Kws to amp hr conversion

[Dot]

Greg want to know what the formula is to convert kw's to amp hrs for the solar system (12 volt) please

[Coolabah1au]

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[Jon and Kay]

Depends on your solar panels, but generally a 12v panel provides 17v effectively overstating its capacity by 30%
So....number one...the away the retailer's lie by reducing the stated wattage e.g. 100w panel is actually a 70w panel
Now Ohm's Law says that 1watt = 1amp x 1volt
That's why you can't buy a domestic appliance greater then 2400w i.e. 2400w = 10a x 240v and the maximum allowed through a domestic power point is 10 amp.
So now to the question
Your improperly labelled 100 watt panel will provide an honest 70 watt divided by 12 volts = about 6 amps.

[Mrcoolabah1au]

Wow

[GregnDee]

Here's the question from Greg

If you have an appliance that uses 3.6 kW per 24 hours, how many amp hours of battery is required to run this, using 12 V batteries through an inverter?

[Jon and Kay]

IF... it uses 3600watt it would be at 240volt i.e. 3600/240=15 Amp at 240 volt

or a quick result, multiply your amps x 20 for 12 amps so 15 x 20 = 300 Amps

However.....I run a 7.5kw washer dryer, two fridges, airconditioner etc, and don't use 300 amps
You have to divide that 3500 watts by the number of hours in a day, multiplied by the number of hours it might run. So....a 3600 watt fridge might only run one hour a day, and so use 150A If run by Inverter add about 10%...so 165A

[Newcastle George]

Postby T1 Terry » Tue Jan 12, 2016 9:27 pm

The Star Rating label will give a number of kWh per yr. Multiply by 1,000 to get Wh per yr, multiply by 1.1 to give the added loses for the inverter (10%), divide by 365 to get Wh per 24hrs, divide by 12 to get Ah per 24hr day. Now to calculate how much solar is required to replace that, Wh per 24hrs divided by 5 (the number of peak sun hrs per day and just a figure for calculations) multiplied by 1.35 to allow for the inefficiencies of solar panels and you have the amount of solar required to power the fridge.
From the Hardy Normal calculator site:
400kWh per yr = 400,000 x 1.1 = 440,000/365 = 1206 rounded up. 1206Wh/12 = 100.5Ah per 24hrs. 1206/5 = 241w x 1.455 = 350w. Backwards, 350w x 0.7 (70%) = 245w x 5 peak sun hrs = 1225w 365 = 447125w/ 1,000 = 447.125kWh per yr.
All the figures are conservative, inverters correctly matched are better than 90% efficient, solar panels can be better than 70% efficient and batteries are generally above 12v...... and while the sun is shining the fridge is powered by solar and not the batteries, but you don't wanna know the math involved there

T1 Terry

[Jon and Kay]

My money is always on T1....did we get the same result? Just a different way of expressing it

[SteveW]

[jon_d]

3.6 kW per 24 hours

3600 watts per 24 hours

150 watts per hour (average)

0.625 amps per hour @ 240V (average)

12.5 amps per hour @ 12V (average)