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Forum Index : Solar : Solar Panel Real World Power Output
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Madness Guru  Joined: 08/10/2011 Location: AustraliaPosts: 2498 |
I have been scratching my head for awhile as to why all my solar panels all make about 2/3 of the watts they are rated at. For example, a 5KW array of secondhand panels I installed earlier this year usually results in about 3.3KW according to the inverter. Others I have give very similar percentages. I was talking with someone recently who lives in a cooler climate (Flinders Island) than we have here in Queensland who said I should get the rated power output. I am about to buy another set of 20 260W panels as per the brochure attached. Looking at the specification it shows 2 figures STC Standard Test Conditions and NOCT Normal Operating Conditions. The NOCT shows the 260W panels putting out 193W, this is not far off the difference I get between the label and actual power output. I am wondering is just my location or are other people finding similar results. 2017-10-27_121018_EN-Eagles-265PP-60_rev2013.pdf There are only 10 types of people in the world: those who understand binary, and those who don't. |
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yahoo2 Guru Joined: 05/04/2011 Location: AustraliaPosts: 1166 |
In dry northern South Australia away from the hills and beach we normally exceed the panels rated output. I have done installs in seaside towns and the panels 1.5-2.0 km inland will be 10-15% lower output that the ones right on the beach. if you live on the eastern side of a big range (like on the slope, well up the hill) you can expect 40-60% reduction in output particularly in winter for southern states. Yes location and local weather matters a lot. dodgy mppt controllers a bit. Latitude not so much. some companies use radiation data from the weather logger machines at airports to calculate solar output, the problem with that is they build airstrips away from hills and on the flattest land they can find. Usually The very best place to put panels for maximum sunshine is close to the airport. They should really factor that in as they move away from the airfield and into the hillier terrain. I'm confused, no wait... maybe I'm not... |
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| Madness Guru Joined: 08/10/2011 Location: AustraliaPosts: 2498 |
I am about 10 km from the coast here and about 10M above sea level with only slight undulation. I have 25M high palm trees to the east on the neighbouring property that shade the panels until around 8.30. All 3 arrays have give similar percentage difference to the rated power. This is with 2 Midnite charge controllers and a GTI, I just remembered we have a 1.5KW grid tie system and it is similar also. Soon I will be moving to about 25KM from the coast and close to 300M above sea level. Temperatures there are often 5 degrees less than where we are now. Although the power output when we have full sun is close to 300% of what we need (have seen this after a few very cloudy days). I am looking more at what we get when the weather is not so good. There are only 10 types of people in the world: those who understand binary, and those who don't. |
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| Boppa Guru Joined: 08/11/2016 Location: AustraliaPosts: 814 |
My ex boss down south was heavily into solar (he ran his house and a workshop entirely off solar) and he did a lot of experimenting with them (note this was back in the 90's) He had a bank of 20 BP solars, and actually removed them from the roof and mounted them on ground stands This actually increased the output by around 10% His final verdict was that the roof mounts (the then standard ones supplied with bp solars) that basically sat the panels on the roof with minimal space underneath, caused the panel temps to rise to the stage they started losing power Putting them on the ground stands where they were open behind brought back that lost power Maybe something like that is happening? |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
From what I have read, solar panel power is rated under "laboratory conditions" with 1Kw per square metre of insolation at 20 degrees Celsius. That total energy is measured with a black body pyranometer that absorbs all wavelengths. Its actually the temperature rise from the absorbed energy that is being measured. What you get out in the actual sun, at various latitudes, altitudes, and ambient temperatures can be rather different. I have also read that in typical "Australian" climate conditions something like 80% of rated power in a clear blue sky might be about right. The same panel might behave very differently in outer space, or in the Antarctic, or the Sahara. It might be possible to achieve more than the rated power under some conditions, and a whole lot less in others. Cheers, Tony. |
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| Madness Guru Joined: 08/10/2011 Location: AustraliaPosts: 2498 |
Temperature is certainly an issue here, very few days are below 25 degrees ambient which is the STC temperature. I need to measure the temperature of the panels but I doubt I would be able to hold my hand on them for long. I have panels mounted at 26 degrees above a flat surface so they get quite good air circulation but still have the lower output. There are only 10 types of people in the world: those who understand binary, and those who don't. |
