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BenandAmber Guru Joined: 16/02/2019 Location: United StatesPosts: 961
Posted: 04:50am 09 Jun 2019
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Is there any benefit to having a small inverter on every solar panel
I've heard that some company make something like this 4 grid tie
Could they be made for off-grid use
could they be made very cheap
Would all of them add up 2 bigger wattages
Could it be done without them talking to each other
Could all of them be same as mppt and inverter combined
Does this ideal sound interesting to anyone
Are there big problems that just don't make this worthwhile to investigate further
Would like to hear from everyone but especially the Great's on here
be warned i am good parrot but Dumber than a box of rocks
mackoffgrid Guru Joined: 13/03/2017 Location: AustraliaPosts: 460
Posted: 05:15am 09 Jun 2019
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If I'm not mistaken they're called microinverters. The idea is sound, but economics keeps beating them, I believe.
hary Regular Member Joined: 15/04/2019 Location: FrancePosts: 89
Posted: 06:10am 09 Jun 2019
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Hi BenandAmber and everyone
I've tried to PM you but it seems you don't receive the message. As my outbox is still empty !
Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406
Posted: 07:17am 09 Jun 2019
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Yes, cost, and complexity.
Cheers, Tony.
Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1578
Posted: 09:18am 09 Jun 2019
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Well I'm far from a " great" but if you are interested anyhow....
Micro inverters main purpose is to allow Better output on strings of panels on a roof where some may get shading. They optimise the output much like an MPPT over a PWM controller.
If you have a string of say 8 panels and some, 1-2 or whatever get shaded, the string does not fall in output by say 2 panels worth, the whole string comes down to just what those 2 shaded panels are outputting because they are all in circuit and interdependent as it were on the lowest common denominator being any shaded panels.
With a Micro, each panel is in effect parallel rather than in circuit. If one panel ( or however many ) are Shaded, the output of the remainder stay at full capacity rather than being dragged down by the shaded panels. In other words, the array goes down in output by 2 panels worth not the whole 8 fall through the floor.
If you have no shading issues, the benefits are greatly reduced. They could be beneficial if you had say 3 panels on one roof face and a few more on another and some facing another direction but shading is the main problem they address. If you have shading issues, don't worry about buying Micros, Buy a chainsaw instead.
I bought a set of panels that came with Micros and I have to say I was not impressed. I found the micros I had, which may not apply to them all and is against their idea, generated less power in total than the panels all hooked in series with a regular ( not so new) single GTI. Having multiple inverters is supposed to have the opposite outcome but I have only played with one lot and that was the result -I- got.
IF one had panels that did not suffer from part of the string being shaded, there is VERY little advantage if at all. I can think of several drawbacks for grid tie that's for sure. For off grid, Moving you panels where they go clear sun would be far the easiest, cheapest, less complicated and reliable and sensible option.
Micros I also found to be a right pain in the Butt to wire up because you have to wire each panel to the micro and then each individual micro to the AC supply. To me it was more complication and potential failure points for no benifit.
I'm sure many would argue with my position, especially those in the solar industry trying to make a buck out of selling the things but unless you had no way of putting panels in clear sun, any possible gains micros -may- have over regular controllers or inverters would be highly negligible at best.
BenandAmber Guru Joined: 16/02/2019 Location: United StatesPosts: 961
Posted: 11:18am 09 Jun 2019
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Buy chainsaw lol lol
Thanks for all the input everybody
I think this was just a silly thought it turns out
Edited by BenandAmber 2019-06-10be warned i am good parrot but Dumber than a box of rocks
Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1578
Posted: 02:12pm 09 Jun 2019
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No Seriously! Fixed the shading issue I had with the panels on my shed right up! I Bought the Biggest Chinese thing they make and it's a monster! Goes through anything! Of course I only Hired the excavator to get the stump out but it was all well worth it.
Full sun on my panels and no messing about with Micro Inverters! :0)
Sometimes some real good things come from silly ideas!
BenandAmber Guru Joined: 16/02/2019 Location: United StatesPosts: 961
Posted: 02:27pm 09 Jun 2019
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You're right davo99
I was saying my idea of inverter on every panel was silly
Chainsaw is very good idea
lots of fun too I bet you can't use it without going vroom vroom
Chainsaw always brings out the kid in all of us
Years ago me and several Neighbors had competitions on who saw would get the fastest
You could shave with the teeth of the sawbe warned i am good parrot but Dumber than a box of rocks
yahoo2 Guru Joined: 05/04/2011 Location: AustraliaPosts: 1166
Posted: 05:00pm 09 Jun 2019
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off grid is usually parallel wired there is no point unless you are running high voltage battery banks. I'm confused, no wait... maybe I'm not...
mackoffgrid Guru Joined: 13/03/2017 Location: AustraliaPosts: 460
Posted: 09:45pm 09 Jun 2019
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Ben, the idea is not dumb at all - it just hasn't panned out to be economical at the moment. Solar panels are 1/20th of the price they were 10 years ago. Sun tracking systems have gone the same way. They're a good idea, it's just cheaper to get more panels than invest in these ideas.
