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KASman

DIY install advice before I start wasting my Cash :-)

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Hi People

I will start by thanking you guys for all the info I have gathered from you by reading this forum before joining! And.... apologize in advance for stupid questions I may ask in the future.... And... my inability to get my thoughts across clearly!!!! I am no author/writer..

Been reading a lot and learning a lot, its one of those where you start off thinking you know a fair amount, learn something, think you know more, learn some more at which point you begin to know you know enough to realize you have a lot to learn he..he

I am aiming at installing a system at home (Northcliff area - 6 folks chowing kilowatts on 3 phase) that will get me off the grid (mostly). I have been in the Cell network business for 20+ years so have a fair idea what I am doing when it comes AC and DC installations, but not much experience with inverters, more especially the new hybrid jobbies.

My Eskum bill reflects that I use average 60kWh per day and have peaked at 72 kWh average per day some months. I have begun my journey by first trying to cut down on my usage by changing a few things at home. I am in the process of installing heat pumps for my two geysers (came to the conclusion that I would rather use extra PV's than a solar geyser as it is more flexible, could be wrong but I already pulled that trigger). Have already changed to gas stove, and gone all LED. Next on the list will be pool pump - looking at the Zodiac Flopro VS, expensive but seems very good and plays into my tinkering with everything hobby :D.

I have thoughts on everything but lets start at the inverter as I have a few beginner (dumb) questions. From my research the Infinisolar 10KW 3 phase is looking good to me since it can obtain help from the grid when the need arises, plus batteries option. I did first look at the Axpert but quickly came to the conclusion that I needed a full hybrid to use my investment better. I also toyed with changing to single phase so that peak loads might be better handled by the inverter/inverters - logic being that on the 3 phase it would be relativley easy to max out one phase where as on a single phase there is more scope for short peaks? All open questions where you guys with experience can help.

 

My first question is about how these inverters actually manage the power they deliver and through my research I cannot find a definitive answer. They have 2 AC connections one for the grid tie and one for the load. My understanding is that the inverter can supply the grid tie connection with all power and the "load" connection would be reserved for some kind of essential load if you need that option like if you were not powering the whole house with battery backup? This would then mean my connection would only be on the grid tied position leaving the "load" not connected. This leads to the next question - what if power from the grid drops? My inverter can obviously not continue to supply. Having said that, the city power meter has relays which I am not sure if you supply power from the output side would actually connect the grid or not - but it likely matters not as at this stage the inverter is not going to supply power to this port as it is not seeing the grid anymore. HELP :(:o:D. Basically I want to setup as a grid tied UPS for the whole house. The inverter manuals are as clear as mud!

 

Let me leave it there for now as I am beginning to confuse myself, after I have this little nugget of info I can request further help without boring you and plan further.

 

 

 

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Welcome KASman! You've come to the right place.

I grew up in Northcliff Ext 15, corner of Rockcliff and California, when there was only newly scraped dirt roads as my parents probably bought the 2nd house on the mountain, after the original farm house. As a 5-6 year old, I used to push and pull the stop streets poles till they came out .... just because. Probably the municipality learned then that they did not put them in enough concrete. :D

Good start with heat pumps, and other measures you are looking at. Good to see you starting there!

Pool on solar, yeah, good idea. Thought in that. IF you have a inverter that can handle a stock standard pool pump startup, then in my opinion that is cheaper than solar pool pumps in cities.

As you, I also started to understand where all the power is going, and then started reducing that as far as SWAMBO and the pups allows me to go. Also geyser first on EV tubes as we are Cpt and have lots of clouds in winter, with changes in regimes ito when one can use hot water, paid off that system in under 24 months.

In the end I realised that I only needed a solar UPS system for essential backup, powering loads like computers and such when we are at the "office".

With that and other habit changes, household of 6 with 4 mostly at home, after many years of tampering, using a Efergy Enegry meter as a guide, today we rarely sees above R1200 pm for Eskom. About R800pm in summer, on a very small system as you can see in my signature. 

