DC Coupled vs. AC Coupled Solar Systems: Find the Best Fit for Your Setup

[@dennislyons3095]

Kelly did a great job of describing the differences & operation of both DC & AC coupled systems. I have had an AC coupled system for 24 years now. I've added panels & batteries & 2 electric vehicles to our use case over the years. I have also replaced three inverters because of failure over the years. Nearly everyone can benefit from well designed solar systems.

[@junkerzn7312]

I've done both over the years but these days I far, far prefer DC coupling because you have less electronics up on the roof. In the old days you had no electronics on the roof at all but these days regulations typically require per-panel rapid shutdown, so there has to be something up on the roof per-panel to do that. But the equipment is dead simple and unsophisticated compared to micro-inverters. Generally speaking, maintenance on DC coupled systems is far, FAR easier and far less expensive because the equipment most likely to break is at ground level and doesn't require partial disassembly of panels up on the roof. DC coupled systems are cheaper to install and cheaper to maintain. Another big advantage of DC coupling is that you don't need to wiggle the line frequency around during a blackout (UL1741SA) to regulate AC micro-inverters. It can just stay locked at 60hz. And there are fewer voltage overshoots and undershoots with variable loads. -Matt

[@mb345]

@8:04 I love the use of the physical whiteboard. This video will be a great asset for folks looking to build a foundation in how the PV systems work. Well done!

[@gdegarimore]

Great video. I learned something new. Especially the AC coupled portion. As an off grid guy, I never fully understood the AC coupled path and advantage. Now it makes more sense. Like adding the hybrid to an existing solar setup.

[@marstekenergystoragefactory]

Very details introduction of AC Coupled and DC Coupled with pros and cons. Appreciated it. Thanks Kelly.

[@2AKNOT]

Thanks for taking a complicated subject and making it easier to digest. Great job.

[@SignatureSolar]

Glad it was helpful!

[@scottbalak7123]

It seems like the major down side to AC coupling is price. I've seen several videos where it is claimed that "power optimizers" are now longer necessary with today's modern panels. If power expansion is the goal it would seem like two hybrid DC coupled inverters would offer all the benefits compared to a combination AC coupled + DC coupled. IMHO.....I've never been a fan of microinverters. They are the most expensive path and the redundancy benefit is a double edge sword. The probability of failure go up at the same time.

[@Tro1086]

Totally agree. Micros have some benefits, but also have a lot of down sides that come with those benefits. Turning 1 point of failure, into tons of failure points, and putting them under baking or freezing panels outside on a roof, are you really gaining that much. Also any system with batteries involved usually has one piece of equipment, whatever it may be, between the entire system and the batteries, so your right back in the same boat of a single failure point between you and having power when the grid is down. I could have a whole nother DC coupled inverter sitting on my shelf collecting dust just waiting for a failure, for a lot less money than the AC coupled system cost in the first place. And then i still have one main failure point that is in my climate controlled basement and not underneath 150degree panels on my roof.

[@zelbinian]

Price is also the major upside, if you think about it. Affordability for most people isn't just about the total price tag but about the velocity of money. Being able to comfortably buy solar in year 1 and then comfortably buy batteries later down the line gives a lot of financial flexibility. It also gives the homeowner time to decide whether they even need the expense of batteries at all or if the net metering with their utility is good enough.

[@AveRage_Joe]

Excellent Job!!! Easily the most informative video on this subject I have ever seen!!!💥🤘

[@Dan-kv8vz]

I'm just starting to learn about solar and this is the most informative video that I have found that really helped me understand what I'm doing with all the different components. Thank you so very much!

[@brucefreeman5207]

This was a very informative video. Great explanation between the two types of systems and how to maximize power management.

[@surfcow]

Well done. Another great instructional video.

[@kaf2303]

Thanks Kelly that’s a great comparison video!

[@nated1971]

One thing I didn't hear mentioned about AC, and the reason AC was chosen over DC for transmitting power over distance, is AC's ability to efficiently move power over longer distance with lower losses. This allows you to move your panels farther away from your home/load and not have the power loss due to wire length.

