Getting Your Grid Tied Solar Array To Work When The Grid Is Down

NOV 26 2014 BY GEORGE BOWER 54

Grid Tied Solar PV System

Grid Tied Solar PV System

Slide 2 - A View To The East

SlideA View To The East

If you have an EV chances are you either already have a Solar array or you are thinking about getting one. Also, if you already have a system you may have one that uses micro inverters (usually Enphase inverters). In a micro inverter type grid tied (GT) system there is an individual inverter under each panel as shown in figure 4.

Preface:

I’ve been looking into using some Leaf battery Cells instead of my current deep cycle lead acid batteries. Everything in this article still applies as far as the low cost DC TAP goes. The only thing that changes is I need a different charge controller. But believe it or not the MPPT  terminology applies between both lead acid batteries and Lithium.

 (There is also an excellent article  in the My Nissan Leaf Forum – Very impressive with Leaf modules)

Looking West

Looking West

Figure 4

Figure 4

Most grid tied system owners are aware that their grid tied inverters shut down when the grid is down.

Figure 5

Figure 5

This is a disturbing situation. When the grid is down is when you need them the most. Sure one could use a portable gen set but what if there is an extended grid outage? Wouldn’t you want your solar system to be available?

The most obvious solution would be to fool the inverters into thinking the grid is up by feeding them a pure sine wave at 220 volts. They would see this sine wave and power back up….problem solved.

Figure 6

Figure 6

The Enphase paper in figure 6 references a MagnaSine inverter that is designed to fool the inverters by creating an AC coupled system that consists of the MagnaSine inverter and a battery bank. The problem is that the inverter alone is $2,500 (USD) and that is not all you need. You also need a critical load panel….and of course the batteries. I already have a small battery bank and inverter system so I’m not that keen on spending $2,500 on an emergency power system that may never get used.

You can read the Enphase AC coupling paper just google “AC Coupling of Enphase Micro Inverters, 2014”.  Things get complicated if the grid is down and all your critical loads are off and you’re batteries are fully charged. Apparently the enphase inverters don’t like being dead headed. They need a place to send their AC output. So in the enphase MagnaSine inverter system the MagnaSine inverter shuts down the enphase micro inverters by shifting the fake grid signal slightly. The enphase inverters sense an out of spec signal and shut down.

If you have not yet installed a grid tied system you should consider the Outback AC coupled system (or Sunny Boy). These grid tied inverters are not Micro inverters though. You still bring back DC to one central inverter as shown in figure 7.

Figure 7

Figure 7

The problem with the outback solution is it’s expensive. You need additional relays and the critical load panel again for a system that may never be needed. A schematic for the Outback system is shown in figure 8. Hooking your generator into this system is also possible. It uses relays instead of frequency shift to decouple the GT inverter in the case of no critical loads and a full battery.

Figure 8

Figure 8

All these AC coupled solutions have a high price tag. Personally I can’t justify it. I wanted a solution that is low cost. The low cost solution I have come up with is fairly simple. It involves tapping into the DC output of the PV panels upstream of the micro inverters as described in figures 9 and 10.

Figure 9

Figure 9

Figure 10

Figure 10

Since the grid is down, the enphase inverters are shut down and tapping into the DC upstream of them should make no difference. The problem would be if the grid came back up with the DC diverted to the battery charge controller. In order to fail safe this situation the DC shut off (DC disconnect) that will be installed at the end of the DC run will have a padlock. So if the grid goes down and you want to tap into the DC for battery charging, you remove the padlock from the DC disconnect and go to the AC solar Panel disconnect and switch that AC disconnect off and padlock it in the off position.  The main purpose of the emergency DC tap out is to charge batteries. In my particular case I will have 4 deep cycle batteries to be charged so the DC tap out needs to go to a battery charge controller. I also have a DC to AC inverter.

In the process of designing this low cost DC tap out system I was forced to learn some basic wire sizing and charge controller guidelines that I would like to share. The good folks at “Northern Arizona Wind and Sun” helped me with the design. Their website is an excellent place to go for all kinds of info when you are designing a system. I plan to go to them to buy the hardware I will need to finish this project in return for all the time they spent with me.

Here are the guidelines I wanted to share. The first guideline has to do with wire sizing. When sizing your DC run you must use short circuit panel amps times 1.25 as shown in figure 11.