The secret ito my savings where in the loads that are on 24/7 loads. The wastage of that is when they are on yet we are sleeping. 

Few comments:
1) You understand that batteries are more expensive than Eskom?
2) The difference between "NEEDS" vs " WANTS" and the price difference between the two?
3) If the people are at home all the time, you can maximize faster and easier a ROI on a solar system versus all is at work/school during the day vs all power is used when the sun has / is setting.

It is very important to temper expectations upfront, saves a lot of frustrations later, and increases the savings if one goes onto solar, even partly.

 

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Hi Kasman I am away from home and therefore also my resources. I will answer more fully when I am home. @Chris-R has 2 of 10kW Infinis and is about to install 2 more at his business. Unfortunately he hardly makes onto the forum these days. For me the biggest limitation of the 10kW is the 3.3kW per phase. 

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7 hours ago, KASman said:

Basically I want to setup as a grid tied UPS for the whole house.

If you really want to do that (and I don't think you do, but I'll explain below), then you simply put the whole house on the inverter output. Depending on what your present distribution board looks like this might be easier than the other way round, because you literally connect the council supply to the input of the inverter (with the required fault current protection devices), while the output of the inverter simply feeds the existing DB.

The distinction on these hybrid inverters are quite simple really. Anything that is on the "output" of the inverter stays up when the grid goes down. Anything that is on the input side might benefit from power fed back out of the inverter, but goes down when the grid fails.

Picture time. This is for a Victron inverter. The principle is the same, in this instance we're supplementing the grid using a battery. You can connect PV panels to the battery to feed PV into the grid: That is what we normally do. It is not important, as long as you get the principle.

multi.jpg.b13da61d1958c1964a76211ed919637f.jpg

We call the part I marked in red the backfeed relay. The black box bottom right is the inverter/charger component. As you can see, during normal operation the three are tied together. Battery power flows both to the right (those are the essential loads) and to the left (those are the non-essential loads). The amount that is drawn from the battery is regulated so that it matches the consumption in the house.

If the grid fails, the backfeed relay opens. The loads on the right will stay up, anything connected to the left goes down.

Now, I said that I don't think you want to put your whole house on it, and here is why: Some big items should be left on the grid side. Heat pumps, geysers, swimming pool pumps, maybe even air conditioners (unless they are inverter models), I consider those non-essential loads. Leave them on the grid side.

In a single-phase house this is usually fairly easy. You choose the circuits that you want to stay up (lights, your entertainment area, home office), then you split the distribution board (you install a new one for the backup circuits in other words) and you put the inverter between them.

In a three phase house I can see that this could be somewhat harder. Rather than convert everything to single phase, I would much rather group my essential loads onto one circuit and one phase, assuming this could be done in a balanced manner.

Hope that helps.

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In fact... why don't you install two separate inverters? Install a nice quality three-phase GTI (grid tied) inverter such as this one, then group the essential loads onto a single phase and install a single-phase UPS for that.

Compared to the Infini, the price is about the same within 10% (I didn't add them up but it looks like around 5k more), and you get much better equipment with a better warranty.

Disclaimer: Yes, I am biased :-)

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13 hours ago, The Terrible Triplett said:

Welcome KASman! You've come to the right place.

I grew up in Northcliff Ext 15, corner of Rockcliff and California, when there was only newly scraped dirt roads as my parents probably bought the 2nd house on the mountain, after the original farm house. As a 5-6 year old, I used to push and pull the stop streets poles till they came out .... just because. Probably the municipality learned then that they did not put them in enough concrete. :D

Good start with heat pumps, and other measures you are looking at. Good to see you starting there!

Pool on solar, yeah, good idea. Thought in that. IF you have a inverter that can handle a stock standard pool pump startup, then in my opinion that is cheaper than solar pool pumps in cities.

As you, I also started to understand where all the power is going, and then started reducing that as far as SWAMBO and the pups allows me to go. Also geyser first on EV tubes as we are Cpt and have lots of clouds in winter, with changes in regimes ito when one can use hot water, paid off that system in under 24 months.