Cheers Andrew
Boppa Guru Joined: 08/11/2016 Location: AustraliaPosts: 814
Posted: 07:52am 10 Jun 2019
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One of the biggest issues I think is that in most cases, the microinverter is wired directly behind the panel, in other words you are putting a electronic device in (in some cases) extremely hot environments- I found even with our existing mppt gridtie that on hot days it didn't like being in direct sunlight and would seem to suffer from reduced output (sometimes going completely offline) where (temporarily) shading it with a large beach umbrella stopped this behaviour completely- currently building a 'cover' for it similar to what we installed over the aircon (aluminium)
Personally I wonder how many of those microinverters are going to still be working even in say five years??? Heat and electronics- never a good mix
Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1578
Posted: 11:01am 10 Jun 2019
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I have an inverter in my shed. I put a 40oc heat switch on it that runs through a relay to a fan on top that pushes the hot air back down through the fins and out. It makes a big difference to the thing in summer when they will derate due to heating up.
Without the fan the thing would get too hot to touch wouldn't couldn't be good for the longevity. The thing has a large finned heatsink but I learned a long time ago that there is no comparison of passive cooling to forced/ moving air. You don't need the fan to blow a gale, I have mine also on a PWM controller and it's turned ring down and uses about 15W Which is a heck of a lot less than even the first step of the inverters derating.
Not even worried about that so much as I make loads of power in summer, it's the longevity of the thing running that temp that concerns me. Hopefully I'll get a good long life out of the thing for my efforts.
I have read on a number of inverters that they are not to be placed in direct sunlight. All mine bar one are outdoor units but I have them under cover in cool, dry shaded places.
I agree that having Micros under panels must be like toasting them. I'm sure they are designed to take the heat, for a while any ways, but the fact was when I went to sell the Micros I had, there was a virtual stampede for the things from people wanting 2 and 3's for replacements and spares of failed ones they had. Could have put double the price on them and still cleared them out.
My view has become trying to make solar efficient is uneconomical. Always cheaper and more efficient especially in winter and on bad days just to have more panels. Least till you run out of roof space.
Then you go to ground mount! :0)
BenandAmber Guru Joined: 16/02/2019 Location: United StatesPosts: 961
Posted: 06:30pm 10 Jun 2019
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I think this post is starting to be a good lesson for some of us newbies
lots of good information on getting a good all-around idea of off grid electricity
and how it works in the real world
Always design for equipment to be in the shade and out of the weather
It's cheaper to buy more panels then a solar tracker
Behind your solar panels is a very hot environment
Some things that's common sense to you guys is new information to others be warned i am good parrot but Dumber than a box of rocks
Boppa Guru Joined: 08/11/2016 Location: AustraliaPosts: 814
Posted: 11:52pm 10 Jun 2019
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I sometimes wonder about the mounting rails most rooftoppers are fixed to, they are almost always run horizontally across the roofline- almost completely blocking the airflow from bottom to top of the panels...
We know that keeping panels cooler increases the output and the life expectancy (although the number of people online that seem to think the 20-25 year guarantee- usually of 80% of original output- literally means they have to be replaced at this time!!!) they probably could be still well usable for a half century or more- but heat does impact this lifespan
So my thinking would be by mounting the rails vertically ie gutter to ridge, you would get a 'heat chimney' effect with natural airflow actually increasing the cooling- and hence the output- of the panels- similar to how heatsinks work better with the fins 'vertical' rather than 'horizontal' and with most mounting rails almost completely blocking the airflow path behind the panels I suspect that this 'trapped heat' would drop the output- especially with multiple stacked rows of panels
The thought that brought this on was I was up cleaning some panels (bloddy flying foxes) and I noticed that at each rail there was a detectablely hotter 'blast' of hotter air near the upper mounting rail of each row of panels, and the third row nearest the ridgeline was hottest of all
Obviously this would be more difficult on rooflines with the old 'corro' waves or colourbond 'ridge and hollow' profiles and you would still need the 'side to side' rails to mount to the roof itself, but it would be interesting to see how adding another set of rails between the rows of panels and those 'flat' rails running vertically instead ie gutter to ridgeline direction instead would both raise the panels by the height of those rails, increasing the airspace behind the panels, and would also make a 'heat chimney' to improve natural convection current airflow for cooling
It would be fun to get some actual measurements on this on an actual install, two sets of panels side by side, each with the different mount methods and get realtime figures on each sets outputs- I suspect there may even be a measurable effect on the arrays output
Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1578
Posted: 02:27am 11 Jun 2019
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I would suggest the rails are not impeding the airflow near as much as you might think.
If you look at a panel, it's virtually hollow in that the actual part the cells are mounted to is above the framing when it's mounted. Most I think are 30? mm deep frames and the backing/ cells glass I would guess would be about 5mm so should have 25mm Clearance under the panel even if it's mounted on a broad flat surface. The rail when mounted usually runs along the top and bottom 3rd or 1/4 of the panel length so there is still airflow under the panel and over the rail.
