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Old 15-06-2019, 10:33 AM
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pmrid (Peter)
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Anyone using a Tesla battery or similar

I've just sold the farm and bought a small house on Bribie Island on the Sunshine Coast. I'm seriously thinking about the best way to balance solar and grid power. Initial reading suggests a 13.5 kWH Tesla battery and about 4 kW of solar would provide a good mix at a cost between $16-18K. I'd be interested to read any other experiences with these systems and the real cost/benefit outcome.

Peter
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Old 15-06-2019, 10:56 AM
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For my own use I did some hand calculations (brand agnostic) a few months ago and figured I needed 3 kW of solar cells and 11 kWh of battery. That suits my needs but may not suit yours. As costs change over the years, those figures might move a little.

Those are only calculations, though, not real-world experience.
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Old 15-06-2019, 12:08 PM
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Hi Peter
Here (at 5 Tabby) there are 4 of 300 (approx actually 290 or 280??) running a 12 volt system with a 1100 amp hour battery bank. The batteries are the gel type..so probably 300 amp hoirs available without taxing the bank..they have not let us down... check Rainbow Power Company but I think they are a little under $5,000.
I have an inverter (suitable for stand alone not a grid conected set up) and separate charger set up...buying the two in one in 12 volt is not as cheap so dont fall for two in one if 12 volt...however two in one if you go 24 volt or 48 volt is a different matter.. my charger cost around $500 ( you need a different charger for gel) but why would you need one as I doubt you would use a genny...the inverter I think was around $1200 and I think it is about 3000 watts...With this stuff work things out in amps as to work on watts...kilo watts..makes systems sound much much better than they really are...in my view.

Ask of the tesla battery..but what do you deliver in the amps I use..ie how many amps at a particular voltage.. .I bet they wont match my gel batteries for price☺
I suggest if you have grid dont bother but heck I could do it for half what you are looking at...also if you are on grid I have some panels and an inverter suitable for the grid connection which I would be happy to sell and convert the cash into more batteries...but if you have the grid just get a genny as a back up. What do you want to achieve here..?
Alex
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Old 15-06-2019, 12:19 PM
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You dont need many solar panels and are somewhat tied to the battery capacity...you can only charge at 10% so there is no point in having 10 300 watt panels if your bank only manages half that input...more batteries rather than more panels is my approach...and if you put a genny in the mix only go for a small one ..again it comes down to the charge the batteries can manage...
Personally I would say save your cash☺
Alex
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Old 15-06-2019, 12:43 PM
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I purchased a 2kva genny on special at Aldi for only $200...I aready had five other gennys but how could you not go for that...it is the same as two others but they have key and remote start..such came frim Bunnings at about $750 and key start is wonderful...

Alex
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Old 15-06-2019, 01:30 PM
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I have a mate who has 2 power walls connected to 7.5KW of panels, and this time of year they are pretty well flat all the time. Mind you he is running a huge A/C 24/7 to keep his Guinea Pigs comfortable of all things. The mind boggles.
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Old 15-06-2019, 02:28 PM
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7.5 kwatts is how many amp hours at what voltage?☺
Alex
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Old 15-06-2019, 02:32 PM
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The panels here pump 15 amps even at Sunrise....but it is called a battery bank for a reason...you put stuff in and you draw stuff out..the bank may have billions but you have to work with what that bank allows you to use☺
Alex
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Old 15-06-2019, 03:07 PM
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If the Tesla battery says 13.5 kwh what does that mean..you can use 13,500 watts or only 30% representing how much you can discharge your battery...I could never get a vendor to tell me exactly how many amp hours a tesla battery is good for..its a simple question you could think but I have not had a simple reply...could a vendor not say...its approx 2000 amp hours at 12 volts which means to discharge 30% or 50% or whatever is the discharge limit you have so many amps hours???
I do it this way..add up in watts daily use and divide by volts to give amp hours. ..if the bank is day 1000 amps and safe discharge is say 30% you know that your usage should not go past approx 330 amps.

