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Forum Index : Solar : Grid connected inverter off grid
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renewableMark Guru  Joined: 09/12/2017 Location: AustraliaPosts: 1678 |
G'day fella's, I'm pretty sure the answer is no, but since there are so many cluey fellas here I thought I'd ask. I have a Aurora 5kw grid connected inverter I got in a deal and was wondering if there is a way to make it so it can be used off grid. From what I can find out they have no voltage regulation, is it feasable to convert/adapt this? If so is there anyone that does it? If not is anyone interested in buying it, it's on the cec current approved list. Cheers Mark Cheers Caveman Mark Off grid eastern Melb |
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| George65 Guru Joined: 18/09/2017 Location: AustraliaPosts: 308 |
I know it CAN be done, I believe the way to do it is to use a small inverter to make it think it's on the grind but I have not been able to find exactly how you do it. I'm sure it can't be as simple as plugging them both into a power board or something but I have read form some boffins numerous times it's straight forward. I'd love to know how to do it myself. Aurora's were not a great inverter but that should still sell. I have 3 aurora's and they are still going for the time being although I have blown the one input on the 3KW so can only get about 1800W out of it. Have to commission my bosch unit and see how that goes. brand new, never fired yet. |
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Madness Guru Joined: 08/10/2011 Location: AustraliaPosts: 2498 |
Yes it can be done if you have the right kind of off grid inverter. If you have a Power Star/Jack low frequency, a Ozinverter like a few of us have built and most H-Bridge inverters will work. Provided it is big enough to handle the power of your GTI. It will actually back charge through the inverter but you need a way to regulate it. Have a read of these threads about how we have built regulators to work with the GTI's, the Aurora senses resistance to ground so must be isolated, I have overcome this as you will see in these threads. https://www.thebackshed.com/forum/forum_posts.asp?TID=9734&PN=1 https://www.thebackshed.com/forum/forum_posts.asp?TID=9903&PN=1 If you live in SE QLD I would be interested in buying the Aurora if you decide to sell it. There are only 10 types of people in the world: those who understand binary, and those who don't. |
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| renewableMark Guru Joined: 09/12/2017 Location: AustraliaPosts: 1678 |
Thanks for the input fellas, I'm not really knowledgeable enough to adapt it myself nor would I be confident of it's safety. If no one out there adapts them then I'll just buzz it off. Unfortunately Madness I'm in Melbourne, freight may be an issue as it's bloody heavy. I was looking at buying two of something like these to use off grid inverter I liked that one as it can parallel Cheers Mark Cheers Caveman Mark Off grid eastern Melb |
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| Madness Guru Joined: 08/10/2011 Location: AustraliaPosts: 2498 |
The Inverter does not need any modification, the regulator sits between the panels and the GTI. You will find the same brand as you are looking at on Ebay from a Seller in Taiwan. The one I had did fail and they were very good as they sent me a replacement PCB at no charge. Keep in mind they are not good for heavy surges from things like induction motors and circular saws. There are only 10 types of people in the world: those who understand binary, and those who don't. |
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| George65 Guru Joined: 18/09/2017 Location: AustraliaPosts: 308 |
I followed the links and tried to read the threads. I really did. Now just pretending I'm not the electronic Geniuses some of you are (  ) Would someone mind simplifying down an explanation of how I can plug my Grid tie inverter into my panels and get 240 directly out.... if that is in fact what you can do? As I understand it, you need a regular 12/24/ 48V to 240 inverter. Must be low frequency like a power jack. Now to clarify that point, How do I know if my inverter is low frequency? How do I measure it? I have a nice 24V/ 2KW unit from Jaycar which cost a a bomb so I hope it's a good one. What do I look for on the spec sheet? Next, I take it that if I have a 2KW GTI, I must also have a 2KW XX>24v inverter? Is this correct? Now we seem to get to the tricky part.. The regulator. What is it regulating actually if I'm not using batteries.... Or do I have to? What is the regulator? I seem mention of PWM, can I use a little 4 Kw PWM board I have or am I lost now... as IF I wasn't from the start. Sorry for the dumb questions, clearly some of you guys do this stuff over breakfast but my talents lie elsewhere. As soon as I find where that is, I'll let you know, but I would really like to be able to just get power from my panels direct and would like to get a better understanding of what exactly is required to do that. Thanks in advance. |