In the end I realised that I only needed a solar UPS system for essential backup, powering loads like computers and such when we are at the "office".

With that and other habit changes, household of 6 with 4 mostly at home, after many years of tampering, using a Efergy Enegry meter as a guide, today we rarely sees above R1200 pm for Eskom. About R800pm in summer, on a very small system as you can see in my signature. 

The secret ito my savings where in the loads that are on 24/7 loads. The wastage of that is when they are on yet we are sleeping. 

Few comments:
1) You understand that batteries are more expensive than Eskom?
2) The difference between "NEEDS" vs " WANTS" and the price difference between the two?
3) If the people are at home all the time, you can maximize faster and easier a ROI on a solar system versus all is at work/school during the day vs all power is used when the sun has / is setting.

It is very important to temper expectations upfront, saves a lot of frustrations later, and increases the savings if one goes onto solar, even partly.

 

Hahaha! I am not on the hill, I am bottom of the hill bordering Fairland.

I get all three of your comments, I do believe costs are getting closer to Eskom even with batteries - not to mention Eskom is increasing every five minutes. I am also considering this big round ball we all live on - ie my families impact on the environment. Also the obvious avoidance of Eskom / City powers very poor service. 6 people are living here and at least 50% of us are here 24/7.

Points well taken - exactly why I figured grid tied is the only way to go, I do welding and such reasonably often!! I also don't want to sit with problems if we have 2 weeks of extreme cloud. Aim would be to be almost off grid - if you know what I mean - maybe convert to prepaid, or hopefully our government realizes that allowing us to feedback to the grid is in fact a good idea given Eskums horses ass. 

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13 hours ago, Chris Hobson said:

Hi Kasman I am away from home and therefore also my resources. I will answer more fully when I am home. @Chris-R has 2 of 10kW Infinis and is about to install 2 more at his business. Unfortunately he hardly makes onto the forum these days. For me the biggest limitation of the 10kW is the 3.3kW per phase. 

Thanks man. Yes I agree, the 3.3 kW is a bit limiting. On the other hand it can be upgraded with more in parallel. It is the best value 10kW with battery backup I have found so far though. Might be workable if I balance my loads over the three phases together with the grid tied aspect?

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13 hours ago, plonkster said:

If you really want to do that (and I don't think you do, but I'll explain below), then you simply put the whole house on the inverter output. Depending on what your present distribution board looks like this might be easier than the other way round, because you literally connect the council supply to the input of the inverter (with the required fault current protection devices), while the output of the inverter simply feeds the existing DB.

The distinction on these hybrid inverters are quite simple really. Anything that is on the "output" of the inverter stays up when the grid goes down. Anything that is on the input side might benefit from power fed back out of the inverter, but goes down when the grid fails.

Picture time. This is for a Victron inverter. The principle is the same, in this instance we're supplementing the grid using a battery. You can connect PV panels to the battery to feed PV into the grid: That is what we normally do. It is not important, as long as you get the principle.

multi.jpg.b13da61d1958c1964a76211ed919637f.jpg

We call the part I marked in red the backfeed relay. The black box bottom right is the inverter/charger component. As you can see, during normal operation the three are tied together. Battery power flows both to the right (those are the essential loads) and to the left (those are the non-essential loads). The amount that is drawn from the battery is regulated so that it matches the consumption in the house.

If the grid fails, the backfeed relay opens. The loads on the right will stay up, anything connected to the left goes down.

Now, I said that I don't think you want to put your whole house on it, and here is why: Some big items should be left on the grid side. Heat pumps, geysers, swimming pool pumps, maybe even air conditioners (unless they are inverter models), I consider those non-essential loads. Leave them on the grid side.

In a single-phase house this is usually fairly easy. You choose the circuits that you want to stay up (lights, your entertainment area, home office), then you split the distribution board (you install a new one for the backup circuits in other words) and you put the inverter between them.

In a three phase house I can see that this could be somewhat harder. Rather than convert everything to single phase, I would much rather group my essential loads onto one circuit and one phase, assuming this could be done in a balanced manner.

