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Thread: Off Grid Solar + Battery advice

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    Senior Member skozzy's Avatar
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    Default Off Grid Solar + Battery advice

    Recently I was given 8 solar panels from a mate that changed their dead 1.5kw system to a new 5kw system. So I was thinking can I use these to power my PC, 2nd PC, Two 5 drive NAS's, 2 Laptops, 2 Monitors (1 is a 44inch TV).

    I recently bought a power meter for the wall socket and have everything hanging off it and i've seen 550 watts read max so far.

    Will these 8 panels + charge controller + inverter (of whatever size) + batterys get all this going 24/7

    My location is Brisbane and have roof space for about 15 panels to face north, currently I have 3kw grid feed running for the past 5 years which is ground mounted and which isnt big enough to get a $0 bill, im home all day, PC on all day and figure making a small offgrid system with these 8 panels might help.

    I do wonder just how many batterys I may need, as prices for these vary a lot.
    Last edited by skozzy; 10-08-16 at 11:56 PM.



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    Will these 8 panels + charge controller + inverter (of whatever size) + batterys get all this going 24/7
    Yes; as long as you are not expecting to draw 550w continuously - half that would be better & even then you may struggle in low sun weather depending on how much battery storage you opt for.
    Also as long as the panels are in good condition? You said they come from a "dead 1.5kw system." What died??

    ATM I would say that it would be more cost effective to add these panels in as an upgrade to your current grid connect system; as the price of an appropriate sized charge controller, inverter & batteries is going to be pricey to meet your demands 24/7.
    The batteries are going to be the killer in the deal.
    I would expect in the $10k - $15k price bracket if you want them to live long; or halve that price & risk being in battery torture land unless you use a backup charging system from your grid system in times of low sun.

    That's my opinion, take it or leave it.
    Cheers, Tiny
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    If you add to the existing system you may lose your 33 cent feed in tariff.

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    Senior Member skozzy's Avatar
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    What died in their system was the inverter, twice and 3rd time the installer has closed shop.

    I rung a local installer and he says I can get away with 4 Batterys, + charger + inverter + installing the panels and wires for Aprox 4k.

    This is why I like coming here asking, cause there is no sales hype, just facts.

    A mate of mine who lives offgrid and miles out of town bought cheapish import 2v batterys which cost him $3k, was cheaper then the brand name stuff for about $8k with the same ratings. His idea was even if they pack it in 1/2 way its still cheaper over all to replace them then go main stream.

    But my idea with these panels is running my computer stuff 24/7 and wanted to get a non sales persons point of view.

    Thanks

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    Senior Member skozzy's Avatar
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    Yeah not adding to my current one, making a stand alone system.
    This meter has been running for 20 hours now
    Its used 3.513 kwh
    Seems to be using 1.2 - 1.4 amps
    Power Factor (what ever that is) is on .9
    Lowest Watts was 79 (guess when I was sleeping)
    Highest watts was 479.4

    Currently is one PC, 1 Laptop, 2 NAS's, Mobile phone charger, speakers, TV, Monitor, and USB drives.

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    Quote Originally Posted by Dishtrackted View Post
    If you add to the existing system you may lose your 33 cent feed in tariff.
    only if you tell them that you have increased the panel number

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    Senior Member skozzy's Avatar
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    Well one thing I have been doing is spending the day watching youtube videos how to make a lead acid battery, doesn't like I got the space or tools around the house to make one (for the sake of it), so will study up more on battery types and try figure out which I should go with.

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    There was thread here on setting up a lithium power wall with youtubes???

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    Are you planning to rewire your house, leaving the power point intended for your off-grid operation in island mode? With separate protection circuit, obviously.
    This might be a bit challenging depending on how your house is wired at the moment - suggest speaking with your local sparky.

