solar power plant questions

Discussion in 'General Electronics Chat' started by Phillip Lucas, Mar 13, 2017.

  1. Phillip Lucas

    Thread Starter New Member

    Mar 13, 2017
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    Hello kind people. new to the forums so please be gentle lol
    So my first thread is part of a greater design. its about renewable energy.
    the idea is to make a portable solar array with add-ons and such. I understand the maths.
    currently my average use is 21kw per day. I get 8-16 hours of sun so need about 3kw of panels to be self sufficient (less then that because I am converting house lights to 12volt LED and aircon/ stove and hot water system are hard wired.)

    I understand that batteries will need to help at night to run a few things like TV and such and when I get numbers on that I will post them.

    so the idea is to have a solar take most of the load during the day. I want to try and get UPS with surge protection for computer and other electronics.
    I also want to be able to upgrade solar at times if needed, I intend to start a workshop so power tools need help.
    the charging station needs to be able to handle the 3kw up to 6kw. I have thought about this and will put each panel on individual chargers that handle 50 amps, so blocks of 600watt panels will suffice. I was also thinking of keeping battery banks around 300ah giving each bay 3600watts of usable DC voltage before upgrade.

    THE QUESTION I HAVE THOUGH is I am trying to find an inverter that can handle a dryer, fridge, freezer, computer, TV and later workshops. The Idea I had was to find an inverter and use it as a Master device, then use add-on inverters that are rated as grid tie in and use them to upgrade watts as needed. So I need to find inverters capable of handling the upgrade. IS THERE ANY SUCH DEVICE FOR OFF GRID???
    something like this awesome pic I made with crayons.... or paint 1.png
     
  2. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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    You are mixing systems.

    If you want solar to take the majority of your load during the day, the your system will be grid tied.
    95%+ of your kilowatts will be used to power household loads like AC, fridge and microwave.

    If you want to run off battery at nights then you an island system that is NOT tied to the grid.

    Grid tie inverters cannot operate unless the grid is operating. If the neighborhood loses power the inverters go down.

    Battery based is much more useful in emergency situations, but daily upkeep gets to be a pain, and batteries are dangerous, messy and tend to die when you need them most.

    Grid tie can save you loTS of money $ ...so there is that.

    What we need from you would be a more specific question after you decide which way to go. Grid tie, battery, or both?
     
  3. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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    Personal preference.

    I would want many different inverters for my appliances. AND Spares as well. Not a single household sized unit.

    Pure sinewave inverters are not needed for everything either. Vacuum cleaners and fridges can operate just fine on a modified sine inverter.
     
  4. Phillip Lucas

    Thread Starter New Member

    Mar 13, 2017
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    ok so the TECHNICAL term for what I want is off grid.
    As a renter, I am unable to mount anything on the roof or make a shed or the likes. but an electrician friend (qualified and actually follows laws and regulations so I like him) said if I can make a small grid with an "upgradeable" inverter he would make a power box with RCD's and safety switches and the like earth the sucker out and make it quite safe. so we made a trailer to store it all....... the panels are going to be movable as a permanent fitting requires council approval. even going to put a new anchor point on the fence which will not be used officially for the fence but may or may not connect to the earth pin.
    the only thing he wanted was power to come in on 1 line so he could distribute it over the switches. we also looked at a few options to help out like an auto power selector on a power board so I plug both the solar and mains in but it uses solar when available and kicks over to mains when it has to, hence UPS on computers for that interval (think he said 15 milliseconds but would rather be safe and not lose data)

    as for multiple inverters I have the unfortunate happenstance to have to use a dryer as reaching clotheslines is getting to be a pain (literally feels like a gunshot) so the dryer will need 3000watts as standard. now if my poor maths is right (which it most certainly is not) 3000watts AC will need about 3200watts DC(From losses in inverter, wire and all that fun stuff) 3200 watts DC is about 260amps at 12volts.... I would MUCH prefer to share this load over a few inverters with extras for redundancy then have it on one and somehow spike/ blow up and lose the system until the replacement is implemented.
     
  5. drc_567

    AAC Fanatic!

    Dec 29, 2008
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  6. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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    Getting multiple inverters to share loads requires them to be synchronized, or put "in phase" with one another.
    Another very expensive luxury price wise.

    Might I suggest you make a 48 volt battery bank instead of 12 volt?

    Cuts your amp draw 400%, meaning cables can be a manageable size.

    Or even 24 volt. 12 volt systems for a household would be drawing hundreds of amps.

    http://www.theinverterstore.com/7000-watt-power-inverter-48-volt-240vac.html
     
  7. MrSoftware

    Senior Member

    Oct 29, 2013
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    Check your area; in some places if you produce more power than you use, you can back-feed it to the power grid and get credits for it. So say you generate 30kwh during the day but only use 20kwh, then 10kwh would go to the grid and you would get credit for the 10kwh. Then when the sun is down and you draw from the grid, you have 10kwh of credits to use before you start incurring charges. You won't get any sort of off-the-grid backup this way, but I think the cash flow would be much more in your favor since battery banks are expensive to buy and to maintain.
     
