Sizing Off-Grid Systems And Using Gen Support

Well, I didn't know that Owatonna Tool Co was building battery hydrometers. And turns out I was right. That's one of those Chinese ones with the paper scale inside the float tube that you have to watch in case the paper slips. OTC (been a manufacturer of specialty service tools for OEM's since 1934, based in Owatonna, Minnesota and now owned by Sealed Power in Muskegon, Michigan) buys and resells that hydrometer from the same Chinese supplier that makes them for everybody else.

Learned a new one yesterday. Cloudy, drizzle & rain. I'd fired up the diesel, and was running loads and charging batteries, and the sun came out of a break in the clouds and slammed the PV arrays. 5 additional KW hit the batteries, and the generator unloaded. I heard the change in sound and thought Uh Oh - what happened? Got to the generator shed, and read the meters, since the XW thought the batteries were full, it stopped charging and the generator was loafing along with only about 100w of load. So it was all cooled down and ready to shut off by the time I figured it all out.

There must have been some huge peak currents into the batteries. When I have this problem (sun comes out while generator is running) I can hit bulk charging currents of almost C/4 (not desirable). My system is DC coupled... no regulation of current until absorb voltage is achieved.

--mapmaker

I've seen 'em do that before. If your charger settings in the XW are correct, it gives priority to the MPPT's for charging. The nice thing is that if you have AGS it automatically shuts the generator down when that happens (assuming it was automatically started due to shortage of incoming RE).

Solar System not Working

HI All this is my first thread, I am not sure if I should be posting here as I could not find a way of posting back in the main screen.
I have read and tried educating myself over the past 12 months, but unfortunately I have a problem, that is just not clear to me, so if you could help that would be great, thank you in antisapation.

the system
8 x 110amp deep cycle batteries wired in 24 volt configuration
5 205 watt solar panels wired neutral to natural and positive to positive back to the inverter
1 50Amp mppt controller

all I am trying to run is a 150wat inverter which in turn is running a chicken brooder which is 75 watt

I was running a 1kg inverter back in peak summer, but found the batteries were going flat so that is why I changed to the 150 watt inverter.
I live in Southern England and we have had really good sun for quite some time.

the problem is the batteries get up to 26.4 volts in the day, but in the morning it is down to 23.6 volts,

I can't understand why the batteries and panels are not coping with such a low draw of power!

an any one please help

best wishes Derek

Welcome to the forum Derek,

Hopefully the moderators will move this to its own thread.

I'm guessing that your batteries are 12 volt batteries. It that is correct you have 440 ah at 24 volts and the batteries are in 4 parallel strings of 2 batteries (in series) per string.

Therefore you have 10,560 watthours of storage and you should try not to use more than 2500 of them before recharging.

Your brooder is 75 watts. I will guess that between the end of one charging day and the beginning of the next day is about 18 hours. 18 hours X 75 watts = 1350 watthours. Of course your inverter is not 100% efficient, so figure you need to draw 1500 watthours overnight.

During the day, your array will typically provide about 25 amps of charge current to your batteries. That's a bit on the low side, considering the panels must charge the batteries while still powering the load.

Chances are you are doing a slow deficit charge. It takes a long time to get a battery up to 100.0% SOC (state of charge). If you only get to 99.9% every day, the 99.9% becomes your new 100% because of sulfation. After awhile you have 99.9% of 99.9% of 99.9%, etc.

I think there are some other issues with your system. The most serious is that (I think) you have 4 parallel strings of batteries. That is a formula for disaster... the batteries do not charge evenly because the current to the 4 strings does not divide evenly.. As the battery strings diverge, you have one string doing all the work while the others die of sulfation. The hard working string(s) die sooner from overwork, and because you daily load is being powered by a smaller battery which then gets over discharged.

Also, what type of batteries are these? They may not be suited for deep cycle service.

--mapmaker

batteries

HI Mapmaker and thank you for your time and answer, it took me ages to find the reply! lol
anyway am here now,
the batteries are 12 volt caravan batteries all brought new and at the same time, the ones with the green lights on them to show charge.
they are wired series / parallel combination bringing the voltage up to 24 volts
does this throw a different light on it (excuse the pun)

What is the spec of these panels? I suspect the voltage may be too low to properly charge these batteries at 24 volts wired in parallels, how far is the panels to the charge controller?

solar panels

HI The panels I purchased are Ideal Thermasol TSPV 205 PE – Solar PV Collectors 205W

they are wired negative to negative and positive to positive the furthest panel is about 12 meters away from batteries and they are all joined together so the last panel is only 7 meters away from battery.

not sure of the spec but will look on back of one of the panels

regards Derek

Yeap, These panels are 26.52 volts Vmp, Can't charge the 24 volts battery bank wired in parallel, You either have to wire in 2 in series with 2 parallel totals four or get one more panels wire 2 or 3 in series to charge your battery bank properly depend on the charge controller.

Good catch on those panels, Paul. I saw he had 5 panels and an MPPT controller and just assumed....

--mapmaker

batteries

battery2.jpg
this is how I have wired the batteries x 8 of course
the controller is EPsolar 40A Tracer4210RN MPPT Solar Battery Charge Controller

Its been a while since my days of wiring please remind me parallel and series
thanks you all for you help, the chickens will be most grateful

Derek

That wiring is a disaster. Look at the diagrams on Smartgauge.


One problem with the smartgauge site is they show you how to do parallel batteries, but they don't tell you how bad an idea it is to have parallel batteries at all.

--mapmaker

wiring batteries

Thank you Mapmaker.
I see that smart gauge site is showing 12 volt wiring.
the reason I wired the batteries as I did in 24 volts was because of the mppt controller only being 40amps
is there a site / image you can direct me to, to show me the correct way of wiring them please?

Thanks again for your kind response

Derek

Your immediate problem is not the battery wiring. it is the panels wiring. you can't wiring 5 panels positive to positive, negative to negative to get high enough voltage to charge the batteries at 24 volts, you need at least 30 to 35 volts to charge the batteries properly. That charge controller only accept 100 volts DC input if I am not mistaken. You need to wire your panels 2 in a series and parallel the 2 series together. that you leave on for spare or you get one more.