solar newbie here

cornwallukcornwalluk Registered Users Posts: 4
Hi all, I'm new to living totally off grid and have recently bought an outback fm60, I've got a very tiny battery bank (if it can be called that) at 2*12v 100ah agms. And being how money situations are I found an advert for panels with their glass shattered some good some bad at a brilliant price obviously :)
I seem to be bringing in enough power off of my pv even though we're in our (modest) UK winter at the moment.
I'm slightly confused with absorption times and end amp settings though, could somebody help me please?
The panels are (were) 250w each and I have 4 plugged in , in series parallel and I have a 1500w sunsolar systems pure sine wave inverter (im only using a laptop at the moment so over powered but I'm working with what I have)
would it be ok to add another 2 12v batteries in to this mess? I'm running at 24v but thinking if I keep wire size and length the same for all of them it'll be ok and stay healthy?
Battery supplier has said that a float voltage of 13.6 and Max of 14.8. Would the max be the absorbing volatage?
sorry for all the questions and I don't know how relevant it is seeing as I'm UK based and you're not.
thanks
Simon

Comments

  • BB.BB. Super Moderators, Administrators Posts: 32,008 admin
    Re: solar newbie here

    Welcome to the forum Simon!
    cornwalluk wrote: »
    Hi all, I'm new to living totally off grid and have recently bought an outback fm60, I've got a very tiny battery bank (if it can be called that) at 2*12v 100ah agms. And being how money situations are I found an advert for panels with their glass shattered some good some bad at a brilliant price obviously :)

    In general, shattered crystalline solar cell panels will start fail when you get some wet weather and some corrosion. Guessing within a few months of exposure to weather. Not worth trying to salvage--Possibly a bit of a fire hazard too (fractured/corroded cells/bonding could get hot under load).
    I seem to be bringing in enough power off of my pv even though we're in our (modest) UK winter at the moment.
    I'm slightly confused with absorption times and end amp settings though, could somebody help me please?
    The panels are (were) 250w each and I have 4 plugged in , in series parallel and I have a 1500w sunsolar systems pure sine wave inverter (im only using a laptop at the moment so over powered but I'm working with what I have)
    would it be ok to add another 2 12v batteries in to this mess? I'm running at 24v but thinking if I keep wire size and length the same for all of them it'll be ok and stay healthy?

    One of the sizing rules of thumb for solar arrays is based on size of battery bank and rate of charge:

    200 AH * 14.5 volts charging * 1/0.77 panel+controller derating * 0.05 rate of charge = 188 Watt array minimum
    200 AH * 14.5 volts charging * 1/0.77 panel+controller derating * 0.10 rate of charge = 377 Watt array nominal
    200 AH * 14.5 volts charging * 1/0.77 panel+controller derating * 0.13 rate of charge = 490 Watt array "cost effective maximum"

    Or looking at it from the other side using 10% rate of charge:

    4 * 250 Watt panels * 1/14.5 volts charging * 0.77 panel+controller derating * 1/0.10 rate of charge = 531 AH @ 12 volt battery bank "Nominal"

    If these are the damaged panels--You should plan on replacing them soon... They will not last.
    Battery supplier has said that a float voltage of 13.6 and Max of 14.8. Would the max be the absorbing voltage?

    More or less--Yes. Typically you will see around 14.5 to 14.8 volts for Absorb set point charging voltage for a flooded cell storage battery. For other types, you may see more or less.

    It is a good idea for you to use a hydrometer to measure the specific gravity of each cell so you know the state of charge. You will quickly figure out if the charging voltage/time is correct or not. Over charging/under charging batteries are both hard on them.
    sorry for all the questions and I don't know how relevant it is seeing as I'm UK based and you're not.

    No problem. We are a world wide forum of volunteers here to help.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • cornwallukcornwalluk Registered Users Posts: 4
    Re: solar newbie here

    thanks for the reply Bill
    i do plan on investing on new panels as soon as financially possible hopefully in the not too distant future.
    i cant use a hydrometer with these batteries as they're sealed can i?
    one of the 12v cells is reading 12.1v and the other is reading at 12.8 or more and they're only a week or so old, would this be normal?
    im only drawing a small amount of power i think so im not sure if these are behaving as they should?
    thanks again
    Simon
  • BB.BB. Super Moderators, Administrators Posts: 32,008 admin
    Re: solar newbie here

    Having two batteries with different voltages is not good... For a "resting battery" (no charging/discharging for 3+ hours at room temperature), ~12.7+ volts is fully charged. ~12.2 volts is ~50% state of charge.

    You are correct, sealed batteries cannot be checked with a hydrometer... However, there are different types of sealed batteries. Some are maintenance free (automotive batteries) that look like they are sealed, but are not and you can still pry the battery caps off.

    And there are AGM (absorbed glass matt) type batteries--These you should not take the caps off.

    GEL batteries are also sealed.

    Each type of battery has different charging voltage requirements.

    Flooded cell are the most forgiving and can be charged at 14.5-14.8 volts (or even higher--depending on brand/model).

    AGM's usually are charged to around 14.2 to 14.4 volts.

    GEL batteries are usually around 14.2 volts or a bit less.

    Over charging sealed batteries can cause them to vent gasses and electrolyte. Will quickly cause a battery failure.

    GEL batteries (at least the common US type) will develop bubbles between the plates and the electrolyte--Permanently damaging the batteries.

    You have a very good charge controller... You need to read about lead acid batteries. Here are some links to start:

    http://www.windsun.com/Batteries/Battery_FAQ.htm
    http://www.batteryfaq.org/
    http://batteryuniversity.com/

    You need to understand what is going on (wrong) with your batteries. If they are in parallel (two parallel 12 volt batteries for a 12 volt battery bank)--You should not see that large of spread--And of course, if the wiring is connected, you should not see more than a 0.1 volt or so spread under load/charging.

    Here is a website that explains how to wire batteries so that parallel strings better share current:

    http://www.smartgauge.co.uk/batt_con.html

    Lead Acid batteries do not like to sit below ~75% state of charge for days/weeks/months on end--They will "sulfate" and fail fairly quickly.

    Read about the batteries and get them back in shape first.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • cornwallukcornwalluk Registered Users Posts: 4
    Re: solar newbie here

    My parents have a battery of the same batch and theirs is acting bad aswell, I think they're a bad batch, the one ordered a week later holds its charge and accepts charge better.
    thanks for the links I'll check them out
    I've worked on a carbon neutral stage over the summer with outback power equipment and was impressed so I had to go that way too, slowly but surely
  • cornwallukcornwalluk Registered Users Posts: 4
    Re: solar newbie here

    My parents have had one of my batteries on a boost charge now for 48 hours, it looks like they were send out without having a decent charge up and our UK weather just could not give it the charge it needed.
    next on the list are panels. Does anybody have recommendations for them in the UK by anychance?
    Thanks
    Simon
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