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Updating the solar power for my shed


  • Registered Users Posts: 1,079 ✭✭✭ jimini0

    I want to update my solar power on my shed. I currently have a 100w panel connected to a 12v car battery. Might need to replace battery it's old. Running two 40w led lights. I need more light. So it's either add at least 2 more lights or upgrade the ones I have to higher watt. Any advice would be greatly appreciated

  • Registered Users Posts: 9,361 ✭✭✭ Say my name

    @emaherx would be the expert on this.

    Do you know the stored amps of the battery? If changing go for the largest you can or link two together.

    Same with the panel go for the largest you can.

    Do solar panels revive batteries? That's a genuine question. I bought a charger lately and one of the features is reviving batteries by desulphuring the plates. It does that by giving a very low charge to the battery. I thought solar chargers did similar and batteries would last times longer than normal.

    Other than that go for the highest lumens you can in the wattage you want. And give a cursory glance at the kelvin of the light - colour.

    There's something called equalising battery charge that seemingly they do to if using multiple batteries. But I'd imagine they'd equalise anyway. Could be something to look at too.

    I presume you had a charge control unit between the panel and the battery to prevent overcharging?

  • Registered Users Posts: 1,079 ✭✭✭ jimini0

    Yes have charge controller. I'm goin to get the battery tested but I'm pretty sure it's knackered. It was in my van since 2005. What size solar panel do you think would be needed? I'm thinking of using a tractor battery. It might store more power so I can run a couple of more lights

  • Registered Users Posts: 5,374 ✭✭✭ emaherx

    Far from an expert.

    Not sure about reviving batteries, solar can be hard on batteries if using a poorly matched panel, any battery that is drained regularly will have a very short life. But I have found old tractor batteries that no longer hold charge long enough to start a tractor that's been idle for a few days have done well in some of my solar projects, but they would have been kept close to fully charged by the panel, I've never tried returning one to a tractor.

    It all depends on how long you need to run the lights for. If you are getting enough runtime out of your current setup then logically if you want to double the number of lights a second 100W panel and 2 batteries (or 1 double the size) will do the job. If you want a better calculation of sizes then I use battery and solar calculators from this site.

  • Registered Users Posts: 1,079 ✭✭✭ jimini0

    Realistically how long will a battery run a couple of lights. I will be lambing some sheep in this shed so ideally need something sorted by march. Only ever used this shed for wintering a couple of weanling. So only needed it for half hour every day. No I got into sheep so will need it alot longer

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  • Registered Users Posts: 9,361 ✭✭✭ Say my name

    Someone correct me if I'm wrong which I probably am as it seems a low amperage.

    But for an example.

    40 watt light by 10 hours use = 400 watts.

    400 watts ÷ 12 volt = 33amp battery storage.

    400 watts ÷ 24 volt = 16 amp battery storage.

    I just threw the 24 volt example in as people that were using 12 volt batteries off grid living are moving to 24 volt.

  • Registered Users Posts: 15,349 ✭✭✭✭ Bass Reeves

    I presume you will use a led light. It will depend on the wattage you require. A 20watt led spotlight will probably suffice if you can move it around. If you go multiple light you will need to switch on/off individually.

    After that it depend on the battery and charging. I would recommend.a solar charging system if possible but a decent solar panel will cost a few bob. It's immaterial whether it's 12v or 24v to an extent it just capacity after that. Ideally you do not want to over discharge a lead acid battery. Power is =VI or voltage by current. 12v 120AH batter using a 20 watt light will use over 1.7amps ( Inc wiring) so if used 4-5 hours/ night it would discharge less than 10% before solar charge kicks in during the he day

    I be more wary of the recharge system than the battery

    Slava Ukrainii

  • Registered Users Posts: 5,374 ✭✭✭ emaherx

    In theory maybe, but in practice you never want the batteries to drop below 50% charge. So you need at least double the AH that you'd think plus a bit to allow for aging batteries. Then you need to work out how many panels will reliably charge those batteries and this will vary according to the amount of daylight hours available at the time of year.

    Battery is easiest to work out, you can always add a panel if you find system under performing.

    Trying to skimp on the battery and/or not having enough panels will cost more in the end with short battery life. A decent charge controller will prevent you from over discharging the batteries but will switch off the lights without warning if the threshold is met.

    Panels are cheap these days at less than €1 per Watt.

  • Registered Users Posts: 849 ✭✭✭ Easten

    Them calculations for 12 and 24 volt are out of context.

    You need to know how much power the lights or whatever is using in Watts.

    A 24V 40W led light uses the same power as a 12V 40W led light so the batteries will last the same length.

    A 100w panel in Ireland will only produce about 60w/h for 8 hours in winter = 480w in total. Converting to amp hours is 480/12= 40ah so a large tractor battery which are usually rated around 110ah should work

    One 12V 40w led light will use 3.3 amps / hour which means you can run the one light for about 12 hours thus 2 lights for 6 hours, 3 lights for 4 hours etc (In theory)

    A 24V system is better if you want to run an inverter as the 24V ones can take bigger loads than a 12V inverter. Since you are running just a few lights then the 12v system if fine. The main advantage of 24V is it is not using as much of a current draw from the batteries.

    What emaherx is saying about simply adding another panel is a bit dodgy. Be careful!!! you need to make sure the charge controller can handle the current produced from 2 panels. Some of them cheap ebay charge controllers are not fit for that. In direct Summer Sun you could find a best case of the controller burnt out, worse case you have a full electric fire and burn down your shed. (If that happens contact emaherx for his public indemnity Insurance policy number)

    If you need a second panel then really you should be looking at a 300W panel 24V system matched to a 24V charge controller

  • Registered Users Posts: 5,374 ✭✭✭ emaherx

    I don't believe I suggested anyone should over load a charge controller. It is a good point though that the power rating of all components should be looked at before completing any electrical installation. But the same point could be made with using one over rated panel with the wrong under rated charge controller.

    Should probably point out that fuses of a suitable current rating are an important part of any electrical installation on a building and should be placed between the panels and charge controller as well as between the charge controller and any loads.

    Of course any omissions or details of any ones posts can and should be debated. Singling out posts/posters to make little of is just childish. I would consider these forums a great place to share knowledge and even learn if and when we are mistaken but some styles of posting just put people off contributing and over all destroying, which seems to be going down hill lately.

    Post edited by emaherx on

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