How do you work out a) capacity of the tesla battery in amp hours at a particular voltage and b)what is its safe discharge rating.
Alex
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Old 15-06-2019, 03:47 PM
Sunfish (Ray)
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Tesla is just a marketing exercise for a product others have made earlier , better and cheaper. My solar installer suggest LG is a reasonable price and performance and pairs well with their panels.

Of course , the longer you wait , the better and cheaper the battery. Take this years Shimano bike capacity which has a much bigger range , 170km, in a battery half the size and weight of last years offering.
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Old 15-06-2019, 04:34 PM
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I lived off grid for years and started with 12 volt battery bank 12volt panels and 12 volt system with an inverter to get 240volt. Also a 7.8 kva gennie to pick up the shortfall.
In the end I scrapped the panels and used 24 volt ones in series to get 120 volt dc. This fed an 60 amp inverter charger and the batteries were 48 volt at 445ah.
I was speaking to my mate the sparkey who does a lot of off grid and grid tie systems and now the way is a different type of inverter charger that lets you use power dirrectly off the panels without using the batteries which trickle charge from the grid tie and only get used at night so the batteries dont get a constant hammering from big loads and when the power goes off theres a disconect circuit so you can use batteries. Its all changed in the period of about 10 years but you pay for it. Tesla is probably the dearest so it does pay to shop around.
Good luck
Andy
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Old 15-06-2019, 04:57 PM
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We have a 8.5kw PV array and TeslaII battery. For us it was a no brainer, as my Peak season (summer and winter) bills were running to around $1800 a quarter, and off peak about half that. Our ROI is less than 4 years.

There is no mains gas in our area (typical NSW lack of infrastructure) so everything is electric. A big reverse cycle ducted A/C system and solar heated pool don't help either...but post Tesla, out bills are slightly negative in Summer and now about $400 annually. Much of this is the $1.00 a day grid connection charge.

I'd say you'll need at least a 5kw north facing PV array to have the battery charged most of the time...but a run of overcast days will quickly make you wonder why you didn't get a larger system....
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Old 15-06-2019, 08:13 PM
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Quote:
Originally Posted by xelasnave View Post
7.5 kwatts is how many amp hours at what voltage?☺
Alex
His panels at 100% are capable of putting out 7.5KW. No panels can operate at 100% so I believe when everything is optimal they will pump out 85%. so on a good day in summer his system generates around 40KW for the day, which is divided up into home use, topping up his Power walls and what's left is exported into the grid. Not sure what the voltage is or amp hours, whatever all Solar Panels are rated for I would guess. The panels generate DC and this is fed into the inverter and converted to AC.
I have a 4.6KW system, no batteries and have not paid a power bill for 7 years, mind you I am not running a monster A/C either.
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Old 15-06-2019, 10:02 PM
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FYI our ducted AC system is single phase, rated at about 15Kw. Flat out it burns about 4kw of electrical power, which will flatten the Tesla in a bit over three hours.

It does not need to be run overnight as the main bedroom has a split system
that only burns 600 watts or so, hence with the PV panels we can cook meals, have hot water and not swelter mid summer without an electricity bill...not so great with limited daylight hours in mid winter....I don't like sitting in the dark in the cold, so have to pay the Piper.

That said, we produce far more power than we consume....but energy providers pay peanuts for feed-in tariffs, and charge you, as I mentioned earlier, about $1.00 a day to say connected.

With smaller A/C systems, and no swimming pool, and gas for cooking, I have no doubt a 5Kw PV array and Tesla II would allow many to effectively go "off grid".....but I'd note our 310 litre off-peak hot water storage system burns 7Kw daily (but that's just 77 cents a day off peak rates)..and is not connected to the Tesla II (I think this is actually not permitted) ...hence you might want to look at solar hot water.
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Old 15-06-2019, 10:29 PM
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pmrid (Peter)
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My sincere thanks for these insights.

The solar industry has taken some credibility knocks in recent years - thanks mainly to shonky operators flogging sub-standard panels and related equipment.

I'm going to go ahead with this plan. But slowly, slowly. I hate being burned by crooks and scumbags. But with care, I ought to be able to navigate around them.