    Your power factor of 0.9 is good meaning 90% of generated power is used to do the real work.
    Lets say your highest power demand detected was 479.4 Watts. With 0.9 power factor your system had to generate 532.7 KVA of power.
    This is your starting point.
    Allow for surges and unexpected disturbances - 10% power reserve you need at least 600 kVA inverter to service your highest power demand.
    To decide on a number and size of batteries, look at your so called load profile or how the power demand changes over time. If you have the same load pattern any day of the week then make your load profile chart for over 24 hours (with 1 or 2 hours steps) and then add the kWh generated. I suggest you also research the solar profile in your area to understand how much time your solar panels will feed the system plus charge your batteries and how much time your batteries will feed the inverter.
    Batteries capacity is important to consider when making your selection so that they do not completely discharge while running your power point.

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    Just noticed I put kW and kVA instead of W and VA.
    I hope the typo didn't scare anyone away

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    No plans to rewire anything, I havnt spoken to an installer about this part yet. My idea is a power point added to my computer room for everything computer related to plug in to.

    I am taking my time to look in to this as well, and with the aid of the power monitor I am trying ways of saving power too, like making use of the Power Options in windows to use Energy Saver when I know i will be AFK for some time and moving external devices like monitor, USB drive, Speakers etc to a power board that has on/off switches (surprised how much standby power some of these things use). With a few steps ive reduced the 300-400 watts an hour to 200-300. And when I am AFK using the power saver mode 100-160 watts an hour. Decent change i think.

    As for power generated from my current grid feed system. Due to a tree next door casting a shadow over my panels around 2pm I am seeing current average daily totals of 10-12kw generated, this is down about 5kw from previous years for the same time of the year. My current system is ground mounted and this OffGrid system i want to put together will go on the roof of the house, which will be facing N-(NE 10deg). As for roof pitch I am not sure, i would say around 15-20deg. I believe I will collect more solar energy from the panels on the roof then my ground mounted system.
    Last edited by skozzy; 17-08-16 at 02:20 PM.

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    Quote Originally Posted by fromaron View Post
    Are you planning to rewire your house, leaving the power point intended for your off-grid operation in island mode? With separate protection circuit, obviously.
    This might be a bit challenging depending on how your house is wired at the moment - suggest speaking with your local sparky.

    Your power factor of 0.9 is good meaning 90% of generated power is used to do the real work.
    Lets say your highest power demand detected was 479.4 Watts. With 0.9 power factor your system had to generate 532.7 KVA of power.
    This is your starting point.
    Allow for surges and unexpected disturbances - 10% power reserve you need at least 600 kVA inverter to service your highest power demand.
    To decide on a number and size of batteries, look at your so called load profile or how the power demand changes over time. If you have the same load pattern any day of the week then make your load profile chart for over 24 hours (with 1 or 2 hours steps) and then add the kWh generated. I suggest you also research the solar profile in your area to understand how much time your solar panels will feed the system plus charge your batteries and how much time your batteries will feed the inverter.
    Batteries capacity is important to consider when making your selection so that they do not completely discharge while running your power point.
    That is a pretty poor explaination of power factor. I haven't done any of that sort of work in 30yrs so my explaination may not be much better but I'll give it a go.
    The basic formulae for resistive power (ie a purely resistive load) is voltage x current and this is what you are metered & charged for by the supplier. Without being pedantic this would be the case for heating loads ( stoves, heaters etc ) However most other loads are not resistive loads but are reactive loads , either capacitive or inductive. These loads cause changes to the voltage /current waveform which is in phase for resistive loads.
    For capacitive loads the current leads the voltage and for inductive loads the current lags the voltage. This causes a corruption of the current/voltage waveform used for metering with the result of often being undercharged for your power. Very common with large arc welders and why capacitors are put in fluro lights to correct the phase difference brought about by the ballast transformer. From memory the power factor is the cosine of the voltage/current phase difference. Most power factors are less than zero (DC load) and indicate that the load is inductive rather than capacitive. It is really of no concern to the end user, the power suppliers are the ones that are interested for charging purposes and grid engineering.
    Thats the best my poor memory can do , others may do better.

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    Quote Originally Posted by watchdog View Post
    That is a pretty poor explaination of power factor.
    .............
    Thats the best my poor memory can do , others may do better.
    Try that for better explanation


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    I have a bit of a surplus of batteries at the moment and a shortage of panels.
    I think I currently have about 150kWhr.
    Yes I am an agent of Satan, but my duties are largely ceremonial.

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