Hope that helps.

Thank you, perhaps I could use the relay output on the infini to switch a contactor that would then switch the house to work on the "AC output" in the event of the grid dropping.

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55 minutes ago, KASman said:

... maybe convert to prepaid, ...
... or hopefully our government realizes that allowing us to feedback to the grid is in fact a good idea given Eskums horses ass. 
... I do believe costs are getting closer to Eskom even with batteries

Ask the guys here about pre-paid. Some meters do not work well with grid tied inverters.

Nope, Gov will not be interested, too much income to lose, with who paying for the maintenance of the actual grid / transformers? 
CoCT saw that coming, and have adjusted accordingly.
Nor did it work out too well for the power suppliers in Europe nor USA, they took substantial losses, changed some regulations and upped connection fees, just like CoCT.
Park the idea for the moment is my suggestion.

And don't fret about the increases. That scaremongering tactic has been used by solar installers for years, no-one tries that anymore for NONE of their numbers they gave, came even remotely close since 2012. It is cheaper to switch things off, get power friendly fridges / freezers / pumps / inverter aircons / heatpumps.

Reducing the 24/7 load, that is the bastard. You will get there. :-) 

Re. Costs of Eskom vs batteries, not a chance. The sums have been done. Panels may last +-20 years with slowly reducing output, batteries and inverters not. ROI gets complete out of whack if you borrow money to go solar. Simple calc of reducing your consumption as low as you can, investing the cash you would spend on solar, solar ROI did not look good. Batteries in cities are only good for small loads in case of emergency, never to run your house at night. Grid tie is the only way to go IF you can use every single watt they produce as I said. THAT is the key.

However, if you decided to classify your solar project as a personal hobby, then cost goes out the window. ;)

 

Check out what Mike has to sell here:

 

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13 hours ago, plonkster said:

In fact... why don't you install two separate inverters? Install a nice quality three-phase GTI (grid tied) inverter such as this one, then group the essential loads onto a single phase and install a single-phase UPS for that.

Compared to the Infini, the price is about the same within 10% (I didn't add them up but it looks like around 5k more), and you get much better equipment with a better warranty.

Disclaimer: Yes, I am biased :-)

:D - I know from all my reading that you work for Victron. I am open to all options however. The infinis do seem like they are very flexible and well priced from my research so far. But as I said, all options are on the table. Your idea of two inverters is worth thinking about for sure. Nice idea. My problem is my house is old and the wiring was done in such a way that it is very difficult to do any rewiring as the wiring is all under the house, even the internal DB is in concrete and extremely hard to work in. My only plan really is to put something between the outside DB which is easy to work on and the house. So I was thinking of installing the inverters etc in the garage wired between the two DBs.

 

 

Just to give you guys an idea here was my first plan of action - before I decided full Hybrid would be far better.:-

First, convert to work the house on only one phase = easy (I have nothing that actually needs 3 phase)

3 x Axperts in parallel, 6 x Pylontech Lithium packs and 36ish 320W PVs spread over the 3 Axperts.

 

Now, with the Full hybrid - I would like something like that but with the benefits. My idea is to maximize my solar useage by allowing batteries to be discharged at night to say 30-40% DOD at which point grid takes over (this number is flexible to ensure lifetime of battery packs - more research / info required).  This would obviously need to include measures to limit things like geysers etc at night via SWAMBO programming and timers etc. (I have 4 x SWAMBO, 3 of which have varying degrees of the "M" value :D:D:D:wacko:) Wife, Mother In Law, and two daughters... Anyway, I think you all have a picture now.

Maybe 3 of the 3kW Infinis in parallel along with the Single phase switch?

Thank you for your time and great replies - much appreciated.

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18 minutes ago, KASman said:

My problem is my house is old and the wiring was done in such a way that it is very difficult to do any rewiring as the wiring is all under the house, even the internal DB is in concrete and extremely hard to work in.

Some had similar issues, some even had new DB board installed. Some had the house rewired.

