Off-the-grid with grid-tie inverter?
 

http://i46.photobucket.com/albums/f1...ar/diagram.jpg


http://ecorenovator.org/forum/applia...-inverter.html


http://ecorenovator.org/forum/solar-...-inverter.html


If this configuration would actually Start up, it seems like the 12VDC-to-120VAC inverter
would be using very little from the battery, since the grid-tie inverter
would try to make it's voltage just a tad higher..

Anyways, I was thinking this might be the lowest cost way to DIY off-grid power..

If it did work, you could stack the little 300 watt grid-tie (or Enphase) GTIs
and get some nice power-point-tracking from each panel.. :)


Comments please:

Thanks,
Rich

It looks interesting. But, in order for this setup to be legal, you'd still need some sort of disconnect going to your service panel. Or, are you thinking the grid tie will take care of that?

It would be cheaper to just use a regular inverter.

I'm thinking more along the lines of taking a couple of 200 watt panels camping with you,
or to some remote cabin site..

The idea here, is to use the much cheaper grid-tie micro-inverters, off-the-grid.

Or, maybe you have to do some light construction work, way out in the boondocks?
Haul out some 220 watt panels, a little power-box to hook up to your 12v truck battery,
connect up some panels and you could run small power tools and charge
up the rechargeable power tools on site. (If the sun stayed out).

Would not replace a gas generator, but might be good if you didn't need 5KW.. :cool:

I'm pretty sure that PV is going to get a lot cheaper, pretty soon..

You can, when the clouds come in.. :p

Of course, it would be even cheaper if you used a hand-cranked generator..

http://www.olive-drab.com/images/mep...and_01_700.jpg

If this setup is completely off grid why do you even need the grid tie inverter?

Because, they are compatible with many PV panels, cheap &,
they are scalable when used off-grid or with a grid-tie system..

Scalability is important if you only need (or can only only afford) a few hundred watts.
You can meet that need at a reasonable price with micro-inverters.


http://www.solartekenergy.com/images...oy_on_wall.jpg

http://www.powerinverter-kr.com/wbyy/grid/300Wgrid2.jpg

I was under the impression that grid tie inverters need to be connected to the grid to work.

Leo, Do you Know what the Gird is? Do you want to know the truth?

The answer, the number 60. As in 60 Hz. The voltage is 120 or 230.

So, as I've said before, if you can trick the GTI into thinking it's
connected to the grid, then it will work.. :D

That's why the 12Vdc-to-120Vac inverter needs to have a pretty clean output.

I'm pretty sure that my little modified-sine-wave inverter would NOT work. :(
But I'll bet an old UPS (computer back-up Un-interruptable Power Supply) would work just fine.

http://cdn2.overstock.com/img/mxc/09...pply_UPS_3.jpg
And, it has it's own LA pack!

I suppose that makes some sense. It just seems a bit more complicated than it needs to be.

Yeah, I guess it could be simpler..

The cheapest SunnyBoy GTI I've seen is over $1,000
SMA Sunny Boy 700U Grid-Tie Inverter, 700 Watt, 150, 200, 250 Volt
Putting out 700 watts (if you have 700 watts of PV panels).

For that price, you could get ten of the cheap Chinese 300 Watt GTIs (3,000 watts)..
If you had 10 panels, you could reap the benefits of power-point-tracking on ten panels..
And, all those panels could be of different brands & power levels.

I'll bet that SunnyBoy has to have the whole array coming in on one pair.
Meaning that a shadow one panel brings down the whole system power..

Put a high efficiency DC/DC converter on each panel. It would actually be more efficient that way.

Not if you wanted AC...

you are going to have issues if your PV systems output is higher then your demand as it's not going to have any load, the grid is acting as a load, back feeding a small inverter as a load is going to do damage, not sure how fast it will let the magic smoke out of the small inverter but it will happen, or fuses will blow, either way it will shut down.

If you have a few Enphase GTI AC outputs tied together in parallel,
what keeps them from destroying each other?

I do see what you mean with the excessive PV power.
The GTI will want to dump that PV power to the grid (or your fake grid), in the largest quantity it can..

Just thinking about it, it seems you would need your load,
be large enough to use all the power from the PV array
and a little bit of power out of the battery..?.


I think the Enphase monitors the AC line in small time slices and then
puts it's own replica AC on the line during it's output cycle.
That cloned AC from the Enphase is slightly boosted in amplitude,
to push power onto the grid.