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| yahoo2 Guru Joined: 05/04/2011 Location: AustraliaPosts: 1166 |
I have been sent poor quality MC4 connectors a couple of times. Actually they were counterfeit sold as multi contact. Some of them got quite high resistance and run hot. I'm confused, no wait... maybe I'm not... |
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| Madness Guru Joined: 08/10/2011 Location: AustraliaPosts: 2498 |
I am using MC4's bought on Aliexpress but have not had any issues with them so far. The 5 KW array is in 2 strings and only 4 of these connectors that are easily accessible to check. The results I get compared to the rated power is consistent across all panels I have. There are only 10 types of people in the world: those who understand binary, and those who don't. |
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| noneyabussiness Guru Joined: 31/07/2017 Location: AustraliaPosts: 512 |
Just to weigh in here... im in NQ.. and we have had rain all morning (so panels are "cool") and the sun has come from behind clouds. .. i have mine directly connected to batteries at mo. (70v panel config, rarely get above 58v on batteries ) and the output shot up to 6.5kw... from " 5.2kw " worth of panels.. battery was at 54 so not really flat (went to 59) and yet full sun all day in summer and ill push to get 4.6kw out of them... so temps make a very big difference IMOP. I think it works !! |
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| Madness Guru Joined: 08/10/2011 Location: AustraliaPosts: 2498 |
You will get a big jump from "cloud edge effect" as they are not running at VMP you are doing quite well to get 4.6 on a normal day. There are only 10 types of people in the world: those who understand binary, and those who don't. |
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| M Del Senior Member  Joined: 09/04/2012 Location: AustraliaPosts: 155 |
My 1050w grid connect gives me about 800w most of the time. Depending on the temp, wind and time of year output is between 750-900w during the 4-5 hour peak period. System has just clocked up 8.5 years. I still see peak watts of about 1190 when the sun comes out from behind a cloud on a coolish day. Output during a miserable rainy winters day is about 160w per hour for about 3.5 hours. Not much difference to your system output. Mark |
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| noneyabussiness Guru Joined: 31/07/2017 Location: AustraliaPosts: 512 |
Lol... today was very warm.. barely got 3.5kw out of em during peak sun... I think it works !! |
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| Madness Guru Joined: 08/10/2011 Location: AustraliaPosts: 2498 |
Join the club that's about what I get, now you will think twice before crowing LOL. 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 have been playing with panels this year in a number of different configs and sizes. I too get about 75% panel rating on average. I have noticed what I just saw mentioned hereas "Cloud edge effect" and commented on it on other forums I frequent. Apparently no one at those largely Engine based forums knew what it was either. I put it down to the clouds modifying the magnetic spectrum of the light output. We only see visible light within certain wavelengths but there is a whole range of " Light" from UV to infra red. I have never seen mention of what panels actually react to but I assumed it may well be outside the visable spectrum we see. I presumed that the panels were sensitive to wider radiation wave lengths (I'm a photographer, I'm knowledgeable about this stuff! :0) ) and that was what they were reacting to with the water vapor in the clouds changing the balance of the wavelengths. I wondered abut clouds being white and gray may bring more red and green into the colour temperature of the light the panels reacted to than the predominant blue reflected by a clear sky. Another thing I have taken note of it the panels temp ratings. They are on the panels I have around 45oC. I have a reasonable perception of temp just by feel and I'm quite sure that my panels exceed that temp in almost any sun regardless of ambient temp. They are very warm to hot even at 9am when the sun is still pretty low and at an acute angle to their orientation. At midday, you virtually can't touch the bastards or even the frame work. By the info I have, that would automatically drop the panels output right there and I thought of it as kind of a marketing deception. "They do this output at that temp but in practice they will never run that cool". I also notice the standard 1000 ( whatever) M sq of light per sq meter. I wondered what the " Normal" light radiation levels were I experience here on the outskirts of Sydney? Maybe that is a reasonable radiation level at the equator but the one thing I have learned in life is ratings are always best case scenario the manufacturer can engineer for the test and usually have little relevance to real life. I have pondered how you get that much light on a M2 of black surface without raising the temp too much. I thought maybe these days they can use LED lights with heat absorbing lenses like they used to have in old Photographic film enlargers and slide projectors. Maybe they bounce the light to absorb the heat? Maybe they turn them over, fill the frames with chilled water and ice, then shine the test calibrated light from below so the panel is actually cool as a cucumber and they can get really good readings? I'm a sly bastard and I'll bet there are a