Author Topic: Grid Tie, Oh My  (Read 1517 times)

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OperaHouse

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Grid Tie, Oh My
« on: October 24, 2017, 07:56:44 AM »
Just a couple weeks before closing camp I bought six Trina 280W grid tie panels. Didn't
really need them, but heard rumors of future price increases and wanted to power more
things at camp without worrying about peak sun. With limited space I also needed to get
rid of older odd shaped 12V that didn't do much in the system and reduced packing density.

At the time of leaving, those panels only powered the dishwasher heating element and added
a little extra watts in the morning to get the fridge going sooner.  I had bought an oil
finned heater to take the bedroom up a couple degrees now that it was fall.  That experiment
was inconclusive as my wife opened the windows every day.

I asked the installer I bought the panels from if he had any equipment that was broken. He
gave me 16 enphase M215 grid tie inverters that had been hit by lightning.  Had hopes that
I could figure a common failure, dig into the potting and fix a few. Maybe come up with some
interesting application for them. Nastiest potting ever, couldn't even salvage the boost
transformer. Could only salvage the MC4 connectors from them.

Grid tie is one of those things I have been thinking about. You see those cheap non certified
units on ebay (and the rebuild kits for them). At least you can rebuild them. Seen some make
it yourself articles for them. One just bumped power at the peak of each cycle with a square
wave and another only bumped power on the positive half of each cycle. The assumption was any
motor would average out the power.

Random trolling of youtube the other day came up with this guy powering his house off line
with three 1,000W Chinese grid tie inverters. A horrible video, but most videos have ten seconds
of actual useful information.  Grid tie inverters have to see some power in order to operate.
He flashed up a scope image of a rather decent sine wave.  Then he flashed the waveform of
the inverter only. It was a MSW square wave!  Obviously a single kick is enough to start it.
Maybe the the three inverters fed off each other once they started each cycle. This is
something worth investigating.

The last week at camp I picked up a LG front load clothes washer. Their direct drive motor
uses only 280 W according to the service manual, easy enough for a small inverter. I was thinking
about feeding the raw panel string DC buss directly into an inverter and avoiding the battery.
Had hopes of running the washer directly off DC, but the washer's VFD doubles the incoming
voltage. Some kind of inverter would have to be used. The heater takes 1,000W and that could be
run directly off DC buss. Grid tie with a 400W MSW offers all kinds of possibilities. The grid
tie raw DC buss could still be powering my water heaters and the washing machine at the same time.
I'm seeing all new possibilities for integration and it still won't be conventional.




Bruce S

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Re: Grid Tie, Oh My
« Reply #1 on: October 24, 2017, 10:38:00 AM »
I haven't been able to push myself into getting one of those grid-tie inverters to play with.

Since these need to "see" grid to start, would it be possible to "start" them with one of the APC or similar UPSs that will start even with AC power?
The 1500XL we have will start without AC all-the while beeping, and the wave looks like a MSW , but maybe, just maybe this is enough to start those grid-tie units?

Bruce S
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OperaHouse

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Re: Grid Tie, Oh My
« Reply #2 on: October 24, 2017, 12:49:29 PM »
Stay tuned, we will find out. I just bought a 350W one on ebay CHEAP.  If a single unit will sync with a MSW inverter that will be great.  Given a dual conversion, efficiency is reported to be about 70%.  The real interesting thing will be what happens to the waveform when the consumed wattage exceeds what the grid tie can produce and it relies more heavily on the MSW inverter.  Still, it presents some interesting opportunities  to get power from the panels over a distance.  From looking at the videos I'll have to mod these units with bigger capacitors.  Everything needs more capacitors!

george65

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Re: Grid Tie, Oh My
« Reply #3 on: October 24, 2017, 06:39:26 PM »

I have read of using grid tie inverters off grid and controllers to facilitate that. not been able to find how to actually do it.
If one could set something up so something like a 2-5Kw inverter as installed on legit solar systems that could be triggered to run off grid, that would be extremely handy!