The nice thing about resistive loads and some motor loads is,
when the voltage does up, the load draws more current (uses more power).
I=E/R

I guess my oddball configuration working is going to be very dependent
on the functionality of the GTI.. Those cheap Chinese GTIs might not
would with this kinda of scheme.

The voltage will stay the same and the amps will stay the same as well, that is where either the grid tie inverter will shut down or the sign wave inverter will burn up, the grid tie inverter is designed for unlimited demand, it's not designed to be limited.

That reminds me of a story my ECEN 441 instructor told. A contractor from NASA asked him about what power system to use onboard the space station. His response was DC. One company had tried to build a 20kHz power system and they could not get it to work properly. Then, based on the note the instructor wrote, another company built it on DC. It worked and DC is what they use today!

The answer seemed almost too obvious. Batteries are DC, as are solar panels. Electronics also run from DC. So why waste energy converting to AC only to convert it back to DC? Motors often run on AC, so use a point-of-load inverter that supplies exactly the right frequency and voltage needed at that time.

The main reason that utilities use AC is because very high voltage can be used.
High voltage and low amperage can deliver the power, to transformers.
(Without the use of monster cables).

Those transformers are about 99% efficient and can step-down the voltage so
we can use it in our homes.

DC melts transformers..

AC makes sense for long distances, but not for short distances. A few hundred or even few thousand feet is not considered long distance.

At the lower voltage ranges (that you might need in a house), DC voltage needs
a Large amount of current..

So, if you have a few thousand feet of wire, it has to be Monster cable..
Otherwise, it will have significant resistance..

Notice that voltage isn't a factor in this formula, P=R x I squared..
In other words, if you have some Resistance, the Power loss will go up with the square of the current..

That's why we no longer use any long low voltage DC lines..

When I was a young man working in Boston, one of the old Phone co. buildings had 110VDC outlets in the offices.
Once in a while, someone would plug in an AC device and watch it smoke..

HVDC is a better solution in our case. At the distances and power levels encountered in DIY solar setups, you don't use particularly high voltages. Common power semiconductors can handle them. Only when you go beyond the voltage ratings of common power semiconductors does AC start making sense. (IGBTs are commonly available up to 1.2kV, and virtually every DIY solar install is far below that.)

Note that virtually every modern inverter converts the incoming DC to high voltage DC before converting it to AC. And most modern power supplies convert the incoming AC to high voltage DC before stepping it down.

I did not know that.. How do they step up the DC to a higher voltage DC?

The only kind of inverter I've looked at lately just went from DC to AC..

http://www.researchcell.com/wp-conte...er-circuit.jpg

That's an old ferroresonant design. All the new ones are dual conversion designs.

Well folks, I'm back!
 

This idea has been festering all year long.. :eek:

I'm bidding on a PSWI (Pure Sine Wave Inverter) on Ebay.
PURE SINE WAVE POWER INVERTER 600 WATTS 12V DC TO AC - eBay (item 330505475020 end time Dec-09-10 18:00:54 PST)
I think it's got the guts to run one of my pumps. If it works out, I'll get two more.


Then, I recalled this old thread.. Why not try out my idea with this PSWI?
I could hook the GTI up to one 200w panel, fire up the PSWI, and see if anything started to cook..?.

If I control the amount of power going into the GTI, and the load on both inverters, I can't see why it would smoke..

Ideas? Comments?


Thanks,
Rich

Edit:
FOUND IT!! It does work!!

YouTube - Test Running small heater and drill on Battery threw inverter fed with grid ties

Yet another vid.
 

Here's the other Off-the-grid video DPDevil1 made..

YouTube - Sun 250 Watt Grid tie & Xantrex 3000 Watt modified sine wave inverter Tied

It's kinda funny that he doesn't seem to realize the implications of his discovery..

A very basic block diagram
 

http://i46.photobucket.com/albums/f1...r/blockdia.jpg

The actual schematic will be classified semi-secret, unit I figure it out.. :rolleyes:

I just heard the news. I won a pure-sine-wave inverter on Ebay..:D

I was thinking maybe I'll need to use the 500w tracking array, since it has
higher output voltage. Which might be needed for the 48 volt batt.

The little sine-wave inverter will use one battery and the PowerJack GTI
will be connected up for 36 or 48 volts, what ever works better.
When I test the theory, I'll just use one 200w CS6P-200 panel on the GTI.



