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Forum Index : Solar : Grid Tie off the Grid
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Bryan1 Guru  Joined: 22/02/2006 Location: AustraliaPosts: 1395 |
G'Day Guy's Well the time has come where I want to setup grid ties on my property so for the first one I do have that spare 1.5Kw of 6 250 watt panels so buy putting them all in series should get the high voltage to power up a sunny boy where my intent is to put in a split system aircon so we can have climate control. Now I do have 6.3Kw of panels and 2off 5kw grid tie inverters but I need to walk before jumping in. So all advice will be great on setting up this sunny boy. Regards Bryan |
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| noneyabussiness Guru Joined: 31/07/2017 Location: AustraliaPosts: 526 |
What is the base load for the grid ties?? I think it works !! |
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| Godoh Guru Joined: 26/09/2020 Location: AustraliaPosts: 498 |
Hi Bryan, first what battery inverter are you using? It will need to be a transformer based one to work. Then the grid tie inverter will need some way to control the output when the batteries are charged, as the GTI will feedback through the battery inverter into the batteries. I use a pretty cheap voltage controlled relay to control my GTI inverters. My batteries are 24 volt so I use one of these voltage controlled relay I switch a high current relay with the voltage controlled relay. I am using some 24 volt 30 amp relays I got from Jaycar, connected in series with the GTI output. That way once the voltage controlled relay operates it opens the high current relay and the GTI thinks there is No Grid available and goes into anti island mode. Make sure the GTI inverters MPPT controllers can handle the voltage the panels are outputting. From memory I am feeding around 220 volts DC from my panels into the MPPT controllers of the GTI inverters. Also make sure that any switches or circuit breakers you use can handle the voltage your panels output. have fun Pete |
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| Bryan1 Guru Joined: 22/02/2006 Location: AustraliaPosts: 1395 |
Morning Pete the inverter we use on the house is a Selectronic SA32 which has been powering our house for over 20 years  Now the house battery is a forklift 24 volt 600AH which has been going now for well over 10 years and that 1.9Kw array I put in has on a sunny day the batteries floating by lunchtime.So under no circumstance do I want to do something stupid and destroy this great inverter. I'm currently in NSW and when I get home I will get some of those voltage relays so they can be setup. Regards Bryan |
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| Godoh Guru Joined: 26/09/2020 Location: AustraliaPosts: 498 |
Hi Bryan, here is a link to the large relays I use in the GTI inverters. Panel mount relay I use the voltage controlled relays ( which only have small relays on them) to switch the relays in the link. I fitted the panel mount 30 amp relays inside the GTI cases, and they control the output of the inverter. When they open the GTI sees no grid so shuts down. There are other ways to control the GTIs, I know that Oztules had a regulator he made for his setup. But for my use the bang bang system works fine. Cheers Pete |
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| Bryan1 Guru Joined: 22/02/2006 Location: AustraliaPosts: 1395 |
Hi Pete so if I have this right the voltage control relay trips when the the battery voltage reach's the max voltage then turns off the grid tie so no more back charging can occur. Now if that is the case I'm thinking well when the sun comes up and the grid tie awakes of turning off the inverter supply and running the house and aircon load straight off the the grid tie. Then if the voltage drops enough to stop the grid tie then the inverter can can come back on to supply the load. By going this method the batteries can sit at full charge thru the day and come online for the evening and thus one can see what the low voltage is overnight so the state of the batteries can be seen. In the main electrical box for the house is a manual switch for inverter/generator modes which could be replaced with a relay. Regards Bryan |
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phil99 Guru Joined: 11/02/2018 Location: AustraliaPosts: 2407 |
The problem is the grid-tie is constantly testing the grid and will anti-island when the main inverter turns off. It is this feature you will be using with the voltage relay. |
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Murphy's friend Guru Joined: 04/10/2019 Location: AustraliaPosts: 671 |
Bryan, I know it's a bit hard to get your head around this GTI thing but just consider what happens to your solar power with the GTI connected to the street grid. The power you feed in (via your GTI) goes to wherever that power is required. It's no different with your minigrid (inverter/ GTI/ batteries). Your GTI power goes to wherever power is required. So, in the morning it will go to your toaster/ coffee maker, etc. AND your inverter to charge the batteries IF they need charging. If the batteries are fully charged and no other power is needed, then the voltage controlled relay turns the GTI off. IF power is still required elsewhere then the GTI will provide it directly without sending some through your inverter to charge the (already full) batteries. All this happens automatically while the battery voltage is below the relay trip point. So, you see, it's *important* that the voltage controlled relay turns off at a set higher voltage than it turns