# If SHTF, can grid-tied panels be switched ...



## DryHeat (Nov 11, 2010)

If SHTF, can grid-tied panels be switched to feed more limited inverter/ battery emergency usage?

We've contracted for a robust 8KW grid tied solar system, 32 x 250W panels each with a microinverter. As long as the grid functions it'll be peachy as our battery. The contract looks to require we maintain the panels and leave them connected for 20 years, again, that's fine. Unless. 

I've looked over thread titles going back to the first of this year and can't spot this particular question, so if anyone can link me to an existing discussion, that'd save time, maybe. If not, what exactly could I stock to jerry-rig DC output from some of those panels to charge some deep cycle batteries then use them, likely with several inverters and extension cords, to power up more important household devices like PC, small TV, radio, lights, maybe a freezer/fridge intermittently? I suppose I'd need a true sine wave inverter, or two, as well as several 1-3KW cheaper ones.

If the grid is dead, is it easy to access panels upstream of the microinverters and divert output to charger -> freestanding batteries, or are there serious issues in play there? Has anybody developed something like a solar bug-in bag list of wiring gauges, lengths, (charge controller?), battery charger(s), deep-cycle batteries, and inverters for such purpose? I think the contractor would help me out with anything that wouldn't violate codes or raise flags with the power company, so can microinverters be connected in such a way as to facilitate switching panel output to such emergency use? I'd anticipate leaving the panel array all in place on their mounts but running lines away to the opposite side of the house for charging the portable batteries, and not trying to have a hybrid system feeding in-wall house wiring.


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## TnAndy (Sep 15, 2005)

Yes, it can be done......but it ain't easy or cheap. It's called AC coupling. 

Outback recently came out with equipment designed to work with grid tie only systems. You can take a look at it at this website:

http://www.oynot.com/product-pages/solar-ac-coupling.html


(At the top of the page, it says 7kw.....but then on down in the description, it clearly says 4kw.....so I don't know what THAT is about.....)

As you can see....it ain't cheap. AND the 305amp/hr battery bank isn't a lot of reserve......few hours or overnight....OK.....but a day or two, and unless the sun is shining bright, OR your loads are very small, you're gonna be out of battery power.

ALSO, it state you can't feed more than 4kw into the inverter, or risk burning it up.

So you'd have to set up some kind of switching to cut out half your 8kw system.

The advantage of this is you wouldn't have to try to "Afro-engineer" connections ( your micro inverters are designed to have the panel leads plug right into them, and their output feeds to a special cable on the 240v AC side ).

Has anybody developed "solar bug in bag" ?? Ahahahahaaaa....I seriously doubt it. In fact, I'd be willing to bet there are a handful of installers that could even pull off re-rigging a grid tie only system to use off grid. I am, however, one of them 

My own system is a "split" system. My first 6kw I set up, ran thru a pair of GTFX Outback inverters with 3 charge controllers, and a battery bank. It's grid tied normally, but in a grid down situation, the GTFX inverters drop out ( to meet UL1741 standards about back feeding ), but a second set of contacts in them close, diverting your solar power to wherever you direct it. That would be a manual transfer switch and a subpanel of critical circuits in my case.

THEN I added another 5kw of Enphase micro inverter based, grid tie only, arrays that are connect to feed the grid only.

Now my personal plan is IF the grid goes down and looks like it's not coming back for a long long time ( like the SHTF ), then I'll reroute the wiring of 5kw of micro inverters to tie into the output of the Outback inverter ( fooling the micros into 'seeing' my mini grid ) and I believe I can get them to give up their 5kw to me.


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## Jim-mi (May 15, 2002)

A whole lot of people are going to be mighty unhappy when the grid goes down.
All that hardware sitting there doing nothing.
All because they took the cheapest route to solar energy.

And they will not be happy campers when they (grid tied only) find out what it will cost to retro fit their systems.
And if it is not done with good quality equipment---not the truck stop junk--- many parts of their system will go up in Smoke.................

There are darn few DIY'ers who could properly retro fit a system.

Dry Heat; you best check with your contractor/installer . . . if You modify your system will that void contracts . .??
And it you have a contractor who doesn't know how to do AC coupled / battery backup . . . . .your in trouble.


