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Forum Index : Solar : 60 v 72 cell panels
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| M Del Senior Member  Joined: 09/04/2012 Location: AustraliaPosts: 155 |
Hi all So I was ready to get a system upgrade using 200w 72 cell panels (my old panels are 72 cell 175 watts)when I was informed that the 72 cell panels I was going to get had been discontinued, and the new 210 - 250 watt panels are all 60 cell designs. There are still 72 cell panels around but most seem to be moving to 60 cell for the grid connect market. As my plan was to eventually go off grid with a separate system using some of the new panels what are the pitfalls of using 60 cell panels in a stand alone system? It seems there are several options 1, Use MPPT as the voltage does not go as high and you need to use MPPT to get a decent charge and to get up to float mode. 2, Use the sunny island system of using a GT inverter to Sunny island inverter and charging the batteries via the sunny island inverter (I think that is correct). There will be more options and I am open to ideas. Mark |
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Madness Guru  Joined: 08/10/2011 Location: AustraliaPosts: 2498 |
My 48 volt batteries bulk charge to 59.2 so long as the panels do actually get to 60 volts it should work. There are only 10 types of people in the world: those who understand binary, and those who don't. |
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Gizmo Admin Group  Joined: 05/06/2004 Location: AustraliaPosts: 5078 |
72/60 cell or volt? I'm guessing volt. I would insist on the 72 volt panel, because its going to reach charging voltage earlier in the morning, or in overcast conditions. Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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yahoo2 Guru Joined: 05/04/2011 Location: AustraliaPosts: 1166 |
60 cell panels use a 156mm2 cell, the current crop of cells are graded into panels from 260 Watts to 280 watts. The current 127mm2 (5 inch) cell panels (72 cell) are in the 225 - 245w range. this is just from increases in efficiency at converting sunlight. The wattage's you are quoting for 60 cell panels is probably three or so year old tech. There is nothing wrong with that, just as long as you know you are not paying for something cutting edge and they are priced accordingly. Best thing you could do is get some names and model numbers and download the datasheets from the interweb and look at the voltages, specs and graphs for yourself. I'm confused, no wait... maybe I'm not... |
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| M Del Senior Member Joined: 09/04/2012 Location: AustraliaPosts: 155 |
Thanks guys, I knew I would leave something out. Hi Yahoo, you are correct, the wattages are higher than I wrote, the main thing I am trying to confirm is the voltages for charging batteries once I change over some of the panels to a stand alone battery system. More explanation, the panels are 225 - 300 watt, 24 volt. The difference is either 60 cells (6x10) or 72 cells (12x6) pattern. The system will initially be grid connect with half(?) the panels to be changed over to a stand alone system later on. Some of the panels will eventually be mounted in a 48 volt configuration which in the 72 cell panels open circuit voltage is close to 70 volts with a charging voltage of 62volts. With the 60 cell panels the open circuit voltage only gets up to around 60/61 volts with a charging voltage of 54/56 volts from what the sales staff offer and the literature will tell me. It is claimed the use of MPPT will fully charge the batteries using the 60 cell panels (56 volts will not quite do it), but there is a recommendation to include a gen set for weekly equalisation charging. The gen set is not required to enable equalisation with the 72 cell panels, it is only recommended to allow for the cloudy periods that occur when panels are not putting enough life back into the batteries. The three major sales mobs in my area only differ in the requirements for gen set back up usage, all claim the MPPT (60 cell panels) will fully charge the batteries, but nothing I find in the literature backs that claim up. The smaller guys are not interested in anything but grid tied installations. My use of 12 volt, 36 cell panels tells me the 24v/72 cell panels only need regulating, but the 60 cell panels would need some form of boosting. Is my thinking correct? Mark |
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Downwind Guru Joined: 09/09/2009 Location: AustraliaPosts: 2333 |
Lets back up a little and for now forget the panels, you suggest using a sunny island inverter charger, which is what i use. There is several levels to the sunny island and what method suits you best. So firstly we need to know what inverter (sunny island) or likes of you will be using, then advice can be given to suit. Personally i think the sunny island is a great system and allows for AC coupling with a sunyboy, to a existing ac sunny island grid. This means you can buy a cheap sunnyboy inverter off ebay (redundant upgrade inverter) and feed PV DC to the sunny boy and add it into the Sunny island AC grid anywhere, as any excess power to the load use requirement will back feed to the batteries. I think the short answer to your question is, you series PV panels together to give an output voltage within the operating range of the inverter, and a wattage rating less than the total rating of the inverter. So a 1100w inverter you could use more than 1000w of panels, as long as the inverter is programmed to a max of 1000w (or 1100w) Although in saying this the sunny boy inverters can be programmed to not exceed a higher wattage input than its rated capacity, even though the input wattage might well exceed the inverter ratings. The important factor is for the PV series string voltage to not exceed the input voltage operating range of the inverter. Pete. Sometimes it just works |
