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Forum Index : Microcontroller and PC projects : Current measurement of solar panel output
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| BrianP Senior Member  Joined: 30/03/2017 Location: AustraliaPosts: 292 |
To balance the contribution of Rf1 and Rf2 in the current sense amplifier gain, an output resistor Rf3 should be connected between pin A1 and Gnd. The value of Rf3 should be chosen according to the following formula. K1 = 10 = Rg3/Rg1= Rf3/Rf1 = Rf3/Rf2 Can any of you maths gurus enlighten me on how to apply the above. I need to end up with a value for Rf3 with Rg3, Rg1, Rf1 & Rf2 known. I'm confused by all the = operators  I know, I should have paid more attention in maths class at school  B |
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| PeterB Guru  Joined: 05/02/2015 Location: AustraliaPosts: 639 |
Rg3 = 10 * Rg1 Rf3 = 10 * Rf1 Rf3 = 10 * Rf2 Rf1 = Rf2 I think that's correct (It's all a bit of argy bargy) Peter The system thinks I'm a guru. They have to be kidding. P Edited 2019-08-18 20:28 by PeterB |
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| Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1577 |
I take it this $30K includes Batteries and other things? That is a LOT of money just for the panels/controllers you have even going back to what they were. I have spent under $2500 on my DIY setup over the last 2 years. I save an average of $1200-1500 per QUARTER on my bill being all electric. No batteries, all grid tied. I have bought everything used and bar winter, make more power than we 3 use including an un economical Daughter and a wife that does not understand/ car about power consumption. That said, she has seen how much my solar mucking arond saves us and what ever I want she gets . In summer I switch off half the system and am still in front. This summer I'll probably have to throttle it back to more than half. Currently, there is 9.5 KW on the shed, north facing on a 5KW inverter. There is a 4KW inverter on the house facing west with 8.2 KW of panels. There is a 3.6 Kw inverter with a mix of west panels on the house and and 3.75 ground array for a total of 6Kw. Over the last week I have averaged 52.4 KWH day. I did a 3.75kw ground mount for winter this year and it's worked very well being at winter tilt and perfect orientation. I'll probably take it down in about a month and put the panels up on the roof. It survived all the winds despite being a very temporary thing and has certainly given me some very useful power. If it were possible and worth while, I'd set everything to winter orientation and tilt because summer takes care of itself anyway. Last summer when I had more panels in a different setup I got up to 72 KWH day. I have a 5KW Inverter I recently got to replace the 3.6. Don't know if it will make much difference, the 3.6 often outdoes the other 2 having the ground mount array on it atm. I am getting some HD circuits installed to take the outputs more safely which is only going to cost about $360 and will allow me to pump back a lot more power without the voltage rise issues in the wiring. I also had a mixture of 175, 190 240 and 250w Panels. I have disconnected all the 175 and half the 180W panels and just bought 25 250 w panels so I can make everything ( bar the 240's) 250w. I can't come near being self sufficient in winter due to heating with AC but If I eliminate that load I probably will be able to. In winter we can use 60 KWH a day on average. Average generation mid winter ( Sydney) is about 35Kwh day. I think I'm about done as far as panels go, not much point going any more although I certainly could. Haven't even touched the north roof of the house yet but I'm saving that in case I ever have to get a legit system.... and the fact that although it is unshaded it's a bugger to put panels on with the pitch and being tin. I would strongly suggest that if you are grid connected and especially if you have the old spinny analogue meters, batteries are not a cost effective way to go. Spend the money on used panels which I buy for $100 KW, usually less, and put up as many as you can. Used panels are Very cheap and the repayment time is months. I have bought over 150 Used panels now and I have had 2 with hot spots but still worked well. I have them as " Play " panels heating the green house and driving the car radiator fans in my shed window which do a fantastic job of keeping the metal box cool in summer and actually nice to be in with the gale for breeze they provide. I put a system on my fathers shed roof. Wrong orientation, wrong direction, shaded more often than not by 100 Ft Gum trees. Overclocked that about double and it still does well. From memory I put about $600 worth of panels and inverter into that system and it halved his power bills 3 quarters of the year and he admits he uses the AC now more than ever before... which is exactly what I want him to do. He broke even on that setup in about 10 Months. Would have been faster had I installed it in spring rather than the end of Autumn but he';s not complaining. You can spend a lot on solar and get little in return or you can spend a little and get fantastic ROI. There are many devices to address shading issues and some are not cheap and would take a very long time to pay for their own cost which is always something to look at. Out of all these Optimisers I have looked at, by far and away the best I have come across is also the cheapest to apply to a whole systems and gives returns like nothing else I have seen. It's called a Chainsaw and applied liberally to any offending foliage, does a great job in increasing solar production. I have been so impressed I have got 3 of these marvellous devices now and to stop the problem coming back in the future, the application of an excavator on the remains as I have done round my place works brilliantly to eliminate the problem once and for all. Also give great peace of Mind when storms and gales blow through. If you live in one of these places where they are particular about saving these things, ( from what I don't know, there is millions of them!) and won't let you remove them, Make friends with your local Fire captain. For a slab or 2 he may decide said foliage is a fire hazzard to your property and issue an order for said solar impediments to be removed and NO ONE can over ride or contest that. :0) |