lot smarter people out there that can come up with better ways to skew a test than I could. Maybe they do something as simple as what I just thought up cause that's all they need to do? Dunno, but I'll bet my arse there is a trick to it that bears no resemblance to reality of the way the panels are installed in practice but gives the manufacturers the best numbers they can get. I'm actually surprised to hear people get rating or over rating out their panels but if the light was intense over the rated standard and somehow the panels were not too hot, I can imagine it possible. ATM I'm playing with the panels and I have them all on the ground. Some are tilted on a framework I made up and a heap are lying flat on the grass ( and Killing it, probably through baking it to death. The panels that are tilted have the grass outgrowing underneath them all around by a good margin. Probably keeps it warmer and they get to absorb more dew as the rain here has been very scarce for months. The weather here of late has tended to be clear in the mornings, cloud over for the middle of the day and then clear up again pretty late. Alternately it's clear all day and clouds over in the last hour or 2 of light. I have a mix of 250 and 190 panels. One string on it's own inverter is 10 panels. They are the tilted ones at the correct summer angle and orientation right now. The other string I had another 12 250's which were flat on the ground. The tilted ones always did better than the flat ones despite there being more on the ground EXCEPT on overcast days where the flats produce a lot more ( low) output than the tilted ones which made sense to me since all the light was diffused and the sun non directional removing the tilt advantage and in fact making it at least somewhat detrimental. About a week ago after trying to read up on mismatched ARRAYS rather than mis matched panels in a string, I worked out that the 12 250 panels weren't that far away in voltage than the 8 109's I had which have a much higher open and loaded current rating. What I read said Current was more important which was miles away between the 2 But I figured the way the inverters work, Current is a product of voltage anyway. The 190s were just providing shade on the top of my Daughters rabbit cage so to kill a bit more grass, I laid them out on a couple of beams that gave about a 5o angle and hooked them up in series as a separate array and joined them to the output of the other array in parallel. The inverter I had them on was a 2 KW with only one input. Normally I would see about 1500-1600W out of the 3K array. Putting the other 8 190 panels worth 1.5 KW, the inverter is pretty much maxed out all the time. The flat arrays now eat the tilted arrays for breakfast in output. I guess they should seeing I have 4.5K of panels as against a 2.5K string even if they are flat rather than tilted. With 2x 2Kw inverters and currently I have 22x 250 Panels and 8 x 190 panels, my best output has been 28 Kwh for a day. Most days with intermittent cloud I'm around 20-24 KWH. the big surprise for me was we had 3 predominantly overcast days in a row a week back and every day delivered 16 KWH on the dot. I would not have expected anything like that output given the cloud cover. I just got another 5Kw inverter this week. It has 4 inputs. I got it used and didn't have the AC connector plug for it so I opened it up and just ran a cable direct from the terminals. One thing I did notice is all 4 inputs are connected. There seem to be 2 MPPT boards but the 4 terminal pairs are Paired together on what looks like one MPPT each pair but then a couple of other wires link them to the other board. To me it looks like no matter what terminals you use they all gget shared to the 2 boards. One of my other inveters, a 3 Kw Aurora is definately seperated inputs. I think I blew the hell out of one controller by accidentally hitting it with about 1200V from my IMAG generator I accidentally over capped. The max on this inverter is 600v. The most I can seem to get out of one side of that now is 1800W conversion. One pair works, the other does not. I also blew another 2 KW inverter. It seems to have lost the MPPT control and the wattage display is radical from 2 watt to 2 kw and is changing every second. I - thought- that having different inputs would control different and possibly mis matched strings individually but on this inverter at least ( Delta) seems to link them all and divide them across the 2 controllers and does internally what I have done externally in paralleling all the inputs from the 2 different arrays. It will be interesting to see what output I do get with the mismatched arrays. On ratings of the 2 groups, they are only 16V apart at their loaded rating. I don't know which way the inverter will pull them. I figure the 250's being the higher total voltage and the higher amperage will be the dominant array but the 190 array may pull them down a little. I'll have to measure the output I get on that inverter from each array separately then together and see how much I loose. I'm sure in this case there is a good chance 2 +2 will add up to something like 3.75 rather than 4. The thing is though I am gaining a GOOD output more than I would have with the 190 panels sitting there doing nothing. The real benefit is having the inverter so overclocked, it's producing full power way before the other array does it's max in the morning and way after in the afternoons. I read after doing this that the current thinking with installs is