What do these grid tie inverters actually look for?  Mine appear to look at the AC voltage, frequency  RISO ( whatever that is? ) and what I think is earth leakage.  Being anti islanding they also cut back feed in a millisecond if the mains disappears.

joestue

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Re: Grid Tie, Oh My
« Reply #4 on: October 24, 2017, 07:06:45 PM »
any good sine wave inverter should be enough to fool them. they look for voltage every half cycle, that's one of the reasons why the power factor is less than 100%, more like 99.5%. note that the power factor and power factor due to harmonics are called the same thing but they are different problems. the grid tie inverter is in fact in phase with the line, but because it doesn't generate any power for a small fraction of the sine wave, you get the harmonic content that drops the "power factor" to about 99%. there is also residual pwm ripple that makes it through.

i would be very supprised if a msw inverter could work, for a couple reasons. one being the msw wave has no voltage at the "start" of each sine wave cycle, secondly most msw inverters can't back feed the battery they run off of.

a msw inverter feeding an LC resonant tank (could be as simple as an induction motor with enough capacitance across the line, or it could be a synchronous motor, such as a petrol generator) with an inductor between the LC filter or the generator, or induction motor, the inductor is needed because msw inverters can't tolerate any direct capacitive load. then you could use a cheap msw inverter to make a sine wave of a fixed frequency, and that should fool the grid tie inverter.

but since you can't backfeed the battery, the grid tie inverters may shut down due to overvoltage if you don't have a sufficient load to draw from them, as they push the line volts up too high.

OperaHouse

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Re: Grid Tie, Oh My
« Reply #5 on: October 27, 2017, 08:44:18 AM »
You have to have guts to plug one of these in!  Got my grid tie inverter arrived yesterday. 
It was the typical ebay "Works, just missing a screw." It was in like new condition and rattled.
Never did find out what that was. No obvious shorts or burnt components.  Someone tried to
fix it, but they never got as far as lifting the board.  Almost a virgin. Notice long black
vertical blobs from lower left of the transformer and fan.  This is where a 4,700uf 50V
capacitor should be. Reports are these blow all the time since they are no bigger than your
pinkie. They tried surface soldering some wires from the board to a replacement cap and insulating
them with this goop. That cap was nowhere to be found. Pretty bad job of soldering.

Not shown in the photo, hard to see even with the naked eye, is a #30 wire grounding the copper
shield on the transformer. Wire this small is hard to use in manufacturing. Cost is not likely the
reason. It probably acts like a fuse should insulation break down from a lightning surge on the
power line.

I just bought 400 electrolytic power capacitors.  I'm waiting for those to show up. They are triple
the physical size and 1/4 the capacitance.  Two in parallel will perform much better than what
was in there.  It will take a couple of days anyway to get the courage to plug this into the grid.


OperaHouse

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Re: Grid Tie, Oh My
« Reply #6 on: October 27, 2017, 01:27:53 PM »
Well that wasn't fun.  I temped in a capacitor and hooked it up to the grid with my XANTREX HPD30-10.  Seemed to be operating normally. At about 29V and 5.9A the power supply started buzzing and then dies.  Must have sent something nasty back down the line.  You can short this supply forever at 10A and not do any damage.

OperaHouse

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Re: Grid Tie, Oh My
« Reply #7 on: November 22, 2017, 03:48:18 PM »
Got my two SUNIVA 280W solar panels today.  Been buying up broken grid tie inverters and sine wave inverters.  Now I can start doing experiments with water heating and feeding power to the house when energy use is sufficient.  Don't want to set off any alarms by feeding energy to the grid.  Don't know how smart my meter is, but it is internet connected. Will be developing a grid tie controller to switch the GTI on and off.  With the number of cheap GTI out there that have gone bad, they don't seem like a good investment for most people.

clockmanFRA

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Re: Grid Tie, Oh My
« Reply #8 on: November 23, 2017, 12:41:49 AM »
Hi Opera House,

Its good to see another using old GTI's.

It will be interesting to see how you control yours.

