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Thread: Solar and Batteries is 400ah 2 x 200ah deep cylcle agm's enough

  1. #1
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    Solar and Batteries is 400ah 2 x 200ah deep cylcle agm's enough

    Hi All,

    On our property we have the following running. So is it correct to say the 3kw relates to a 250ah draw per day if we have 2 x 200ah batteries. The solar system consist of 5 x 60watt panels and 2 x 180 watt panels on the roof so not easy to change the angle, they also sit in gum tree shade for 40% in summer and 60% in winter, the max I have seen on the epever is a 17a push into the sells

    per hour hours Total
    Inverter 30 24 720
    GSM booster 6 24 144
    Lights 40 6 240
    Respirator 40 10 400
    Fridge 50 24 1200
    Charging 50 6 300
    watts 3004
    kw 3.004

    Given that we only push in about a 100a via the solar on a good day we should be ok for 3 days approx.

    just a general comment on how you would set your system up and if perhaps my calculations are off.

    thanks

    J

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    Need to understand a bit more about your energy storage.

    What is your system nominal voltage? You say only two batteries so it can be either 12 or 24 volts.

    What is the individual battery voltage and how are they connected? Series or parallel?

    Your energy demand table indicates an electricity use of 3 kWh/d.

    Do you know what the inverter efficiency is?

  3. #3
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    Hi mate,

    thanks for the reply:

    2 x 12v x 200ah AGM deep cycles in parallel - nominal 12v

    Manufacturers specs for the Giandel 2000w pure sign wave inverter


    • Surge Power: 4400W
    • Continuous power : 2200W
    • DC input : 12V
    • Input voltage range : 9.5-16V DC (rated power 12VDC)
    • Input over-voltage shutdown : 16VDC±0.5V
    • Input under-voltage shutdown : 9.5VDC±0.5V
    • Input under-voltage alarm : 9.8VDC±0.3V
    • Dimensions : L 430mm W 240mm H 90mm
    • Output voltage : 240V AC±10%
    • Output frequency : 50Hz
    • Output wave form : Pure sine wave ( THD ≤ 3%)
    • Efficiency : 90 %
    • Over temperature protection : 65±5℃
    • Over-load protection : 2200-2500W
    • USB Output : 5 VDC Max 2.4A

  4. #4
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    As for the fridge, it's a bar fridge rated at 50watt's, that would only be when it's running, perhaps 20-30% of the time and for an hour after it's been stocked.

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    Quote Originally Posted by TheEntertainer View Post
    Hi All,

    On our property we have the following running. So is it correct to say the 3kw relates to a 250ah draw per day if we have 2 x 200ah batteries. The solar system consist of 5 x 60watt panels and 2 x 180 watt panels on the roof so not easy to change the angle, they also sit in gum tree shade for 40% in summer and 60% in winter, the max I have seen on the epever is a 17a push into the sells

    per hour hours Total
    Inverter 30 24 720
    GSM booster 6 24 144
    Lights 40 6 240
    Respirator 40 10 400
    Fridge 50 24 1200
    Charging 50 6 300
    watts 3004
    kw 3.004

    Given that we only push in about a 100a via the solar on a good day we should be ok for 3 days approx.

    just a general comment on how you would set your system up and if perhaps my calculations are off.

    thanks

    J
    I am not an expert! One comment on your numbers and systems stability. My work U.P.S. set up was fantastic with about 5000w load and a little more peak. Yet failed at times. At my place it was our kettle 2500 watts and Microwave..... Via a Goodwe 5kwh ES hybrid inverter.

    A few other little items possibly a hair drier just might make your peak load a issue if not very careful.

  6. #6
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    Hi,

    Luckily no one ever takes a hair dryer out to the property, my fil did have a 600w water pressure pump, we have replace this with an IBC up the hill and only now use it to pump water up now and again and we use the gennie to do so.

    revised calculation, the fridge does not run all the time:
    per hour hours Total
    Inverter 30 24 720
    GSM booster 6 24 144
    Lights 40 6 240
    Respirator 40 10 400
    Fridge 50 5 250
    Charging 50 6 300
    watts 2054
    kw 2.054

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    urm, you're very marginal.

