Off Grid Home Forums Technical Discussion Hi need expertise on off-grid electric in France

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    Hi my name is Shaun

    i have recently joined the site for some information on off-grid electric as i have recently purchased a property in france that needs renovation.

    I want to eradicate a grid source of electric for the long term, and I’m trying to find a low budget temporary system that will allow my family to run a 3kw system for the static caravan that we will be living in whilst we do the renovation.

    To give you a better picture, i will explain the current situation.

    The house does have electric, but being in France,(Brittany) the local area has sub stations that are not quite sufficient for what we need, our light goes dim, even using a moderately low power item. as the sub station is too far away to give us decent power. However, my plan was always to be off-grid anyway, so I’m really after a semi low cost option to give us 3kw system.

    Things I’ve looked into are as follows:

    Solar and turbine, yet this confuses me somewhat, in relation to planning and laws that are in france.

    My idea is this:

    I worked out that on a regular day, we would use various appliances that total 2500 watts in the short term, in the caravan.

    My initial approach was to use 4 l16 deep cycle batteries with 390ah installing 24v, 4 x 6v, through a 2500 watt inverter, and using a boost charger allowing me to charge the batteries within 2 hrs. (i can only use the batteries upto 50% drain)

    where i get stuck is how long the batteries last in relation to the power we are using…my maths is not that great, and i get confused in how or what i need to make a consistent cycle using this system, i worked out that to charge the batteries i would use a 3kw generator that uses 2.5lt an hour (this seems expensive) totaling £4.00+ a day.

    i do understand that the figure of 2500 watts is peak power and probably less than this on usual i way off or is this quite realistic, as it does seem quite expensive to do.

    any help would be very well received and i would appreciate any help in regard to this matter, as it is make or break in terms of the project.


    hmm this site is really busy >_<


    I’m not a expert Shaun but I think you’re expecting a lot out of those batteries. My experience is that the batteries always hold less power than you expect once you start hooking a inverter up to them. Do you really need that generator? If you are connected to the grid could you not re-charge to batteries from that? which is what I thought you meant to do at first.

    I do think that you’ll need a bigger battery bank though.



    Hi Shaun2k, try to have some patience with us :)

    You asked some fairly technical questions, not everyone here has the expertise to answer such questions, there are some good and knowledgeable people here who might be able to answer you.

    Another place you can go for answers for these types of technical questions is

    that group is all about 12 volt off-grid power.



    shaun- a couple of places to start.

    first maybe convert your power usage from watts to amps. since this is the battery rating. look on the tags of each motor and get the amps. multiply amps x the amount of hours you will run the appliance.

    i.e fridge. good ones are about 6 amp then there are 12 amp and then 15 amp. lets say you have a 15 amp fridge.

    15 amp x 24 hours is 360 amp hours. of course actual use may be less but always pad you figures so you don’t under build your system.

    another example. i use x-mas lights. 50 led in a strand cost about 8 u.s. dollar the day after x-mas.

    power is .036 amp. lets say you have 3 strands plugged in and on for 4 hours at night. .036 amp x 12 = .432 amp.

    so lighting isn’t an issue refrigeration will be. 360 amp hours would be 8 L16 batteries using 50 % per day.

    on the inverter decision. i would not recommend less then 4000 watt inverter. this will allow you to grow with your needs and wants. a hand skill saw will not run on a 2500.

    a typical u.s family home 3br 2 ba washer/dryer electric hot water uses about 1000 kilo watt hours a month(100,000 watts). 50 % of this is the electric h20 heater and fridge. on a good solar day with a 500 watt solar array you may capture about a 3 kWh or about 100 amp hr ( about 25 % of a 4 battery bank) just like padding your amp calculations i would not build a system to use 50 % of your storage daily. i think the 25 % is good. compensating for clouds or higher usage.

    another thing to keep in mind is not to have more battery storage then you energy sources can maintain. if your reasouce can not produce enough recharge on a regular basis you will harm you batteries or have to run a generator often.

    hope this helps.


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