Figure 11

Figure 11

When sizing your battery charge controller you must use open circuit panel voltage times 1.25 as shown in figure 12

Figure 12

Figure 12

Another thing I learned in this design project was that all charge controllers are not created equal. There are 2 basic types: PWM and MPPT chargers. There is a good tutorial at the Northern Arizona Wind and Sun web site but the bottom line is that I need to use an MPPT charge controller. That is because my grid tie solar panels are somewhat of an odd ball voltage as they are specifically designed for grid tied inverters. They are 60 open circuit Volts and most battery systems are 12, 24 or 48 Volts. If you charge a 24 Volt battery pack with a 60 Volt Panel with a PWM type charge controller you are wasting almost half of your Voltage. In order to use a PWM charge controller you need to match your battery voltage to your panel voltage.

The charge controller selected for my system is an MPPT charge controller that can charge at 12, 24 or 48 Volts and 60 amps as shown in figure 13.

Figure 13

Figure 13

As I mentioned earlier I plan to use 4 deep cycle batteries at 24 Volts. That will give me 4 kwh of storage as shown in figure 14.

Figure 14

Figure 14

Your reaction may be that 4 kwh isn’t enough. I also have a Honda eu2000i generator that is very fuel efficient because it is variable speed. I am currently modifying it for tri fuel capability. I have a 250 gallon propane tank that is used for heating so the plan is to tap into that tank for another source of emergency power.

Figure 15

Figure 15

The low cost DC wire tap system is not finished yet. A few things still to do before installing it as shown in figure 15. When it is finished I’ll publish another article.

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54 Comments on "Getting Your Grid Tied Solar Array To Work When The Grid Is Down"

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Leptoquark
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Leptoquark

I thought people put in a transfer switch to grid-tied systems to temporarily take them off the grid, and hence make them active during a power outage. See http://www.aeesolar.com/grid-tied-solar-systems-with-backup-power
for example.

Remember the reason grid-tied solar PV systems turn off during an outage: it’s so your system doesn’t electrocute the lineman working on the wires.

Does this design account for that?

Kosh
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Kosh

+1

And what are these long term grid outages anyway? Seems like a lot of hassle for at most a couple hours. In my experience, that usually happens at night anyway…..

Just pick up a good book and a flashlight.

GeorgeS
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GeorgeS

@Kosh

The battery back up systems get seldom used that is for sure but it’s nice to have it when you need it.

Just another reason why I can’t justify 2500$ + on a battery backup system.

That’s the purpose of my low cost DC tap…….low cost.

Aaron
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Aaron

This past year, in the city of Dallas, we had 3 days without power after a storm in October. We lost all the food in our freezer/refrigerator. Being able to switch over to solar only (even if it’s a manual cut-off switch) would have saved that food and allowed us to do other things in the house that required power.

Spec9
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Spec9

But how many times has that occurred in the last 10 or 20 years.

For me, the last time I had a power outage of more than 4 hours was the 1989 San Francisco Earthquake.

Dan Hue
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Dan Hue

Here in PA, it happens quite a bit. Lots of trees and suspended power lines make for a bad combination. One tree can cause a short term outage, but hurricane remnants, which commonly pass us over from the south, and of course the dreaded ice storms can wreak havoc on the system.

Spec9
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Spec9

I’m with you, Kosh. People are not very good at analyzing risks. We freak out over Ebola despite the fact that more people have married Kim Kardashian than have died of Ebola in the USA.

Unless you have a remote off-grid cabin or a notoriously extremely unreliable local grid, you are far better off to spend that extra money on more solar PV panels for your system than to waste the money on batteries & charge controllers that will rarely ever get used. The world will be better off too.

Grendal
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Grendal

And let’s be very clear that marrying Kim Kardashian is far more unhealthy for you than catching Ebola.

GeorgeS
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GeorgeS

@Lepto
Yes one could just install a transfer switch if one had a central inverter but not a micro inverter system where you have an inverter under each panel. In the micro inverter case we bring back AC.

So my solution IS somewhat like a transfer switch as I will divert the DC upstream of each inverter and bring it back to a charge controller.

Kalle
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Kalle

Arent they shuting down to not electricute some poor electrishian working on the system down the line?

GeorgeS
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GeorgeS

Yes that is why.

In my system that problem is taken care of. The DC tap just goes to a battery charge controller. and a battery bank.

When the batteries are charged I have a small independent inverter of 2500 watts that I can power loads in my house with.

The safe way is to just plug the individual appliances into the portable inverter/battery system.

If I manually disconnect the grid in my electric panel I can back feed thru my main breaker panel also.

My inerter was just 500$ with 3 deep cycle batts total cost of my emergency system was only around 700$.