    I'm assuming that the situation is you're only out there every other weekend and when you're no there everything is off so the batteries can top up during the week/fortnight?
    Dave

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    Spot on, max would be 3 days there and 3 days home. Skipping some week all up. So by the time we or my father in law returns they should be fully charged.

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    Just some quick back of the envelope estimations and observations based on the info at hand... for what it is worth... I hope it assists the planning but as with all this type of advice online, caveat emptor.

    Quote Originally Posted by TheEntertainer View Post
    we should be ok for 3 days approx.
    I am assuming you mean 3 days of energy stored in the batteries? This is the usual interpretation of a question like this. That is, the number of days of autonomy assuming solar doesn't provide for you e.g a storm for three days etc.

    Quote Originally Posted by TheEntertainer View Post
    2 x 12v x 200ah AGM deep cycles in parallel - nominal 12v

    Manufacturers specs for the Giandel 2000w pure sign wave inverter


    • Surge Power: 4400W
    • Continuous power : 2200W
    • Efficiency : 90 %
    From this information we can calculate the amount of energy you can draw from the batteries you have indicated.

    12V x 400Ah = 4800Wh or 4.8kWh of energy storage in the batteries - total. Assuming you don't run them down below 50% depth of discharge, 2.4kWh of energy available at a depth of discharge of 50%.

    Quote Originally Posted by TheEntertainer View Post

    revised calculation, the fridge does not run all the time:
    Watts hours Total
    Inverter 30 24 720
    GSM booster 6 24 144
    Lights 40 6 240
    Respirator 40 10 400
    Fridge 50 5 250
    Charging 50 6 300
    Watt hours 2054
    kWh 2.054
    Corrections to the table in red. Watts is a capital W. It is named after James Watt and so is capitalised in the unit W, Wh and kWh.

    OK, here a third of your load disappeared from the previous table so is now 2.1 kWh/d and not the 3 kWh/d as it was previously. This will make a big difference.

    Some comments on the load. Not sure why your inverter draws 30 Watts. Is that the standby loading? It is your biggest energy user in that list. I would disconnect it if I wasn't using it at that power rating. You have some very low power loads such that if everything was on at the same time would be 216 Watts. So unless you absolutely need a 2kW rating (2000 Watts) you could also look at getting a smaller inverter and try to reduce that standby load to a few Watts only.

    Anyway...

    If you had 2.4 kWh of electricity in storage based on a 50% depth of discharge (DoD) and you lost 10% due to inverter efficiency loses (i.e if you wanted 2.1 kWh out you would need 2.3 kWh in there as you'd lose 10% to get the 2.1 kWh) you would really have just over a day of energy in the battery bank you indicate.

    To get to 3 days autonomy you'd need to reduce your already small loads or add more of the same batteries to your system or get batteries with a bigger Ah capacity.

    Don't forget to consider the impact of the depth of discharge percentage has on your overall battery sizing capacity calculations.

  10. #10
    JDNSW's Avatar
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    Speaking with the experience of living on stand alone for twenty-five years.

    I was on a system that had 1.2kw nominal panels on trackers, with 24x2vx1100Ah deep cycle batteries, and two 2kVA (6kVA for five minutes) inverters. This proved 'adequate' for years, but I used the backup generator a lot, and battery life suffered.

    Following a lightning strike a few years ago, this was replaced (under insurance) by 5.5kw nominal fixed panels (they are a lot cheaper than they were in 1994), same batteries and a single 7kVA inverter. The only time the backup generator has been started since was to check that it was wired in correctly. And my power use has increased - electric kettle, toaster, electric blankets, stopped worrying about power use as much.

    The key is the amount of panels. Even under cloudy skies these provide significant power, meaning less load on the batteries, and fully charge the batteries with a much shorter period of sunlight than previously.

    In my view, you do not have enough panels, but I would also think you need more battery capacity - discharging below 50% is a recipe for short battery life.
    John

    JDNSW
    1986 110 County 3.9 diesel
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