Delta9

With AC Coupling would it be fair to say that if you want to be able to run connected to the grid but also be able to use solar to power the AC loads but with the twist (and its a BIG twist to the story) that because the local grid is not that robust and suffers from loads of load shedding, that to be able to do this from inverters successfully one needs a big battery connected to the inverters simply to be able to technically power those AC loads when the grid is down? Not to be able to power those large AC loads from battery when the grid is down but because the inverters provide the sine wave for the Symo to operate when the grid is down. By this I mean with an electrical system of say, a 100 kVA 380 volt transformer from the grid feeding into the main DB plus 3 Victron 15kVA inverters and a 20 kW Symo PV inverter connected together to supply the AC loads on the AC output bus from the inverters. When the grid is down (because its almost useless or because they load shedded us YET again for another 12 hours - take your pick because either is likely at any given time) and we need to use solar to power the AC loads because of the Victron 1:1 rule it means we have to have this huge battery bank in order for the system to work correctly. So even though the HEAVY AC loads wont ever be run from batteries we need the battery bank in place in order to keep the mini AC grid up that the Symo needs to sync too....and for all that to work right we need this massive battery bank in place to keep it all stable....even though those batteries will never carry those big AC motor loads. So to me it seems like batteries with a max of 1C discharge rate with a "normal" continuous discharge rate of 0.2C would be good enough for this task as the main requirement of the batteries is to be big enough to absorb "shock loads" from the Victron AC / Symo system if a big AC load suddenly gets shut down. There is no need to discharge large amps from the battery to supply the big AC motors because the solar panels connected to the Symo (Fronius 3 phase PV inverter) are supporting the load directly (which is what AC coupling is all about - right? ... power AC loads directly from the panels through a PV inverter connected to the AC output BUS of the Victrons).....so in essence the batteries in this case are merely there as a "buffer" for sudden AC loads going on and off. Is that a fair appraisal of the situation? This is the cost of running large AC motors from solar using both AC from the grid and AC coupling on an inverter system. When the AC grid is down the Symo needs an AC waveform from somewhere to lock too to carry on producing AC from the solar panels. In grid down scenario's that AC wave form is coming from the Victron inverters which in turn need the big battery bank behind them to keep everything stable.

This explains a bit about what inrush current is https://www.facebook.com/2082031392023647/videos/2341453072570941

Does anyone know how many cells there are in a Freedom Won battery - 48v ? I believe they use Sinopoly prismatic cells - are they 15s or 16s ?

The question is, why do you have a 3 phase pump in the first place? Is the motor size such that you only have a 3 phase option? What size is the 3 phase motor of the pump? You have to allow for inrush current to start the pump. So how many amps does the pump draw in normal running mode? Once you know that, you can then approximate the start up current draw to then work out how much inverter you need to start that load. A soft starter is your friend.

This video talks about this.

My main concern was the frames expanding and contracting in the sun (heat). Would it be a different scenario re the heating up issue with bi-facials ? (that is, the panels retaining too much heat because they are joined together....not the expanding and contracting issue which I would imagine would be the same with any panel)

Is it doable to join solar panels together with a sealant on thier edges so that rain does not get through to the underside? Thinking of a carport style installation where a car or other things are under the solar panels. So the solar panels become a roof. A few drips here and there is fine but would not want an actual air gap between the frames of the panels. I dont know if using a sealant to join the panels together is something that can be done or not. I know lots you here have installed PV so what are your thoughts on this? How would one achieve a carport with not too much water getting through to the underside ?

