically have TWO output ratings:

a) GRID-TIED(!) output - which is how much power the inverter will generate when it's connected to a live electrical grid (this is NORMAL operation)

b) OFF-GRID(!) output - which is how much continuous power the inverter can make when the grid fails

The second output rating is the one that is exactly like the generator we discussed above! Let's use the Q.Home+ ESS 8.6kW Hybrid inverter as our example:

a) when the GRID IS ON and your solar array is feeding your home (or the power company when you're making excess power, via net metering) this inverter will output a maximum of 8,600 watts

b) when the GRID IS OFF and your solar array is feeding the house loads (in off-grid mode), this inverter will offer you 7,500 watts of continuous output power

This part of the comparison has now equated the hybrid inverter output to a generator output - so our hybrid inverters are much like the motor/generator combo on your gas generator: they both have a rating in watts (which is how much power you can expect to have when the systems are running.)

So... onto #2 for our comparison: the auto-transformer. This gizmo is what is responsible for creating the correct voltage for your home to use. In our case the auto-transformer will output 240 volts (120 per phase), which is exactly like the power you're buying from the power company for your home.

It's important to know (at this point) that some generators are 120v generators and others are 240v (120/phase).

If some of my readers here (that already have a generator) are following me up to this point, then it might be worthwhile to look at your generator to see what the output is (typically, a generator with an output over 3,000 watts is usually a 240 volt generator). So - which part of our comparison is the auto-transformer similar to a generator? Well, it's the actual generator piece of the equipment that is exactly like the auto-transformer: as the gas motor turns the generator, it will output either 120 volts or 240 volts, depending on what you buy. Our auto-transformers are designed to create a perfect 240 volt grid for your home so that you can use some (or all of your appliances - more on that in a later blog post). Our auto-transformer converts your battery (or solar power) - which is stored or generated in a DC voltage - into AC power for your home.

Finally - onto #3 - the battery bank.

Remember when we talked about the "gas tank" on a generator? Well...that is exactly what your battery bank is: the gas tank. The bigger the tank, the longer the run-time. The smaller the bank, the less run-time you can expect. The battery side of these systems is (honestly) "mutually exclusive" from the rest of the system (even when the batteries are sold and installed as a single unit - with all of the other above mentioned parts housed in the same enclosure. Some battery systems allow you to choose different sizes of battery banks - but be very mindful of what that means! If your sales advisor is unfamiliar with how these systems work, they might try to lead you to believe that a single battery can run your entire home - but depending on the equipment, you might not even get enough power output to run more than a microwave and refrigerator at the same time. If you'd like to dig deeper on this part, call us!

So... where are we? Well, we have a generator that now consists of a hybrid inverter (that turns the power from the batteries and the solar panels from DC to AC). We have an auto-transformer that creates a 240 volt grid for your home. And we have our battery bank (which stores the solar power and allows you to use it - day or night).

So... where do the solar panels come into play here? Well, if we're still sticking with the comparison to a generator, then the solar panels are the "gas" that fills up the "gas tank" (ie: battery bank).


Here's where a solar array with battery backup SHINES (pun intended):

When the sun is shining on your solar panels, you don't usually use much (if any) of your battery storage. In fact - with a properly designed system, your solar panels will usually give you enough power to BOTH power your needs (during a grid failure) AND recharge your batteries (from their overnight consumption). This means that (unlike a gas generator), your system will offer you similar outputs to a large portable generator, while not using up the batteries DURING DAYLIGHT HOURS (unlike a gas powered generator that starts burning your FINITE fuel supply the moment you start and run it).

If you are diligent about your electricity consumption (while you're off-grid) you can go for days or weeks with your system - using minimal power after sunset, and using substantial power during the daylight hours.

We know - because the first battery bank system we installed is still running our office, day-in, day-out without any noticed power outages in the last several YEARS.

But... remember - if the battery bank is like a gas tank on a generator, then when it runs out of power, you're out of power, too! So...use good judgment when the power fails and you'll have plenty to get you through days and days of power outages.

Here's the most special thing about a battery bank: unlike a gas tank on a generator, our fuel supply is...SOLAR PANELS!!!

I told you I'd get there eventually!

That's right - the gas IS the solar panel power! Which means having a battery backup (with solar panels) is like having an open tap to the gas station. Your solar panels will "refill" your batteries (instead of you needing to hike a bunch of gas cans into your car and run to the local gas station).

FUN FACT: Did you realize that if power is out in your neighborhood, then that means that power is likely also out at your neighborhood gas station? That means their pumps aren't pumping, either. So if you DO run out of fuel for your gas generator, you'll need to drive to the nearest gas station to get fuel (and hope they haven't run out due to supply demands). This is another reason to consider a solar array with battery backup included: your "gas" supply is coming from sunlight and solar panels, filling up your tank (your battery bank).

Well - I KNOW this is a lot to read. I've spent years explaining this in person and over the phone, but putting it in writing where it is concise and relays the same message was a bit more challenging than verbally explaining it out loud. I hope that you now have more of an understanding of how these items work with your solar panels and where the advantages live.

Call us at (503) 857-0099 if you have any questions about Solar + Storage 101: Basic Battery Backup Parts!

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