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How many solar panels do i need

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  • 06-04-2022 9:24pm
    #1
    Registered Users Posts: 319 ✭✭


    Got some quotes on solar projects. I have my own house and live alone. About 3000 kw hrs pa. One shower a day so i believe there is no point in going for the water/heat conversion? I am interested in a hybrid invertor/convertor to charge batteries although the solution provided requires significant investment up front so i would prefer to have the proper invertor installed and maybe charge a few deep cycle off grid batteries for an emergency supply either now or at a later date? Would i need a 2.4 kw hr panel system or would few fewer panels suffice? How many batteries would i need and is there ia cheaper option of traditional batteries as opposed to these new lithium systems?



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  • Registered Users Posts: 10,969 ✭✭✭✭the_amazing_raisin


    This online tool is pretty good to calculate your potential generation based on location and how many kWp you install

    https://re.jrc.ec.europa.eu/pvg_tools/en/

    However to provide a simple answer of how many panels, cover the roof 😁

    Regarding batteries, while the cost per kWh of lead acid is much cheaper, lithium still works out better. There's 3 major characteristics with batteries:

    Discharge power: how many kilowatts you can get from the battery in a given moment, measured in kW or as a ratio to batteries capacity. Drawing more power than this will damage the battery. For lead acid batteries this is 0.5C as I recall, for lithium it's over 1C


    Capacity: how much energy the battery can store, measured in kWh. Usually for batteries you might be ratings like C5, C10 or C20, this is the capacity of the battery when it's discharged from full over a given number of hours, 5, 10 and 20 in this case. You'll want to look at the C20 rating if provided

    Depth of discharge: what percentage of the battery you can safely use without damaging the cells. You can go lower but it'll shorten the batteries lifetime. For lead acid, the depth of discharge is typically 50% to get a reasonable lifetime. Lithium batteries have a depth of discharge of 90%

    So for the 3 characteristics above, lithium is better in all respects. For example if you wanted 10kWh of capacity, you'd need an 11kWh lithium battery, or a 20kWh lead acid


    In a similar respect, if you add up the power draw of your appliances and it comes to 5kW, you only need 5kWh of lithium batteries, but 10kWh of lead acid


    Also, you can't charge lead acid flow batteries in your house. They vent hydrogen which creates an explosion hazard. You'll need a shed or something to store them which then creates temperature concerns

    By contrast, most lithium batteries for solar are a type called lithium iron phosphate (lifepo4) which literally cannot catch fire. Here's a video of fire testing of some of those cells



    "The internet never fails to misremember" - Sebastian Ruiz, aka Frost



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