Off-the-grid with grid-tie inverter?

[NiHaoMike]

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.

[Xringer]

Originally Posted by NiHaoMike

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

[NiHaoMike]

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

[Xringer]

This idea has been festering all year long..

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

[Xringer]

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..

[Xringer]

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

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

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..

[st2288]

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.

[Xringer]

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..

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.

[Xringer]

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)

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.

[gbbengi]

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!