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| Madness Guru Joined: 08/10/2011 Location: AustraliaPosts: 2498 |
George a low-frequency Inverter has a big heavy transformer, not one of the lightweight type that run at HF like many GTI's do now. If you can pick up the one you bought from Jaycar without groaning then it is most likely not suitable. If you are not planning to be off grid then there is not much point, the reason we use GTI's and regulate them is to not overcharge batteries. A GTI normally is required to make as much power as it can so you can get a credit from the power company. The PWM has the same effect as putting a cloud over the solar panels to reduce the power output. The other threads describe what is going on with the PWM, but if you are not going off grid there is no point worrying about it. There are only 10 types of people in the world: those who understand binary, and those who don't. |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
Its not possible to simplify it all down to a few simple steps, its a pretty complex thing to get going. And if you get it wrong the damage can be rather unfortunate. For the Guru's a bit of smoke and a few flames are part of the natural learning process and not terribly discouraging. But unless you can diagnose and repair any damage yourself, its very likely going to end up a horrific and expensive experience. A grid tie inverter is made to couple into the grid, which can be considered a sort of infinite power source (or power sink). What you draw from it, or feed into it is going to have minimal effect on the grid voltage. For safety reasons a grid tie inverter first measures the incoming grid voltage, synchronize to that, and makes sure that the incoming voltage is within fairly close limits. Only then will it start to supply any power. Without a grid connected, its just going to shut down and do nothing. Now you might think that connecting it up to some kind of inverter and fooling the grid tie inverter is a simple thing. It is not. Suppose you try that. The grid tie inverter sees 240v and synchronizes to it and thinks all is well. As soon as it starts feeding power into the system, the output voltage may start to rise uncontrollably, because there may be considerably more feed in power than there is load to absorb it. Several things can happen. The grid tie may shut down safely, or the other inverter may experience a massive over voltage and be destroyed. Or it may survive and feed power back into the battery, assuming there is a battery. That might be good, or it might overcharge and eventually damage the battery. If the grid tie is more powerful than the other inverter, the level of uncontrolled power fed back into the battery may be high enough to destroy the inverter, even if the battery survives. So assuming you get this far, some kind of power regulation needs to be applied to the grid tie inverter to protect the other inverter, the battery, and to prevent system over voltage that can destroy some of your household appliances. There are so many different combinations of equipment, that its not possible to know what the potential problems might be with a totally untried combination. If you have the skills to understand the complexities and are prepared to take some risk, its certainly all possible and has been done successfully. Usually after a few failed attempts. But its not possible to advise a total novice how to go about it all successfully with a few simple basic steps. Its a whole very nasty can of worms best avoided. Cheers, Tony. |
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| renewableMark Guru Joined: 09/12/2017 Location: AustraliaPosts: 1678 |
That's the answer I was expecting. Thanks, Warpspeed. Cheers Caveman Mark Off grid eastern Melb |
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| renewableMark Guru Joined: 09/12/2017 Location: AustraliaPosts: 1678 |
I don't mind messing about with low voltage low amp stuff but high voltage stuff ups can kill Cheers Caveman Mark Off grid eastern Melb |
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| Madness Guru Joined: 08/10/2011 Location: AustraliaPosts: 2498 |
Yes I agree, if you think you are getting out of your depth take a step back and reconsider. High Voltage DC is far more dangerous than the same voltage AC, but if you are careful you can work with it safely. Fortunately, there is no issue regulating the AC voltage with a GTI connected with one of our DIY Inverters. The AC Voltage regulation is so close to perfect I never have to give it a second thought. The only part that has been taken a bit more work is regulating the DC fed back into the battery so it charges correctly, Oztules circuit and code does that well. Also you can blow Inverters, I have done it a few times and was able to repair it and carry on, fortunately, GTI Inverters are becoming more and more readily available secondhand. Henry Ford said "If you think you can or you think you can't your probably right" There are only 10 types of people in the world: those who understand binary, and those who don't. |
