Batteries for household PV system




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  1. #1
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    Default Batteries for household PV system

    Just over three years ago we installed a PV system at our house with 3.6kW panels and a 5 kW inverter. I added a bunch of regular deep cycle batteries in the hope that these would last long enough for a proper long term battery solution to become more affordable. The system is grid-tied.

    Well it seems the batteries are kaput. Earlier this week the mains went down and the batteries lasted 30 minutes. I used to get over 12 hours from them and then only reach 50% SoC.

    So has batteries like Li Ion become cheaper and are there any that I should consider strongly? Another source recommended Pylontech but I would like to look at alternatives as well.

    Second question, given the cost, can I install 2 kWh now and a few years from now scale up if necessary or is it not a good idea to combine batteries of different ages?
    Niel
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    Default Re: Batteries for household PV system

    Quote Originally Posted by Musashi View Post

    Second question, given the cost, can I install 2 kWh now and a few years from now scale up if necessary or is it not a good idea to combine batteries of different ages?
    I started of with two batteries (24V system).
    I expanded with two at a time every six months till the eight I have now. I use SonX 150Ah AGM.

    All I ensure is that the two in series are of the same age.

    To fully say if this will work in the long term, the long term must first transpire

    So far going on three years and every morning I am at between 24.9V & 25.1V...still.

    I have to say I only run a 1kW inverter.

    Edit: I am fully off-grid
    Last edited by Prof; 2018/07/06 at 12:44 PM.

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  4. #3
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    Default Re: Batteries for household PV system

    OK Prof, no problem in dropping names.
    (I am merely avoiding having to defend why brand "A" served someone in Durban better than brand "B" in Upington.)

    For lithium - do take a look at these guys in Somerset West.
    They do local work, and they are pushing lithium over lead-acid.
    Should you be prepared to make a long term investment, lithium is said to be far superior, cost effective solution.


    Personally I have no experience with high power lithium (yet), but if I were in your shoes, this type of thing would interest me big-time.


    http://bluenova.co.za/
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  6. #4
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    Default Re: Batteries for household PV system

    Thanks for the replies thus far. It seems this technology still has some way to go to becoming cheaper and cost effective but we're close to a tipping point. Taking the BlueNova 52V 4kWh battery for example. The best one can get is 7000 cycles at 2.8kWh, i.e. 19,600 kWh in total. It goes for around R39,000 so close on R2 per kWh and very similar to what CoCT charges. If they become 10% cheaper, they are an alternative to Eskom and 20% cheaper would be a no brainer. But we're not there yet.

    * I'm referring to my situation where I have access to mains power. The situation would be very different for an off-grid installation.
    Niel
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  8. #5
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    Default Re: Batteries for household PV system

    Subscribe to powerforum.co.za
    I have 4 x pylontech 2,4kwhr batteries with a hybrid infinisolar 4kw inverter, as a backup only system, and it performs faultlessly.
    You will struggle to motivate such systems financially.

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  10. #6
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    Default Re: Batteries for household PV system

    Quote Originally Posted by Musashi View Post
    Thanks for the replies thus far. It seems this technology still has some way to go to becoming cheaper and cost effective but we're close to a tipping point. Taking the BlueNova 52V 4kWh battery for example. The best one can get is 7000 cycles at 2.8kWh, i.e. 19,600 kWh in total. It goes for around R39,000 so close on R2 per kWh and very similar to what CoCT charges. If they become 10% cheaper, they are an alternative to Eskom and 20% cheaper would be a no brainer. But we're not there yet.

    * I'm referring to my situation where I have access to mains power. The situation would be very different for an off-grid installation.
    This only the cost of the battery uniits, not total cost?

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    Default Re: Batteries for household PV system

    Quote Originally Posted by Musashi View Post
    Thanks for the replies thus far. It seems this technology still has some way to go to becoming cheaper and cost effective but we're close to a tipping point. Taking the BlueNova 52V 4kWh battery for example. The best one can get is 7000 cycles at 2.8kWh, i.e. 19,600 kWh in total. It goes for around R39,000 so close on R2 per kWh and very similar to what CoCT charges. If they become 10% cheaper, they are an alternative to Eskom and 20% cheaper would be a no brainer. But we're not there yet.

    * I'm referring to my situation where I have access to mains power. The situation would be very different for an off-grid installation.
    I am currently sitting far far away. I havenít slept or eaten anything better than a stale bun, limp whatever and a glass or two of cheap plonk in nearly 40 hours.

    We need to be carefull with these calculations, and resultant motivations. I will try to pen something coherent when the grey sponge stuff rejuvenates in the morning.
    Cheers

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  13. #8
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    Default Re: Batteries for household PV system

    Quote Originally Posted by SAND View Post
    This only the cost of the battery uniits, not total cost?
    Quite right. One has to add the cost of the PV panels but these are quite cost effective over a 20 year lifetime. Similarly the inverter. What I am looking at is marginal cost. I have the panels and inverter. So Iím weighing up the cost per kWh from the batteries vs the cost per kWh for Eskom/ CoCT.
    Niel
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  15. #9
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    Default Re: Batteries for household PV system

    During sunlight hours you have the obvious benefit of power availability straight from the panels (batteries not included). That will even out the high cost of batteries a bit.
    Eggie.

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  17. #10
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    Default Re: Batteries for household PV system

    Quote Originally Posted by Eggie View Post
    During sunlight hours you have the obvious benefit of power availability straight from the panels (batteries not included). That will even out the high cost of batteries a bit.
    Yes absolutely! In summer we generate more than what we use during the day and we've moved as much load to daytime hours as possible to reduce the dependence on batteries. So my options really are 1: loose the extra generated electricity and use Eskom at about R2 per kWh, or 2: Buy a battery if it can store and provide the additional PV electricity at less than this R2 per kWh.
    Niel
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  18. #11
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    Default Re: Batteries for household PV system

    Why did your batteries only last 3 years?
    What batteries did you have and did you maintain them?

    I'm also keeping an eye out for the new tech, but calcs show nothing still beets the Trojan lead accids, but you have to top them up with battery water every 6months or so..
    Now 5 years in, not sure how long they will last further?
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  19. #12
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    Default Re: Batteries for household PV system

    Quote Originally Posted by Kamakazi View Post
    Why did your batteries only last 3 years?
    What batteries did you have and did you maintain them?

    I'm also keeping an eye out for the new tech, but calcs show nothing still beets the Trojan lead accids, but you have to top them up with battery water every 6months or so..
    Now 5 years in, not sure how long they will last further?
    I can't remember the name now, but it is a set of 102 Ah deep cycles, sealed. The inverter is set to draw maximum 10% of charge overnight and recharge daily so daily the SOC fluctuated from 90% to 100%. BUT during the first few months (when we still had load shedding) the batteries were drawn down to less than 50% and I suspect that caused some damage that reduced the life span of the batteries.
    Niel
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    2015 Bush Lapa Miskruier (B503)

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