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My Grid tied installation


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13 minutes ago, jdp said:

So are you telling me this inverter can only make power from PV if the grid is there? If so then that is a crappy design of a inverter. I wont buy it. Why does it need the grid to make power from PV to carry the load ?. I can understand that if the grid is not there then it should not push back into the grid the extra power the panels make. But why will it shut down if there is no grid and drop the load as well?

Because GTI inverters do not come with battery backup such as a true Hybrid inverter does

A GTI inverter uses the grid as the "buffer" for when it waits for the MPPT to ramp up PV production as load increases. It will pull the power needed from the grid until the PV can carry the load. I would say if you somehow made it work without grid you would have constant "trips" as loads start up and shut down waiting for the MPPT to adjust

Edited by viper_za
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26 minutes ago, jdp said:

So are you telling me this inverter can only make power from PV if the grid is there? If so then that is a crappy design of a inverter. I wont buy it. Why does it need the grid to make power from PV to carry the load ?. I can understand that if the grid is not there then it should not push back into the grid the extra power the panels make. But why will it shut down if there is no grid and drop the load as well?

The standard GTIs all work that way - you connect its output in parallel with your grid connection and while the grid is available the GTI will generate AC (from the connected PV) and tie that with the grid in order to supply the load (your house). When the grid fails the GTI also stops generating power. The grid tie limiter is another add-on to the system which monitors the power flowing to the grid and if the GTI generates more power than what is required by the load, it communicates with the GTI and the GTI then reduces its output power in order to prevent power from flowing into the grid.

Since the OP is not really affected by loadshedding a GTI should work fine and will only shut down occasionally when the grid fails.

I also investigated the GTI option initially, but when I learned that it will switch off during loadshedding I realized that that is not an option and decided on the true hybrid, which can grid tie and still supply the load when the grid fails.

Edited by superdiy
Sorry viper, you beat me to it.
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Hehehe love it. You CAN run a GTI without the grid as long as whatever you use as a grid replacement is designed to do it.

This is precisely how Victron's hub-2 works. GTI ties with the output of the Quatro/Multiplus, and using frequency shift it adjusts the GTI to avoid that problem of pushing back. In addition, the batteries serve as the buffer for sudden load changes, which is necessary for the reasons viper pointed out.

I definitely don't think you should make a GTI tie with a generator of any kind, not without some kind of buffer.

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8 minutes ago, plonkster said:

I definitely don't think you should make a GTI tie with a generator of any kind, not without some kind of buffer.

So we are back to just bypass it all. We went full circle on this one :P

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Now just to throw a spanner in the works. Sunnyboy does make GTI inverters with an emergency power feature, so that some power is available even when the grid is down. It is however limited to around 25% of the inverter's normal capability and is meant to charge phones and stuff like that...

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1 minute ago, jdp said:

So we are back to just bypass it all. We went full circle on this one :P

I think what we were unclear about is whether the grid-tie limiter (Microcare is one of the few makes that have this) is sufficient to handle load changes. I suspect it isn't. If you set it to the 100W position (so it adjusts the GTI to consumption minus 100W) you can in theory handle changes of no more than 100W, but even an A++ rated fridge is going to blow that allowance...

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From my experience trying to make a GTI run from a generator in the event of a power failure is just looking for problems. In rare instances where we have done it the capacity of the generator was much much larger than that of the PV generator to avoid too much feed back into the genie.

I would also rather recommend the suggestion of just by-passing like JDP described.

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49 minutes ago, plonkster said:

Now just to throw a spanner in the works. Sunnyboy does make GTI inverters with an emergency power feature, so that some power is available even when the grid is down. It is however limited to around 25% of the inverter's normal capability and is meant to charge phones and stuff like that...

I'm pretty sure the infini would do the same. You can use it without batteries, and I think if the load is smaller than the generated PV it will supply the load, but I need to confirm that.

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1 minute ago, superdiy said:

I'm pretty sure the infini would do the same. You can use it without batteries, and I think if the load is smaller than the generated PV it will supply the load, but I need to confirm that.

I don't know the infini, but from what I remember on this forum, it needs either grid or battery before it can do anything with the incoming PV. To be confirmed though :-)

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A generator cannot be a sink for excess current. If it does it is going to over rev.

