 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. |
Forum Index : Solar : Stand alone solar
Page 1 of 2   |
|||||
| Author | Message | ||||
paul_mac1 Regular Member  Joined: 17/05/2010 Location: AustraliaPosts: 74 |
Hi all, I'm thinking of setting up a trial stand alone system for my shed. Will these panels be to powerful for a 24v battery bank. Cheers  |
||||
Madness Guru  Joined: 08/10/2011 Location: AustraliaPosts: 2498 |
Unless you use an MPPT charge controller those panels won't give 250W as they will be limited to 5.57A which at 24V = 133W and at 28V = 156. There are only 10 types of people in the world: those who understand binary, and those who don't. |
||||
| George65 Guru Joined: 18/09/2017 Location: AustraliaPosts: 308 |
Something learnt every day.... Although I have a vague recollection of MPPT and may have known but forgotten this.  I think my understanding was that MPPT would Boost low input voltages rather than buck and convert high inputs. With that, PWM will then only take the Chunk of power in it's range and convert and output that? Other thing, panels are limited in current over wattage? In this case 5.5A wether doing 50V or 5V? Would answer something I was doing before with a test setup. I was also using house panels, although only 36V Pmax with a PWM controller on 2x12V Batteries and was getting far less amps than I calculated as the total power available. This would explain why. That said, I was running 2x12V batteries into a 2000W 24V inverter and it worked pretty well. Ran the outdoor fridge for months off this setup without problem. I also added a Kettle through a PWM speed controller and had that doing about 70W Constant. Just enough to keep it under the boil. When I wanted a cuppa I'd turn it up to 500W ( had a meter on the output) and the water would be at a rolling boil in about 15 sec. As I limit myself to about 10 cups of coffee a day, this was quite a practical and fun bit of playing around. Paul, This will work but You will have to watch the voltage on the controller you buy. I used Cheap PWM controllers ( some far better than others!) and they worked well but are inefficient as pointed out, If that does in fact matter. If you have a bunch of these panels as I did and are just mucking around, it probably won't. You will just have to be careful of their input rating as from what I remember, that will well be at their upper limit. I was looking at tapping into the panel where the diodes were and bypassing one so as to get a lower voltage. I was aware of the lower output as well but it seems that may not matter. I am wondering now if you may be able to do better with this and the gurus here may advise. If One used 2 of the 3 " circuits" from each panel and paralleled the 3rd leg with the spare from the 2nd and subsequent, then 2 panels would give 3 lots of 5.5A.... would they not? It would seem on a 50V panel each pair of legs would give 33V at Pmax which would be a nice voltage for a PWM Controller to output 24V and increase the output from each panel nicely. All seems nice and convenient, what am I overlooking and missing? |
||||
| Madness Guru Joined: 08/10/2011 Location: AustraliaPosts: 2498 |
MPPT = Maximum Power Point Tracking which means it allows the voltage of the panels to rise to where the controller thinks it is receiving the most power. Then it steps that down to the battery voltage. Lots of info on the web about MPPT, be very careful if you are considering a cheap chinese one as many are fakes. PWM controllers simply reduce current flow when needed to regulate the battery voltage. Short circuit current is shown on the label as 5.75 amps and that is the most you will get whether it is 1 volt or 49 (@ 25 degrees panel temp). Multiply voltage by current and there is your watts. If you connect those panels to 12 or 24 volt they will work but it will be a greatly reduced amount. There are only 10 types of people in the world: those who understand binary, and those who don't. |
||||
| paul_mac1 Regular Member Joined: 17/05/2010 Location: AustraliaPosts: 74 |
Hi guys, thanks so much for the replies, this renewable energy stuff is confusing, as you can tell, I'm not a sparkie and new to solar battery storage. So my understanding is the above panels would be wasted really on the system I was planning, so, the following panels would be better suited?  Thanks again, Paul |
||||
| George65 Guru Joined: 18/09/2017 Location: AustraliaPosts: 308 |
Depends on the controller you use. If you pay the extra for an MPPT it would be efficent. With the cheaper PWM, ($20) not so efficient. You would get 8A out of these panels Vs 5 with the cheaper controller or closer to the full Power with an MPPT. If you go the MPPT, be careful of what you get. Loads on fleabay are said to be MPPT but they are not. The cheapest true MPPT is this one. https://www.ebay.com.au/itm/MPPT-LCD-Solar-Charge-Controller-24V-72V-10A-Compatible-DC-DC-Boost-Charge-E6V1/142537532578 ?hash=item212fe624a2:g:yfoAAOSwJTZZ4CIY This unit has come down a LOT in price since I last looked at them! Didn't realise they were so cheap now. Might buy one myself just to play with even though I don't have any real use. at that price would be fine to have to connect up to some of the machines in the shed to stop