on again (I use 0.5V difference) - this is called hysteresis and prevents the relay turning on/off rapidly. If you buy the correct relay, then these settings can be programmed easy. Here's what happens at my place: In the morning the GTI wakes up and charges the batteries via the inverter (they are also getting charge from my MPPT controller, at the same time, via a different set of solar panels. Doing it that way makes the charging work a lot smoother than with only the GTI bang, bang method, BTW. So, after a while the batteries are full and the voltage controlled relay turns the GTI off. What little power is still required gets supplied from the MPPT charging, keeping the batteries full during the day. But, say its stinking hot and there is some cloud cover, if not enough power comes from the MPPT to run the A/C, the battery voltage drops (by 0.5V - see above), then the GTI wakes up again and supplies that extra power. At my place I often see then that the A/C is powered from the GTI power and nothing goes into the batteries as their voltage is below the turn off voltage of the voltage controlled relay. You can only see that if there are Ampmeters (via shunts or Hall sensors) connected to monitor battery charging directly at the battery and at the MPPT output. This lets me monitor what goes in or out of the battery and how much comes from the MPPT. Any difference (in charging) comes from the GTI. All that happens fully automatically. It is *important that you set the voltage relay trip points correctly and you wire that relay so it works reliably *all* the time. Keep in mind that these relays usually run off 12V so a small power supply is required. You *must* wire the relay contacts so they are open if that 12V supply fails, thus disabling the GTI charging until you fix the problem. Also, the GTI relays are at 240V mains so they need to be suitable for that and have a current rating to exceed the GTI power output. Take care with that, no dodgy installation allowed   . |
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| rogerdw Guru Joined: 22/10/2019 Location: AustraliaPosts: 882 |
I don't know if there are any "rules" around ac-coupling. I vaguely recall comments about using only small inverters when you try ac-coupling. Clockmanfr always suggested using 1.5-3kW inverters ac-coupled to an OzInverter for example. Not sure if there was a specific reason or whether someone found out the hard way that it was important to stay small. Is your Selectronic SA32 around 2.4kW or something like that? And that will provide your minigrid. Then you're going to ac-couple a 5kW Sunny Boy. Thinking about it ... is it the fact that when there's not much load and the Sunny Boy starts pushing charge back through the Selectronic and into the battery ... that the mosfets may not be able to handle the potential 5kW of power because they are only rated to 2.4kW perhaps. I was pretty gungho when I hooked up mine, but it was still only 5kW into my 15kW Warpverter ... which has managed it perfectly okay so far. Cheers, Roger |
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| Godoh Guru Joined: 26/09/2020 Location: AustraliaPosts: 498 |
Hi Roger it is best to keep the GTI inverters output just under what the output of the battery inverter is. In my case my battery inverter is around 4kw. ( the board is supposed to be 5kw at 24 volts) But in practice 4kw is about all the 24 volt system handles with ease. I also have a 3kw Latronics inverter and can switch between the two inverters when using the GTIs to back feed. Both my GTI inverters are 5kw inverters, but they don't have enough panels on them to supply that much. If I am charging the car I have seen 5.5 kw going into the car, there is usually around 3kw to 4kw coming from the GTI inverters and the rest from whichever battery inverter I have switched in. I have two changeover switches so I can connect one or two GTI inverters to either battery inverter, depending on what i want to run. As you say if you try to push more through the battery inverter than its rating it is likely to get too hot and blow up. In reality the sun comes up and there is power coming first from the MPPT regulator panels, then after a while the panels connected to my GTI inverters get sun and start charging. Before the GTI inverters get anywhere near full power the batteries are charged and the GTI inverters turn off. The only time my GTI inverters are running at their maximum is when I am charging the car, even then the other panels connected to the MPPT regulators are also assisting in car charging. Murphy was a great help when I set my system up. It works great and does everything I could want Pete |
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| rogerdw Guru Joined: 22/10/2019 Location: AustraliaPosts: 882 |
Hi Pete, that makes sense. My GTI has been switched off all summer because I just can't use the power and the battery is full pretty quickly every day from the mppts. Maybe I need an EV too, though I do next to no miles per year. Hey, maybe I need to find a neighbour with an EV and charge them. During the previous 6 months I had it running flat out whenever the sun was strong enough and wasn't unusual for it to put out 5kW for hours and hours on good days. I'd turn on the underfloor heating and other space heaters to keep the house warm and use up as much power as I could generate. That alone meant the GTI rarely pushed much back through to the battery ... so I didn't have to worry about overcharging. Mine sounds similar to your setup, in that if I just had average loads ... the load was shared fairly evenly between the Warpverter and the GTI. And as I increased them (provided the sun was good) the GTI would top out at its 5kW and the Warpverter would/could go to 10 or 11kW. Pouring as much heat into the house, especially during the shoulder periods meant we only used the wood heater for 2 months instead of 5 months. Saved an enormous amount of time and effort chasing wood. Makes me want to find another 5 or 6kW of panels and GTI to add just for the cooler months. Cheers, Roger |
