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Batteries for solar power

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  1. #1
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    Default Batteries for solar power

    Just an "For Interest/for information and opinion " question.
    If you are setting up a stand alone or totally off-grid system what currently is considered the best battery system to install?
    A cost based question and a best practice question combined.
    Li-Ion or Lead Acid and if lead acid would you use a set on nominal 12V/24V batteries or go with single cell 1.2V?
    Would you install enough to do 240V DC or a lower voltage and use a transformer and absorb the conversion losses?
    "A big boy did it and ran away"

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  2. #2
    Senior Member ForeverYoung's Avatar
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    My simplistic research (because I refuse to waste too much time on it) has concluded home batteries are not cost effective. Take 15 years to pay for themselves and battery warranty is 10 years.

    I am inclined to wait til EVs are cost effective and use them as the home battery.
    EV chargers for V2G and V2H to arrive in Australia within weeks, after long delays - ABC News
    I am currently building a new shed so will be looking into what wiring is required.

  3. #3
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    Default Batteries for solar power

    Moondog55,

    For off grid Iíd definitely go lithium based.

    Typically configured in 48v banks then stepped up to 240v as needed.

    Lead acid can work but needs more room and care to manage state of charge. Poor care can mess with their life.

    Lithium is more costly, but tougher for numpty uses.

    There are a few sellers who sell complete off grid kits on eBay. Theyíre a good place to look at costs of relative off grid systems.

    Whatís interesting to me is the massive supply of solar cells off houses pretty well for free means if you have space you can add heaps of solar panels and charge all day even when itís raining. This means batter banks dont need to be huge anymore. So the old metrics of small array and big battery are redundant. Now you can make enough power to charge in the rain.

    For example Right now my house solar is putting out 6kW and itís raining - Iím charging the car and running my pool pump and running two home offices and three fridges in the rain and still exporting 1.5kW to the grid. So if I liked I could transfer to off grid right now by using the car battery for vehicle to home or by having a 10KW batter bank in the house. Note the battery bank for the house could be an old Nissan Leaf wired up as vehicle to home.

  4. #4
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    Moondog, without a lot more information on location and expected loads it isn't possible to give more than hypothetical indications. Having said that for any sort of residential application I would not consider anything other than a 48V system. If the batteries are lead, then best to use a string of 2V cells of the Ah capacity required. For example my system has 24 x 2V / 960Ah lead/carbon batteries.

    Because the problems of DC arc-ing become more severe at higher DC voltages, domestic systems are generally limited to 48Vdc, with an inverter used to produce 230Vac for consumption.

    Grid-interactive and grid-disconnected are two entirely different scenarios. Being independent of the grid makes system reliability and energy captured on the worst few days of the year of paramount importance. Reliability comes from minimising points of failure (i.e. system simplicity). The design criteria for maximising annual output for a grid-interactive system has little relevance to worst day performance. Off-grid requires a different paradigm to grid-interactive design.

    For system robustness and reliability I have three paralleled DC charge controllers from three sets of PV panels giving triple redundancy. I have two inverters, one for the house and one for charging the car, giving a 100% backup should one or the other fail (neither have so far). Additionally, quite deliberately none of my solar equipment needs to communicate with other components in the system or my smartphone or network. There is no software involved that can be broken by an update to a third party operating system like Windows, OS-X, Android or iOS. It just works. On dark days when a generator backup is required I have a 48V DC charger that is parallel with the solar charge controllers to keep the system simple as possible and remove yet another point of failure, namely the AC charging system normally used in off-grid inverters.

    It's a mistake to think that 10kWh of lithium battery is interchangeable with 10kWh of lead battery. To keep to 50% design depth of discharge for lead instead of the 100% depth of discharge you can get away with for lithium, for the same average daily load the capacity of a lead battery bank needs to be ~double that of lithium battery bank. However rather than being negatives these are two bonuses for the lead battery bank, namely that when the design capacity of the system has been used up, the system still has 100% of nominal rated capacity to draw on (i.e. the other 50% - using the extra depth of discharge a few times a year has minimal effect on lead battery life) whilst having a large margin of capacity over nominal depth of discharge hugely improves battery life.

    Sealed lead/carbon batteries do not need sophisticated battery management. The complicated battery management required has historically been a disadvantage and source of reliability problems for lithium batteries.