[@matthewwakeham2206]

Dc is more efficient over longer distances as i understand it. New high power grid interconnectors tend to be high voltage dc.

[@nated1971]

@@matthewwakeham2206 DC will require more step-up transformers to account for losses in the line. I don't think solar will deliver high enough DC voltage to matter...could be wrong..wouldn't be the first time

[@junkerzn7312]

The efficiency of transmission is primarily a function of voltage, not whether something is AC or DC. AC is actually a bit less efficient than DC. The reason AC is used for most short-haul transmission lines (less than a few hundred miles) is that it is a lot easier to step-up and step-down an AC voltage than a DC voltage. However, for transmission lines longer than a few hundred miles, AC must be phase-synchronized (often multiple times), which is more costly and DC winds up being the most cost effective. So very long distance transmission lines these days tend to be DC.

[@nated1971]

@@junkerzn7312 Guess I should have paid better attention in Power Systems

[@samueladitya1729]

you can string the panels for up to 500V usually for the hybrid inverter, and the panel itself are rated for up to 1500V system

[@freeheeler09]

Great video Question 1. How much more efficient is a DC-coupled system? 2. Do I need to install optimizers with my solar panels? How much more efficient do optimizers make my solar system?

[@SignatureSolar]

Hi! DC-coupled systems are around 5-10% more efficient than AC-coupled systems due to fewer energy conversions. Optimizers are not always required but are useful in systems with shading or complex roof layouts. They can increase efficiency by 2-25%, depending on shading conditions.

[@paulkish007]

ThankYou Kelly!

[@ibenglish]

I always learn something new from these videos. Can you do a video on which microinverters work best with different wattage panels? Also my grid tied SolarEdge inverter and SolarEdge optimizers were not cheap. I would prefer to utilize the optimizers and ditch the inverter for the 18kpv and add EG batteries. Our local power outages are getting ridiculous and this grid tied set up is starting to really wear on me. I would still like to back feed to the grid but their control over my 24/7 power use needs to come to an end. “So my question would be if the SolarEdge optimizers will work for me with the 18kpv and minus the SolarEdge inverter. Also if I doubled my array and added micro inverters to that section of panels would this work well”?

[@magnumcj]

I have a very similiar setup but would like to be able to use the solaredge to AC couple to my EG4 inverter system after disconnecting from the grid during a grid down event

[@ibenglish]

@@magnumcj wish they had these inverters back when I got my install done 🤷🏼‍♂️

[@carlosf7776]

Excelent Video 👍👍👍👍💪

[@s.lionelmcauley4455]

The news cycle is full of reports on extended grid-down scenarios in the US southeast. Kelly, you missed a primetime opportunity to explain the microinverter vs the string inverter. You could have shared the FEMA recommendation on the subject.

[@alejoalamillo8707]

Congratulations. Great video.

[@securityvlogger6825]

I hope she’s a millionaire; well-deserved, great clarity

[@user-jm7jk6xu2r]

I'm somewhat confused with the AC coupled example. It shows the Enphase micros and the eg4 18k providing AC to a critical loads panel. It does not show the Enphase controller connected to the gen input of the eg4 18k. I assume the only direct connection with the breaker panel is between the 18k and the panel? I have 2 200A panels connected to 1 meter. Panel 1 is net metered and backed up by an Enphase system. I would like to utilize Enphase IQ8+ micros to provide sunlight backup on Panel 2, so the idea of connecting the gen output from a second IQ controller to the gen port input on an 18k so I could both power loads during sunlight hours AND charge NON-Enphasw batteries is intriguing. Thoughts??

[@thomaseames7264]

Does signature assist or answer questions a customer buying a complete system work out the AHJ and PG&E issues before buying? Does signature offer any schematics or diagrams that can be used in AHJ and PG&E applications when buying a complete system such as an EG4 18K with 2 EG4 wall-mount batteries and solar panels?

[@SignatureSolar]

Our design department can answer questions and give some direction! If you'd like to call in at 903-441-2090, we can assist!

