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Forum Index : Solar : Solar GTI input Maths
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| Mulver Senior Member  Joined: 27/02/2017 Location: AustraliaPosts: 160 |
Hi All, I am after some advice to make sure I am on the right track. Whilst i am planning on slowly making my OZinverter it became apparent that I first need more solar panels. I currently have a Growatt 4200MTL with 8 x 190w panels. My original plan was to buy 20 x 250w and sell the 190's. Maxing out the inverter with 2 x 2500w strings. But considering i have plenty of space, 190's are in abundance and cheap too. I was thinking of running 4 strings, 2 in parallel of 11 x 190w panels, with the parallel strings at different angles (virtual tracker style) The inverter allows max 600v DC and 2 x 15amp (15amp per mppt) Each string of ll is 490v max, 5.6amp max, in parallel 11.2amps. My understanding is as long as the volts are kept within the inverter specs, it should have no issue controlling the excess amps. Any advice appreciated! |
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Madness Guru  Joined: 08/10/2011 Location: AustraliaPosts: 2498 |
So you are suggesting 44 X 190W? There should be a figure for maximum watts input per MPPT, 15 Amps would be for a lower voltage, as the voltage is higher you would have a lesser current at the maximum watts. As far as I am aware going over a little, perhaps 10% is okay, I have had a 3KW Aero-sharp connected to 5 KW of panels. It randomly errored out and completely shut down, most of the time it kept it under control. I was not too concerned about it as I have lots of spare Aero-harp PCBs. There are only 10 types of people in the world: those who understand binary, and those who don't. |
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| Mulver Senior Member Joined: 27/02/2017 Location: AustraliaPosts: 160 |
Yep. I know it's a lot but they would be facing different directions. Inverter specs Max Dc power 4400w Max dc voltage 600v Start voltage 150v Dc nominal voltage 360v Pv voltage range. 100v to 600v Mppt voltage 175 to 550 Number of trackers 2 Input current per string 15amps Ac voltage 230 Ac amp 18.5 |
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| Madness Guru Joined: 08/10/2011 Location: AustraliaPosts: 2498 |
Is the 490V at maximum power or open circuit? You need to be careful about that too especially on cold mornings, voltage is highest then before the Inverter clicks into the grid and pulls the PV voltage down to maximum power voltage. Power output from the panels is still quite high when they are at a more acute angle to the sun, I would be inclined to get a second GTI. If you have AC running everyday when the there is plenty of sun you will reduce the amount of power your OGI needs to push back into the batteries. Once you get to float that will drop back to near nothing too. There are only 10 types of people in the world: those who understand binary, and those who don't. |
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| Mulver Senior Member Joined: 27/02/2017 Location: AustraliaPosts: 160 |
490v is open circuit voltage. 44.5v each panel 400v maximim power voltage 36.2v each panel This is for on grid use at the moment! |
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| Madness Guru Joined: 08/10/2011 Location: AustraliaPosts: 2498 |
If you are connecting to the grid there are all sorts of rules, have a talk with your installer before buying secondhand stuff. One of the local solar companies was selling off brand new panels at a discounted price as they no longer were able to be used for a new grid system. There were substantial Clean Energy Council credits for installing new solar systems which may work out cheaper. Current government would prefer we used coal though. There are only 10 types of people in the world: those who understand binary, and those who don't. |
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| Mulver Senior Member Joined: 27/02/2017 Location: AustraliaPosts: 160 |
Thanks Madness, the system is already on the grid and been running for a few years, I'm planning on adding more and re configuring the panels to extract the most out of the inverter. |
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| George65 Guru Joined: 18/09/2017 Location: AustraliaPosts: 308 |
