24volt system

santsalvadorsantsalvador Registered Users Posts: 12
Hi I Have 390ah of batteries (8 year old Hoppeck) 4X75 watt and 2X80 watt panels, a 500 watt wind turbine and morningstar MS40, I know, I need to upgrade
I'm thinking of 1400ah Gel batteries, what panels would you suggest for this system could I incorporate my original panels, am also thinking of a solar tracker and MPPT charge controller MS60.
I have a 6KVA generator as back up and need to get away from the generator back up system as much as possible, I live in Spain.
All help much appreciated.


  • BB.BB. Super Moderators, Administrators Posts: 33,327 admin
    Re: 24volt system

    In general, GEL batteries are not recommended by our host NAWS:

    Deep Cycle Battery FAQ
    Gelled electrolyte

    Gelled batteries, or "Gel Cells" contain acid that has been "gelled" by the addition of Silica Gel, turning the acid into a solid mass that looks like gooey Jell-O. The advantage of these batteries is that it is impossible to spill acid even if they are broken. However, there are several disadvantages. One is that they must be charged at a slower rate (C/20) to prevent excess gas from damaging the cells. They cannot be fast charged on a conventional automotive charger or they may be permanently damaged. This is not usually a problem with solar electric systems, but if an auxiliary generator or inverter bulk charger is used, current must be limited to the manufacturers specifications. Most better inverters commonly used in solar electric systems can be set to limit charging current to the batteries.
    Some other disadvantages of gel cells is that they must be charged at a lower voltage (2/10th's less) than flooded or AGM batteries. If overcharged, voids can develop in the gel which will never heal, causing a loss in battery capacity. In hot climates, water loss can be enough over 2-4 years to cause premature battery death. It is for this and other reasons that we no longer sell any of the gelled cells except for replacement use. The newer AGM (absorbed glass mat) batteries have all the advantages (and then some) of gelled, with none of the disadvantages.

    On the other-hand, while AGM are just about the "perfect" Lead Acid Battery system (for various reasons)--They are also ~2x (or more) as expensive and don't (from what I have read) last as long as a good heavy duty flooded cell battery.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • santsalvadorsantsalvador Registered Users Posts: 12
    Re: 24volt system

    HI Bill. Thanks for that, I will stick to the flooded type in that case.

    Our electricity out is small in comparison, TV evenings only, fridge/freezer, Lights 30 watt max, PC, water pump 500 watt 10 mins a day average max, washing machine cold wash,all other appliencies are gas.

    When we came here 8 years ago our system was enough for what we had at the time now we need to upgrade, i'm looking at spending 10.000€ so must get it right this time.

    what would be the ideal battery storage and how many panels for that, see my first post as to what im thinking of.

    Regards Terry. Sunny Spain.
  • stephendvstephendv Solar Expert Posts: 1,571 ✭✭
    Re: 24volt system

    Hi Terry,

    To design the system to just the right size it's good to know exactly how much energy you use per day. An old fridge freezer can use more than double that of an A++ type. From a "thumb in the air" look at your loads, you can easily build a quality system for around 6000 Euros. But if you get a pro to do it for you, you'll probably be looking at closer to 10k.

    It's worthwhile applying for the 'subvenciones', even though they're paying less than previous years, they picked up 30% of the cost of my system which was installed this year. You have to apply before getting the system installed and then you have to complete the installation before the subvencion expires.

    I'm guessing the Hoppecke's are the OPzS type - they have a 20 year design life, so could still have some life in them. How are they doing, do they still hold a good charge? How much do you draw them down each day - and how many days between generator runs in winter?
  • BB.BB. Super Moderators, Administrators Posts: 33,327 admin
    Re: 24volt system

    If you can, get a Kill-a-Watt or equivalent to measure your loads...

    Next, how much sun do you get daily (number of hours of sun per day)... In North America, we can usually assume that people get at least 4 hours a day for 9 months of the year. But that may be way underestimating your sun (5-6 hours a day 9 months a year)?