It is a road you start on, that is going to cost, as you get more and better ideas. :D

Budget for that now. 

Me, I had separate circuits installed feeding selected points in the house. So technically it is a UPS, nowhere near the dB board, so I can skirt the regulations, as per CoCT.

 

18 minutes ago, KASman said:

6 x Pylontech Lithium packs

Again. Be very wise ito cost on batteries.

Your load will reduce, your Eskom rate will drop per kw, you will pay less and less to Eskom.

Batteries only make sense off-grid on a farm or remote cabin, when compared to running a generator. Never in the cities. As a matter of fact, a generator connected to your inverter may make more sense in the city, auto start and all that. Get a old Lister gennie, use oil, or biodiesel, instead of diesel. :-) 

Do the numbers with extreme prejudice before you go big with batteries to use at night, for it is all cool till you have to spend R50-120k for the 2nd time within +-10 years on a new bank. 

 

PS. I am harping on certain points, for sorting the inverter and all that, is the easy part. The part that bit us all are the expenses we did not know of when we started. Most of us bought during power failures, what we know today, some of us would have done it differently, for you cannot easily sell 2nd had solar equipment. 

Pss. Look at SMA also.

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Here is a process I took, high level overview, it may take a while, and it will cost a pretty penny, but the goal is to half your current bill, or even lower, before you even think inverters.

1) Get you average load per day, per month. Especially the peaks, to spec the correct max kw inverter you may need. (see *)
2) Find out where all the power is going. I literally stood at the DB and switched each circuit off, watching the Efergy meter. I was shocked.
3) Now start reducing it:
3.1) Heatpumps with larger geysers - the more hot water the better, to a point. (see **)
3.2) Make sure all is A++ or A+++ ito fridges/freezers/washing machine/dryer/aircons. This is the costly part.
3.3) Oven kettle, microwave. (see ***)  
3.4) Gas for cooking, you got that sorted already.
3.5) Lights are the least, all obviously LED. Switch off when not needed.
4) Decided on the pool pump, as it is a huge draw. Use std pump, that inverter can handle, or dedicated solar pool pump, much more expensive than bigger inverter.
5) Now train the household to think before they switch anything on, leave fridge open, use more than 50l pppd, or more than 90sec showers ( :D ).
6) And don't forget, no more things on standby like TV, media center, laptops, computers. Switch off at the plug. Another shocker.

Now that all is as low as you could get, now find out why you are not <100w per hour at night when everyone is asleep! This one is the bastard ito cost per kwh, and more so on batteries.

Now you are ready for solar, probably needing way less than what you expected to install when you started this post.

Your consumption could be 1/2 to 1/4 of where you started this post, and you saved a ton of money going forward.

For the biggest mistake, in my opinion, that solar installers used to make, is to take your current consumption, and solarise it, not telling the customer, in no uncertain terms, that the real and only savings you will make, is when the sun shines and you use all that power you had installed ito panels.

Now you start looking at how you can install the panels, some facing east and some west with most north, at the right angle ... 
And inverters ... 


(*) Loads like microwaves, kettle, oven, welders may be high in watts, but short in duration. The effect is you need a bigger more expensive inverter ito peak watts, to not trip the whole system each time too much is switched on. And if on batteries, they pull a lot of amps.
(**) Heatpumps should be driven by solar system so make sure of max load, or timers etc.
(***) Kitchen is cheaper on Eskom, T&C apply, as it is not on for hours. It impacts hugely on max inverter specs. Plus, if the power is off and you need the kitchen, that impacts on the cost of the battery bank, why would you bother with cooking if you have a gas stove. Consider it carefully.

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Yes, a lot to think about. Thats why I came here to get some advice.