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| PeterB Guru Joined: 05/02/2015 Location: AustraliaPosts: 639 |
Davo If you come near my gums with a chain saw I'll... I'll...I'll...think of something. I really will. How dare you. Peter |
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| BrianP Senior Member Joined: 30/03/2017 Location: AustraliaPosts: 292 |
Hi Davo The $30k includes everything involved in the installation, including panels, controllers, 3kva & 5kva inverters, batteries, cable, circuit breakers. For safety & convenience each parallel connected battery bank has its own circuit breaker. Back then a 175w panel could cost $300-400, 200ah batteries (12v) were many hundreds of $. All these things are much cheaper today. Regarding gum trees, there are 2 main offenders quite close to the house. I've been hoping mother nature might rise to the occasion & let them fall over (fortunately strong winds come from a direction that would push them away). At this time of the year thanks to the trees we only get 3 to 4 hours of direct sunlight on the panels, & that is subject to how much cloud. Trouble is, one of the trees is a koala favorite so it's protected  This whole journey originally started as an experiment to which extras have been just added on. So it's not the most efficient design. We average about 18-20 Kwh per day consumption. P.S. Sounds like you'd better stay well clear of Pete's place  B |
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| Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1577 |
HAHAHA! I have the biggest gum tree in my area. It's listed as.... something significant. It's been said by experts to be at very least 450 Yo with the general agreeance putting it at likely 600 Yo. I can't get my head round figures like that. Makes it a hell of a tree even when Captain cook arrived. I'm sitting here now watching the 50Kmh wind blowing the crap out of everything and just being thankful the wind always comes from the house to the tree, rather than the other way round. I couldn't live here with the wind blowing it toward the house. One limb of that thing could take out at least half the house. I'm not against trees but I don't like them anywhere near Buildings and Civilisation. |
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| PeterB Guru Joined: 05/02/2015 Location: AustraliaPosts: 639 |
I can't be sure but I suspect the tree was there first. Peter |
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| BrianP Senior Member Joined: 30/03/2017 Location: AustraliaPosts: 292 |
but how can we be sure?   |
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| PeterB Guru Joined: 05/02/2015 Location: AustraliaPosts: 639 |
Quite easy really. We cut Davo in halves and count the rings. Don't they teach you young blokes anything in school? Peter |
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| Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1577 |
I was given a little 12V 1.5 A panel and already had a cheapy controller I had on a battery charger so I wouldn't cook batteries when I forgot to turn them off. Having a panels was kind of fascinating. From there I got some new panels from a Neighbour who thought my place was a convenience for Building his house and went home and left some panels in my driveway. Suffice to say they weren't there the next day. I eventually set them up on some batteries with a UPS and a PWM Controller. That used to run a small fridge and an Urn through the day which provided me my 10 or so cups of daily coffee. Before I moved in here I bought a used array of 20 180W panels and a GTI. Hooked them up on a ground mount ( Lent them up against the bushes for about 3 Months) And then just built it up from there. We have saved a fortune on power and we can run the AC day and night and do anything else most of the year and not have to worry a bit about the cost. I have gone out on a bit of a limb this last week and forced an estimated read of our winter power bill. I estimate it would have been about $525 which is good for this area as all the homes around average $12-1800 quarter. Given I am starting to get ahead on daily production, I estimate by the next read in November I will have cancelled out the winter bill or a big chunk of it. I'm building a 3 Phase generator atm to be able to backfeed during winter so next yeah will be able to keep up with what we use. I'm also hoping to put in an oil fired heater which I was going to do this year but got complacent. If I can take the heating off electric, I think we will be OK all year round. If you add any more solar, check out the used market. You have to look but I now get shrewd and buy good panels for $15 ea for 250s and often get the inverters as well. When I get all my old sub 250's down and replace them. I'm going to think about using them to build a carport off the side of the shed with as that could probably me more economical than buying Colour bond. How much power do you generate on average and what is your total array sizes atm?? Can you do a ground mount somewhere that is not so shaded? If the whole yard is shaded ( !!!) so much of the time, the best thing is to go for brute force and just use a heap of panels. With all that shade, I'd be setting them flat as that will get more reflected light from the sky and get the most from overcast and summer days. |
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| BrianP Senior Member Joined: 30/03/2017 Location: AustraliaPosts: 292 |
