A Peril of Going Solar

Yes the guarantee on a battery is 10 years but that does not mean it needs to be replaced. It may not have the same capacity but I expect our Tesla Powerwall will keep working. Batteries will become larger and better - coal is a far greater burden on the environment

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Export max depends on your power company, change companies

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Iā€™ve been on this earth for 67 years, and have yet to see any battery last 10 years, let alone more. Donā€™t be swayed by a big name like, say Tesla, or Apple.

Ask your Iphone friends how long their batteries last :slight_smile:

Oh, and the more frequently you cycle your battery, the shorter itā€™s lifespan. One would assume that to go to the cost of installing a solar battery, the ideal solution would be to flatten it every day.

To accurately determine that coal is worse for the environment than manufacturing and disposing of batteries may well be the subject of someoneā€™s thesis somewhere, but the reality is that the use of coal for power generation is not going to stop any time soon.

Iā€™m tipping not too many folk would step on a direct flight to London on a battery powered Jumbo jet either. Fossil fuels are still the foundation of the world economy.

But I digress, haha.

That constraint is not the retailer it is the ā€˜distributorā€™. Each area is a monopoly.

Most cap at 5KW from my understanding. The 5KW is not a daily limit it is a feed in rate (for lack of a better technical description); the inverters are required to ā€˜throttleā€™ to 5KW for approval to connect to the grid and export power. FWIW during recent days I produce about 35KWH per nice day and have been exporting 16-20KWH on many Dec days, but clouds frequently shade where I am located so some days are real stinkers from rain and cloud.

Another thing to consider is that a 5.5KW array on the roof is DC not AC. There is loss in the inverter so what the power distributor ā€˜seesā€™ is less than your PV array spec.

A 6.5KW PV array with a string inverter will be well matched to a ā€˜5KWā€™ inverter, and that overcapacityā€™ is an approved design. ā€˜5KW grid connectā€™ string inverters for Australia are usually rated at or just under 5KW. After all the loses the 6.5KW DC array would rarely if ever get ā€˜clippedā€™ at 5KW AC for export in Victoria.

OTOH if you have micro-inverters they are commonly 270 or 290W (AC) and eg 17 panels (290W or higher) with the 290W variety is 4.93KW max export regardless if each is connected to 305W, 335W, or larger panels. The panel size affects ā€˜efficiencyā€™ (eg production during cloud passage, bird doo, dirt, and so on) but not the max the inverters will produce. Of course an inverter cannot produce more than the panel can generate.

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That would be a good question to ask if you were contemplating buying an iphone. However for solar system batteries it might be better to ask someone with a solar system with batteries with as much experience as you can find, or rely on the warranties from companies that will probably be around in a decade. Technology changes, and the design criteria for different uses are not ā€˜just oneā€™.

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Solar battery systems havenā€™t been around long enough to know what will happen to them after 10 years. Your suggestion to find someone with years of experience is rather impossible, I dare say.

But a lithium battery is a lithium battery, so my Iphone example is not invalid.

As for the design criteria, there are only two for Tesla Powerwall, only one of which is suitable for a household.

Battery warranties are a bit like tyre warranties - if your worn out tyre fails you wonā€™t get new for old, so when your 8 year old Powerwall fails, you wonā€™t get a new one free.

Yes, technology changes. The point of this whole thread is for current technology, though. I hope technology develops enough that any household can go off grid for ever, but weā€™re not there yet. Plenty of vested interests will ensure households have their finances plundered regardless.

Actually it isnā€™t, there are a number of different Lithium battery chemistry variants with different characteristics. Comparison with I- or any other phone battery is not valid- different chemistry, different operating temperatures, charge and discharge rates, depths of discharge etc.