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Clockmanfr Guru Joined: 23/10/2015 Location: FrancePosts: 427 |
Hi renewableMark, As 'Warpspeed' has mentioned there are complexities, lets see if I can break them down a bit into the basics. I am rewriting the 2015 'How to make a 6kW-15kW OzInverter' and bringing my update supplements, PCB masks etc, into the new book. The basic idea of the book is to condense all that is out there on the 3 main forums with the OzInverter, and make it possible to build your own stuff if you follow the books guidelines, yea lots of Pics. And tech stuff as well, plus stuff on the toroid from 'Warpspeed'. (he loves transformers hehe). The actual 'OzInverter' is the brain child of forum member 'Oztules'. He had a need, and I had a need as I had fallen out big time with a European Inverter manufacturer where there machine would not do what it is supposed to do with out their expensive ancillary control equipment, and they certainly don't mention that at the beginning. 'Oztules' progressed from the 'Powerjack' boards and winding our own toroid, to using our own Power Board PCB, OzControl PCB, now at No12 version, and the OzCooling PCB. I like things Simple and Robust and very very importantly Cost Effective. In the latest re-write I will do an extra chapter on a OzInverter AC Coupling GTI controller. A couple of general things. 1. The GTI needs to see a good AC Grid, the OzInverter creates a good Mini Grid. 2. Most good GTI's have internal Country code settings, these allow variances and have AC voltage parameters, say 260vac output/input then the GTI shuts down automatically. Now with the early OzInverter PowerJack Chinese made/assembled boards the GTI pushes AC back through the OzInverter into DC into the batteries, that's if you are not using the power from the GTI on your created Mini Grid. With the PJ boards when the batteries fill the DC voltage rises and correspondingly AC voltage rises and shuts down the GTI. (I posted a table somewhere) 3. The new OzInverter PCB's (mostly 'oztules' design), especially the No12 OzControl board, is very good at controlling the AC voltage as its rock solid, so we need to monitor the batteries DC voltage and to use a Relay on the AC input/output of the GTI to shut it down, especially if the DC battery voltage is getting to high. I particularly like this method as its a deadmans handle type. The GTI is also designed to shut down on the AC side, as well as lack of DC from the panels, ie 'Oztules' & 'Madness' DC proportional controller of the DC Panel side of the Input to the GTI. 4. Your batteries are the buffer with the OzInverter. I have 1300ah 48v lead acid, Golf cart types and they are robust. This gives sufficient leeway for the AC backfeed from the GTI's, (I have 8kW 4off GTI's),not to overcharge/damage your batteries. I have tested at 800ah battery pack and the GTI's still shut down quick enough to stop the batteries suffering. Loads on your OzInverter Mini Grid will also dictate what battery size. If you suddenly switch on the kettle and the Mrs has the hair drier on then the Batteries voltage will drop as the OzInverter powers in, but there will be a delay as the GTI's come on line on your mini grid. So can your batteries take that load for that short time? I will never produce a commercial manufactured version of the OzInverter, as in this day an age there are just to many hoops to jump through. However, at present I do all the PCB's and a book of 'How to' with full parts lists. Maybe in the future we will do a kit of parts. (I remember the old Heathkit days). Oh yea just to remind folk we are a non profit organization, and we look for covering out Printing costs, PCB manufacturing and the blasted Postage costs. Here in France we are passionate about getting the Simplicity, Robustness, and cost Effectiveness of renewable Energy out to the World, and if we can help folk across this Planet then that's bloody brilliant.!!! The OzInverter AC Coupling yes its possible. The links below are the present book, and have all the latest info and PCB's. http://www.echorenovate.com/the-ozinverter.php http://www.echorenovate.com/new-book--make-a-6kw-inverter.php Everything is possible, just give me time. 3 HughP's 3.7m Wind T's (14 years). 5kW PV on 3 Trackers, (10 yrs). 21kW PV AC coupled SH GTI's. OzInverter created Grid. 1300ah 48v. |
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| George65 Guru Joined: 18/09/2017 Location: AustraliaPosts: 308 |