I wonder how accurate the 6000 cycles on the Lithium Ions is? How many cycles if you cycle between say 90% and 40%.  10000 cycles on 1200 Watts would be 12000 kWh, which is what say R12000 worth of Eskom, so I lost R3000 compared to Eskom? That seems liveable. If I got even better 12000 cycles would be breakeven on the batteries? Or am I miles and miles off on my figures? :huh:

 

edit: The pool pump I want to get is the Zodiac Flopro VS which can be programmed to increase power for a cleaning cycle to run the creepy, and run on much lower wattage (motor speed) the rest of the time. It has a very programmable control unit. You can have four different times of day on your choice of motor rpm and therefore watts being consummed. Its also a more efficient motor in the first place. It is not for solar specifically.

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I started out on this journey as my town suffers from repeated blackouts for various reasons. 

I am retired and only wanted it for convenience sake and as a backup system.

Costs were an issue.

I finally settled on a infinisolar 4kw hybrid with 4 pylontech batteries and a cabinet. All supplied by Full Circle Solar.

I love the way the pylontechs manage themselves. They charge at 49 amps irrespective of how much they have been depleted.

My house runs on two circuits - one for the high amp side directly from the municipality (or 7kw generator via change over switch) and the convenience low amp side via the inverter (which also cleans up the power). This side runs idling at 6% but can go up to 95% when the borehole pump runs to fill the 10kl tanks. It handles the booster pump comfortably as it is an energy efficient model. The rest is on computers, router, lights, fridges, tv and a gas hot water system for two main bathrooms. I still haven’t run a trial to see how long it can sustain the output before shutting down. The low amp side can also be diverted to run from mains only via a seperate change over switch.

You can follow my posts. 

Advice from me is the following:

Start thinking in amps. 

Measuere all the currents - startup, running and maximum per device. I bought a true rms clamp meter for this purpose. This exercise will show you what your real needs are.

Consider splitting your db into a low amp and a high amp part. I did this at great expense but it was worth all the sweat and costs. It sorted out several issues I never even knew about as I have an old farm house. This also gave me the opportunity to modernise everything. Bear in mind that surfix wiring allows you to make really quick wiring changes inside your roof. This will also ensure that you can look at your earthing systems. I used 10mm wire between the db and the inverter as I could buy it per metre, 6mm would work easier but then you need to buy 100m rolls. I also used bootlace ferrels everywhere which make for good connections.

My system has been running well for a few months now. I don’t know about power failures anymore. When it happens in the morning we simply make breakfast on a gasbraai on the stoep. Same for coffee. Swambo dislikes gas in the kitchen.

When you are young you might recoup the costs over a loonng lifetime of usage of 30 years. Don’t trust the calcs by other people as you need to add lifetime costs per item. And this is far from clear.

I made my system swambo friendly as she is not technically inclined. On a recent trip to the Kgalagadi (we were out of cell phone range and could not receive alarm warnings or give advice) my system tripped and two men who tried to help could not id a tripped earth leakage. Fortunately they powered the fridges, gates etc from leads. The pylontechs have shut down but I reckoned the power was out for a week.  This taught me more lessons. This fault I traced to an outside db which was done by town electricians - still to be fixed but isolated now as I am busy painting the house. Oh, and the house is on shutdown the next break we take as I still cannot fathom how this has happened.

Low amp (energy efficient new generation) washing machine, fridges, dryers and solar geysers etc can change your amperage requirements drastically. With the obvious benefit in lowering capital costs and running on a less stressed system (low amps is better by far). Hot water systems can be tied into a gas heater for convenience. Plenty of posts on this.

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10 hours ago, The Terrible Triplett said:

Batteries only make sense off-grid on a farm or remote cabin, when compared to running a generator. Never in the cities. As a matter of fact, a generator connected to your inverter may make more sense in the city, auto start and all that. Get a old Lister gennie, use oil, or biodiesel, instead of diesel. :-) 

I think he said he wants the backup. I suppose the important thing is you have to understand that at present backup is still a luxury. It costs extra money to have it. If you're okay with that, then go for it.

Many people with home offices absolutely need the backup, but then you're doing the sums at the hourly professional rates you charge, and that is by far the quickest ROI you'll ever get.

7 hours ago, KASman said:

I wonder how accurate the 6000 cycles on the Lithium Ions is?