[@JohnD993]

Will the 18K turn on the micro inverters in an off grid setup? Thought the gen breaker was an input.

[@ter450]

Researching solar installation. Correct me if i am wrong, but the whiteboard has grid to the main load/panel to the inverter. Should it not be grid to inverter to main load/panel?

[@Tro1086]

The diagram is correct. In both diagrams you have a main load/grid panel, and a backup panel. The inverter connects to both panels, sells excess power up stream to the grid panel, when grid goes down, it disconnects from the grid panel and powers only the backup panel

[@kabandajamir9844]

Thanks the world's best solar Queen teacher thanks

[@christalbert722]

I think this would have made more sense and been more understandable if you'd shown separate charge controller / mppt / inverter / micro inverters instead of an all-in-one... it would have made the diagrams a bit more involved, but would have more clearly shown the different functions. Showing a AIW system sort of makes for a magic box that isn't very understandable. Actually then you could show side by side diagrams showing how an AIW system simplifies system design and installation. And maybe some situations where going separate is still better? (I would have loved to have seen a tree with a shadow showing the cause for different solar panel outputs, as it is no reason shown for the varying outputs.) (always easy for some jerk like me to criticize from the back of the room!)

[@philippserrin8268]

I am curious how much power you actually lose in total with Panel to Inverter DC to AC, then Inverter to Battery AC to DC, then Battery to Inverter for actual use in the home Is it possible that one kWh of power harvested by the Solar Panels only produces 80% of one KWh by the time it is used in the house ?

[@nated1971]

agreed, would like to see some data about how much power is lost in the conversion process

[@junkerzn7312]

It adds up. Actually it multiplies. You take each stage's efficiency and you multiply them all together. So, for example, if a micro-inverter is 98% efficient and the AC battery charger is 95% efficient and (when discharging the battery) the DC-AC inverter is 92% efficient, you get: 0.98 * 0.95 * 0.92 = 0.857 = 85.7% end-to-end efficiency. Also, these efficiencies are actually quite variable and depend a lot on how much power is actually being transmitted. Higher efficiencies are possible with higher-voltage topologies... for example, a Tesla Megapack has a round-trip efficiency of (I think) somewhere around 93%. Generally speaking, having more conversions is bad but some conversions are worse than others. Reducing the voltage tends to be quite efficient while boosting voltage is less efficient. DC-to-AC can be made fairly efficient while AC-to-DC is less efficient. And output regulation also matters. Micro-inverters can hit 99% efficiency if they have something (like the grid) to push against, primarily by not regulating their output as well as an inverter powering house appliances would have to regulate its output. The trade-off is that a micro-inverter can easily overshoot and cause the line voltage to increase beyond specs if it doesn't have anything to push against. -Matt

[@volodumurkalunyak4651]

​@@junkerzn7312, your calculations arent complete. 98% efficint microinverter, 95% efficient battery charger, 95% efficient battery and 92% efficient inverter get the following: A. 98% for portion of power that is used immediately. B. .857*.95=.81, you get 81% efficiency for storing electricity.

[@junkerzn7312]

@@volodumurkalunyak4651 Indeed, I forgot to include the battery round-trip (which is 95-98% for LiFePO4 depending on the C-rate and DOD). The rule of thumb is AC-coupling works really well when you are primarily exporting or consuming the solar energy in-home. DC-coupling works really well when you are primarily storing the solar energy. In past decades grid-tie and export was a big deal due to government policy decisions and incentives. That gave a huge boost to AC-coupled solar. But now numerous states (including California) have de-valued direct export in favor of storage... DC-coupled solar is better in the new regime. In terms of cost, DC-coupled has always been cheaper than AC-coupled and still is, but it is more important now when batteries are added to the fray because batteries are rather expensive. Installers love AC-coupled because of the per-panel reporting (diagnosing panel damage is easier). But that's the only good thing about it in my view. Most states require rapid shutdown devices at the panel level now so even with DC coupled you can't avoid having zero electronics up on the roof, but such devices are only around $30 a pop whereas micro-inverters are $100+. -Matt