Here in Europe there are good quality used/second hand working GTI's for sale, around the $40 to $200 depends on the kW. Folk here upgrade to a bigger PV system and hence their old GTI is just scrap value as it can not be used on another official system

I tend to go for the LF types, has a toroid inside, and a certain brand as I have the internal parameter re-set codes. Re-set mine so they start up within a 10 second period, so my batteries take the short time loads.

My 4 GTI's, under 3kW rating, are operating on my OzInverter Mini Grid, and I allow a little feedback from the GTI's to backcharge through the OzInverter to my battery bank.

When the AC voltage, domestic house supply,  on my mini grid climbs to a pre-set selected voltage, ie I am not using the power produced, each of my GTI's shut down in sequential order.

So you will need to really carefully monitor the Incoming AC grid and constantly compare with what you are actually using.

At .....  http://www.thebackshed.com/forum/forum_posts.asp?TID=9903 several methods are being used with the GTI's, and some experiments by 'madness' regards controlling the HF, high frequency, no torroid, GTI, and some interesting Blow Ups!.

1. My method which is bang bang when the AC voltage rises on each GTI, although with the latest OzInverter AC control, this may not work as the AC is now rock steady!.

2. Controlling the DC from the PV panels coming into the GTI by monitoring the DC battery voltage, ie a battery charger.

3. Monitoring the AC voltage and allowing certain amount of power back to the AC mini grid.

4. Monitoring the DC voltage and allowing certain amount of power back to the AC mini grid.

As you can see with the Backshed forum guys, they are heavily into using Arduino/Mega coded systems.

Hopefully some of the comments may help you.

My coding skills are non existent, yes I can change the speed of the blink, but that's it, so I will watch your endeavours with great interest.

Would be nice to see a simple, robust, cost effective GTI controller out of the box, so to speak.

« Last Edit: November 23, 2017, 12:46:17 AM by clockmanFRA »
Everything is possible, just give me time.

OzInverter man. Normandy France.

3off Hugh P's 3.7m Wind T's (9 years).  .. 5kW PV on 3 Trackers, (5 yrs) .. 9kW PV AC coupled Used/SH GTI's, on my OzInverter created Grid, and back charging with AC Coupling to the OzInverter to my 48v 1300ah batteries.

OperaHouse

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Re: Grid Tie, Oh My
« Reply #9 on: November 25, 2017, 08:56:42 AM »
Mistakes will be made.  Lessons will be learned. Good thing these broken ones are so cheap. Managed to fix everyone so far. I find the idea exciting that I can put a GTI right at the solar panel and send high voltage 160 feet to the garage and minimize losses. There will likely be problems having multiple GTI on just a 300W sine wave inverter with very little load, even with automatic dump load.

Bruce S

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Re: Grid Tie, Oh My
« Reply #10 on: November 27, 2017, 07:05:31 AM »
OperaHouse;
Have you looked at the sine wave of these? I'm curious .
Thanks
Bruce S
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OperaHouse

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Re: Grid Tie, Oh My
« Reply #11 on: November 27, 2017, 08:48:49 AM »
A long time ago, I built everything from scratch.  A few years back I started buying circuit boards to populate and modules. Never seemed to have the time to make a cabinet so I started buying broken things.  Not that hard to fix and when done I had a case and was finished.  Now I just bought two new GTI for less than the price of shipping a damaged one to me.  I'm becoming irrelevant.

Haven't gotten around to testing though I have two working units I would have to sample the current going into the grid and the grid could have 3% distortion.  I've just started heating water directly with panels.  560W of panels can put next to nothing into the tank with a direct connect to element.  It is as bad as George found.  The self powered wattmeter only gets enough voltage to run about 3 hours.

Bruce S

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Re: Grid Tie, Oh My
« Reply #12 on: November 27, 2017, 12:06:35 PM »
The water heating idea is a good one, but because of the nature of the heating elements ; I'm thinking that most of the power is being dissipated slowly which won't actually heat the water due to it's ability to loose the heat quicker than it can store it.

Wouldn't it be better to slap a high current amount of heat all at once rather than a slow warming trickle?