Not anywhere near the 3000$ mark for the magnasine or SMA system.

My system just gives me battery charging off my panels in an outage.

kompot
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kompot

Yea, that is exactly what I was told by my provider. They dont want any electricity coming back to the grid, so they can safely work on repairs.

GeorgeS
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GeorgeS

I would also add that a NON pure sine wave works fine on all my appliances. I’ve run TV’s, Computers, lights and even my roof top Gas pack on a non sine wave inverter. No problem.

Again. Why spend big bucks on the EPS if you don’t have to.

jkw
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jkw

Almost all appliances will work without a pure sine wave, but it will often lead to a higher failure rate. Cheap electronics are designed for a sine wave and can’t keep the internal voltages constant if the power is too far off. The oscillating voltage in the device can lead to random problems such as flipped bits on a hard drive or shorter time to failure for televisions. If you don’t have any data you care about, then it probably doesn’t matter if it is just a backup for when the power goes out.

My computer’s UPS will turn on if the power deviates too much from a sine wave because it actually does matter.

MrEnergyCzar
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Interesting work around. For those with low energy use homes, you can use your Volt for extended power outages. Here’s a short video explaining….

https://www.youtube.com/watch?v=T0CSs3yorFs&index=5&list=PL3C7D1EBDF618528E

GeorgeS
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GeorgeS

@ Mrenergyczar

Good point. The Volt also makes for a great EPS. Just hook a 1000 watt inverter across the 12V battery and you have 10 kwh of juice at your fingertips with the RE as back up.

Clarksoncote has a nice system @ EVextend.com

GeorgeS
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GeorgeS

Just to add another point to the article.

There are other reasons for battery backup than emergency power.

If you are on TOU rates you can charge your batteries at night and use the power during the day. That way your getting your power @ 50% off.

That is what the guy in Norway has done in the link to the My Nissan Leaf Forum.

The other cool thing this guy has done is use a salvage Leaf battery pack for the batteries. 2000$ bought him the 24 kwh pack. That is cheaper than lead acid.

Very cool (but expensive system TOTAL cost). If you’re into PV and Li batts you should check it out.

Spec9
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Spec9

Meh. Trying to do time of use rate arbitrage is not likely to be very profitable. Again, you are much better off spending that extra money on more solar panels than batteries. However, it might make sense if you live in an extremely Northern latitude like Norway where the Sun doesn’t shine much in winter.

Bill Howland
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Bill Howland

Some of us already have off-grid power from our Solar Arrays.

My 38 panel system in Buffalo probably makes less juice yearly than your 14 panel system in Arizona, for various reasons, but mainly since we get as much sun as Alaska.

Using just spare parts, I have 2- 1500 watt Secure Power System outlets providing up to 3000 watts in theory during a bright sunshiney day. Wintertime operation, when most power failures occur, limit the actual power to a few hundred watts here.

The feature is included at no extra cost in my two SMA 4000 watt transformerless inverters.

GeorgeS
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GeorgeS

Yep,

I think if I had to do it over I wouldn’t have gone the micro inverter route.

The Sunny Boy option is a good way to go.

So you are bringing back DC to ONE inverter yes?

What Voltage are you bringing back the DC?

Bill Howland
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Bill Howland

Almost trivially easy to implement: All DC wiring (and Ac wiring) remains the same.

Just added a switch, and outlet to existing terminals inside each inverter, and ran them to 2 remote outlets (the two switches controlling the feature I have mounted on the Inverter Board). The Sunny Boy(s) take care of all the rest. Since the 2 outlets unfortunately are asynchronous with each other during a grid-outage, I can’t parallel the outputs, so motor starts are out of the question. But as I say, it was free so why not?

Bill Howland
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Bill Howland

To clarify I’m not adding any extra DC wiring since it uses whatever is hooked up to each inverter.

I have 2 – identical systems, each of them being 4000 watts (9120 solar panel watts total).

Each inverter has 2 seperately watched current sources. (4 #10 RHW per inverter).
13 panels on 1 input, and 6 on the other, so around 350 and 155 volts with more volts but less current when it is cold.

pjwood
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pjwood

But doesn’t the 1:1 pairing of the Enphase units protect you against one panel temporarily taking down your whole system?

I like the Leaf scenario. Those cars will keep falling in price, until the “re-purposed” battery market steps up.

Spec9
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Spec9

Nothing wrong with microinverters . . . in fact they have a lot of advantages. For example, if your central inverter dies then your whole system is dead whereas with a microinverter system, you just lose 1 panel and you can easily fix it by replacing that one microinverter.