Appreciate your 2c worth. Thanks. My three inverters of choice are 1/ Victron because they are the Landcrusier of inverters in Africa. The only thing I dont like about them is 48v limit. I also like 2/ Studer because they are Swiss and I feel I could literally put my life on thier reliability. They have a new 3 phase Hybrid coming out early 2021. Expensive and also only 48 volts. 3/Selectronic in Australia have a great rep and are highly regarded as good and reliable. They go up to 120v (so 144v nominal?). Expensive and not easy to get here. Then there is also....... ......SMA. Too dammed complicated to wrap my head around !! The webs site sucks and they are just not easy to understand. By all accounts good though and once its installed there is not much interaction with them, so they could also work for me. Anything Chinese for inverter is out. Just dont feel I can trust Chinese electronics. Batteries are different. Where else does one get a LiFePO4 cell from ? These BSL BULL/Shoto/ZTE/Hubble batteries look interesting. They all pretty much look the same. The ZTE batteries are at a good price although the cells from Lithium South Africa (is the seller Bim?) come out at a lower price per kWh for raw cells. But of course by time you add all the connectors and odds and ends and a BMS its more expensive then the packaged ZTE battery. But how good is the ZTE BMS? At least with raw cells you can build whatever you want. With the Shoto/ZTE/Hubble class you are locked into what the vendor says you can do. So thats my 5c. I could be wrong though as I am new to this.

Yes it is a big system. I will use a pro designer to figure out the final layout and how it all goes together. I am doing a deep dive so I know the in's and out's and how it all works so I can have an intelligent conversation with a pro system designer about all the options and why I think I need to use certain components/brands etc. I will probably do a smaller system first to get a feel for it all. Some rules of batteries dont change though. To get a large number of cycles requires that the battery be discharged as low (DOD) as possible. So the larger the battery bank the better because it means we can discharge a good amount of energy and not take the DOD too low if the battery bank is big. To offset that is calendar life of the batteries. Its no use having a 30 year design life of the battery bank in terms of cycles when the electrolyte life of the battery is thought to be around 20ish years. Then we have to consider that in around 10 years time, most definitely 15 years, the battery tech will be very different and probably a lot cheaper per kWh then it is today (look back at the history of solar prices). So its no good to invest too heavily in a huge battery bank today to get 10000 cycles out of them (27.3 years if cycled everyday) when its more cost effective to aim for 6000 cycles (16.4 years if cycled everyday) and then buy into a new cheaper battery in 15 to 16 years at probably half the cost of todays cost. So there is all that aspect to consider. Then we have to be thoughtful of the inverter design rules which force us into a certain battery size if we want to ac couple and power big ac loads without a grid being up (we have a lot of grid outages and load shedding around here). So there's that. Then it comes down to raw cost per kWh. The more you buy, generally the better the cost per kWh. I plan to have a lot of PV - there is a whole other logic to that I wont even go into. Bottom line is it works for me in my scenario. So charging a big bank wont be a problem. I prefer to build the battery bank myself if I can. 1/Because I will enjoy the journey and 2/ because I am in a remote area and if I build it I know it and can fix/service it. I like Battrium for a BMS. Expensive yes, but good. You may well be right. It might just be easier to go with something like this for the price ..... https://lithiumbatteriessa.co.za/collections/frontpage/products/100ah-3-2v-lifepo4-new-a-grade-cell. Its only .5C discharge though so I dont know how good they are for big loads. Its quite the juggle this battery/inverter/ac coupling story.

So I have reached out to some Chinese suppliers...... the Chinese two step has started already. Its not pretty is it......

These seem like an interesting option. At least for a smaller 40-50 kWh pack. Its along the lines of the 18650 power wall builds that are all over the place on the net. Has anyone here gone this route? Price is OK @$200 kWh

Yeah I know. But according to the 1:1 rule that only gives me somewhere around 40 kWp of PV. Thats roughly 100 x 400w panels. I looked at this about a18 months go and got a quote for a water pumping system and it consisted of 120 panels at that time (in the 300 watt class I guess). Power situation is only getting worse not better. Of course I would prefer to spend money elsewhere, but it is what it is. The grid has let us down big time and there is no viable business with the grid being like it currently is, so we have little choice to either make a plan or close up.