@Davo99 said: How much power do you generate on average and what is your total array sizes atm?? Can you do a ground mount somewhere that is not so shaded? If the whole yard is shaded ( !!!) so much of the time, the best thing is to go for brute force and just use a heap of panels. With all that shade, I'd be setting them flat as that will get more reflected light from the sky and get the most from overcast and summer days. Hi Davo When all the panels are lit we have about 5Kw capacity, daily totals vary from 24Kwh to only 1 to 2 Kwh on a really bad winter's day.  Unfortunately ground mounting is not an option (no shading benefit) so we are stuck with the status quo. Here's a couple of profile images to illustrate the variation.   The max. daily generation is also limited by the house consumption at the time & the battery capacity. If they are full, they are full! Currently on a full summer day charge we have just enough battery capacity to last overnight on the areas of the house that are connected to the inverter. So, I need more panels & more batteries  Incidentally, the advantage of batteries is you still have power when there is a mains outage. With a battery-less grid feed installation no mains, no power! B Edited 2019-08-20 18:18 by BrianP |
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| Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1577 |
Nothing unusual about that! Obviously summer but you can't have too much shading to get 24KWH from 5 Kw of panels. The year graph looks as I'd expect as well. These battery Chainsaws are reeeeealy quiet now Brian!! And powerful! My Father bought an AEG 58V and the thing did better on the dry 50CM hardwood log than his Mini boss petrol saw did. just wait for the wind to come up then 3/4 cut the trees on the windward side and they will go over and you can plead complete Innocence. Better still, take the neighbour out for dinner and get a contractor to come in and do the dirt.... errr, hard work for you then you have the perfect Ali-by. Don't forget to pay cash! Yeah, I know that feeling, sometimes, often times, we just don't use enough hot water and my biggest power storage just wont take any more. When I put in the outdoor bathroom. I'm going to get another hot water tank as backup. Panels yes, batteries.... My ideas are Different. Batteries just don't recover their own cost atm and I don't think they will for the foreseeable future. That being the case, I'd strongly suggest that putting all your available finances into panels and taking the FIT would be a better investment than batteries. I have not batteries but I always have power in the few blackouts we have had. I have a GENERATOR! Several of them actually. Working on another big one atm. Wish we had more blackouts here. The grid is just too reliable but I think i'm going to get my wish this summer. The grid was on the ragged edge here last summer and I think the straw that has broken other camels back's in other states has made good progress this way. You CAN actually hook your GTI inverter to a generator and get the solar power. It has to be done the right way, so there is enough load to take all the solar so it isn't trying to push back to the genny but it does work. The solar will do all the main work and the genny will give the GTI the grid reference and take up any extra requirement the GTI can't provide. Edited 2019-08-26 21:01 by Gizmo |
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| BrianP Senior Member Joined: 30/03/2017 Location: AustraliaPosts: 292 |
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| BrianP Senior Member Joined: 30/03/2017 Location: AustraliaPosts: 292 |
Davo99 said: If I went FIT I would lose the substantial discount currently in place & with the current feed-in prices available I think I'd be worse off. Regarding batteries - If you are fortunate enough to know (or know someone who does) then there are ex Telco batteries available which are usually in quite good nick. They throw them out on a scheduled basis & can be sourced for a fraction of new price. If I was getting more batteries I would be going this way (I do know someone )I notice the so-called Energy Regulator is warning of potential widespread blackouts at peak times this summer, so I might need my batteries... Make sure your generator is fueled up & ready B |
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Gizmo Admin Group  Joined: 05/06/2004 Location: AustraliaPosts: 5012 |
Fixed this thread. Remember when you quote or use other forum codes, dont edit the forum codes structure, especially make sure the trailing ] is there. The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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| Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1577 |
Yeah, I noticed the report too and remember watching the AEMO live output last summer when nearly every day they were below reserve capacity and stretched to the limit. I put a post on another forum about potential Blackouts this summer and most people virtually laughed and some referred to the Eieio report and said blackouts were unlikely. I asked if anyone wanted to make a bet and put the money in escrow and we'd see how we went march 1 But typically, no one would put their money where their indignant opinions were. I said I suppose after it happens these people will blame something else or claim that only 50K houses were affected for only 4 hours so wasn't really a blackout or make some other excuse. Someone suggested that I couldn't claim " Current limiting" as a blackout. Well if there is no power because they were running out, I guess the amount of power was Limited but its still a damn blackout! I'm going to talk to the sparky about putting in a changeover switch this week. For the most part NSW was spared power shortages last summer but I don't expect that to be the case from here on in. Looking at the way power is transferred around now, the only place that looks to be OK is Qld. Everyone else seems to be robbing peter to pay Paul and as soon as the hot weather hits a couple of states at once.... Good Night. You are most fortunate being able to source the batteries. Love to get some myself at the right price like that but unfortunately don't have the connections. Even a small setup that could be run from solar would be an advantage. |
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