    Lead/carbon batteries have an activated carbon coating on the anodes, which minimises sulphation and allows rapid charging, thus overcoming two of the main deficiencies of traditional lead storage batteries. Lead/carbon batteries have much longer design life and tolerance of deep discharge than conventional lead storage batteries. In 5 years off-grid with lead/carbon I have not yet needed to equalise the battery bank. I do not expect to need to replace the lead/carbon batteries in my lifetime.

    In five years the system has never gone down. About 1% of the electricity consumed in a typical year comes from the generator backup. It would probably be 0% except for the BEV car. Typical daily consumption is ~8kWh for the house and ~8kWh for the car.
    Before you speak, ask yourself: Is it necessary, it is true, does it improve on the silence? - Baba

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    Good general article that might assist with your questions:
    https://www.solarquotes.com.au/batte...parison-table/

    https://www.solarchoice.net.au/is-ho...rage-worth-it/
    Interesting 1/4 down the page above is a table that a 3 to6Kw battery could suit most home owners and payback periods.



    Whats interesting is the actual amount a battery can save you over the solar which appears to be small for a grid tied system
    Will see what it is for my situation over 12 months in Nov 2022 but with solar only, I'm estimating I'II be shelling out at best $800 per year...lets call it an even $1,000.

    Based on ~$10,000 for an average battery system installed, it would take ~8 to 10 years to break even and start to get a return (wonder what the reduced capacity would be??) as opposed to the solar componant which appears to take (for me) 3 years at most with a 25 year warranty on a 84% output.

    Of coarse if your domestic property doesnt have power availability and you need to shell out 10,000's for a power extension/substation etc, then its almost a no brainer...as in John2b's case.

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    Hypotheticals are all that's needed unless our numbers come up tonite.
    "A big boy did it and ran away"

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  7. #7
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    Quote Originally Posted by Bart1080 View Post
    Good general article that might assist with your questions:
    https://www.solarquotes.com.au/batte...parison-table/
    Solarquotes all the way.

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    I personally know 3 off grid homes that spent between $30k and $45k on their solar-battery systems because grid connections were quoted at $70k to $120k when they were building. Each of them are very happy with the economics and performance of their different systems.

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    Quote Originally Posted by Moondog55 View Post
    Hypotheticals are all that's needed unless our numbers come up tonite.
    Tell us how much you'll actually care about battery storage if you win the big one

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    Quote Originally Posted by nealeb View Post
    I personally know 3 off grid homes that spent between $30k and $45k on their solar-battery systems because grid connections were quoted at $70k to $120k when they were building. Each of them are very happy with the economics and performance of their different systems.
    I was grid connected and spent ~$40k on a solar-battery system and then disconnected from the grid which I already had for free. I am not merely very happy, but ecstatic with the with the economics and performance of the system. Frankly, the sooner one makes an investment in a benefit, the sooner the benefit starts to pay back.
    Before you speak, ask yourself: Is it necessary, it is true, does it improve on the silence? - Baba

  11. #11
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    Thanx all
    We were interested in the cost/benefit even if at this stage we can't go any further as SWMBO didn't win the lottery again, it remains an open option if we decide to sell and move somewhere more remote from power lines.
    "A big boy did it and ran away"

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    Quote Originally Posted by Moondog55 View Post
    Thanx all
    We were interested in the cost/benefit even if at this stage we can't go any further as SWMBO didn't win the lottery again, it remains an open option if we decide to sell and move somewhere more remote from power lines.
    It was a while, at a previous locale, that I looked into it in any detail but they were 2 details I recall:

    1. was if you decide to connect to the grid you can be hit with the upgrade costs to the transmission/distributors if they say extra capacity is required to service you
    2. some countries/locales had already looked into charging a service charge even if you elected to be off grid - their rationale was the grid is expensive and the cost should not be borne by those left on the grid as more and more people left it

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    Quote Originally Posted by Moondog55 View Post
    SWMBO didn't win the lottery again,
    If that happened paying for power would be the least of your concerns.

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    Quote Originally Posted by Bros View Post
    If that happened paying for power would be the least of your concerns.
    Nah, it we had won we'd want to keep as much of it to ourselves as possible, as I think we already pay far too much to governments and big businesses. Those concerns don't need any more of my money
    "A big boy did it and ran away"

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    Quote Originally Posted by Moondog55 View Post
    Nah, it we had won we'd want to keep as much of it to ourselves as possible, as I think we already pay far too much to governments and big businesses. Those concerns don't need any more of my money
    Not my words but "Ask not what your country can do for you – ask what you can do for your country,"

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