Bruce S
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OperaHouse

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Re: Grid Tie, Oh My
« Reply #13 on: November 27, 2017, 02:55:23 PM »
It is finally running.  At 4:40pm with the sun behind the trees I am still putting 3W into the tank. A half hour earlier I was putting in 22W.  At 2:30 with direct connect the heater would have been dead.  The tank loses about 65W an hour.  Everything you put in subtracts from that, conservation of energy.   A heater running at lower power density will never develop scale.  260W is about the maximum I can get out of the current heater element which is 240V.  That may be ok even though I have a 120V element here that will double that.   I have a 300W grid tie I want to hook up that can see a max of 60V  The water heater will act as a GHURD type shunt regulator to keep the voltage within spec.  My HPWH only costs 47 cents a day to run.  Can't save any money putting energy into that.  The grid tie is the way to go and part of that energy can run the heat pump for twice the effect.
« Last Edit: November 27, 2017, 03:03:39 PM by OperaHouse »

JW

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Re: Grid Tie, Oh My
« Reply #14 on: November 27, 2017, 04:06:49 PM »
Just as an aside we are aware that inline image posts are not working. At this time pics will only display under the post.

were working on this and its a temporary condition. There are some other modifications not working as well, 12 to be exact.

This will be fixed soon

petect

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Re: Grid Tie, Oh My
« Reply #15 on: December 08, 2017, 06:59:07 AM »
Hi all
I like the idea of saving $$ by buying a quality used grid tied inverter and “tricking “ it into working off grid. I’ve looked on ebay for used GTIs, but haven’t found any. Maybe they’re there and I just don’t recognize them. So, I would really appreciate it if someone would be kind enough to point me to a couple ebay adds for used GTIs/ That might help me know what I’m looking for.
Thanks in advance………… Pete

OperaHouse

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Re: Grid Tie, Oh My
« Reply #16 on: December 08, 2017, 10:02:49 AM »
After a month of looking for them, I'm awash in grid tie inverters.  Of course all of mine were broken except for two I just got from POWERJACK.  Well they said they were new if fans coated in dust is new and it is the year 2012.  These had been return/repair units with scratches.  I could complain, but I got the units for just about what I pay for shipping of a broken unit.  All these units were 12V and I'm trying to find one that works with my two grid tie panels, just out of the voltage range for standard units. These are going to force me to keep my 12V panels at camp.  I've just started testing these units and often the capacitors have issues even if they work. The cheap ones are a con.  The tested efficiency with a battery or power supply is not what you will get with a solar panel.  You get wild voltage swings and the cap is just large enough to keep it stable. This high ripple current many times the rating of the capacitor is the reason they fail in a couple years.  The actual failure may not even be casually noticed. These units need a large external capacitor bank to make them efficient with a panel.  I estimate you get a 30% extra loss with a panel.

Grid ties are still a little hot to be on the market used except for failure.  I just put ebay on automatic email notice and wait.  I've bought them that they said were working and they were missing parts inside.  It is still the wild west. Don't run one beyond 50% of rated power unless you want to add fans and they all work better at the very high end of the voltage rating.

clockmanFRA

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Re: Grid Tie, Oh My
« Reply #17 on: December 08, 2017, 01:18:22 PM »
Giving my secrets away.......  :)

I hunt for GTI's by manufacturer most of the time.

I also find folk listing them under 'Solar Inverter' etc etc.

Here's a typical USA listing, obviously for USA voltage/HZ, but that is a bit pricey for me, here in Europe it would be half that, but you get some idea.

https://www.ebay.co.uk/itm/SMA-Sunny-Boy-SWR-2500U-240v-Grid-Tie-Inverter-30-day-Warranty/322830249665?hash=item4b2a2eaec1:g:uQ4AAOSw161Z4qWT

That GTI is a Low frequency, and has a toroid inside.
Everything is possible, just give me time.

OzInverter man. Normandy France.