Edit:

I wonder if the DPDevil1 off-grid method would work for those folks who have
20 panels and 20 Enphase inverters on their roof, but can't get a watt out of it,
if the grid goes down on a hot day.?.

What if the black-out went on for a few days??
(In 2009, some people around here, lost the grid for a month).

I wonder if they would do something illegal?
1. like opening their main breaker
2. opening ALL their breakers
3. connecting the output of a 220 generator or 12v to 220 inverter to a 220 outlet?
4. and then close a few breakers, where they needed some back-up juice?

If those Enphase units woke up, that could be pretty sweet.. ;)

I wonder if they would do something illegal?
1. like opening their main breaker
2. opening ALL their breakers
3. connecting the output of a 220 generator or 12v to 220 inverter to a 220 outlet?
4. and then close a few breakers, where they needed some back-up juice?

If those Enphase units woke up, that could be pretty sweet.. ;)[/QUOTE]

I dont see why it will be illegal since you cut off to the grid. I know that how people hook up their generator. The problem will be where will the excess power goes, when you use less than the solar inverter output.

I think it's against the law to self-power your house, without an approved change-0ver box installed.

Otherwise, some forgetful goof might go down and reset the main relays,
BEFORE taking the generator off line. Which could be shocking to the
NStar lineman working down the street..

I think most people just plug in a lot of extension cords and wouldn't even
know how to go off-grid any other way.

Up in NH, after the days turned into weeks of no power, the Lowes
and Home Depot stores ran out of 220 plugs & sockets for generators.

So, it seems that a bunch of folks were making Suicide-Cables.
(Cables with a male plug on both ends).

~~~

When I was a sailor, we would tape warning signs over the open breakers and the control
panels for the Radar, to keep from getting zapped with microwaves
while painting near the antennas.
But there were times when it didn't work.. We would be up there painting
and suddenly we would get radiated by some dimwit.. (Non-reader?).

~~~

"The problem will be where will the excess power goes, when you use less than the solar inverter output."


If the GTI is taking 800w off the batteries, after a short while, it's going to drop the bank voltage.
The charger is going to see that low voltage and start charging the bank back up.
It's going to increase the charge current (most likely in bulk mode), which is also going to be feeding the GTI.

I think the mail problem is going to be, limiting the amount of load that I put on to the inverters.
Since I don't want to run my bank down too low.

I don't want to try to run my Chinese GTI at 1200w.. I think 1kw might be
it's max safe limit.
So, I'll need to measure each load's worse case, making sure the sum is less than 1kw..
I think the system should be able to handle some motor start surges, if they are short..

The little one looks like it's got some good specs..

Specification:
1)Model: NC-600-P
2)Output waveform: Pure sine wave
3)Continuous power: 360-400W
4)Surge power: 600W
5)Input volt: 12V DC
6)Output volt: 110V AC
7)Frequency: 50 / 60Hz
8)Efficiency: > 86%
9)No load current draw: < 0.45A
10)Automatic protection: Overload, Short circuit, Over thermal ,Fuse ,Under/Over Volt
11)Operating temperature: -10° ~ + 50° celsius
16) Battery chip cord length: 60cm


The Powerjack GTI guys tell you NOT to connect a battery.
It will get discharged VERY quickly into the gird..
Careful load management is the only way this scheme is going to work for me.
IF I'm lucky, it will work.. :D

My theory is:
The GTI will supply the load, as it's syncing with the Sinewave inverter.
It follows the frequency and phase, one for one.
And it will increase it's voltage a bit, to dump more power
(that's it's getting from the panels and battery bank).

But, it's got an upper limit. It will not just keep on kicking up the voltage,
into a light load.
At higher voltages, the loads will consume more, and it will be fighting
the Pure sine wave, trying to boost it's fixed voltage higher.
But, it should self-limit somewheres under 130vac. Maybe lower.

Well, long story short, the little pure sine wave inverter didn't hold sync with the 1200w PJ GTI.
It would work for a while, but then drop out randomly, 1 to 3 times a minute. (IIRC).

So, I have not done anything with the 1200w GTI for months..

Then this week, I figured that two of my new Canadian panels in parallel might supply
200 or 300 watts, even with their low voltage (28v). In series, the open voltage (72v) is too high.

So, today I hooked up the panels to the GTI, and connected the AC output
to the AC output of my 2500w MSW inverter, that was running this PC.
(and a few other small loads).