to over clock the inverters because 10 panels do not produce 10X their rating. IE, If you have 2Kw of panels, you won't get 2KW out which is what I have seen. Current regs allow for arrays to be sized up to 33% over the inverters rating which is to make up for the fact the panels in practice are over rated and there are losses in the inverter. I also see some companies now doing systems with 6.5 KW of panels on a 5 K inverter. Part of this is because in the greater part of sydney they have limited single phase installs to under 5Kw inverters but the amount of panels is open. And before anyone thinks this will burn the inverters out on a good day, no, it won't. The inverters just run at their max conversion and ignore any excess. You could run 10Kw of panels on a 2K inverter providing the voltage is in spec and they are fine. Now I have done all my " Learnin" with the panels on the ground where I can re-configure arrays and play with tilt etc, I'll start building frames to put them on the garage and patio roofs. I was going to do adjustable angle frames but given that idea away. I am going to set them at the summer angle. I looked up outputs on the PV watts site and found annually there is bugger all difference in output over the course of a year. The inefficiency of having them at the summer angle over the ideal all round at latitude angle would be compensated by ONE extra 250W panel on the 10 KW array I plan to put up. And that's theoretical. I have seen that the weather with clouds, a big bird sh*t, accumulated dust from long periods of no rain and other things are going to make more difference to my calculated yearly output than the difference between the summer and all round angle. The reason I'm going for the summer angle is firstly, I will want to run the AC in summer a lot as it's hot here. Secondly, there's bugger all power relatively in winter to start with and even the extreme variations of summer and winter angle, is only about 40 KWH a month over the worst winter month. Again, calculated and I'm betting weather will be the real dictator on what I get rather than angle. I also am in the process of setting up an induction motor as a generator and I can make up an extra 40 KWH in a few days running with either my 6 HP lister or even quicker with the 12 HP ruggerini driving the 3 phase motor. Probably use the lister as the ruggerini is a beast of a thing that I'm thinking of putting in a small boat for cruising the local river and the Lister is much more quiet and pleasing to listen to when you can hear it. The one thing I have learned with solar is that chasing efficiency is a mugs game. I'm buying 250W used panels for $40 on average. Talking to a bloke to get some next week hopefully for $35. I have loads of roof and yard space so far and away the cheapest ( and most secure mounting) way to make power is to just put up more panels. The side benefit is that efficiency measures like tracking and tilting mainly work in sunshine. When it's cloudy, the far and away most effective thing is more panels. If you have only 1KW of panels, tracking may be worth while. When you have 40 panels, forget it. One thing I do want to try when I get set up is fan cooling the panels. I have learned through other frivolous waste of time interests that moving air is a HUGELY more effective way to cool something than passive cooling. I want to see if I can produce a net benifit using some power to move air under the panels to try to cool them a bit rather than their " Natural" temp. I don't expect if there is a difference it will be much at all but i'm interested for another reason than efficiency alone. I plan to use maybe 2 car radiator fans in series off one panel to slow them down and move the most air at the lowest input. I'll measure the power used to drive the fans and the power output with and without over a bunch of days/ weeks and see what comes out best in the wash. I have had an idea in my head about using panels as a roof themselves. No reason they can't be screwed together and sealed with silicone between to be water tight. That done, a panel, Gyprock, whatever could go underneath as a ceiling and the air in the gap ducted for heating. I reckon there could be a lot of warmth to be gained from sucking the air from beneath panels and ducting it into an area such as a shed or home. Solar co-gen in effect. Anyway, sorry for the long rant but this solar stuff is something I have become very interested in and am very much enjoying taking my mind off other grief and woes experimenting with it and learning whats real and whats' misguided or internet waffles. I am back feeding my analogue power meters so saving a heap of money on the power bill in the process of having some fun and learning a lot. :0) |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
Efficiency might be more important on a camper van or a boat where installation space is extremely limited. But have to agree, on a house, panels are now so cheap, just keep piling on more and don't fret about losing small amounts efficiency. Cheers, Tony. |
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| Madness Guru Joined: 08/10/2011 Location: AustraliaPosts: 2498 |