the batteries going flat. Anything below that you can guarantee is not MPPT regardless of what it says on the controller or the listing. One of these would give you the maximum efficiency of any panel you put on it. I have seen these things reviewed on YT and they seem to be good even long term. I seem to recall one guy having trouble with the capacitors and he simply externally wired in some larger ones and the things were working perfect 12 months later. Depending on the size of your battery bank and how many panels you want to throw at the project, you could get a couple of these and parallel them or have the panels offset in direction etc an make 2 strings. There is a bit of learning with this stuff but I did the same as you 12 months back. Someone gave me a panel, I got a controller and some old batteries and went from there. it's a lot of fun and rewarding. Although on grid, I have a stack of panels sitting in the back yard that are now making me more power than the house is using. I'm backfeeding and spinning my power meters backwards during the day and using the power I have " banked" at night with a little excess atm. It's great to have something to play with the Mrs even wholeheartedly supports and is behind. Was just discussing something else for this and said not sure if I'll need it. She said well if you want it lets go get it and if it's not what you want you can always sell it again. Long time since she's ever said anything like that! :0) |
||||
| Madness Guru Joined: 08/10/2011 Location: AustraliaPosts: 2498 |
Those panels with maximum power at 31 volts are perfect to use with a PWM controller on a 24-volt system. On bulk charge, it will charge at 28V with a PWM controller so there is only a very small percentage difference to the theoretical maximum power. There are only 10 types of people in the world: those who understand binary, and those who don't. |
||||
| paul_mac1 Regular Member Joined: 17/05/2010 Location: AustraliaPosts: 74 |
Thanks again guys, George65, the link doesn't seem to work, it says the item may have been moved or is no longer available. I'll be getting 5 of these panels, if they are still available when I get home (I work away) and 4x12v batteries, 100+ah. I know it won't eliminate my bill, but as more panels appear on the net forsale, i could expand the system. They are poly panels tho, would I be better off buying dedicated 24v mono panels off fleabay? The seller wants $150 each, but will negotiate as a job lot. The Mrs is behind the idea, as she hates paying what the power companies charge. OK I found the item, I just typed in the item no. Thanks for that. Paul  |
||||
| Madness Guru Joined: 08/10/2011 Location: AustraliaPosts: 2498 |
Panels do sell for a lot less than that, $50 per panel is not unheard of. Nothing wrong with poly panels, I believe they are better in cloudy conditions anyway. I think that ebay controller is the same as this one If you continue with your plan as it is you are better off with a 48 V battery if you plan to grow it into a serious system. This may be something you have covered already but why not just install a 5KW grid tie system? I see them advertised for less than $4k installed and you could get finance on it if needed. There is also the option to add batteries but that would increase the cost quite a bit. There are only 10 types of people in the world: those who understand binary, and those who don't. |
||||
| hotwater Senior Member  Joined: 29/08/2017 Location: United StatesPosts: 120 |
How have you gone from powering a shed to knocking down what the power company charges. First off you have batteries and you loose from the start. Per KW used from the batteries is the sane as from the utility. Second you are buying stuff without a plan. I can just about live on that number of panels, but no one can squeeze an electron like I can. Grid tie is your best pay off if it can make it through the regulatory process. You might want to consider something like this for a payoff. https://www.youtube.com/watch?v=ZClpSM8Z6do |
||||
| paul_mac1 Regular Member Joined: 17/05/2010 Location: AustraliaPosts: 74 |
Hi hotwater, I can't see how that system is compatible with my gas hot water system. I do homebrew beer and a stand alone system for my shed would save on power costs as I run fridges and heaters for my beer. Cheers. Paul |
||||
| George65 Guru Joined: 18/09/2017 Location: AustraliaPosts: 308 |
Where abouts are you Paul? I'm buying 250W panels for as little as $40 ea in lots of 20 in Sydney. Guy turned down an offer for 20 On friday saying he wanted $50 ea. 5Kw for $1000. You can recover that in easily under 12 months. The controller is the same as mad linked but I also agree with Hotwater. You have gone from one thing to totally another. With 4 panels, controller, inverter wiring/ switches and all the rest, you are going to be lucky to see a dent in the power bill and it will take you probably 2 years before you are in front. I currently have 6.5Kw of panels in the back yard waiting to go on the roof. I am running 2x 2KW inverters, one is a bit cripled and won't do more than 1800W out from the 2.5Kw of panels it's hooked to. Today it produced 11KWh, yesterday 13. That's where I am, $7.5 worth of power in 2 days. Lets say I average 10 Kwh a day, $3.00. x90 days in the billing cycle, $270 off your bill. THAT you will notice. My setup is bootleg. I have 3 phase power and have 1 electronic meter which can't be backfed and 2 spinny meters that run backwards very nicely indeed. I moved everything except 1 leg of the 3 Phase AC and the off peak hot water to the analogue meters. The inverters atm are back feeding through a power point on a circuit on each of the spinny meter phases. As we get more into summer I'm getting around 25KwH+ per day from the 2 arrays. 