That's also a discussion we've had at least three times already :-) Generally there is an inverse proportion between the maximum discharge rate of the battery and its expected lifetime, in other words, there are trade-offs. The design of a battery that can do sustained discharged of 0.5C (ie from full to emty in 30 minutes) generally means it will wear out a little quicker. Conversely, batteries designed towards the other end (eg Pylontech which has a C/2 sustained discharge rate, from full to empty in 2 hours) will have higher cycle lifes.

Most LFP batteries are rated at at least 2000 cycles to 70% DoD, and almost all of them will do better than that when used at the lower average discharge rates used in houses. So I think it is fair to assume that you will at the very least get 2000 cycles out of your battery, at which point the battery won't be dead... the definition of EOL is that it has irreversibly lost 20% of its capacity. So ten years is not an unreasonable lower limit.

Another data point: Early data from Tesla car owners (note, different battery chemistry) suggest the batteries do last longer than their rated cycle life, sometimes as much as 50%.

There is some creative accounting going on in the business as well. One particular supplier -- they make a good battery but you have to keep this in mind -- rates their batteries at C10, and quote 7000 cycles or something like that. That's around 20 years. I'm a tiny bit skeptical about that.

So just picking a number in the middle, you'll probably be good for 12-15 years with any of the LFP batteries on the market. It is too soon to say if it will really do 6000 cycles.

What is true though is that a Pylontech rack of a comparable capacity now costs about the same as a large lead acid bank, and even if it only lasts 2000 cycles it still beats the lead-acids by about a year or two in lifetime.

12 hours ago, KASman said:

the 3.3 kW is a bit limiting

Question though, if I recall previous discussions, this inverter does allow you to go up to 7kw on each phase as long as the grid is there to make up the difference, right? Because it that is the case... then there is no problem here right? Certainly the inverter I suggested (3kva Multi) can do this, it will allow almost 12kva as long as the grid is there, but if the grid drops out then obviously you're limited to 3kva.

It sounds to me like you can just put the inverter of choice in where you wanted to... and just put the whole house on the inverter output. Then just make arrangements to have the large loads disconnected when there is an outage so you don't have a geyser turning on and tripping out the inverter.

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Here is an interesting article I am sure most of you have seen similar on increasing battery life (life cycle that is, not capacity).

http://batteryuniversity.com/learn/article/how_to_prolong_lithium_based_batteries

This info is interesting and agrees with what I know about Batteries in general

 

I am qualified in electronics so have a good grasp on Current, Volts, Amps, Watts, KWh, etc etc. Just so you guys know!! I been doing it for a while - not trying to sound clever, just letting you know where I am coming from :D. Experience in my opinion counts more than any degree/theory!! Some years ago I built my own inverter with some transistors and a transformer and it was basically the same as what you could buy in the shops, HAHAHA, things have sure moved on. I think I remember calculating at the time that something like 50% of my 12V car battery was going to heating the heatsink on the transistors!:DThose days a 330 watt 12 volt solar panel system would have cost an absolute bomb and a car battery was top notch! Only a few years ago a 2.4 KW Lithium battery would have cost more than a new car, its now down to R15K. 

I am very much appreciating the experience, knowledge and advice here.

10 hours ago, plonkster said:

There is some creative accounting going on in the business as well. One particular supplier -- they make a good battery but you have to keep this in mind -- rates their batteries at C10, and quote 7000 cycles or something like that. That's around 20 years. I'm a tiny bit skeptical about that.

For sure!

 

10 hours ago, plonkster said:

What is true though is that a Pylontech rack of a comparable capacity now costs about the same as a large lead acid bank, and even if it only lasts 2000 cycles it still beats the lead-acids by about a year or two in lifetime.

Another advantage of Lithium is the efficiency of putting power back into the battery which is far higher than Lead Acid, so more of your energy actually gets stored. This in turn means more daylight solar is actually doing useful stuff.