Thanks again for the useful inputs.

Peter
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Old 15-06-2019, 10:52 PM
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Quote:
Originally Posted by pmrid View Post
My sincere thanks for these insights.

The solar industry has taken some credibility knocks in recent years - thanks mainly to shonky operators flogging sub-standard panels and related equipment.

I'm going to go ahead with this plan. But slowly, slowly. I hate being burned by crooks and scumbags. But with care, I ought to be able to navigate around them.

Thanks again for the useful inputs.

Peter
Good to hear. One other word of warning. Our first installer said we'd be getting "tier one" PV panels....which means absolutely nothing when it comes to performance. The Q cells we ended up getting from them are VERY average
with low solar incidence angles, (winter) and only deliver 50% of their rated output this time of year.

LG's newest panels (as on our northern roof) are awesome. They have excellent overcast/low angle performance (80%) and if you are offered anything else say NO. Cheaper Chinese PV panels simply don't cut it IMHO.
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Old 16-06-2019, 07:17 AM
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h0ughy (David)
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Quote:
Originally Posted by Peter Ward View Post
Good to hear. One other word of warning. Our first installer said we'd be getting "tier one" PV panels....which means absolutely nothing when it comes to performance. The Q cells we ended up getting from them are VERY average
with low solar incidence angles, (winter) and only deliver 50% of their rated output this time of year.

LG's newest panels (as on our northern roof) are awesome. They have excellent overcast/low angle performance (80%) and if you are offered anything else say NO. Cheaper Chinese PV panels simply don't cut it IMHO.
Having just spent some coin getting a 10kw system to cover daytime operation in summer I went with the solar edge 320w panels, and no battery. Only been functional for 3 days and it's winter so time will tell And I have a 25year guarantee on everything .

We got solar hot water system in October last year and that made a huge difference, so I am hoping this system will help reduce the overall amount again. The graph shows the results for the solar hot water

One stipulation from SWMBO was not on the front of the house
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Old 16-06-2019, 10:39 AM
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Originally Posted by h0ughy View Post
Having just spent some coin getting a 10kw system to cover daytime operation in summer I went with the solar edge 320w panels, and no battery. Only been functional for 3 days and it's winter so time will tell And I have a 25year guarantee on everything .

We got solar hot water system in October last year and that made a huge difference, so I am hoping this system will help reduce the overall amount again. The graph shows the results for the solar hot water

One stipulation from SWMBO was not on the front of the house
Really interesting output curve, as on the same day we caught some afternoon cloud, but our 5kw LG northern array plus we have 3.5 kw facing east, while not the same PV capacity did pretty well.
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Old 17-06-2019, 09:53 AM
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I think I have worked it out correctly ...13500 kwh is equivalent to the total capacity of my battery bank approx 1100 amo hours at 12 volts but the usable charge is only say 25 to 30 percent of that total...for tesla to have 13500 kwh it may mean it and discharge that storage to 100% or its storage is greater and the 13500 is the usable percentage of charge...from the way Ki look at it☺
The real test I guess is to add a meter on the outlet and see how many watts tallies until it goes flat...if they say 13500 that is watt..er what that meter should read...I am more asking here than telling so please point out anything that I may have wrong.
Alex
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Old 17-06-2019, 03:20 PM
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From my memory looking at them a couple of years ago the Telsla battery systems are rated in terms of their deliverable discharge capacity.

They are also lithium ion batteries rather than lead acid so the depth of discharge largely amounts to "Just not to 0% OK"


Apparently some are recycled from Tesla cars as the current demand in the cars is more or less explosive and in the case of a powerwall setup, much more gentle so a battery that is no good in a car is still fine for many years in a less demanding application.

When you consider the acceleration times the Tesla cars are capable of they much be calling on half a megawatt or more for short periods if someone decides to see just how hard it will go! I recall someone building EV sports cars 20 years ago and puching the motor cotnroller technology of the time commenting on the lines of "Nothing much really happens under about a thousand amps"

Last edited by The_bluester; 17-06-2019 at 04:34 PM.
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