And as I point out below, Enphase is building their own “AC battery” system that you can easily add to your system if you really want a battery back-up. But again, I think that is a waste of money unless you have a notoriously unreliable grid.

Spec9
Guest
Spec9

I’ve got an Enphase microinverter based system as well. However, I think that although an off-grid back-up system that works during a power outage is an interesting hobby project, it is really just pointless waste of money if you have a reliable grid.

You are far off better served by spending that extra money on more solar PV panels and more inverters until you generate more power than you use.

However, since the whole battery-thing appears in the news all the time (which it really shouldn’t because it doesn’t matter until we get like 30% of the grid solar PV and right now it is less than 1%), I believe Enphase has been working on their own system. Just searched . . . yep, the Enphase AC Batter or Enphase Energy Management system. Looks like a way to easily add a battery to an Enphase microinverter based system.

GeorgeS
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GeorgeS

Yes that’s an option as I pointed out in the article. The problem is it is big bucks and I don’t want to spent 3000$+ on battery backup.

I like Bills outback set up. It gives you access to your panels if the grid is down and the sun is out. So as I understand it right one could charge some batteries in a grid outage.

Yes you have a point on the failures. If you lose some micro’s the system still works you just lose the output from the panels under which the inverters are that failed.

I’ve already had a couple micros fail in the 5 years my system has been up on the roof. It’s a harsh environment up there in AZ in the summer.

If Bill loses his ONE inverter then his whole system is down. However his ONE inverter is not on the roof and therefor is not as prone to failure.

So I still think I would consider a SINGLE grid tied inverter over 14 Micro’s if I had to do it over.

Spec9
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Spec9

But Bill is a wealthy hobbyist . . . I understand him doing it. If I were you, I’d spend my money on more Solar PV panels & microinverters. It looks like you have plenty more space. I’ve got a 24 microinverter system and it generates more net electricity than I use such that the power company owed me $204 at the end of the ‘true-up’ period. (And another thing I like about microinverters is that it is easy to expand the system. If I get a second electric car, I can easily throw up another 8 panels to cover its ‘fuel’.)

If you have an electric bill, install more panels! My monthly electric bill is just a $5/month distribution fee.

Bill Howland
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Bill Howland
No, I’m not wealthy, and no, I have 2 inverters in 4 strings. Snow covering one panel kills the whole string of 13, or 13, or 6, or 6 panels (38 total). My cost for the system, after tax credits, will be $8500, the majority of it being ‘professionally installed’ (I did a minority of the work to lower the cost) since if it isn’t you don’t get the 30% fed and 25% state, plus $9120 from NYSERDA. Feed-in-tariff-wise, in NY State you get to use the grid as a big piggy bank so it doesn’t matter when you charge your cars but it is very grid friendly anyway as I’ve mentioned in other posts. In buffalo that is still alot of money for the trivial amount of sunshine we get, so the payback period is long, but at least we can do it, unlike Florida where only the utility is allowed to have solar power. The SPS (Secure Power System) is never professionally hooked up since there is no incentive to do so. I just ran from greenfield from my inverter board and ran switches (to tell the inverter to switch over to the sps) and outlets so that… Read more »
Spec9
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Spec9

Bill . . . you have 38 panel PV system, a Chevy Volt, and a Tesla Roadster. Objectively, that makes you wealthy. Maybe not super wealthy but well above the average person. Nothing wrong with that and you spend your money on good things.

And I hope all the recent snow is not hurting your roof or PV system. And watching out for flooding.

Bill Howland
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Bill Howland
A Lawyer calling me rich… Now that’s… rich! GEORGES I don’t know which is the best way to go. I went for the cheapest way possible. I don’t have internet access on the Solar, I did some of the work myself to save $$$, and I went with 2 basement mounted inverters since they were much cheaper than individual inverters. I’m hoping, that even though their warranties aren’t great, that cool basement operation (out of the weather extremes) will greatly lengthen their lives. Where I am there is no flooding. Roof is much sturdier than 1200 pounds/sq foot so I’m good there. The biggest danger the system has survived was a DIRECT LIGHTNING STRIKE to my house during the summertime. My solar system is below my Ham radio Needle Antenna on one side, and my Bow Tie array tv antenna on the other, and are both protecting my panels. The ham radio antenna took the direct strike, but since I follow the ‘Ground Window’ principle, I had no damage to the radio(s), nor other damage to the house, although the green covering on my grounding wire you can tell was stressed. But I’d rather deal with lightning (especially a big… Read more »
Spec
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Spec

You might want to look into DC optimizers to help handle shading or partial snow coverage issues.