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| Bryan1 Guru Joined: 22/02/2006 Location: AustraliaPosts: 1395 |
Yes the SA32 is rated at 2400 watts and has supplied everything we have thrown at it over the last 20 odd years Now the sunny boy is rated at 10 amps which I think is a perfect match for the inverter and my intention was to hook the split system aircon straight off the circuit breaker for the the grid tie. I did setup a double pole circuit breaker for the solar input from the 1.9kw and the 1.5kw panels so off the 1.5kw array it will go to the grid tie circuit breaker and there is a single circuit breaker for the AC output of the grid tie. When I get home I'll order the voltage relays and I'll check all the relays I have in my shed where I may just have one handy. Regards Bryan |
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| Bryan1 Guru Joined: 22/02/2006 Location: AustraliaPosts: 1395 |
G'Day Guy's, Looking on FB this afternoon saw a brand new wall mounted aircon for $400 So got onto it straight away and it's now sitting in the back of my Foz  It's rated at 1.7Kw cooling only and I still need to setup it up in a lounge room window and make a frame for it. Those voltage control relays turned up and this week I'll head down to town and get those DPDT relays Pete suggested then I'm all set to go. So now my next job is drawing up a mud map of the circuit and make sure everything is correct and today I had a chat with the local sparkie who will come around and check everything so no dodgy wiring here guy's. Regards Bryan |
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| Godoh Guru Joined: 26/09/2020 Location: AustraliaPosts: 498 |
Sounds good Bryan. We have had three days around 30 degrees here. Lucky today has cooled down a bit. Where I live any day over 25 is hot. We are just not used to temperatures like the North Island gets. Fortunately I took the roof of our house a couple of years back and put in lots of insulation, so the house never got above about 24 degrees, but still for us that is too warm. I had an idea that I haven't tried yet. I was thinking that the MPPT controllers that are connected directly to the batteries could be used to be the voltage controllers. They have a load output that switches the loads on and off when presets are reached. I have not used them for much. I do use one MPPT on a small hot water system to control an inverter to switch the element on and off. That works great. So maybe the voltage controlled relays I have on my system could be replaced later if they fail. So far they are working fine , but if they die then I will try the load section of the MPPTs. Good luck with the air con Pete |
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| Bryan1 Guru Joined: 22/02/2006 Location: AustraliaPosts: 1395 |
G'Day Pete with these voltage controllers there are 6 outlets, now the left 2 look to be the relay output and with the remaining 4 outputs the 2 centre ones are ground. Now one would think only 2 outlets would be used to connect to the battery and with Chinese writing on the back is no help in working which pair should be used. Now I did order 2 of the voltage controllers so I have a spare onhand if it dies Regards Bryan |
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| Godoh Guru Joined: 26/09/2020 Location: AustraliaPosts: 498 |
Hi Bryan, here is a photo of the board connections on mine.  |
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| Bryan1 Guru Joined: 22/02/2006 Location: AustraliaPosts: 1395 |
Thanks for that pic Pete and it does clear things up now as the relay is a 12 volt one does that mean the power supply is 12 volts ? Regards Bryan |
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| Bryan1 Guru Joined: 22/02/2006 Location: AustraliaPosts: 1395 |
G'Day Guy's, Well went down to town and got that panel mount relay this morning and typical win10 doesn't have the original paint program so I just did it in Sprint Layout and used paint 3D to sort the picture.  Now assuming the power supply is tied to the 24 volt battery and I reckon I have the panel mount relay correct. There isn't much into it really is there, just a couple of sense wires and a panel mount relay. Regards Bryan |
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| Godoh Guru Joined: 26/09/2020 Location: AustraliaPosts: 498 |
Hi Bryan, you may find that the way your diagram is showing the connections that there is no voltage at the relay coil that connects the GTI inverters. You probably have to pick up a negative to go to the 24 volt relay coil, and put a jumper in from the power supply terminal on the voltage controlled relay so that the voltage controlled relay contacts switch the positive to the 24 volt relay. Pete |
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| Bryan1 Guru Joined: 22/02/2006 Location: AustraliaPosts: 1395 |
So like this Pete  I did have the relay coil the wrong way around and doing this mod should give the relay the battery voltage to switch on. Now my understanding with the Selectronic AC connected to the centre pin of the DPDT relay and the grid tie on NC pin when the relay energizes the grid tie is taken out of circuit. |
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