3off Hugh P's 3.7m Wind T's (9 years).  .. 5kW PV on 3 Trackers, (5 yrs) .. 9kW PV AC coupled Used/SH GTI's, on my OzInverter created Grid, and back charging with AC Coupling to the OzInverter to my 48v 1300ah batteries.

petect

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Re: Grid Tie, Oh My
« Reply #18 on: December 09, 2017, 07:20:52 AM »
Hi Guys
It looks like I'm not finding lots of used GTIs  because there aren't a lot to find. First, I'm looking for a quality 2 - 3 k inverter that I can count on to work. After that I might be willing to look for GTIs to play with.
clockmanFRA   Don't worry. Your secret is safe with me.  ;D

Thanks
Pete

george65

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Re: Grid Tie, Oh My
« Reply #19 on: Today at 04:30:16 AM »
Hi Guys
It looks like I'm not finding lots of used GTIs  because there aren't a lot to find.

I think it depends on where you are.
The one thing we her is OZ seem to have over the people in the US is cheaper used Panels and Inverters.  There is a big chunk of the industry here upgrading older systems for newer higher power ones.
Due to our regulations ( seemingly) constant changing rules, none of the Old stuff ( 2ys +) can be used or have newer additions because the old stuff does not meet the new regs.

As such, If you want to upgrade your 2Kw system to a 5, you have to buy a complete new 5KW system.
If you have a system and it gets damaged say by hail on one panel, you can't just replace the panel, you have to replace the whole system. Insurance will and has to cover this. My neighbour lost the inverter on his 3.5 system last week. They will supply a new inverter but for $800 more than the cost of that, they will do him a whole new 5Kw system.

As such, there is a reasonable supply of used panels and inverters around.

People regularly advertise used systems ( frequently at idiotic prices based on what they paid 7-10 years ago) and many broken inverters " For parts or repair". Trying to get an inverter repaired here is like shoving the proverbial up hill. If the inverter has an error code the fix is buy a new inverter.

I bought a 5KW inverter about a month back. It's not a well known brand but firing it up, the hours on the thing seem very reasonable.  It's working perfect now and non of them from what I read are any more dependable than a fridge or a dishwasher. They have a service life and that's it.
It seems that in some places, used solar gear is hard to get and supply is low. We have had subsidies here for a long time making our solar installs pretty cheap in comparison to the rest of the world it seems.  I think we also have a pretty high take up rate which means more stuff around.

Maybe you should look a bit farther afield that your local area. Paying more for shipping from further out in a place where solar is big might be counteracted by a lower purchase price.

I'm looking at going up north where solar is more plentiful and cheaper used and bringing back a trailer load of gear and visiting family and friends in the process.  I'll use what I need and I'm sure be able to sell the rest to cover the trip and the stuff I keep.

Looking at this market as I have been doing for over 18 Months, it seems to me the price of used gear is going up here. Maybe I should shut up about my used solar setup?   ;D
I have decided to buy another 5KW of panels, probably 250's  and install them with the 5KW I already have.
Long story but I have been reading up on the power industry here and it seems the huge increases we have already had ( more than doubling in most place and well beyond that in lots) is the tip of the shipstorm of what is to come. Several analysts I have read have said they believe power prices will double again by mid 2020.

I can't find anything to undermine that prediction but a lot that points to it being very creditable.
I want to reduce my grid consumption as much as possible and if it goes further over the top, then I have the generation side well covered when I go off grid and panels, old and new will be a lot more costly still.


It's not easy finding this stuff at the right price but it can be done. I just suggest doing it as soon as you can.  :0)

petect

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Re: Grid Tie, Oh My
« Reply #20 on: Today at 07:59:44 AM »
Hi George
" I think it depends on where you are. "  I'm afraid that you're right. It seems to me that most people in the US think we are on the cutting edge of all technologies. It sure ain'r true for re. PV is slowly catching on, but  there aren't enough older systems around to generate used used equipment. I'll keep looking though.
If your used PV business goes international. email me. The shipping charges should be interesting.  :(

BTW  I watched a vid last night about brown @#*&% snakes that are found in parts of Australia. The guy caught a couple in  a woman's pantry,  and back yard and, by law,  had to reloacte them nearby. They were relaesed at a nearby swimming hole wher kids play. NOW THAT'S INTERESTING!!
Pete