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| M Del Senior Member Joined: 09/04/2012 Location: AustraliaPosts: 155 |
Hi Pete, what you said made it fall into place. Utilising a couple of sunny boys with panels wired to about 275 volts will get me up and running, allowing time to work out the battery system. Then when ready to set up my off grid battery side (wife will not allow complete disconnection from grid) get the required sunny boys connected to a sunny island and the sunny island controls the battery charging. That almost takes the fun out of setting up a PL20/40 and working out panel voltages to suit battery charging and regulating. More reading, and searching, and list making. I just need to pick a path and do it before the boss changes her mind. cheers Mark |
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| yahoo2 Guru Joined: 05/04/2011 Location: AustraliaPosts: 1166 |
I have had a few inquiries from people with systems without SMA sunnyboy inverters on their grid connected system, from my point of view the options are still quite limited. A couple of brands have very mediocre backup and some others products are still very new (untested) on the consumer market, not ideal if I have to service it. I expect there will be a run on hybrid stuff this year, one company that custom builds already has orders till late November. I'm confused, no wait... maybe I'm not... |
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| Downwind Guru Joined: 09/09/2009 Location: AustraliaPosts: 2333 |
Im not sure what you mean here? Was that meant .. with sunny boys or without sunnyboys. Or are you talking about using other inverters with AC coupling on an off grid system. As for backup, i can not fault SMA, they have always been ever so helpful and without the need of being a accredited installer to get past the front desk to ask a technical question, to me they offer a AAA+++ service. Pete. Sometimes it just works |
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| yahoo2 Guru Joined: 05/04/2011 Location: AustraliaPosts: 1166 |
without sunny boys Pete. I guess you could call it high voltage DC coupling at a pinch, basically a grid inverter and a 500+ volt MPPT battery charge controller are sharing a solar bank. I'm confused, no wait... maybe I'm not... |
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| Downwind Guru Joined: 09/09/2009 Location: AustraliaPosts: 2333 |
Yahoo, You do realise any transformer base off grid inverter will also allow the H-bridge to back feed to the batteries, should AC supply be greater than demand. Quite simply a H-bridge works both ways, forwards and backwards, its what they are designed to do. So basically you can use any off grid transformer based inverter to create a micro grid and then AC couple any GTI to it, and when the AC supply is greater than AC consumption the inverter will work backwards and feed AC to DC and charge the batteries. This also has the advantage of the GTI AC power will be used for any AC load first, with the load difference being made up from battery power, but when AC supply exceeds demand it will reverse charge. BE WARNED The problem is in this case, there is no voltage regulation with the DC side in reverse charging, unless its a inverter charger designed for charging, which has voltage charge control inbuilt. The reason this is not widely used is 2 factors, 1) its not well understood by the average person, and simply it will back feed without voltage control to charging. 2) it requires some electronic skill to design a reverse charging control system to disconnect the charge to the batteries, and also allow feed to the micro grid on AC demand. Just remember if you get it wrong it will boil a high priced set of batteries dry, and FRY them. Pete. Sometimes it just works |
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| M Del Senior Member Joined: 09/04/2012 Location: AustraliaPosts: 155 |
Pete If I read correctly what you are saying the voltage coming out in reverse mode (240AC-DC) is not regulated in any way unless the inverter is also a charger? ie, it will be a 48vDC to 240vAC inverter but when reversed the DC voltage could be anywhere from 12-200volts DC. Unless it is a charger I knew the amps would be unregulated but thought the voltage would be 48-60ish, a bit like a dodgy unregulated power supply. More reading and thinking. Mark |
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| Downwind Guru Joined: 09/09/2009 Location: AustraliaPosts: 2333 |