Iā€™ve got over 6 years of Lithium battery use experience myself, but my DIY battery might be up for replacement this year sometime, as capacity is down a bit on new in a few cells, and I place very heavy demand on my battery and need near full original capacity (21kWh). However, my battery cost only a fraction of the cost of a Tesla or any other commercial brand.
My existing battery wont be junked, as I have use for the cells in back-up applications not needing as much capacity as my main house supply.

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I did just over 7000 kwh FI last year which has proven my solar installer wrong, in a nice way - he was less optimistic.

I donā€™t think Iā€™ve ever seen 35 out of my 5 kw system, but heat could well be a factor here at the moment - its nudged over 45 C yesterday and today :slight_smile:

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Hey Gordon,

What does a fraction of a power wall cost look like in the price of 21kW of lithium batteries? Iā€™d be keen to get some decent home batteries if they wouldnā€™t cost Tesla levels

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The battery I built with 16 CALB 400AH cells (nominal 53V) in 2012 cost me just over $10000, including a BMS which I discovered very early on was dangerously not up to the task, and modified extensively it to make it safe. (melted plastic, burnt wires etc inside the box!)

CALB 400AH cells donā€™t appear to be available in Oz these days, but Winston have a good range, and Iā€™ll probably go with them (I suspect they will last longer), after I check a couple of other options. Theyā€™d cost something like $12K for the same capacity with a BMS from the least expensive supplier I know of.
Not all battery prices are going down despite the hype, in part because the Oz dollar is down so much in recent years.

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Any recommendation for a good BMS? HAvenā€™t delved into home battery tech much yet, however given the ranges of those batteries, gather you need a few in series to produce a convenient voltage, and then something (the BMS?) to regulate which cells are good, degraded, need more charge, etc?

Also re grid for shore power, gather default regulation of such a system is it would only draw upon such power if/when home generation is insufficient (rather than classic ā€œshoreā€ scenario of always when available)? And if just using grid as shore power do you need to go thru the energy providerā€™s solar tariff changes? (Sounds like tariffs for partially solar households may be worse when youā€™re not feeding in?)

Over the past few years Iā€™ve found myself to be quite a good BMS :grinning:

I use a good quality data logger on my system and long term each of the LiFePO4 cells operates at very close to 3.3V on average (current log file over 113 days has battery voltage average of 53.02V, IE 3.314V/cell) You could actually operate most 48V inverters with 15, 16 or 17 LiFePO4 cells.

I initially had my cells configured as 8 pairs of 2 parallel cells = 26.5V, but needed a larger inverter about 4 years ago, so changed to 16 cells in series. I sold the original BMS with my 24V inverter, and have had no BMS on the battery since then. The main functions of the BMS are to make sure individual cell voltages, and overall battery voltage stays within certain limits, by isolating the battery outside the set parameters. However, it should only be the failsafe!
Other methods should be used as the primary battery protections. I had my inverter modified at the factory by Latronics to change the Low Voltage Disconnect, and have found that to be reliable on the few times it has operated. Iā€™ve had it set so that even one cell going low will likely trigger it. I trust my Outback Power charge controllers not to take the battery voltage too high, and they have reliably performed that function so far. I did hear of one Midnite charge controller fail taking the voltage too high, damaging a LiFePO4 battery a few years ago, so Iā€™d be wary of them. I do have a cell balancing system connected, which transfers charge from high cells to low cells, effectively increasing available capacity before the lowest cells gets too low. It will supposedly transfer 10A, but I suspect it is effectively somewhat less than that, since it operates at high frequency (I can just hear it operating), and the cables donā€™t get warm.
Keeping an eye on my data logger I can judge quite well how things are going, and have found that a dedicated BMS is not really essential, despite all the warnings about them being absolutely necessary. You need to have a bit of tech knowledge and full understanding of the system though- itā€™s not something Iā€™d recommend the inexperienced user (ie most people) try.
If I wanted to automate it a bit more, Iā€™d use a relay driver such as the Morningstar RD1, which can be set up to cover LVD and HVD and low/high cell battery disconnection.
I can remotely log onto my data logging laptop from anywhere with internet or phone signal, so can (and often do) keep an eye on things when away.