I have done a similar thing to what you are thinking. The drawback with smaller panels is the mounting costs. I found some cheap universal brackets at bunnings and just remove a screw from my metal roof, place the bracket underneath, screw back down and then put a tek screw straight into the panel frame. Solid as and costs me about .40c per panel. I also wired the arrays in square groups so the connection ends can be beside each other and I don't need to run a long single wire back from a long single string. If you want to rack them, that can cost as much as the panel itself per panel. As long as you keep the Voltage within limits the amps will take care of themselves. I ran a 2 KW inverter on just under 4 KW of panels for a couple of months with no probs. The thing will do their max output and reject the rest. Regulations ( If you are concerned about them) allow for a panel to inverter ratio of 1.6. In other words you can put 1.6Kw of panels on a 1 KW inverter or multiple there of. The advantage of this is you generate more power for longer in the day. Peak output is relatively short lived, it's the ramp up in the evenings and fall off in the afternoon that from my experience makes the Biggest difference to the KWh's generated by sunset. As to the different angles, I am doing that too. Not sure it makes any practical difference, all averages out, just makes for easier mounting. 400V max power on a 600V inverter should be fine. I have not found mornings to be a problem rather cloud edge effect sends the voltage soaring. All the inverters I have used just shut down and reset when they get something they don't like so i think you should be safe. I have a string Of 250W panels running on the same inverter ( Single tracker) with an array of 190W panels. Everything I read said no good. So I tried it. Works fine and definitely contributes worthwhile power. Because the 190s are higher voltage than the 250's the end voltage of a string of 11 250's and 8 x 190s is only 16V away open circuit so it plays together fine. I have each array on it's own breaker so I can isolate them and see the output change. The 190's definitely pull their weight. |
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| Mulver Senior Member Joined: 27/02/2017 Location: AustraliaPosts: 160 |
Thanks George that's exactly the information i was after! |
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| Mulver Senior Member Joined: 27/02/2017 Location: AustraliaPosts: 160 |
Probably should have put the other post here, not in electronics ..... whoops sorry! Link to it. Solar Diverter |
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yahoo2 Guru Joined: 05/04/2011 Location: AustraliaPosts: 1166 |
There is like a temperature threshold where mosfets start to degrade. High temperatures for extended periods under load will deteriorate them. if you are going to run a GTI at higher loads for extended periods you should consider some active cooling. KarlJ and a few others done a lot of testing on this over a decade ago and come up with some simple duct and fan goodness. sigh, good times!  I still remember the first time I had panels bristling from all sides of a house, it felt like a new era had arrived. I'm confused, no wait... maybe I'm not... |
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| George65 Guru Joined: 18/09/2017 Location: AustraliaPosts: 308 |
I have a 5KW inverter that seems to get way too hot for my liking doing 3.5kw output. It's inside the shed out of the sun and next to a usually open door. Atm I have a tube fan sitting on the top of the thing blowing down. The air that comes out the end would put a fan heater to shame when the thing is doing 3kw consistently. I just bought some little thermostat switches set for 40oC. I'm going to stick one of those to the heatsink and then to a fan so it will come on automatically when the thing heats up. I'll look for a couple of large computer fans. I did have some rippers out of a server but I threw them away when I moved as I had them forever and had never used them. Always the way. Active cooling is so much more effective than passive cooling. I don't know why they all don't have fans on them. My indoor aurora does and that never really gets how even when sitting there flat out all day. I think the power consumed is well worth it. Inverters back off hundreds of watts when they heat up. 30 or 50W on a fan is only a fraction of what you'd loose when these things go into self protect mode. I want to find some more busted panels. I have a couple of shattered panels on the garage roof driving a pair of car radiator fans for ventilation. If I could find more and wire them to the fans the same as I have now, wouldn't need the thermistors. As the day gets brighter and the solar radiation goes up the fans spin harder. Totally automatic and proportional and at full tilt they really put out a gale. Maybe I should make some sort of mounting for the fans I have and direct them to the inverters and put the thermistors in the shed for running a fan? |
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| Madness Guru Joined: 08/10/2011 Location: AustraliaPosts: 2498 |
At what temperature do they normally start to reduce output? 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 |