  8. andrewmm

    Active Member

    Feb 25, 2011
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    Solar PV,

    fun isnt it..

    key questions,

    size of panels => power output . If you have 8 hours sun light, and can store all you generate, then proximate numbers of max available is 4 * watts of your panels. So if you have 6 KW of panels your going to get MAX 24 KWh of power off them.

    6KW of panels is about 10m by 5 m , not small, and costs a few bob,

    24 KWh of batteries , is a lot.

    You can't use car / lorry batteries, they cannot take the constant discharge, they are designed for short burst of power,
    your looking for deep discharge batteries, which cost a lot more.

    The batteries should not be charged above 80 % , or discharged below 20 %, else there life is affected in a negative direction,,,

    so you now need 40 KWh of batteries to store and use 24 KWh of your power.

    High DC current is not good for efficiency,
    solar batteries are normal in series strings , in the 200 to 400 volts range to get around this.
    400 v DC is more than deadly,

    bottom line, unless you have free / cheap access to batteries it is not cost effective by a long way.

    and don't try to combine the ac output of UPS's. If they are a good make they will auto shut off as they are being back driven, if they are cheap , they will catch on fire due to the back current
     
  9. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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    Good info, except that part about not charging batteries above 80%

    Leaving lead acid batteries chronically undercharged will destroy them in short order. 100% recharged daily is the SOP. Bi-weekly or monthly, flooded cell batteries are given an over charge, called an equalizing charge.

    Just correcting the record.
     
  10. MrSoftware

    Senior Member

    Oct 29, 2013
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    Different battery chemistries require different treatment. There is a ton of good info here:

    http://batteryuniversity.com/learn/

    That said; lead acid are probably the most cost effective solution, and they do like to be fully charged.
     
  11. Phillip Lucas

    Thread Starter New Member

    Mar 13, 2017
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    this appears to be grid tie in.... not exactly what I wanted
     
  12. Phillip Lucas

    Thread Starter New Member

    Mar 13, 2017
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    yeah I was thinking about this.... redesign again but oh well maybe best choice
     
  13. Phillip Lucas

    Thread Starter New Member

    Mar 13, 2017
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    that would be awesome except I rent.... as such not allowed to implement anything that would require a drastic change to the house or power system. lets say I buy the system and install for $500... if the lease is not renewed I have to pay $1000 for the uninstall and reinstall plus whatever for the make good is.
    the idea is to make something that is portable for a renter
     
  14. Phillip Lucas

    Thread Starter New Member

    Mar 13, 2017
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    got most of what you said except
    solar batteries are normal in series strings , in the 200 to 400 volts range to get around this.
    this sounds silly as heck to me. but ok.
    so will look at 48volt battery banks to minimise wire gauge. will have to look at different inverters too now.... and new regulators... ok just redo the whole system..
     
  15. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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    I have a 48 volt battery bank and inverter. It has seen me through a hurricane and a flood. 4 12 volt batteries at 210 lbs each. Got them at 350 each, but would pay closer to 800 each today. Marine deep cycle 8D body size.

    Check out boat power plants. They don't have to be floating in water to work :)
     
  16. Phillip Lucas

    Thread Starter New Member

    Mar 13, 2017
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    yeah thinking about that.... I am hoping to find parts that can start a small plant and then upgrade.... might go design the individual parts myself..... its weird that there is very little to do as I wanted. as will always be the case thanks for the help
     
  17. Phillip Lucas

    Thread Starter New Member

    Mar 13, 2017
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    so heres a silly question. if I use an off grid inverter as the primary, and then add tie in grid connect inverters, would the latter not sync with the former as the system increases?
    I mean they would sense the off grid wave and then sync to that one right? then add a wattage boost to the system
     
  18. KeepItSimpleStupid

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    Mar 4, 2014
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  19. Kermit2

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    Feb 5, 2010
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    Theoretically the small grid tied inverters would work, but the national power grid is practically infinite power wise in relation to the inverter. Hard for the little thing to dictate phase relationship with such a huge reserve, but it will only be slightly less powerful than your main inverter and could have an electrical "argument" over phase timing in the scenario you just proposed.
     
  20. Phillip Lucas

    Thread Starter New Member

    Mar 13, 2017
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    I saw these, but the devices don't seem to hook to batteries as standard.
    I assume the charge controllers and battery bank could work but that's an assumption so would need more detail.
    also do these devices automatically adjust to each other or do you need to sync them? its hurting my little brain lol
     
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