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## DryHeat (Nov 11, 2010)

Thanks, guys. Gives me some informed details to go over with the contractor. I'm sure it would be violating the contract to do any jerry-rigging for a few days' or weeks' of grid collapse that would be expected to be back up solidly after a short period, like in NO after Katrina, for example. I'm thinking in terms of if things descend into a "World Made By Hand" for many years, what gear to be sure to have for scavenging function from panels with any contract issues long voided by absence of the utility itself. Sounds like something like another $10K, and maybe without any 30% fed tax credit, would be the add-on cost if not done as a fully hybrid setup from the start.

If I could drive 50 miles and shuttle deep cell batteries for charging elsewhere, or run a generator with gasoline, even if, again, a long distance and high price to buy any, or charge them during a rotating blackout situation, that would be fine, I'd not think of touching installed solar panels. I feel like "collapse" worse than those situations isn't certain over the next decade or two, but possible, so I'm trying to game out the extreme contingencies.


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## SolarGary (Sep 8, 2005)

Hi,
I have a setup that goes from a grid tied (Enphase inverters) to an off grid system with a battery pack for emergencies.

My system uses the battery pack in my ElecTrak garden tractor (six golf cart batteries), an Xantrex MPPT charge controller ($450).

I basically rehookup 6 of my 10 PV panels into two series strings that then tie into the charge controller.
Power is supplied to the house using the Triplite charger/inverter that I use to charge the batteries on the ElecTrack from regular 120VAC power during normal times.

I stow all the stuff in the barn and when there is a power outage, I drive the ElecTrack to the PV array, hang the charge controller (which is in a plywood enclosure to protect if from the weather) on a hook on the PV array supports, rewire the panels (which is all done just moving a few plugs around), hook up the extension cord and run it to the house. There is really not a lot to it -- takes less than half an hour.

This provides enough power to run a few thinks like the frig, furnace, TV -- but maybe not all at the same time. 
This setup provides about 5 KWH of usable power, and the 6 215 watt PV panels can recharge the battery pack on a sunny day. 

This is obviously just for emergencies and it involves some hands on hookup and monitoring, but it works fine for us -- especially given that we don't have a lot of power outages.

I also have a small generator for the lots of cloudy days scenario.

All explained in excruciating detail here: http://www.builditsolar.com/Projects/Vehicles/E15ElecTrak/Main.htm

Gary


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## DryHeat (Nov 11, 2010)

Update now, two months later. We have an 8 KW grid-tied system in place, inspected by the county and utility, turned on, and producing a nice excess of power beyond what we're using at present, given we aren't running AC now, nor space heaters though we may do that later to reduce natural gas use in the main furnace. The last two completely sunny days, peak production got up to around 6.5 KW around noon, with total daily in the 43-45 KWH range.

After multiple repeats of what I wanted to have as a backup, and why... for a longer grid-down situation than a genny could cover... my contractor finally "got it" and agreed to come back by in a while after getting things running with secondary plugs and advice and diagrams for what I was asking about. Essentially, I think what I'll plan on having on hand is the wiring (I have several tote boxes full of 12-16 ga extension cords bought at various auctions and yard sales), the connector plugs, 4 or 5 30 amp charge controllers (from eBay), plus 7 or 8 inverters running from 300 W up to 5 KW capacity with a couple of pure sine wave models included. The only thing I'll not try to have in stock is a batch of deep cycle batteries, though I'm figuring to go ahead and buy a couple more of those, maybe really top grade ones since all I have now are a couple aging ones of the economical Wal-Mart models. The gamble will be that any SHTF situation will give me personally sufficient warning that I can go out and spend the money for suitable batteries off the shelf, fresh.


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## Gray Wolf (Jan 25, 2013)

I think you're joking.


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## Jim-mi (May 15, 2002)

I think you are more than a bit misguided.
I have found that the majority of those "Grid tied" joker "installers" don't have a clue about what constitutes a good "Off grid " system.

Your gonna go get stuff just before the stuff hits the fan . ?? . . say that your kidding.
Since when does ANY of the potential grid killing events give any warning....????

Of course your idea to use your system when the grid is down is fine . . .but you will NOT do it with wally-farts batteries and truck-stop inverters.

Your thinking was flawed from the beginning when you signed the contract for a grid tied system only..........

Any reputable designer/installer is, for safety and liability reasons, not going to, over the internet, give you step by step instructions of how to do what you want.....
One misplaced wire will be the cause of a lot of smoke and fire......

And beware the idiot cowboys on the internet who think they "know how"

Yes there is a couple of us here on HT who know how to do what you ask....