If you have  a GTI then a change over switch and your options are either grid and GTI or generator power only. You cannot have GTI+ generator the generator is going to burn out.. 

2 hours ago, jdp said:

So are you telling me this inverter can only make power from PV if the grid is there? If so then that is a crappy design of a inverter. I wont buy it. Why does it need the grid to make power from PV to carry the load ?. I can understand that if the grid is not there then it should not push back into the grid the extra power the panels make. But why will it shut down if there is no grid and drop the load as well?

jdp it is  a safety feature. If your panels are carrying the load and the sun goes behind the clouds momentarily what is going to happen? Your voltage will drop and you will have all the associated problems. One could have a complex system whereby it shuts down and only switches on once your compressors in your cooling appliances have lost internal pressure and any motor is not going to like the stop start.

 

Oooh my internet is playing up I see there is a raft of explanations. 

Edited by Chris Hobson
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Yep Chris. I did not know it did not have battery back-up to carry the load if the PV falls away. I am used to the Infini and Axperts that all have battery back-up as standard. For me if you have a house that is the only way to go. For a business it makes scenes to run pure grid tied but with full genset back-up that will bypass the inverters  when the grid falls away with auto start. And then have ups on all hardware that can not go off.

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3 hours ago, jdp said:

So are you telling me this inverter can only make power from PV if the grid is there? If so then that is a crappy design of a inverter. I wont buy it. Why does it need the grid to make power from PV to carry the load ?. I can understand that if the grid is not there then it should not push back into the grid the extra power the panels make. But why will it shut down if there is no grid and drop the load as well?

JDP, from what I understand, you CANNOT run a GTI without the grid being up and operational OR if the grid is off, then the inverter has to have anti-islanding built in or added to it.

And then you need batteries for you cannot grid tie if there is no grid, and a generator is not a grid.

Or am I missing the plot?

Ps. I do not think Microcare are crappy inverters either. It depends on what you want to do. :P

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1 hour ago, jdp said:

TTT you are 3 posts to late. 

Only saw the posts now, screen did not update.

Edit: Shucks ... a whole page full of posts was not there when I posted. Interesting.

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Over the weekend I've been able to put up the panels on the roof. It was a learning curve for me an I thought I'd put down my experiences (good and bad) here for others to learn from my mistakes and to find out if there are better ways of doing it.

Firstly it was a bit more difficult than I thought it would be. Getting the panels to align up was was not so easy. I am sure that for people that do this for a living its a lot easier, but for me, doing it for the first time it took longer as I had to figure things out as a went along. I have 2 rows of panels. The top has 7 panels and the bottom row has 6 panels. The thing that made it difficult was the railings are not completely rigid, they tend to flex and sag slightly when holding the panels weight. Eventually I figured out that that fixing the bottom row of the panels first work for me. I then used the mid clamps as "spacers" to rest the top panel on them before fixing it to the rail. If I had to do it over I would have started with the middle panel of the bottom rail. Its critical to get it perfectly straight as all the others will take its alignment from it.

The railings I have are galvanized steel and the panel frame's are aluminum. I've read on the forum about galvanic corrosion could occur between dissimilar metals. I've read that galvanic corrosion "might" happen between galvanized steal and aluminum but that its not a high risk combination. I think at the coast its more problematic. The way to prevent this is to isolate the two metal from each other. So what I did was to put some double sided tape (not the spongy mirror tape) between rail and the panel frame before tightening the mid clamps. The mid clamps are aluminum so no problem there. Its only where the panel touches the rail. I've read that some people used bitumen strips as well. The tape I use is called "nail it with tape" and is reportedly UV resistant and approved for outdoor use. It's quite sticky and was not easy to put in place.

On the second day I decided to attach the earth wires to each one of the panels and railings. I used an insulated 4mm2 earth wire and crimped on some ring terminals. The terminals was attached with a spring washer and self tapping screw to the demarcated grounding attaching point of the panels. Cable ties were used to tie the earth cable to the panel frame and the railings to keep things neat and tidy.