The Victron (and some other brands) inverters can start a generator or switch to mains to charge the battery at a set voltage, or combine mains/generator with battery power in some models I believe. You could use a timer switch to only use off-peak power. If you are not feeding any solar in, and only operate a charger from the mains, I canā€™t see why solar tariffs would apply.

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In Vic if one has an off-grid solar system running part of a property, and a completely separate grid connected system running another, and the parts never meet on the supply side, the power distributor is not a concerned party. Thus the tariff will be non-solar, noting when going solar one usually goes to a peak/off-peak type tariff where peak can be breathtakingly high in comparison to non-solar. The off-peak is somewhat lower. The net outcome would seem to be heavily weighted on the daily supply charge while the amount of consumption for battery charging would be negligible as compared to no solar in the reset of the property, and as you implied, this approach gets no ā€˜pay backā€™ from the ā€˜gridā€™ but reads like a good fail safe in lieu of keeping a generator with its attendant testing and maintenance. Yes?

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I am sorry, but canā€™t real compare. But I pay approx.8.5c for what I consume, and get 75cent for what I deliver. Sure, that is only since I installed solar decades ago. But by reading aboves commentā€™s, I get the impression the retailerā€™s make a difference as well. Why donā€™t ask some of you powershop.com.au for a quote? If you change to it, please tell them you have it from siegrist@melbpc.org.au By the way: I make approx. $100./ month profit with my solar, without battery

If you signed up today you would be getting $0.118 not $0.75 FiT (or $0.718 as pFiT shows for my area).

Powershopā€™s current offer in my area (without their ā€˜packsā€™) are

so I am curious where your $0.085 per KWH comes into play.

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Strange, I have a complete different bill. But I am aware a similar good price want appear again. But a few decades ago, as I bought solar, for enviroment reasons, everybody called me an idiot.And why I getting different prices to chose from? I donā€™t know.

[ā€¦]
10 Dec 2018 Customer Purchase CURBERS Thank You Powerpack $1.49
Green Power Saver $8.81
100% GreenPower (8.50 c/kWh x 14 kWh) $1.19
Your Community Energy $9.08
Your Community Energy (6.60 c/kWh x 14
kWh)
$0.92
20 Dec 2018 Account Review For period 20 Nov - 19 Dec $0.00
20 Dec 2018 Feed In 4673381:002 Feed-in Tariff ($227.73)
20 Dec 2018 Closing account balance ($587.13)

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Thanks for that, but I am unable to reconcile what those amounts mean after perusing the Powershop web site, to understand what your actual KWH rate is. They do not make it easy excepting they reference discounts that are not easily revealed.

They do make the base plan rates and solar FiT and pFiT clear though, as I posted above, noting there are 2 other rate documents for my area that are similar enough to that above, for the purpose of discussion.

Some things that I can discern include (Green Power): This Powerpack is greener than the standard Auto Pay, attracting an 8.5c/kWh premium. The word premium suggests it is an extra cost above some other cost rather than the base electricity cost.

The 6.60 c/kWH Community Energy amount appears to be a donation you are making, ā€˜youā€™ll also contribute a 6.6c/kWh premium which is used to fund community renewable energy projects around the countryā€™

Are either shown to be in addition to your consumption bill (even though probably paid for inside the pre-paid packs)? Bills typically show a simple line such as (an old pre-solar bill before discounts, with the discounts clearly shown elsewhere.

image

Regardless, with your ā€˜grandfatheredā€™ pFiT you are probably doing quite well with your solar.

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Walmart is suing Tesla after their solar installations caused fires at 7 of their stores.

Walmart is also demanding Tesla remove their installations at all 200 stores.

Looks like Elon Musk will really be having a fire sale on used solar systems.

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An article regarding scientists discovering the cause of problems in lithium metal batteries.

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