[@Tro1086]

A lot also depends on how much you are using the battery. If its a normal grid tie application that spends 99% of its life on the grid, and the battery is just for backup during power outages, then you will almost never incur the inefficiencies associated with the battery. If you live somewhere where using the battery for peak shaving and time of use rates are a thing, and you are cycling the battery a lot day to day, then the inefficiencies will start to add up. The efficiency penalty only occurs if the power has to go thru the battery, if you can use/sell it as its made, then you get a high(maybe even higher or equal to the most efficient systems), if you need to store it for later, thats when you suffer from one of the least efficient designs, having to invert it multiple times.

[@jl-7992]

Can i have an inverter connected to the PV and batteries and another inverter that is in parallel to the first, which is connected to the load panel?

[@stibbs11]

Do you have a solar for dummies or Solar 101 video?

[@donniebrown9562]

I bought two 24 volt from you I need a code just set them up I will be in contact with you guys set gets it done right

[@SignatureSolar]

Let us know if you have any issues setting them up!

[@jefflucas_life]

4:54 this point on, to many wires.

[@MrThaiLuan]

Too much information. Not enough clarity. Do I want a DC coupled or AC coupled system? At one stage I thought a combination of both? But then how that works should have been clearer in diagram format. I was looking for ways to utilise all power generated rather than have some clipping occur and thought DC coupling was the answer. I'm now confused.

[@amigatommy7]

I need to buy some stock in an inverter maker.

[@WAsolarguy]

The conversion losses in a AC coupled system is 3% more than a DC coupled system. Typical DC coupled will loss around 6% during the entire process, it can store up to 3% higher efficiency than AC coupled systems. That is huge impact on a commercial/utility scale eco system but residential…. Fractional IMO. DC is ⚠️ high voltage ⚡️ unsafe. Why should your solar be at voltages 300-600v when there’s a better and safer alternative but question the conversion loss over safety 🔥? So you lose 3% big deal safety should be the priority. RSD devices help yes but that’s a separate component added in conjunction with your single point of failure inverter that micros have integrated. All homes run off 240V.. not 600V why should your solar be different.

[@danielking2944]

Good point to be considered. However 120v is just as dangerous as 500v . The tiny current that will stop your heart can be generated by even lower voltage. I worked with 480v for years and my experiences while part of those circuits was no more painful than the 120v shocks. Higher voltages save money because the lower current makes components and wires much smaller for the same power.

[@danielking2944]

I agree that the 3% conversion loss is insignificant considering how inexpensive solar panels have become. In a 10 KW solar array,that’s just one 300 watt panel. I’m gravitating toward moving the whole system to a power shed and letting the house panel simply see it as it if were a grid connection. I already am totally done with panels on the roof of the house because of the fall hazard. Also,if it’s not a square surface clear of vent pipes,the installation has a Frankenstein appearance.

[@mrwombat24]

Many dc to ac conversions and vice versa generate very high levels of dirty electricity, which are very dangerous to human health. DC coupled systems are simpler and require fewer inverters so it should produce less dirty electricity.

[@drumboy256]

It depends on what your goals are. DC tied via string to inverter and batteries, you’re more efficient with the energy than with a micro-inverter. You also have less moving parts and fewer single points of failure. Safety of DC vs AC is funny because in all likely scenarios, the systems are shut down; typically, if installed to code/spec, this will be a non-issue. Full disclosure, I have a 12kWH DC coupled system with 20kWH of battery from QCells. Their systems just work.

[@modquad18]

@@drumboy256 I’m just diving into all this as I plan to install a system to power my farm next year. Does Q-Cell offer a set of matched components at various capacities? I’ll be doing all the labor myself and would be great to have a single source for a proven setup. My goal is to tap the grid only as a backup during periods where my system is unable to meet demand.

[@krslavin]

A microinverter with each solar panel, is less reliable than just solar panels, so having many on your roof is not as reliable in general, and replacing a microinverter means getting on your roof.