Moving to 24v system

[Mallison359]

Hi everyone, I've been looking through other reports to prevent reading a question but can't find anything- I apologise if this has been asked before.

I have a 12v off grid system in my shed. It consists of 3 individual 100watt panels in parallel, this goes to my 12v pwm charge controller feeding my 500watt inverter (not pure sine). I have 2x 12v 95ah batteries in parallel.

My problem here is the system is great when there eisenhorn sun, I can run a hell of a lot off it, in the evening/night I can't power anything more than lights and charge a few items before it cuts out.

I'd like to move to a 24v system, I don't know what to do though. I used a lot of online help to build my system from YouTube and forums etc. I'd like to do this without replacing too much of what I own or doing it as cheap as possible.

Any advice or pointers would be appreciated.

[inetdog]

Your problem may be that your battery bank is too small or the batteries are no good anymore. Check the SG of your battery electrolyte with a temperature compensated hydrometer instead of just looking at battery voltages.

To move to a 24V system you will probably have to go to a new charge controller to work with 24V, although some PWM CCs are dual voltage. And since you have 3 panels you will either have to leave one unused or go to an MPPT CC and put all three panels in series. (Much better efficiency in any case.)

You will have to replace the inverter, since no inverters that I know of are dual input voltage.

You can increase your battery bank capacity without adding more batteries in parallel or going to 24V by making up your bank from 2, 4, or 6V batteries instead of 12V batteries.

A 500W inverter is not outrageously large for a 12V system, although 24V would be better. If you are not going to get a bigger inverter you could still get along with 12V.

Your three 100W panels are just large enough to effectively charge the battery bank you have. If you switch from an PWM to an MPPT CC you can handle a 50% larger battery bank without adding more panels.

[dennis461]

http://www.powerstream.com/battery-r...calculator.htm
Are you able to measure the amps drawn from the battery during the night?
You did not tell us how many lights you have connected or what type they are.

http://www.powerstream.com/battery-r...calculator.htm

The math will go like this assuming your panels fully charge the two batteries during the day
a couple of other assumptions regarding the inverter

95+95= 190 ah available from battery bank
100 watt lighting load
100/12= 8.3 amps
inverter losses
.75 amps
inverter efficiency
50%

8.3 /0.50 = 16.6 amps to run the lights through the inverter

16.6 + .75 = 17.35 amps

190 ah / 17.35 amps = 10.95 hours

[inetdog]

Are you able to measure the amps drawn from the battery during the night?
You did not tell us how many lights you have connected or what type they are.

We actually need to know the amp-hours drawn from the battery, not just the amps.

[Sunking]

You have two strikes against you,and likely 3 strikes you are out.

Strike 1. You have a prime number of panels of 3. That means you can only configure them all in series or all in parallel. You have 12 volt battery panels and I bet a PWM charge controller which prevents you from using 3 panels and would have to loose a panel or gain a panel to move up to 24 volts.

Strike 2 Your batteries need replaced.

Strike 3. Is I bet you have a PWM controller,

Your SOL, and basically at least have to buy new batteries and a MPPT controller so you can wire all your panels in series. The bad news is since you chose to use battery panels are stuck with antiquated over price technology. To expand, you have to find those exact same over priced panels for $3/watt. You could replace then with a $300 300 watt grid tied panel with a MPPT controller.

Smart money is replace your controller with a MPPT controller, wire your panel in series, and replace the batteries. Then when you need to expand get rid of those 12 volt battery panels and buy inexpensive grid tied panels at 1/3 the cost of battery panels. You could have 300 watts of GT panels for what you paid for a single 100 watt battery panel.

[inetdog]

What he said....

[PNPmacnab]

Suggest you go on ebay etc and search for power meter 130A. These $10 and less devices are really handy for figuring out loads and daily charge from a panel. They only measure one way, either charge or discharge depending how the negative leads are connected. They say 130A, but I wouldn't go over 30A unless you use an external shunt. A 100A shunt is about a 8.5 multiplier. They will display instantaneous volts, amps and power, store max power, amps and total WH. You don't need to go to 24V, you need a new battery. One battery I have was fine last year and now dies with a 9AH nightly load. There is always a possibility your controller damaged the battery. Only numbers will tell.