This is an extract from the solar quotes site but I believe it is incorrect: Here are the derating temperatures for some inverters that are popular in Australia: Modern SMA transformerless inverters: usually start to derate at 50°C. Modern SMA HF Transformer based inverters don’t derate at all. Samil Power River Inverters derate at 45°C Delta Soliva inverters derate at 50°C They say the inverters derating temp is ambient. Reading the manual for my inverter ( which I now can't find) it said it was the INVERTER temp that was the basis or derating not the ambient. Makes sense to me. Obviously if an inverter is pumping out 5KW on a 20o day it's still going to run a lot hotter than one doing 2KW on a 30o day. I check mine often enough to know. In any case, don't think anyone would argue that heat is not a good thing for electronics, especially caps like those found aplenty in inverters. Cooler you can keep them the better off they will be. |
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| Phil23 Guru Joined: 27/03/2016 Location: AustraliaPosts: 1664 |
This is what I have ATM. A cut up shallow storage tub to sit over the top of the inverter, it's not sealed, has about a 1/2" gap ATM. Some 4" sewer pipe, 4" inline fan and some 4" foil flexible duct that ducks under the house where the air is much cooler. The fan consumes 26W on high, 23W on low. 198m³/h & 165m³ respectively. Some they of thermostat is on the to do list Cheers.   |
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| Madness Guru Joined: 08/10/2011 Location: AustraliaPosts: 2498 |
You could get a job in China translating manuals to English  There are only 10 types of people in the world: those who understand binary, and those who don't. |
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Ralph2k6 Senior Member Joined: 24/09/2017 Location: AustraliaPosts: 129 |
Clever arrangement Phil. Is your green inverter there one of those Axpert/voltronic/infiniti/giant/other brand, inverters that have the fans pulling the heat downwards? Ralph |
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| George65 Guru Joined: 18/09/2017 Location: AustraliaPosts: 308 |
That's simple and impressive ingenuity! I like that so much I think I'll steal the concept. I'll do the same thing with the tub but mount a bunch of computer fans in it so they all blow into the plenum the tub forms and exhaust out through the inverter fins. I think that will be cheaper than a tube fan and I have dug out a couple of ripper fans I pulled out of an old server. Used to call that thing the Tumanski after it's weight and the way the 16 Fans spun up in stages till the thing shreaked like an old non bypass jet engine. I can power the fans being 12V off one of my broken panels which will make them automatic. More the sun shines and the more power the inverter is producing, the faster the cooling fans will run as well. I have also been thinking of using something similar for a test setup with a ( broken) solar panel to heat water. I want to silicone something like a shallow tray onto the back of a panel and have an in and out hose with a little pond type pump to more the water through. When I go to move my test panels after they have been in the sun even on a cool day, they are up to over 50oC (going by the temp threshold of what I can handle and have measured many times) So on a hot day, they must really be cooking. I think one could get useful heat out the things with a water cooling setup and I'd like to try it. I think the real test will be the panel backing and it's ability to stand up to long term water exposure. |
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| Boppa Guru Joined: 08/11/2016 Location: AustraliaPosts: 814 |
I found this,has some interesting figures in it regarding heat losses in solar panels with various cooling systems attached study eta I dont know about the backings ability to handle water longterm, maybe sticking an Al or copper panel to the backing plate with heatsink compound of some sort and soldering copper water pipes to it? duuno, just throwing some ideas out there |
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| Phil23 Guru Joined: 27/03/2016 Location: AustraliaPosts: 1664 |
Yep that's the type. The box (Bunnings under bed storage tub), clears the inverter by about 15mm. Cut it to fit with the angle grinder (cut/melt). Also cut the lid out so it can screw to the ply & make the other bit easily removable. Re Computer fans, I find they have very low air flow once there's any restriction. The transfer fan doesn't suffer that. During our hottest days, the ambient air on the N/E side of the house, (shaded) was 36°C, while the air pulled from 2 feet under the house near the floor joists was just on 32°. Well worth the effort of the 3 feet of flex. Phil. |
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