How about these ? https://lithiumbatteriessa.co.za/collections/frontpage/products/48v-16s-120ah-lifepo4-lithium-ion-phosphate-diy-kit-pre-orders-dispatches-from-2-november-2020 Are these new cells or second life ?

Right got it. My preferred target kWh range is about 120kWh plus looking at maybe 50ish kWh for my ex as well (yeah I know its dumb to look after the ex as well, but what can I say, I'm a hell of a guy). So a lot of batteries. So probably worth the time, effort and expense of shipping them in. But my issue is finding a good reputable seller. I dont think my volume is enough to buy direct from manufacturer ?

Thanks Chloe. Had a good read through that. Interesting stuff for sure. I did at one time look at 18650's but came to the conclusion that 1/ I would never find enough good used cells and 2/ all those systems are mostly Lithium - Ion ....so about 500 to 1000 cycles. After lots of reading I came to the conclusion it was better to go for LiFePo4. I was interested in those ZTE 4.8Kw batteries as they have a can bus converter board to be able to connect to the Victron's but they only allow a max of 16 batteries to be paralleled which is going to be limiting to me because of the 1:1 rule. Edit: The 1:1 rule. Is this a reason to look at SMA instead of Victron? I decided on Victron because there is a lot of local support for them but if SMA has a more favorable ratio, is it better to look at SMA ?

Thanks for that heads up. I still have to research that angle but thinking it should be doable to get a consolidation shipment in a container. Maybe have to go to a half container even? Not sure but will dig in to find out. What the in's and out's of sellers using there own shippers? Is it a problem or some sort of issue or a way they drive price up etc?

When you say you were quoted $34 per cell ++ is that from the suppliers link you posted? As you say, for the price it seems likely they are second life. Did you ask them about if they were second life? I want about 120 kWh of battery so its sizeable and expensive. Need to get it right.

Had a read through of that thread. Great information in there but it quickly went from batteries to other topics. Still, it shows others are out there doing what I want to do, so that's encouraging.

Thanks for the input but those batteries are not suitable for what I want to do.

I am doing a deep dive into the whole solar thing from panels to inverter to batteries to control of it all. Looking at posts here on this forum about Victron led me to researching the 1:1 rule. This implies a big kWh battery and I think lithium is the only way to go these days (on my second set of AGM's in the past 10 years - but that setup was never solar - only using grid to charge batteries and using inverter as a UPS for when the grid goes down) So I need a big battery as per the 1:1 rule for my plans as I want to run a water pump. Looks like I can build a battery cheaper then I can buy one. I have watched many youtube videos on systems using Battrium BMS, so it seems feasible to build out a battery and use Battrium as the BMS. But not so sure second life is the way to go. So lots more research to do , questions to ask. It is enjoyable though. Making power from the sun is fascinating to me and saying goodbye to the grid will be a great thing.

Had a look at the link you put up. Are those 2nd life batteries then? There is no mention of this on that Chinese site. However the price per kWh seems too low. So there has to be a reason for that. I dont think new LiFePO4 are that low in price per kWh yet ?? Others that I have looked at are way too high www.orientpower.asia https://www.orientpower.asia/collections/lithium-3-2v-cell/products/3-2v100ah-lifepo4-battery-cell The orient power cells seem to be reputable but silly pricing. I can buy Freedom Won cheaper then that !

will take a look at these options, thanks for the replies

I am also into fish, what do you keep? Tropheus and Frontosa are my specialties.

Sorry, who is Bain ? How does one contact him?

I wanted to get a number of 16s strings - so worth the effort. Problem remains the same - how to find a good Chinese seller. There are 1.4 Billion of them......they are not all crooks. But finding that elusive honest trader out of China is no easy task without a reference from someone solid. I will most likely sea freight them in a consolidated shipment. I suppose the people who have GOOD contacts for batteries are not sharing that info - its how they are making money themselves.