for the solar buffs

Discussion in 'Designing, building, making and powering your life' started by missf, Nov 17, 2008.

  1. missf

    missf Junior Member

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    we are setting up a solar system as we have no power (in a remote area)
    I presently have 90 watt in solar panels (3x15 watt , 1 x45watt) 3 x 12volt 24 amp gel deep cycle batteries, 1 inverter.
    we need to have a fridge running a home computer and lights at this stage Any ideas on how to put something good together??
    My panels will be facing the north side as you can see it is the only roof space we presently have. Miss F
     
  2. dgriffith

    dgriffith Junior Member

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    Re: for the solar buffs

    The fridge is going to be the big issue. 90 watts of panels and the 72 amp-hours of batteries should be able to run a small camping fridge (like a waeco esky-sized compressor one) *relatively* indefinitely. There won't be much left over for anything else - depending on clouds and ambient temps you might find a few days of cloudy weather leaves your batteries flat and your fridge off. Possibly you might be able to get away with a compact fluro or two for a couple of hours a night as well as the fridge.

    I would suggest a gas fridge for the time being. An old three-way (240V/12V/Gas) caravan fridge goes for fairly cheap if you scrounge around. I have a whiz-bang $2000 Consul 200L fridge/freezer here and a 9kg bottle lasts about three weeks.

    Regarding the rest sans fridge, it really depends on how much you're going to use it all.

    I'll throw you some numbers to give you a rough idea.

    90 watts for 7 hours of sun a day in summer is 90x7 = 630 watt-hours a day coming in.
    - Lose a bit for storing in your batteries = 550 watt-hours a day.
    - Lose a bit for running the inverter = 480 watt-hours a day available for lights/computer/etc.

    Compare this to the average 'energy-efficient' grid-connected usage of 4000 watt-hours a day. It's going to be a bit..... austere. :lol:

    So - 480 watt-hours a day means that every day of good sun you can :

    Run 480 watts of appliances for one hour.
    Run 240 watts for two hours.
    Run 120 watts for four hours.
    Run 60 watts for eight hours.
    etc.

    Use compact fluorescents and the lowest wattage you can bear.
    Say you use 3 x 15 watt fluoro's for 2 hours a night on average. That's 3 x 15 x 2 = 90 watt-hours of power used a day.
    Your computer could be an issue. My desktop PC draws around 80 watts. Assuming your's is the same, then two hours a day gives 80 x 2 = 160 watt-hours used per day.

    So, that's 90 watt-hours + 160 watt-hours a day to give a total 250 watt-hours a day.
    On a good day you're getting 480 watt-hours/day in, so there's enough (480-250 = 230) watt-hours a day left over for charging the batteries. Speaking of which -

    Your batteries hold 12V x 24 Amp-hours x 3 = 864 watt-hours full to empty, 432 watt-hours from full to half-full (to prolong battery life). So basically, you've got nearly the equivalent of one day's full sun in your batteries as reserve. With no sun and you using 250 watt-hours/day, you've got just under two day's reserve. You then need to charge the battery again, and with the 230 watt-hours a day left over from above, it will take about two sunny days to recharge again.

    So that's the sunny season. Depending on when your cloudy season is, you might only end up with half that amount of power coming in at other times of the year. At that point, you're pretty much using as much as you make, and you might need to top up occasionally. (eg, for a 12V system, jumpering over to a car battery and running for an hour or so)


    Hope that makes some sense!
     
  3. ant1

    ant1 Junior Member

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    Re: for the solar buffs

    Don't you need a charge regulator? Or diodes at the least, connected for max volts low current (series)?

    my elec knowledge is limited..!
     
  4. springtide

    springtide Junior Member

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    Re: for the solar buffs

    You might be able to get away without a charge regulator on this set up but if you are expanding then they are a great help, most of them will also give you an idea of when your batteries are empty/charging/charged - cheap ones colored lights n stuff, expensive ones give nice digital readouts n turn generators on/off etc. My first one cost me $38 on ebay and is good for 6.6 amps 12 or 24 volt. Thats probably the first consideration - how big do you want it to get? - Fridge, computer, lights 12v is great. For something bigger you might consider 24v - its just easier and cheaper to upgrade with a few 100amp batteries that will fill plans for the future than to collect bits in very small increments (are you eligible for a RAPS grant?)
    Here is a pic of my garage "test" set up - 25w of solar, 200a gel battery and 2*70a lead acid, 6mm2 cable in conduit (some scrap metal merchants will sell you back scrap cable by the kilo rather than by the metre at a shop - much cheaper) double throw circuit breakers - sunday markets, shunt n gauge from ebay.
    test board #1.jpg[/attachment:r6hekpxd]
    The system i am slowly scrounging for will eventually have to cope with a family of 4 and 3-6 eco chalets - so the next one is going for gold at the london olympics :D :D :D :D

    Good luck n choose your appliances carefully (just bought a F&P washing machine 8kg :shock: - direct drive uses 185 w / cycle (cold) and 300 w peak draw)
     
  5. Woz

    Woz Junior Member

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  6. ppp

    ppp Junior Member

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    Re: for the solar buffs

    my 100AH battery lasts two and a half days running my engel 40L camping fridge. I estimate that an 80 watt panel would be plenty for this, but I don't have a panel yet. I currently charge it from my car.
     
  7. ant1

    ant1 Junior Member

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  8. springtide

    springtide Junior Member

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    Re: for the solar buffs

    Just thinking - have you considered a wind turbine? - there are a few 500w 12/24v ones on ebay putting out 100w at 10km/hr and 500w at 42km/hr - 750 or so bucks with a 6m tower sounds pretty good provided you don't have too many trees (an afternoon breeze could charge everything).
    Also with the lousy aust dollar now is not the best time to buy solar panels - but divide the cost by the watts - this will give you a consistent comparison. I bought 2 50 watt panels a couple of months ago and paid $6.2 / watt on ebay, now the best i have seen is $8/watt and i can do better with an online store.
    This is the site i use for cable sizes and to figure out if i'm getting a bargain on ebay - iv'e talked to them about some stuff a few times and they were very helpful. https://www.energymatters.com.au/climate-data/cable-sizing-calculator.php
    Batteries are dependant on how much you discharge them, generally 80% = 2 years or less, 50% = 5 years (ish) and 30% about 10 years (ish), super expensive sonnenschein batteries might last 20 years - twice that of a good lead acid battery but at 3 to 6 times the cost i don't know if they are worth it.
    Regulators - check that they suit the type of batteries you are using and go for something a bit bigger - dont wire up the inverter to the "out" terminals of the regulator (20a regulator with 100a surge rating on inverter will blow fuses).
    One last thing - keep things out of reach of kids/pets/etc, i have been k.o. by 24v dc when i was a lot younger and waking up on the floor isn't reccomended.

    Hope this helps :wink: :wink: :wink:
     

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