At first, there were 3 to 4 amps of DC going into the MSWI from the batteries (48v).
But within 15 seconds, the GTI started pulling in PV power.
It took over running the 300w house load (this PC too).
I checked the MSWI again, the current was 0.07 amps. (That's it's idle draw).

So, it does work. The MSWI was providing a master AC signal to a GTI
and it was producing pretty good power into a medium load.

After about an hour with the MSWI & GTI tied together without any smoke,
I figured the GTI's pure sine wave was filling in the gaps in the MSW waveform..
And then, I connected the O-scope.. WT heck? It was still a MSW!!
The GTI is copying the MSW waveform perfectly!!

I was hoping that some of that Sine wave would show up on the AC line, but no luck.
I just ended up with a really powerful MSW system (2.5 + 1.2 = 3kw) :mad:

When I added another 150w to the load, the panels weren't up to it.
They were doing their max, so the MSW started using amps (to make AC)
and the extra load was fed.
I assume that up to 3kw of load could have been connected..


If someday, I do get a larger PSWI, then I'll be able to connect the
1200w GTI with it, and it should sync up and make some nice sine waves.

I'm also thinking of hacking the 1200w GTI, by adding a 60hz sine wave
source signal that would trick it into becoming a stand-alone solar PSWI.
Likely need a schematic for that hack.

working on my off grid
 

Hello all,

First post! Yup, I'm a newbie! :)

So, here is the deal. I built myself a small sweet little battery back up bank. I am currently disconnected from local utilities, so I am technically "off grid".

Here is my video: Never mind, it wont let me post my you tube video. But if you want to find it, go to you tube, and in the address bar add this "watch?v=_Ryw-6R0l9o"

I was looking into purchasing one of the tie in inverters and "tricking it" into thinking I am on grid, I don't need it to do much, basically just power on bathroom lights when needed, and also outside lights for a couple hours per night so it looks like I have power to my neighbors! LOL :) (every bulb in my place is 10 watt energy star spiral)

I do have a smaller set of solar panels which I will be adding to next week, also will be getting a small wind turbine.

What is the easiest way to set it up so that I can minimally use the household wiring that I would normally be using everyday anyway? I thought about the "suicide cable" and turning all circuits off but one and putting a protective harness on the extra male end to keep it plugged in, but I was told this could still start a fire through reverse polarity, hence the reason I was looking to use the GTI-because it has reverse polarity protection.

Thanks for any help I can get!

A cautionary tale
 

My GTI experiments have been terminated, after my last mishap with a new inverter.

This summer, I purchased a Chinese 48vdc 1500w 120vac 60hz Pure SineWave inverter.
The PowerJack specs said it would do 3,000w peak load.
I found it would beep and shut down, when my new dehumidifier compressor came on.
Sometimes, it would come back on, and sometimes, it would stay off.

So, I decided to try beef up the sinewave output by adding the 1200 GTI output to the 1500w Sinewave inverter.
Wow, 2700 watts total.. But, not really. Since the 1200w GTI was connected to 800w of panels. (4 in parallel).

Anyways, it worked fine for hours. Then suddenly the (PowerJack?) AC voltage started increasing.
It hit about 150 vac, in a matter of seconds. Before I could kill the load,
the Sinewave inverter popped it's fuses (and/or transistors), gave off a little puff of smoke and died.
I have not taken the time to open it and survey the damage.

Anyways, my curiosity about tricking GTIs hasn't been cheap to satisfy..
I did learn it's possible, but maybe too tricky for the average hacker.

Cheers,
Rich

Hello, I was able to watch your youtube movie.

In your video, I think you were charging your battery pack (from the grid) to use during off-peak hours.
I've never heard of that being a good solution to paying peak hour prices,
since charging up and then using a battery bank is very inefficient.
Way too many losses in that cycle.
When you include the price of the hardware (and periodic battery replacement), it's very expensive.


How much PV are you going to install? And how much power do you
plan to feed your off-grid appliances?

Unless you plan to use very few KW hours, going solar PV is going to be very expensive.
It's not something that most people would even consider, once they look at the cost.
Now, if you're rich, that's a different story. Since you would not care that
breaking even would take 20+ years.. :eek:

Small wind turbines are pretty much a joke, when installed on a typical home site.
Location, location, Location is everything. If you don't have to hang on to
your hat while outdoors, forget it.
If you are interested, check out the Fearlessthinker videos.
Car PMA Wind Turbine performance II - Reality check - YouTube

As for connecting inverters to your house wiring via an outlet,
that can be dangerous.. The reason Enphase and others does not sell
a plug-in-the-outlet inverter system, is the fact that it won't pass code. (In the USA).