Mark, I am not suggesting you take this path, and was merely responding to Yahoos comment. And to also add a little information to a somewhat unknown method. The sunny island uses this method with built in voltage control, making it a inverter/charger, all in the one package. Using reverse charging is not that different to adding a wind turbine, as both have the ability to overcharge a battery without some form of control, except with a AC coupled system to need the inverter to supplement any increase in in AC demand greater than the AC inverter (GTI) supply. This is how the sunny island and sunny boy AC coupled system works, is the sunny island inverter changes the AC frequency by up to 2Hz, when the sunny boys are set to off grid mode they respond to a frequency change and back off their output, which in turn controls the excess voltage to the battery. This allows for any amount of sunny boys to be AC coupled as they all respond to a frequency change. On average the sunny island works between 52Hz (full back off mode) and 48Hz, the reason for below 50Hz is for the time spent above 50Hz, it will also spend equal time below 50Hz, so within a 24 hour period the total Hz equal 50Hz/24 hours. The reason is many clock devices count Hz, and if the 24 hour period dont equal the required Hz pulses then all your clocks will be out of time. The sunny island has a built in function of controlling the frequency over 24 hours to correct this. Pete. Sometimes it just works |
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| yahoo2 Guru Joined: 05/04/2011 Location: AustraliaPosts: 1166 |
the systems with these charge controller fitted are basic, there is a DC transfer switch between the GTI and the charge controller and an AC transfer switch between the off grid inverter and the grid. There is no interaction. There is no battery charging from the grid. They dont make a lot of sense to me, looks like it they were originally designed as a grid failure battery backup then the marketing guys fiddled with things. I'm confused, no wait... maybe I'm not... |
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solarwind Regular Member  Joined: 03/02/2008 Location: South AfricaPosts: 51 |
If I were you and if you are going to keep the old panels, I would wire them separately from the new ones, position the old array to cash in on the early morning sun and the array with the new panels can be orientated as normal for the rest of the day. Then I would feed each array via an isolating diode to a common DC rail which then feeds whatever charging system you choose. This way, you make your "solar day" much longer (starts to charge batteries earlier in the morning). Just some thought from my side. You don't have success until you've tried it! |
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home heater Newbie  Joined: 03/03/2010 Location: AustraliaPosts: 9 |
OK, too much info there to absorb it all, for what it is worth here is my advice:- You cannot use a grid feed inverter with a standalone inverter, something will smoke and you will have an expensive repair. And it will smoke again in the same configuration. As much as it seems a good idea it wont work. A grid feed inverter unloaded will go to 260v and shut down, trying to start again after a delay. Feeding a standalone inverter with a grid feed inverter may work as long as the load is always greater than the grid feed inverter, as soon as the load goes under the grid feed output, the voltage will rise, giving you inverter a very hard time trying to adjust its output to 240v, this is the time when the smoke will escape, you cannot guarantee the load. You need to arrange you panels in strings of less than 150v and use a Midnite MPPT to charge your batteries. (Outback is good too, I have Midnites) This separates the charging components from the inverter side. I advocate separate components for reliability and ease of repair should something break down. If you have an inverter charger and it breaks, you have neither inverter or charger. 4 60 cell panels have the same (close enough) voltage as 3 72 cell panels so they can be paralleled in this configuration. All the panels in the string should be the same wattage, if not the string will only output to the lowest wattage panel. General rule, 72 cell panels are 5 amp panels, 60 cell (grid feed panels) are 8 amps. Buy quality gear, SMA, Selectronic, Midnite, Outback. I will disclose that I do install solar, both grid feed and standalone, I do not retail any gear, I just install. I am retired so my work is not a business, it is my hobby. I have enough experience to know that my selection of brands cannot be bettered. I am over 65 and have been off grid for 30 years. So my advice, keep it simple and get the best gear, you only need the best gear once, it will probably last you a lifetime. I have a 20 year old SA30 Selectronic inverter, goodness only knows how many hours it has run, but it has just done another 18 months of 24/7 with me. I have just installed a PS1 so it is getting a well deserved rest. We use power 24/7 so our inverter never goes to sleep, we have a load all night with air filters running. Allan from Portland Vic .......... 11kw of panels, both 190w 72 cell and 250w 60 cell panels. 2x SA42 Selectronic inverters, 48v, 3.6kw PS1 24v 5kw Selectronic inverter plus an SA30 (2kw) 2,500ah of various used batteries 3x Midnite MPPT chargers It wasn't long ago that my life's goal was to have 10kw of solar. Now I have that and a new life's goal, to have 20kw of panels. Panels produce more return than money in the bank, it is better to be energy rich and financially poor as I cannot be both. do it yourself |
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