Bill Howland
Guest
Bill Howland

basically dc-dc converters so it adds plenty of extra unreliability into the system. Plus now I’ve got an added inefficiency.

Plus added cost. If I put the panels on rotateable mounts, I’d gain another 35%. That is almost worth doing but I’m not sure how to do it. I think I’ll wait until someone comes up with a commercial cheap tracker.

io
Guest
io

Au contraire, Bill. Optimizers result in greater overall efficiencies compared to both micro-inverters and regular string inverters.
http://www.solaredge.us/files/pdfs/technical_comparison_microinverters_power_optimizers-na.pdf

Reliability of optimizers-based installations should be greater than micro-inverters, due to their simplicity, and similar to (not lower than) regular inverters, because the MPPT and DC-DC conversion done by the optimizers can then be skipped in the inverter: http://www.solaredge.us/files/pdfs/se_application_fixed_string_voltage.pdf

Bill Howland
Guest
Bill Howland

I’ve read the pdf’s. No.

Spec9
Guest
Spec9

You’ve had a couple micros die? Hopefully that issue has been fixed. I think the electrolytic capacitor issue might have been the problem and they’ve got rid of those.

Kosh
Guest
Kosh

I had just one Enphase M190 die on me, well, it never really died, it just kept throwing ground fault interrupt exceptions and shutting itself down.

Enphase replaced it free of charge, was about 2 years old I think.

And yeah, the rest of my system kept going, in fact, I didn’t even notice it for a month because I’d accidentally turned of email notifications!

GeorgeS
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GeorgeS

@Spec

You haven’t had any failures?

Mark H has had failures also. Luckily all of us are still on warrant. but it’s still a PITA changing it out. Especially in the summer.

Spec9
Guest
Spec9

No failures but my system has only been operational for just over a year now.

I think (hope) they changed the parts that they use such that the newer inverters should be a bit more reliable. One of the reasons I went with Enphase is that they have the longest history with microinverters so I figured they would be in best shape to have the bugs worked out.

ModernMarvelFan
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ModernMarvelFan

I thought you can just do this by hook up a generator to your panel (2 phase) and then cut the main breaker (to cut the power from the grid). Then you already have a local system.

Based on the generator/inverter, it should keep your house at a steady 240V that should turn on the grid tied solar inverters.

Am I missing something?

GeorgeS
Guest
GeorgeS

@MMF
It’s not that easy as far as I know after researching it. Your idea is exactly what I thought initially.

Not sure I’d want to try it.

Bill Howland
Guest
Bill Howland

I have a cheapie ($400) portable 5000 watt chinese generator I bought 8 years ago for a big systemic power failure at the time. The problem with my 2 inverters is that, although having a wide voltage range (200-260 volts), they are very tight on the frequency, much more stable than the speed or my generator (its an old-fashioned setup so the new inverter machines may not have this problem). I’d expect the inverters constantly to crap out on over frequency, but, with the cars already charging on the generator, this may be enough load on it to allow the 2 inverters to attempt to parallel themselves back onto the generator..

Unfortunately aince my panels are implemented with a Service Entrance Line side tap, I’d have to jerryrig the wires to attempt this, so that’s a Definite Maybe.

ModernMarvelFan
Guest
ModernMarvelFan

Well, I know people have long been hooking up their 240V generator to their own house while cutting the main breaker. It has shown that it would power the rest of the house if there are enough current coming out of the generator.

Now, if the grid tied solar is depending on the grid to “sync” the phase of the 240V, then you should ONLY need a somewhat sinewave on the local system to keep the inverters on.

I have the solar panels (SMA inverters). But I don’t have a 240V generator. If I do, I would definitely give it a try…

ModernMarvelFan
Guest
ModernMarvelFan

Oh, my solar inverters just tap into my main panel (after the main breaker) with two 30A 240V breakers. So, if I can tap a somewhat “clean/accurate” 240V signal onto my panel with a steady 240V, I don’t see why it can’t be done…

Spec9
Guest
Spec9

This is what I’m wondering if the new Enphase “AC battery” will do. Can it disconnect from the grid and provide a synthesize 240V signal such that the microinverters operate when the grid is down. If so, that would be a great plug & play product for microinverter people that want to have battery back-up.

I would like to know that such a product is available if I wanted it but as long as my local utility is grid-tied friendly, I seen no reason to buy it.