25Kwh x .30C Kwh x 90 days is $675 worth of power per 1/4, $2700 per year. I got the inverters for Nix and have 2 more, a 4KW and a 5, also given to me and working. I'm going to try and get everything up on the shed roof this week and order the steel to build my own frame in the next day or 3. Once I get the panels up on the roof which is more clear of obstructions and will get at least 90 min more light a day, I may get as much as 30 Kwh Consistently depending on time of year. Will be half in winter. For a 10Kw System which is my end goal, The PVWatts site predicts a generation of over $4200 worth of power over a year. My max so far is 32 Kwh in a day a couple of weeks ago. Buying the panels ( at the right price) used and the inverter, you should be easily able to recover the cost in a year with a 5 Kw setup. Our place is pretty power heavy as we have to run pumps for the sewer 24/7 for a start as well and the Mrs and daughter loving to have the max number of lights and appliances going at all times so you may offset the majority of your bill with 5 KW. I don't believe in saving power and I'd be bored out of my mind trying to watch every watt of power. I come from the other way where I want to use/ waste all I want and cover it through my own generation. ATM I am over producing but as soon as the hot weather and the AC is used, I'll be coming up short. How short I'll keep an eye on but I would like to get another 5kw up so I can keep the bill small as I can without getting disconnected. The key to my setup is that I still, for the moment, have the old style meters. When they go, I'll have to spend some more money on a work around or go offgrid which may be a no brainer when the time comes.I'm trying to get some of the ducks in place now so if I want to do that I'm not starting from scratch. At first I mucked around with some panels and batteries PWM charger and inverter to run a fridge and kettle and that was all good fun and a great learning experience. I knew I was spending more than what it was worth and that was fine. It's called a hobby. If you want to get serious and shave the bill, then you need to take a different approach. If you have an old analogue meter it's real easy, If you don't it's a bit harder. Myself I couldn't ever see buying a new system with the ripoff feed in tariffs and other BS they subject you to But who knows in the future? I'm talking to my brother in law about a new system though because he works from home and has astronomical bills. A 10Kw system for him would repay in under 2 years just on the offset charges let alone any (if) feed in returns. His major consumption is through the day and minimal at night so works perfect for him. If you have a spinny meter you could start with 4 panels and a Powerjack type inverter which plugs into the power socket and backfeeds off setting your usage and rewinding the meter with any extra. If you have an electronic meter you need to be careful because almost all will record any backfeed to the grid ( ie what you generate in excess of what you are using) as a COST. You have to do the maths though. Work out the cost of your setup including all the hidden things like wire, switches, clamps, connectors etc, work out your power cost, how much you will be producing and come back with the return on investment time. We all bitch about the cost of power but it's not that easy to produce your own cheaper than you can buy it. Once you include batteries, it's very hard |
||||
| paul_mac1 Regular Member Joined: 17/05/2010 Location: AustraliaPosts: 74 |
I'm in Adelaide, There are a few systems around for sale but the amps differ, making them not that efficient, so I learned today. The idea is to start small and expand over time, starting with my shed then expanding to the whole house. We use 7.5kwh per day. Cheers |
||||
| Madness Guru Joined: 08/10/2011 Location: AustraliaPosts: 2498 |
You should have a good hard look at a grid tie systems before you spend any money. It is the most cost effective even though it would be new, you can't diy install secondhand stuff connected to the grid and still be legal. It would be the best to keep your wife happy too. You can replace your gas hot water with a large electric and have a timer on it so it only runs during the day when the sun will power it. There are only 10 types of people in the world: those who understand binary, and those who don't. |
||||
| hotwater Senior Member Joined: 29/08/2017 Location: United StatesPosts: 120 |