    Also, I usually suggest that you design for 9 months of "solar PV" operation and figure on using the genset during the 3 months of winter/bad weather.

    If fuel is very expensive and/or difficult to obtain, you may wish to use more solar panels and/or plan on using less power during bad weather.

    Also, going from 390 to 1,400 AH of (I assume) 12 volt battery bank is a pretty good sized increase. First, for larger battery banks/loads, you may wish to look at 24 or 48 volt inverters/charge controllers and such.

    Also, there does become a minimum amount of solar panel to properly recharge a flooded cell battery bank. Normally as a rule of thumb, we start with 5% to 13% as the recommended charge rate from solar into your battery bank. 5% works OK with "shorter" batteries and AGMs (you do not need to "mix the electrolyte"). However, some manufacturers recommend ~10% rate of charge for their "Tall" Batteries.

    In any case, if you want a fairly "hefty" rate of charge--say 10% with a large battery bank:
    • 1,400 AH * 14.5 volts charging * 1/0.77 system derating * 0.10 rate of charge = 2,636 Watt Solar array
    Or 1/2 that at 5% rate of charge or 1,318 watt array at a minimum (to run without genset/grid for much of the year).

    In the "olden days", installers usually recommended throwing batteries at any installation. These days, we try to get people to build balanced systems (solar panel to battery bank to generator). This is usually more cost effective, batteries and other hardware last longer, and generators are more fuel efficient (a 6kW genset charging through a 1kW AC battery charger will consume about the same amount of fuel in liters per hour as if the genset was supporting a 3kW AC load).

    So, to avoid throwing too many numbers out there, do you have a good idea yet of your loads and daily sun? Then we can make some suggestions from there.

    And people like "stephendv" will be much more help to you than I can be--They live in your region and can help you identify material and sources that are local to you.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • santsalvadorsantsalvador Registered Users Posts: 12
    Re: 24volt system

    HI. Thanks BB and Stephendy for your valued answers, I run a24 volt system my hoppecks are 390 ah and think fork truck batteries, two packs of six in metal case there 8 1/2 years old and still hold a good charge, unless I have wind, not me the turbine I have to run the genny every night, summer or winter. when they were new they would last four days before charge.
    As I said, now 8 years on we have more appliencies but near enough the same system.
    Yes I have a meter that will show amps watts out so will check it out over the weekend, and sun, we get plenty of that, too much some times, in the summer maybe 13 hours a day at peak for maybe 5 months, winter not sure will ask around for average but still not bad.
    Were very frugal on electricity as we only have a one bedroomed place and theres only me and the wife.
    Will check all out and get back, where in Spain are you stephendy, were up in Catalunya near Tortosa, 2 hours south of Barcelona.
    Thanks again.
  • stephendvstephendv Solar Expert Posts: 1,571 ✭✭
    Re: 24volt system

    Hmmm, the batts used to last for 4 days between generator runs and now they don't even last 1, so yeah, looks like they've had it.

    Once you know your daily loads you can size the new battery bank according to that. You can keep your existing panels and charge controller and then add new panels and a new independent charge controller for them. Now's a great time to buy PV, if you go directly to the big distributors like ibc-solar or proinso you can get Yingli or Canadian Solar panels for around 1.5 Euro/Watt. If you then buy an MPPT charge controller for them, then you're not limited to having to buy 12V or 24V panels, but can buy the cheaper grid connect panels that have higher voltage. Something like the morningstar tristar 45A MPPT could do the trick depending on how many new panels you add.

    I'm based near Barbastro, Huesca about 2.5 hours west of Barcelona, some pics of our place here: http://www.casanogaldelasbrujas.com/blog/

    If you want to get in touch with installers in your area there's a spanish forum frequented by many here: http://www.solarweb.net/forosolar/
Sign In or Register to comment.