Congratulations George, that has to be the longest post I have seen on a forum  .If you look at the PDF on the first post in this thread and the NOCT of those panels you will see the expected output is 185W for a 250W panel. I know someone who set up micro sprinklers to cool panels which did gain an increase in output but the power to run the pump canceled most of the gains. I am with you just add more panels, as for angles the ideal angle for grid tie is supposed to be 10 degrees less than your latitude. Where I am here in QLD it is 26.5 so the optimum fixed angle is 16.5, this is supposed give the best total annual output. But as I am off grid maximum annual output means diddly squat. I need to aim for the most output on the worst days which is when there are thick dark clouds. What myself and others here have discovered is that for this situation is to have the panels laying flat. This gives the most power when there is full cloud cover diffusing the sunlight. Flat panels see more of the sky and therefore produce maximum possible output. As for your comment about running 10KW of panels on a 2KW inverter, have you actually done this? I have been told most inverters will cope with 10 - 15% oversized array but 500% is probably pushing it way too far. Here is my result from yesterday which only had a couple small clouds, the array is 5KW laying flat, it peaked at 3.85KW. After that, the output was reduced due to a regulation system I am using to control battery charge.  There are only 10 types of people in the world: those who understand binary, and those who don't. |
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| Alastair Senior Member Joined: 03/04/2017 Location: AustraliaPosts: 161 |
When we built our house in 2016 I always intended to put on as much solar PV as was possible. I was informed by the installer that 5Kw was the maximum allowed. I argued that it was quite legal to fit more panels provided that the inverter output was 5Kw max. In the end it turned out that the vagaries of the roof shape meant that after the 24 tube HW unit was installed, the remaining N & W facing sections could only comfortably fit 18 x 280W panels (5.04Kw). A few more could be fitted but would have stuck out like the proverbial and spoiled the appearance. Veto by swmbo. The panels are in two equal strings, one to the N and the other facing W. The roof angle is just about right so they are flat on the metal roof with about 75mm clearance. We are near (200m) the coast south of Sydney so there is a cooling breeze most of the time. The best I have seen is 4.5Kw on a very warm clear day. I do not (yet) have any data logging so this was just a chance observation when I guessed it would be high. We have nett metering and after 10 months we have exported 50% more power than we have imported. We pay ~27c/KWh and get reimbursed 9c  . Next month a 12.5KWh Tesla battery system should get installed.What I have also observed is that due to the separate N&W strings, we get power consistently through a sunny day. Because we are near the coast the morning is often cloudy and clears about 10.30 to 11. The afternoon generally is quite sunny so we do well right into the late afternoon. I cannot claim brilliant design of the roof. It is just the way it worked out, although when I did the CAD design I did the best I could. We have lots of trees around but again fortuitously, the big ones are to the E & S so the panels are unshaded all day. If I was 20y younger I would have built a lot of it myself but a tall 2 storey house with sloping steel roof really did not attract me. I look forward to having the data logging that will go in with the batteries. I hope to be able to post nice plots like madness next year. Cheers, Alastair |
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| Madness Guru Joined: 08/10/2011 Location: AustraliaPosts: 2498 |
I was lucky and found a seller on gumtree who had 2 of the devices needed for the Zeversolar. If anyone else has a Zeversolar and wants one send me a PM.(private message, I don't want to see the Prime Minister) How much is the Tesla power wall going to set you back? There are only 10 types of people in the world: those who understand binary, and those who don't. |
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| Alastair Senior Member Joined: 03/04/2017 Location: AustraliaPosts: 161 |
Madness, The Tesla is going to cost me a bit over $10k installed. When I had the original system installed I told him that I would be putting in a battery system once the market had settled down. He made the wiring easy but ... I doubt I will ever recoup the $ outlay over the battery life (or my own) but it gives me some satisfaction and hedge against blackouts as it will do a switch over. At the moment it will only power 1 phase whilst the house is 3 phase. I should have ensured that the inverter was 3 phase - can't think why I didn't. I will have to rearrange the wiring a bit so the kitchen and a few lights are on one phase or change inverter. The problem is we are all electric and have an induction cook top and ovens. The cooktop is on a 45A circuit because of the surge current so that is out. I think the fridges, microwave and a few lights are all we need to keep functioning. That should be easy. make sure that the TV is not so we can regain a bit of sanity. I have dual citizenship so I can not become an MP thank goodness. Cheers, Alastair |
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| Madness Guru Joined: 08/10/2011 Location: AustraliaPosts: 2498 |
One thing is for sure, power prices are going up not down. How long before it is $1 per KWH? You might pay for the batteries in less time than you think. There are only 10 types of people in the world: those who understand binary, and those who don't. |
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