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## DryHeat (Nov 11, 2010)

> Since when does ANY of the potential grid killing events give any warning....????


Plenty of them would. Pandemics, for example, develop over weeks to months before impacts would cause people to start sheltering in place and emptying just-in-time stocked inventories. A super-X rated coronal mass ejection that happened to be coming right at us like the Harrington event would have a solid couple of days' notice. I wouldn't expect there's *high* odds of an emp or Stuxnet virus/worm attack without foreign affairs and military activity ramping up worldwide from what's happening now. I'm not certain there'll be such a grid-down situation within the next 10-20 years, even. I'm not interested in living off-grid voluntarily, not in my main residence here, anyway. What I want to be able to set up is pretty much exactly what "SolarGary" posted, I didn't notice anyone saying his approach was a joke. Everything about prepping, to my mind, revolves around probabilities and cost/benefit analyses. I see a very low probability of a grid-down TEOTWAWKI situation without having time to stock a half-dozen really good batteries to rotate charging versus moving to several locations to feed inverters. I don't envision having household wiring powered at all, nor air conditioning, rather being able to run a fridge and freezer, lights, and some electronics like small TV, laptop, radio, with batteries that I can continue to recharge for months without worrying about fuel for a generator, though I may put a genny in place as a further redundancy, too. The idea of having a golf cart and using its battery bank for storage is one I figure to keep in mind in the near future as I look around at auctions, Craigslist, and such.


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## 12vman (Feb 17, 2004)

I don't understand why anyone would put big money into a battery bank and may never use it. The battery could set there for years without it ever being used! 8-10 yrs. goes by and you must replace the battery for what? A big investment on the thought of what if..

What if the grid was destroyed and down for a year or more? Who could scramble and find a bunch of batteries in a hurry? I don't believe that would be an easy chore because of the situation..

I don't mean to sound condescending but personally, I don't understand any "in-between" of being "on the grid" or "off grid". I can understand having a back-up for a short time outage to keep basic thing alive but what happens in a year or more if the grid is still down at night? (Maybe this should be another thread)


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## DryHeat (Nov 11, 2010)

> what happens in a year or more if the grid is still down at night?


That's what the batteries are for, whether the setup was initially grid-tied, or not, to begin with. Deep-cycle batteries stay functional with proper recharging for 4+ years, right? Same idea as prepping water-harvesting equipment, dry cell batteries, vacuum sealed seeds, fuel, antibiotics, clothes, and so forth. Eventually a lot of things run out or wear out but there's a transition period during which something like modest availability of AC electricity would help bridge the gap. I can see the point that one would've just wasted money if a bunch of batteries were bought then the grid just stayed functional, I suppose I'm fairly confident in my personal ability to assess whether a true collapse were approaching rather than just a bunch of hair-on-fire nonsense. I did take a close look at the Y2K concerns, for example, and more or less yawned about the idiocy about thinking critical systems hadn't been reprogrammed in advance. With a battery bank at the absolute top of the list, I'm also fairly confident I could find decent ones. That's a probability call on my part, and I agree I might be wrong. Well, *then* perhaps I could find a few later from people who'd been recharging them from generators and had run out of fuel.


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## farmrbrown (Jun 25, 2012)

Here's a suggestion for you for batteries.
Electric forklifts.

If SHTF, the forklifts wouldn't be much good to anyone anyway, and they might part with them, pretty cheap.


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## Gray Wolf (Jan 25, 2013)

If you're actually serious, you better learn a lot more about solar and electricity in general before you proceed.

You need more batteries.
You need fewer charge controllers.
You need fewer inverters.
You need wire/cable, not extension cords.


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## 12vman (Feb 17, 2004)

*"Deep-cycle batteries stay functional with proper recharging for 4+ years, right?"*

My point was would you have (or, plan to have) enough battery to operate your entire home system "as normal" if the grid was to down for a long time. Chances are you wouldn't..

I was blessed with 8 yrs. from a set of golf cart batteries. I believe I got my moneys worth from them. I used them daily, being I'm not connected to the grid. I took good care of them because they were my only reserve, not the grid..

If one didn't have enough battery to replace the grid as the reserve, I'm sure that there would be issues in the long term. Needing to be extremely ultra conservative with power would provide lots of grief, I'm sure, after living the comfortable lifestyle that one is accustomed to. Short term would only be an inconvenience..