 IMG_0903.jpg 

 

The panels are connected in one large string. Voc for the string is close on 500V. That could really spoil your day if you were to touch that!. The two end wires are fed back into the roof between two tiles. To prevent shaving of the wire against the tiles I cut two small pieces of gas pipe and fit it around the PV wire. It fits snug but not to tight. It was placed between the two tiles and holds the PV wire from touching/shaving against the roof tiles.

IMG_0906.jpg

I attached two PVC 4x4 junction box to the rafters closest to where the PV wires comes through the roof tiles. Inside it will be the MC4 connector that attaches the wire that leads to the combiner box. The wire going from the PVC 4x4 junction box to the combiner box is a 6mm2 Solar PV wire and will be placed in a 20mm PVC conduit.

For now I've secured the two open ended MC4 connector into the two PVC 4x4 junction boxes to prevent them from touching anything. As soon as the combiner box arrives I will attach the wires to it (at night when the voltage on the wires are low. :-)

My next step is to fix the inverter, grid tied limiter and combiner box in the "inverter room" wall. Then put in the trunking and do the wiring. Hopefully I get some time to work on it this weekend.

Given what I've done with the panels so far, would there be something you would have done differently? One think I would have done differently is to try and attach the earth wires before or, as part of putting up the panels on the rails.  Trying to access the back of the panels by moving tiles and working from inside the roof was not an easy or comfortable job!  Some of the tiles can not be moved because the railings rest on them! That means you have to bend and work in very uncomfortable positions.

 

 

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7 minutes ago, Janma said:

I've read that some people used bitumen strips

I use bitumen strips, because I have a painted mild-steel frame*. It works well, but it is very messy. If you ever decide to move the panel, you never get it off again. Be careful not to get any of it on the glass :-)

Your trouble with alignment reminds me of two other farmer problems. First, when putting up a fence, you can't work end to end, first you put up all the wire strands, then you attach all the poles, then you attach the droppers. If you attempt to attach the droppers in the same pass as attaching the wire to the poles, it completely screws up the tension lower down the fence and you can't get the wires in place anymore. Second similar problem: Putting up a windmill wheel. It goes on in six sections. If you put them on in order, the wheel becomes so heavy after the second section that you can't turn it into position for the next one, so you have to put them on in a balanced across-from-each-other manner.

* In terms of rust on the steel frame: The one frame is very well painted with two layers of P5 and 3 layers P4 ("rooi lood", as we used to call it). This one does not rust. With the second frame, I used Duram DTM (direct to metal). This one is showing signs of rust. In theory, the frame should be made to last at least as long as the panels, around 25 years in other words. In my case, they are on a flat roof, easily accessible, and they are certainly not going to be there that long. Considering how much cheaper steel is than alluminium, I think it's an acceptable compromise :-)

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35 minutes ago, plonkster said:

 I used Duram DTM (direct to metal). This one is showing signs of rust.

I know exactly what you mean. About a year and a half ago I used DTM to paint a new security gate. It's rusting now. I'll have to redo it again! If there is one think I do not like is to "redo" things. :-)

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  • 3 weeks later...
12 minutes ago, superdiy said:

Neat and clean installation! ;)  Well done.

It just needs the 14th panel to get everything on the roof symmetrical. :D (My OCD again)

Thanks Super,

I constantly have to remind myself that the panels purpose is more important than the esthetics (or so I'd like to believe).  I SO wanted to have the 14th panel but the VOC would be just to high :-( I seriously considered putting the 14th one in place but not connecting it. The moment I find a use for an extra panel it will be going up to joint the others :-)

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2 minutes ago, Janma said:

The moment I find a use for an extra panel it will be going up to joint the others :-)

You have a use!! Like one panel with a separate charge controller to charge a battery that powers those other stuff you need off-grid like the alarm system. :D

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5 minutes ago, The Terrible Triplett said:

You have a use!! Like one panel with a separate charge controller to charge a battery that powers those other stuff you need off-grid like the alarm system. :D

That sounds like a plan! But, it will have to wait for a while. If I spend one more day in the roof wiring up stuff my wife will probably divorce me :blink: I'll give it some time before starting on "Solar installation v2.0" :D

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