A 150mA solar panel can maintain a battery up to about 75Ah. And you need a charge controller suitable for a solar input of at least 11/16.5 = 0.7A www.selectsolar.co.uk 01793 752032 So you need 1200 / 250 = 4.8 hours of bright sunlight. Now as I said before, this is a high power example, more typical of a large offgrid caravan or motorhome, but the approach is the same. The higher the watts rating larger will be its size. Hi Jane, this will certainly work. Also if you are charging your battery from your solar panels, you need to ensure your solar regulator is up to the job. I find that manufacture specify 12.8V 40AH LiFePO4 battery in case for a 40W Solar Street Light whereas 12V 100AH Lead Acid Battery. You’ll need to make sure you connect your fridge and solar panel directly to the battery, don’t connect the solar panel directly to the fridge. Solar panels come with different ratings that can be 10 W, 100 W and even more. Keep in mind that this is only a calculator, and it will directly reflect whatever you, the user, inputs into the fields. That’s about the size of the battery it can maintain. • Your battery size needs to be (43 x 7 x 2)/12 = 50Ah. Solar Panel Calculator Notes and Instructions. Do you need a … First, the notes: We hope this solar calculator will make sizing your panels and batteries a little less painful. Is there a different yardstick to determine battery size incase of Li-Ion or LiFePO4 battery vis-a-vis Lead acid battery. It will depend on two factors, And here's a quick tip: We don't recommend to discharge your battery anymore than 50% a day. (A solar panel at the ideal temperature and aligned with perfect sunlight) Similarly how much power flowing out of the battery can be also measured in watts. How many solar panels you need? A 100 watt panels will be standard size that can be used and installed easily. Add 5W for each additional 60Ah of conventional battery capacity or 120Ah of sealed gel/AGM battery capacity. From here there is a bit of mathematical mumbo jumbo in selecting the correct blanket size based on the loads you're taking and the battery bank size. Secondly, how many solar panels does it take to charge a 100ah battery? This ensures best battery life. A single solar panel of 280 watts will do the work for you. A charge controller is recommended (necessary for gel-AGM batteries). Volts - the pressure of electricity being produced by the solar panel, similar to the height of water stored in a water tank: the fuller the water tank is, the more water pressure you have. So that 120Ah battery you have, esentially cut the useable amount by half. A rough estimate is a 20W solar panel for the first 120Ah of battery capacity assuming that the solar panel receives some direct sunlight at least 6 hours per week. When charging your batteries from a good battery charger over a number of days, you can get to 100% charge. There are other solar panels with various power ratings you can install to charge your batteries such as 100 watts, 150 watts, 235 watts, 250 watts and many more. To work out the size of the panel we need, we simply take the 28.45 x 18V (average voltage of a solar panel) = 512W. What will happen is that the fridge will be draining power from the battery whilst the solar panel is putting power back into the battery. 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