Lets say, you plug in a 1200w GTI into a 120vac socket (rated for 15a).
And then started plugging in loads to that circuit, until it was sucking
in 1800w from the grid, and 1200w from the GTI.
Now, you have 3,000 watts, ruining on a circuit designed for 1800w.

But, you don't see the wire heating up inside the walls,
so everything seems just fine. Until the clouds roll in..
Now, your 3,000 watt load is going to be fed by the grid.
That 25 amps is going to pop your 15A breaker..
But, if there's a problem and it sticks?
There is a good possibility you will see some smoke..

Check out this site for more info.. Solar Electric Power Discussion Forum by Northern Arizona Wind & Sun - Powered by vBulletin

Got to run,
Cheers,
Rich

Hey Xringer, if you are thinking about parting ways with one of those inverters let me know. I could put it in my car. It's overpowered to be sure but the cig lighter is dead on my new vehicle and I'm just going to wire an inverted straight to the battery with a cable for a car stereo amp.

Good luck!

I'm hanging on to both of my 12V inverters. They are not only handy for the car or SUV,
I can also use them on one of my little 12VDC PV setups.
http://i46.photobucket.com/albums/f1...lar/2batts.jpg
These are fed by little 10w PV panels, but they do provide a bit of backup.
The black battery runs the bedroom LED lamp and the other is for Ham radio gear.


That 48Vdc sine-wave inverter might not be repairable.
I have not looked inside yet :eek: I'm glad it wasn't expensive!
But, when/if I get it going again, I will not be using it for experiments.. :o
It would be good for running small transformer power supplies, TVs etc..

Hi everyone.
Interesting discussion.

The problem that I have with proposed setup, is that my PV system is setup to a very high voltage (350V) per channel, thus getting it to the batteries is a bit of a problem with a proposed setup.

But, I thought to myself, why cannot I just use 240v battery charger from the mains (Australia), that is only running during a day (timer switch). Since the solar is channeled to the mains through grid tie inverter, I'll be able to charge batteries using 240v charger. I know it would probably be less efficient, but way less wiring.

Once the batteries are charged (and not used), the charge controller would not pull much from the mains. If there is a power outage, all I would have to do is switch off the master switch (so that voltage does not go back to the mains and no one gets hurt), and connect the battery>240v inverter to the batteries. Turn it on - presto! Grid tie will think that there is power, so will start using solar to 240v conversion, which will charge the batteries through 240v>battery charge controller (plus whatever else needs power around the house)

What do you guys think? I already have 3.8kW grid tie solar installed, the only cost would be the batteries, charge controller, quality 240v inverter and some wires and switches.

Sergey

(the only thing is that batteries must be charged before the blackout)

Like I said above, connecting a GTI (+PV array) to a Sinewave inverter (to fool it),
does work, but sometimes, it can go nuts on you..

You idea of timer/charging batteries during the day, right off your home outlets isn't bad.
Just to use as a backup supply during power failures.

Products Applications

http://www.apc.com/resource/images/s..._h_448x150.jpg

I've got a large Solar backup system (plus gasoline powered gen backup)
so that I can run pumps during a 2 or 3 day (maybe a week) gird failure.
Without power to my pumps, my basement can flood..
I know, it would be easier if I moved somewhere else.. :o

Have to read up more on the PV vs Sinewave inverter battle.
Backup is great, but I don't want to have 10 batteries charging "just in case".
I was thinking of having, maybe, just 1 or 2. Just enough to fool the PV inverter into thinking its connected to mains. Might need to put a large diode in between, so that power does not flow back into the sine inverter

Have a look at this. Too bad its only 120v AC, would have to find out if they make a similar
theinverterstore.com/the-inverter-store-product.php?model=pwric300012w#

Sorry for spamming... The more I read the more I post =)
The link I posted above, is for a great inverter, but it is Modified sinewave, not true sinewave =( Otherwise a great product.

What I am thinking happened to those Chinese "pure sinewave" inverters, was due to those inverters been modified, not true sinewave. Thus the intermittent results.

Since it's AC that's being tied together, adding a Diode, (which changes AC into DC) would likely cause a malfunction.