Everyone has their own sense of reality. What can be done and what someone can do are quite different. Many things in a home require heat. We have a dishwasher that takes next to nothing to run, I could run one with a SLA battery. Heated dry element takes 1KW. I take the wires going to the heater element to a relay to switch solar panel DC buss to the elements. No big expensive inverter required. Takes a little work to do it. I just bought a $20 low flow pump for my water heater so I can add an external heater to the tank. I only use my chest fridge during the day and store cold for night. Think of ways to avoid a large battery. I just use mine for surge current. Buy yourself a new car battery so your wife doesn't get stuck somewhere. Use the old battery for your projects. |
||||
| George65 Guru Joined: 18/09/2017 Location: AustraliaPosts: 308 |
True but depends on your risk assessment. My setup will be over engineered and protected so all I'll have to worry about is the power company getting their knickers in a twist. The way they are here the chances of an inspection are less than winning the lottery. I'm happy to take that risk. This is the next thing I'm looking at. For me being grid connected, the cheapest and easiest way to do everything is just back feed and use what I want as normal. I could change the hot water from off peak to the normal circuits I backfeed. Thing is, the back fed power is worth 30C Kwh. The offpeak is only 11C. Unless I have excess power and have to shut down part of the system to avoid going into credit, I'm better off using that power on the normal appliances. I just did the numbers on the hot water cost ( haven't been here a full billing cycle yet) from a meter read and I can't find the paper I worked it out on but I do remember thinking it wasn't worth worrying about and unless I was given a load of free panels I had no use for, it was going to be better just to buy the power at that rate than try and supply it myself. I'm far better off using the power I make to run the AC which will cost .30C KWH than the hot water at .11C Kwh. If one were on a FIT it may be different. If you were only getting 6C a kwh and buying it for 11 then obviously self supply would be more economical. A timer is OK but there are a number of inverters now with the water heating dump load circuit built in. They send any excess power to the water heater first and only when that is not accepting power will they back feed it. I know Fronious are one inverter that do that and there are others. There are also separate controllers now that will do the same job although they are damn exy for what they are though one can be built from a kit. If someone were only using 7.5 Kwh a day of power, the return on investment on any solar system is not going to be fast. If my quarterly power bill was only $290, I wouldn't be worried about paying that in the least! At least $80 is going to be supply charge which you'll still pay ( or more) when solar is added. |
||||
| George65 Guru Joined: 18/09/2017 Location: AustraliaPosts: 308 |
Just got the latest power bill. Hot water cost me a grand total of $75 for 90 days or 85C day. That's supply and power charges. Total use was 675Kwh or 7.4 KWH day. I suppose 1.5- 2 Kw of panels and an inverter would take care of most of that but still better off to put that power towards the regular billed supply until I have an excess there. I had another idea I'll keep in mind and see how I go with our useage over the next couple of months. The Mrs and Daughter have a fking annoying habit of doing washing at night and then using the dryer because they don't want to hang it out. I might look at running a cable from the hot water to a power point in the laundry and have that for the washer and dryer. That way they can fill the washer and set it to come on automatically and only use the dryer on the cheaper rate. I can imagine the screams of protest that will entail but not that the main culprit, my daughter, is paying for the power.... or much else for that matter. That would cut the cost of the power used by .19C Kwh so would be worthwhile. The meter read was the 15th of this month. Right now I'm 50KW up on one phase and 17 Kw in the red on the other I back feed. I had a bad connection on one array while I was away so I think that's why the power has got away there. I can always put both arrays on the same phase to line them up if need be but that phase is coming back slowly. |
||||
| hotwater Senior Member Joined: 29/08/2017 Location: United StatesPosts: 120 |
I am lucky being off grid and doing the system on the cheap. The savings in monthly service charges alone pays for the system. Short of grid tie that is difficult to get the economics. I talk about hot water which is low hanging fruit and one of the few ways to store energy. It only makes sense as a dump load of last resort when energy can't go somewhere else. Without some continuous load the payoff isn't there when still connected to the grid. An elaborate control system does make a payout possible. Changing peoples attitude from I want it when I want it is just as improbable. Some day we will be paying really high costs for grid demand and time of day use. The internet of things will have every device connected for big potential cost savings. Only if you have a 12 year old in the house. Technology advances, but we don't. The VCR went out of production before we could figure out how to make it stop flashing 12:00. I'm as pro solar as anyone. For grins go to solarpaneltalk. They cut first timers to shreds there. |