But if the local grid started getting hostile to grid-tied solar PV systems, it would be nice to know that their is an easy option for going off-grid. Speak softly and carry a big stick.

GeorgeS
Guest
GeorgeS

@Spec

Spec quote:
“This is what I’m wondering if the new Enphase “AC battery” will do. Can it disconnect from the grid and provide a synthesize 240V signal such that the microinverters operate when the grid is down.”

Of course it can. That’s it’s purpose. but it costs 2500$

MMF is wondering if you could just back feed a 220 sine wave and fool the micro’s to come up.

ModernMarvelFan
Guest
ModernMarvelFan

Yes, exactly.

Or, in this case, fool it with a real generator which will be under light load while provide the voltage and frequency.

I assume that inverter only needs the grid for voltage and frequency so it can be lock onto the same frequency with their own power.

I don’t see logically why it can’t unless the generator (external signal) can’t produce the quality of the signal required (frequency stabiltiy and phase stability between two phase required)

GeorgeS
Guest
GeorgeS

@MMF

best I can determine you can’t dead head the inverters.

They need to have a load.

I’m not sure though.

Spec9
Guest
Spec9

It is not clear to be that it will allow the solar PV microinverters to operate when the grid is down. It might just be a thing to do some time-of-use rate gaming and a short battery back-up if the grid goes down.

QCO
Guest
QCO

The author’s mistake was to deploy those silly Enphase inverters in the first place.

A central inverter would have given him the flexibility to do several things, including a DC tap to charge a separate battery and inverter set or an integrated grid tie inverter with battery bank changer that are now becoming available.

The best solution for him now is to charge a set of batteries from the grid (which you are solar charging anyway via grid tie) and use them with a dedicated inverter for key loads during outages. Maybe put up an extra panel dedicated to the battery bank, if you feel the need to last a bit longer.

But if you want the “whole house” UPS solution, get rid of the Enphases and build a float charge system using conventional charge controller, battery and inverter components.

GeorgeS
Guest
GeorgeS

Forgive me.
I’m not as smart as you.
I put my system in 5 years ago and didn’t know.

I’m actually agreeing with you if you would read what has been said so far and not trying to prove how smart you are.

Spec9
Guest
Spec9
Meh. I’ve previously installed a central inverter but went with microinverters instead for several reasons: 1) It is easier to install. No dealing with High-voltage DC. Very plug & play. 2) Works great with shading . . . shading on a panel only affects that panel. However, situation can be now be remedied with DC-optimizers I guess. (They were not available when I designed my system.) 3) Easy to expand the system. I designed my system such that I can easily add another 8 PV panels or so if I want more power. 4) Any single panel or inverter that dies doesn’t take out the system, it only takes out that one panel. 5) My local building department demanded DC disconnects on the roof. I wasn’t sure what to buy for that and how I’d install them. And since my system is split into two parts, I’d need at least 2 of them. And then I’d end up with these ugly switches on my roof instead of my nice clean install that uses Solodecks so all the conduit & wiring is hidden in the attic. 6) I’m guessing it is a bit safer to have 240VAC than 400+VDC running in… Read more »
GeorgeS
Guest
GeorgeS

Happy Thanksgiving all you PV freaks 🙂

David Hrivnak
Guest

Another option is the newer SunnyBoy SMA inverters have a switch to put them in stand alone mode. Each inverter can output 120V 1500 watts of power when the sun is shining. I tried it and it was able to charge my EV and keep the refrigerator running. It is isolated so the line-men are safe.

io
Guest
io
CAUTION — George, your planned rewiring (fig 10) is NOT SAFE, on many levels. I completely understand your desire to add a low-cost minimal emergency power capability to your grid-tie PV system (in fact, I’m planning the same stuff), but let me describe a few safety issues I see here: 1) You effectively connect many PV modules directly in parallel (all the time, not just when micro-inverters are off). Even if you size the additional DC wire correctly, the module’s aren’t: their connectors, wiring and innards can usually only take 15 A max. If a short develops in one module, it will be sinking the current from all the remaining ones. Very unsafe conditions like overheating conductors or arcing will likely result. For that reason, you must not put more than 2 modules in parallel without protection diodes or fuses for each module. 2) You also connect multiple micro-inverters’ inputs in parallel. They are absolutely NOT designed to be wired this way. Even if somehow they manage to not interfere with each other (I suspect that at the very least their MPPT is going to get seriously confused), feeding them multiple modules violate their specifications. A malfunction like an internal… Read more »