The heat would have to build up and push below the lip the frame makes but that's going to happen no matter where the rails are. It's just another of the many things with solar where trying to make anything more efficient is chasing your tail and the cost Vs performance increase is never worth it.
To scare all the purists, I have a metal roof and my panels are all mounted direct on the roof with the normal solar clips/ brackets through the screw holes holding the metal down. I take the screw out, put a dob of silicone on the hole, put the screw through the bracket, put it back in the hole and firm it down. Being a metal roof there would still be some airflow under the panel through the roof corrugations. I don't say it would be near as much as with the things on rails however....
Last summer I had 2.5Kw of panels on a ground mount. OK, it was some lengths of rails across some Milk crates while I was testing the panels. On another forum there was discussion of cooling panels so I went out and looked at the output of the panels, gave them a good hosing down and came back and looked again. On average the output went up 150-200W.... for maybe 90 sec then the panels obviously heated up again and went back down.
If you wanted to get that 200W all the time, You would more than spend that amount of power on a pump capable of providing enough water flow to keep 10 panels cool plus the cost of the setup plus water cost if you had to pat for it because the evaporation would be significant. That is after all what is going to cool the panels and water in a closed loop system.
There was also a suggestion of fans but on a warm/ hot day, the I doubt there would be enough temp differential to make air cooling effective and, in order not to go backwards, you have 15W per panels to Spend before you would be better off doing nothing. I'm no expert but the experience I have with thermo Dynamics gives me the gut feeling no 15W fan is going to lower the panel temp by one degree. You -may- cool a part of the panel a degree or 2 but then I wonder about having the panel at different temps and the stresses that may introduce.
Just to confirm what I have seen before, I just went out and shot the temps of another ground mount set of panels. They are leaning on only one rail and have virtually unlimited airflow underneath, certainly more than if mounted on a roof. The ambient temp here right now is 22oc. It's clear and sunny skies. The temps my panels are running at is 44 o for the ones lying too flat and the ones at nearer the correct winter angle are a significant 10O higher at 55o C. I shot the back and the front of the panels and there was no temp difference.
I also note the rating of the panels like all I have seen is at 25o C. In other words, soon as the things start making any power, unless they are in a place that's covered by snow, they are above rated temp anyway and falling off the curve. If they can go 55 on a 22o winters day, WTF is there temp in summer on a 35 or 40o day?
I was going to try and cook an egg on one in summer after I burnt my hand trying to pick a panel up that was in the sun. I have no question it cold be done with ease. Probably cook a steak if you just kept moving it round the panel.
One would have to look at the performance data of a panel to see what the temp increase does on performance. guy feeling tells me there is probably a bigger difference between 25o and say 60 or 70 than there is between 70 to 100 or whatever the high end summer temps might be.
It should also not be hard for the intelligent and educated people to work out what the energy absorption is of a panel. As a very rough guess, the panels rating is 1000 w per m2. A panel of 250W capacity is roughly 1.6m2 So at rating is collecting probably near 1.5 Kw of energy given the thing is significantly black.
Like an IC engine, only a small part of that energy is converted to electricity, probably 16% for a good 250W vintage panel which works out pretty close to the surface area/ power output calculation. If we take 250w of electrical energy from the 1.5 Kw guestimate of heat the panel is absorbing we have 1250 W of heat to dissipate.
1000w m2 is pretty good sun but achievable in good aussie summer sun so rounding down, that' still going to leave us with 1Kw of heat to dissipate Per panel JUST to bring the panel temp to ambient which if using air is going to be 35o easy in summer and you are never going to be able to achieve anyway. None the less, you'd need a significant amount of airflow to do that and I can't see that being any less than about 80W and probably a lot more. And of course that's only to bring it down to a temp still 15oc above panel rating so there is still going to be some falloff.
I did see a think where they have water cooled panels which is used for water heating as well but the things cost a bomb and by accounts I read aren't that good. I can see where they would be counter productive anyway. Might be better to have your panels at 50o than 100 but question is how much and would you be better off just putting up more panels even if you have to limit your grid feed in?
I have yet to see any method of improving panel efficiency that is financially efficient.
I sure look forward to the day I do though! :0)
Edited by Davo99 2019-06-12
Boppa Guru Joined: 08/11/2016 Location: AustraliaPosts: 814
Posted: 03:22am 11 Jun 2019
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If the panels are mounted 'vertical, they might be, but I have noticed many are mounted 'horizontally'- I suspect because they can use three rails per two rows of panels instead of four
They were like these
rather than like these (which your 1/3 &2/3 mounts are commonly used with) and do provide an air path between the panel and the rail
As the rail sits on the actual frames of the panels (one rail shares both the top and bottom panel edges, with several bolts between the two panels and a 'washer'/aluminium fitting on top of the two panels) there is no airpath over them, and at the ends you could feel a stream of distinctly hotter air coming from the lower edge of the rails (here's a blurry closeup of the clamps between the panels, mouse pointer is pointing at one)
Notice. New forum software under development. It's going to miss a few functions and look a bit ugly for a while, but I'm working on it full time now as the old forum was too unstable. Couple days, all good. If you notice any issues, please contact me.
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