||||
| George65 Guru Joined: 18/09/2017 Location: AustraliaPosts: 308 |
I read this a lot but other than hot water, in what other form is this stored energy any good? Is there a way to convert it back to something useful like electricity? Only so much hot water I need or can use. As for heating, I don't see a lot of value in that. I'm far better off running my reverse cycle AC to warm the house which gives more heat out than the amount of energy put in and certainly more than an electric element. I only need heat 3 months of the year anyway. Rest of the time I'll want Cooling or the ambient temps are fine. That said, I'm currently looking to buy a slow combustion wood heater when hopefully they are cheaper over the summer to convert to oil fired. MUCH easier to collect and give oil a basic filtering than Cut wood. Done enough of both to well know. Not exactly sure what you are refering to but think I may be one of those people. I'm not interested in saving and counting every watt of power, I want to generate all I want to use anyway I want. To be totally honest, I have done it tough all my life both financially and emotionally. I spose the hard work and scrimping has paid off now and I am very comfortable and well off thanks to some investments that paid off big time. I just want to be comfortable and enjoy the rest of my days and spoil the wife and daughter. I'm happy to pay the upfront cost and do the work to make my own power to allow me to do whatever I want without worrying about the cost. might be a bit ironic now given I can afford any amount of power I want but after a lifetime of having to be careful, doing it any other way would make me very UN comfortable..... unless I win $5M+ on lotto... which I'll have to start playing to do that. Couldn't agree more there! Already some of these Time of use rates which are supposedly to save people money are ludicrous here. One rate I have seen is almost .60C Kwh in peak period. The off peak is not all that cheap either. I am always astounded at how people fall for and really believe a company with shareholders to answer to really wants to save you money and therefore make less profit/ Dividends to pay their execs and investors. Do people seriously not see through this crap? Anything a company does to supposedly save you money they have crunched the numbers with their huge data gathering so they can actually make MORE money from you. Do people really believe that power companies would spend 10's of millions replacing all the old meters so they could put in new ones which would have the effect of reducing their profits? Yeah, well I spose some people will fall for whatever rubbish they are fed without a 2nd thought. The Ads that really get me are the ones being run here promoting smart meters and smart appliances. They show people out at dinner or on holidays gleefully looking at their phones checking on their power bill.... anywhere, any time. Really? You are out to dinner with a hot date and the thing foremost on your mind you think is a real worthwhile convenience is checking your power bill? Is that because you are crapping yourself over what the next bill will be and trying to figure out if you can afford the meal or are going to have to fake a heart attack at the end to get out of paying it? Yeah, you hear about it whenever you are out with friends, every one having a a good time but always talking about how they wish they could check on their power bill right then. Well gee wizz, isn't it great that after lamenting that all these years finally you can log on and check your power bill when every the overwhelming desire grips you! The worst part is people fall for this crap. They are already talking about being able to turn off your AC when power is short with these " connected" appliances and can tell what you are using/ doing by what your power consumption pattern is. It sounds like big brother gone mad to me. I spose these "Smart" appliances will be forced upon us because you won't be able to get anything else. Hopefully by the time that happens, I'll be either dead or living in assisted care so won't give a damn. Sounds like fun. Maybe they might get more back than they bargained for if they try it on with me. Not something I have ever shied away from! :0) |
||||
| Boppa Guru Joined: 08/11/2016 Location: AustraliaPosts: 814 |
OUCH, just spent the last few hours browsing through SPT, , I'd be banned there within hours there are people there with a lot of knowledge, but some of them are so abusive I'd leave long before I found out anything useful from them And the ones that are `the book says this and thats the end of it' made my bread and butter for the last quarter of a century lol- what the book says and what works in the real world are two entirely different things, something I had to almost `punch into their brains' with some uni degreed types who were long on theory and short on real world experience Whats in the books doesnt always translate well into the real world, and while they might be good `engineers' in theory, to turn them into good tradies is almost impossible, they simply over run costs and generally do a pretty poor job in the field |
||||
| Page 1 of 2 |
|||||
 Print this page |