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## Jim-mi (May 15, 2002)

After the fecal matter has hit the fan blades, "going around" and finding a set of--for instance--Trojan L16's just ain't gonna happen.
Afro rigging together assorted 2nd hand batteries is a really bad idea......


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## DryHeat (Nov 11, 2010)

Hey, look, I am NOT trying to plan to power my house as normal, in a grid-down situation. I'm looking to use a *few* of the large number of panels on my roof right now to charge a battery or two at a time, then move them around to needed locations in the house with an inverter for each location. This would be like buying a small stand-alone setup for a motor home or detached structure, like the packages sold by Costco, only having several of them available starting with the roof-mounted panels. I agree there are a lot of reasons including remote location (possibly due to cheap land prices for such), philosophical insistence on personal independence, and assessment that serious SHTF is surely immanent, for going the off-grid solar power route. I know that if you do so, or if you choose a hybrid setup that can be disconnected from the grid, you would be incompetent not to have a massive charge controller and inverter, heavy wiring in conduits, and battery bank (of all identical high capacity batteries) so you keep your wall wiring as power source.

I've chosen, partly for level of available finances, to go the grid-tied route. The question is how I can be fairly ready to rig up the equivalent of several of those stand-alone small solar aux power systems should something more than a few weeks' grid-down take place. (I am thinking more and more now that I should have a gas-powered genny to cover that "several weeks" grid-down scenario, so am glad to have had my thinking focused some by this debate.) That idea of scavenging electric forklifts for good batteries is one to keep in mind; I'm not very close to industrial and warehouse districts but there might be one in service here or there near me.


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## Jim-mi (May 15, 2002)

Your best plan now would be to find a competent designer/installer who does off grid systems.
And not the jockey who put in what you now have.

The off grid installer will see what you have and then be able to recommend the right equipment for an AC coupled system upgrade.


Forklift bats --that still have some life in them--are a reasonable deal, but you must locate---lift---transport---lift them, well before *everything* shuts down from the grid being down.. Some fork lift bats are upwards to 5000 lbs.


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## Gray Wolf (Jan 25, 2013)

Yes. Get on-site advice.

Use house wiring, one or two charge controllers and one inverter to power the 110 volt circuits in your house. 220 use is probably is beyond your system. 

You'll need more than a couple of panels and a couple of batteries. (We live off grid and use 8 panels and 16 batteries to live a conserving lifestyle.)

You WILL need a generator or two for backup and to power large loads. (We have 3 that we rotate usage among. We use generator for 220 loads - welders and for the well pump to fill our 1,000 gal holding tank.)

The charge controller and/or inverter will fail sometime, either minutes or years after you start using them. What then? (We have backup 'everything' setting on shelves in the shop.)

How will you get water?
How will you stay warm?
How will you dispose of sewage? Some systems require a pump.

Think, learn, plan, and only then buy.


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## DryHeat (Nov 11, 2010)

We have a septic system, gravity-fed, electricity is irrelevant to it.

We're in S. AZ, lots of mesquite wood, heat is nat gas so likely down if grid is off... and I need to make sure a battery + inverter can run the furnace fan and thermostat, but we could survive the cold that almost never dips below 20F, anyway, and is well above freezing for daytime. Cooling during hot days would be the real issue, and that would be back to fans with occasional use of a portable evaporative cooler unit, assuming we could spare water to run in it, which we might not, anyway.

Water would be the key issue. This is a desert. Private wells aren't allowed. Rainwater harvesting is fine, I have several adapter kits to divert flow from downspouts to barrels, and plan to buy a couple good food-grade 300 gal storage drums. A few years ago, I had a chat with some neighbors who *thought* they'd verified access during emergencies to a municipal water wellhead a couple of blocks away, and had bought a hand-operated pump they thought could bring water up at a reasonable rate. I'm skeptical of that being a viable plan to distribute to various neighbors, but anyway, people are thinking about such ideas, at least. Maybe 1/3 of the houses in the area have swimming pools, too. Long-range, though, there'd be zero chance of growing veggie crops due to water issues, other than maybe just a few container plants for variety mixed with stored and canned foods.

A *really* sustained collapse of services, for years, we'd be refugees, period, due to widespread water shortages, if nothing else. Household electricity supply wouldn't matter for that.

The contractor who installed our grid-tied system also does off-grid and hybrid systems.


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