Yeah, me too. The geniuses always make it look easy. :0) Solar power to me seems very difficult to use in the same manner you would any other power source, IE, plug into it and use the power. If you had a generator that's no problem but with solar, BIG can of worms. Unless one is very knowledgeable, it seems very inefficient to do that. Get your solar output, regulate it into a battery then have inverter to ramp it up to the mains voltage. If you have a KW of power coming in and want to only draw 800W, you could have a small battery and just take the load off the panels but it's still an inelegant way to do it to me. I'm surprised there is no devise available that gives you rated power up to what the panels can supply. Pretty much like an inverter. If there's a KW coming in and you only need 500W, no problem. Cloud comes over and you are only getting 300W, like a regular inverter the thing shuts down on overload. To the ignorant ( IE, ME!) it seems pretty simple but the fact there is nothing like this tells me it only seems simple because I don't know enough to understand how difficult it must be..... otherwise it would be done by now. Even applying PV power to something like a water heater isn't that straight forward Where as with a generator, I have run a heater with over double the capacity of the generator quite happily just through a little PWM controller. Monitored the output and sat it at a comfortable level for the genny and all was well. Not so easy with solar though. Yeah, I used to think like that but I learned a bit more and realised it wasn't hard or much different to low voltage DC I was very familiar with. Even as a teen, I was the only one in the group of mates that would wire things in cars like Driving lights, CB radios and stereos. Other mates would rebuild an engine over the weekend and drive the car to work Monday morning but add a graphic equalizer to the sound system, no way! Mains scared me a bit but I worked with a sparky mate and realised it wasn't really that much different and all you have to do is be pedantic and triple check nothing is live before you touch it. From there the only thing that can happen is something trips out.... assuming you have protection in somewhere. I'm very fussy with that. I have played around ( a LOT) with 3 phase motors using caps to turn them into generators. That can be 415 at enough amps to kill you right quick so you have to be careful. But this is the same for anyone working on mains power. As my sparky mate said, They can teach you how to do something but they can't teach you not to have a brain fade so everyone is on an equal level there. I just wired up my 5KW solar array. Had a nice relaxing time doing it. Ran a new board back to the mains, put in a couple of extra power points while I was at it and "Improved" some wiring that was there. I put a master switch for the shed in the shed itself rather than just at the fuse box. Put all the power and lights on RCD's. I know there is one in the box but I'm not sure if it covered lights and power and in the shed so now I know it does. $30 well spent I'll feel comfortable but not complacent about. I over rated the wiring I did and under fused it. Put individual breakers for the power points I wired in. Put isolators on every array, another breaker for the inverter AC, 20A instead of the 32a specified, (NFI what they were thinking!) and basically over did everything and enjoyed doing it. As long as that breaker is off at the fuse box while I am playing, I have no problems. A trick mate showed me was to short the wires at the first point so if any moron does come along and flip the breaker, it will trip out straight away stop the power trying to go through you and give you a lot better chance of remaining alive. Do all your wiring up to that point and then as the last thing, finish your connections there. I think the main thing is being aware you are taking your life in your hands and paying due diligence to that. You can't be lazy, you can't be distracted and you DO have to know what you are doing in the basics even if you don't know the more advanced stuff. |
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| hotwater Senior Member  Joined: 29/08/2017 Location: United StatesPosts: 120 |
I will be experimenting with PWM of the input voltage. Panels make that easy because they are a known current source. I have one concern with what you have done. I've noticed on the GTIs checked that the input capacitor is a minimal value that the inverter can deal with. Seen significant voltage swings which means high ripple currents. Adding extra PWM on top of that that could cause problems long term. Have you investigated this and considered an additional capacitor bank? |
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| Madness Guru Joined: 08/10/2011 Location: AustraliaPosts: 2498 |
I have not seen a GTI that measures capacitance, the one I am using measure resistance to ground, if this is less than 1m ohm it will give a ground fault error. Adding capacitance take the panels from fixed current to near unlimited instantaneous current, best to not to this as having large amounts of energy available may overload the inverter. Every GTI I have seen has filtering on the input anyway. So far I have been running this for more than 6 months and have had no problems caused by the PWM, I have had the GTI fail due to a ground fault. Here is what my battery current and voltage looks like with the regulated GTI operating. The graph is one complete day, the dips in volts and current are caused by clouds/heavy loads on the inverter. The light blue vertical bars are the power output of one of my Midnite charge controllers, it is not putting any power out when the battery is on float as the GTI is powering everything then.  There are only 10 types of people in the world: those who understand binary, and those who don't. |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