 

If we take Pylontech at their word which is 6000 cycles at 80% DoD then 1.92kW x6000 = 11500kW, which at City power rates R1.13 = R12 995, which is not that far off of the R15K the battery costs? Or am I doing something horribly wrong, I have the feeling I am being dumb over here. Please correct me if I am wrong. I am guessing the new inverters can convert 48Vdc to 230Vac at somewhere around 80% efficiency which has to be accounted for also.

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On the inverter, if I connect the house to the load port and only the grid side to the grid, then I would be limited to only drawing what the inverter can supply so plugging in 52 welders would be a no no - yes?:D Whereas, if my house was connected to the grid side, I can connect my 52 welders while using all my inverter power to supplement? Or am I looking at it completely wrong?

I am thinking, I could have the on board relay switch a contactor that switches over to the load side of the inverter and perhaps informs me that I should switch some non essentials off. Then the same thing in reverse when the grid comes back?

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11 minutes ago, KASman said:

Another advantage of Lithium is the efficiency of putting power back into the battery which is far higher than Lead Acid, so more of your energy actually gets stored.

I have often heard this argument in favour of LFE, but if you read the next subject relating to real life PV systems you will hear about how systems go into idle once the batteries are charged. On a good day my system will reach float around midday and my efficiency drops off because there is nowhere to send the power - if my batteries were more efficient it would happen at 11am instead of midday. That doesn't sound like a good reason to buy more expensive batteries. I am not knocking LFE, just saying that the efficiency factor is overrated.

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2 minutes ago, pilotfish said:

I am not knocking LFE, just saying that the efficiency factor is overrated.

Agreed, it is a relatively small advantage -  the biggest advantage being the cycles!

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19 minutes ago, KASman said:

I am guessing the new inverters can convert 48Vdc to 230Vac at somewhere around 80% efficiency which has to be accounted for also.

I dont think you can put a straight percentage to the loss, in my case the (2 parallel) inverters seem to have a basic loss of around 100w which doesnt climb significantly as load increases. So losses are much higher at 500W load than at 1500W load as an example.

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2 minutes ago, KASman said:

the biggest advantage being the cycles!

No arguments there, then it just boils down to the maths to see which battery gives the best bang for buck. I think Pylontech have made it a much closer calculation.

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13 minutes ago, KASman said:

guessing the new inverters can convert 48Vdc to 230Vac at somewhere around 80% efficiency

The new inverters with the high-frequency DC/DC boost stage does somewhat better than 80%. I think the worst I've seen with mine was around 89%, but I believe it's around 92% on average. The MPPTs are quite efficient, as high as 98%. And the Lithium batteries themselves are mid-90s themselves.

The efficiency varies: If the inverter needs 50W to power its own internals, then at no load you're using 50W to make nothing, at a 50W load your efficiency is a mere 50%, and so forth, and even though efficiency generally gets better as the loads go up, it also gets worse when the fans come on later. But 92% is not a bad estimate for a good inverter.

5 minutes ago, KASman said:

On the inverter, if I connect the house to the load port and only the grid side to the grid, then I would be limited to only drawing what the inverter can supply

Not necessarily. Many of these inverters can pass more current than they can generate themselves, for example the 3KVA Multiplus I mentioned can deliver a whole 50 amps on the output as long as the grid is available on the input. As I recall, the Infini also has this feature.

7 minutes ago, pilotfish said:

if my batteries were more efficient it would happen at 11am instead of midday

True, but because the LFPs can also deal with deeper discharge we usually deal with that by allowing them to drop a bit lower so that they fill up at 3pm instead of 11 :-) Of course that's in a self-consumption setup, in a full off-grid setup you make a good point: PV panels to cover the inefficient final stretch from 85% to 100% SoC might well cost less than the fancy battery.

 

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5 minutes ago, pilotfish said:

I dont think you can put a straight percentage to the loss, in my case the (2 parallel) inverters seem to have a basic loss of around 100w which doesnt climb significantly as load increases. So losses are much higher at 500W load than at 1500W load as an example.

Very interesting, I am sure I have read somewhere what inverters you are running, please remind me.

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