What may not be obvious to most people, is that a sine wave inverter always draws a heavily pulsing current from its dc power source. During the ac zero crossings, the inverter input power effectively falls to almost zero, and rises to a massive peak at each crest of each ac cycle. If the power source is from a massive battery, that is not much of a problem. But a solar panel is a VERY load sensitive current source. As soon as you start drawing any significant current, the solar panel voltage falls away significantly. There is absolutely no short term overload capacity from a bare solar panel. All grid tie inverters will have large electrolytic capacitors fitted directly across the dc supply from the solar panels. Cost saving being what it is, these may be be made miserably small. There may be some worthwhile gains in adding extra capacitance externally between the solar panels and the grid tie inverter, although the point of diminishing returns applies. As Mr Hotwater has quite rightly pointed out, if you are going to introduce some kind of PWM power limiting control ahead of a grid tie inverter, the pulsing nature of the load needs some consideration. With the correct approach, I think there might be some really bright possibilities with this approach. Cheers, Tony. |
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| renewableMark Guru Joined: 09/12/2017 Location: AustraliaPosts: 1678 |
Very interesting, Clockmanfr, that Ozinverter project looks great, for the moment I just need something plug and play, but that looks like a fantastic winter project. Cheers Caveman Mark Off grid eastern Melb |
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| hotwater Senior Member Joined: 29/08/2017 Location: United StatesPosts: 120 |
I had 5V of ripple on a 12V GTI system. It took 54,000uF on the input to clear it up. Not long ago I saw a youtube video where the guy was using a PWM motor speed control from his 48V battery to the GTI to limit output. He had some external caps connected to the GTI input with about six inches of wire. He commented those wires were getting warm. Duh, that source is too ridgid. I'll be trying throttling using PWM from a large array and will probably need a simple buck to lower ripple currents. For grins you ought to look at incoming voltage of panels only on a scope. It was way beyond what I estimated. |
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| Clockmanfr Guru Joined: 23/10/2015 Location: FrancePosts: 427 |
Nicely put Warpspeed, this PWM power limiting control ahead of the GTI ie, direct from the panels, has concerned me for some time. Hence my simple bang bang on/off comparator circuit, it reads the battery voltage and switches the AC side of the GTI. But you are correct. there are great possibilities for DC control. Everything is possible, just give me time. 3 HughP's 3.7m Wind T's (14 years). 5kW PV on 3 Trackers, (10 yrs). 21kW PV AC coupled SH GTI's. OzInverter created Grid. 1300ah 48v. |
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| hotwater Senior Member Joined: 29/08/2017 Location: United StatesPosts: 120 |
The point is that there seems to be less than optimum capacitor size on the input and these already experience high ripple. I'd rater replace an external capacitor bank than tear a unit apart. You wouldn't put that little capacitance in a sine wave inverter you built. Higher efficiency might also be gained. The PWM input works because it takes advantage of the solar panels constant current nature, but it will add additional capacitor currents. If done from a stiff battery bank, these currents are much higher. It could be very easy to also blow the PWM FET in that case. In my situation all my arrays go into capacitor banks and devices feed off those. Besides an additional capacitor bank at the input here will be an additional diode and inductor forming a simple buck to reduce the surge current. Just a heads up for those with scopes to look at input ripple voltage. I'd be interested in what people see and if additional capacitance raised the power output. Not everyone has great access to inductors and I've done some experimenting with UPS and microwave transformers used as inductors in a low frequency buck. Not great with a lot of iron core heating but workable with acceptable losses. The FREE part overrides those concerns. This approach would be preferable over straight PWM on an array buss that would feed some other devices by not dragging down the array voltage. |
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