Complete re-thought about my Solar System

[Al Slitter]

I am considering upgrading my solar system from a lead acid battery system using 2-55 Amp panels connected in parallel with a cheap but good working PWM controller.
This system was set up about 2-years ago as a testing environment in my small workshop. At present the system has a 12 volt DC light source (Night Light) which is connected to the output ports on the PWM controller.
Is is still working good, yes is the answer!
However with lithium cells pricing dropping and the battery in use aging it is now time to think about a redesign and upgrade to the system.
I want to keep my panels as I do no have extra room for additional units. My shop is facing the wrong way.

Can someone please provide me with the main advantage of going to 24 Volts from 12 Volts.
I am fully aware of the cost of cabling and the cost factor of a BMS needed, but what else?

With the cost of the batteries and my limited utilization I would most likely stay in the 100 to 200 Ah cell range. Why 200 well because of the fairly low cost difference.
There is in my mind an idea of adding to the system a small inverter and using that to test out possible future plans?



Thought please anyone.

 

[Johncfii]

For such a small system, there is not likely to be any big advantage to converting to 24-volts, especially if you have already paid for the wire sized to support your 12-volt system.

With a 24-volt system, you will have half the current, and thus less wasted energy, within every current-carrying wire, including the BMS, for any given load size, no matter what size wire you are already using. However, if going to 24-volts means you have to buy a new charge controller, the value of avoiding that energy waste is probably trivial.

Before investing in a 24-volt charge controller, you need to be sure that your panels put out a voltage high enough to support it.

 

[45North]

I would think that if it's mainly for "testing" you be better off staying with 12v. (If you're doing this mainly as a training exercise then efficiency is not really an issue.) This allows you to use a wide variety of 12v appliances and automotive stuff. That's what I do at the moment.

But for my small system I'd consider switching from 12v to 24v if only to get new experience in that area. Your SCC may already be capable of handling 24v input and your panels may be able to be rewired in series to produce 24v.
Works either way. Up to you.

 

[Al Slitter]

Thank you for the replies it is much appreciated.
What would be the situation if I was to add to this new system 1000 Watt Inverter to test out this function?
Would that change the 12 to 24 volt equation?

 

[Johncfii]

Thank you for the replies it is much appreciated.
What would be the situation if I was to add to this new system 1000 Watt Inverter to test out this function?
Would that change the 12 to 24 volt equation?

Not much .... unless it might fit your future needs better.

The advantage of 24-volts over 12-volts is only that conductors (including those in the inverter) can be smaller for any given energy/power capacity. That can be a significant savings for any large system.

And for large systems it could be hard/expensive to find 12-volt components, because almost nobody would buy them

There is no other magic about it.

Since you are having a hard time deciding .... just let me decide for you .... make it 24 volts. That’s what I would do — but mostly because I just hate the idea of wasted energy, and because a 12-volt inverter is somewhat more likely to be cheap consumer-grade junk. And while you’re at it, get an inverter that is twice the wattage that you think you need. It will run cooler, probably last longer, and give you room to expand,

 

[Al Slitter]

OK, 24 volt has my interest. I have 2- 55Watt solar panels connected in parallel, I could wire them in series but I am not sure I can find room for a 100Amp panel to add to my solar array?
A question here, if I was to go to 24 volts would I have have a battery system of 24 volts or would the MPPT controller convert the voltage to 12 volts. This may sound stupid but do not know the answer.
Thank you again.

 

[45North]

Think of it this way:

The SCC sets itself automatically to the voltage of the batteries, be it 12 or 24v (and that's why you must connect the batteries first)
After that you hook up the PV panels to the SCC. The SCC then regulates the panel voltage to the correct charging voltage for the batteries.

So, when you say you have a 24v system, it means you have a 24v battery setup. And, in that case you'd need to configure any 12v solar panels in Series for the Controller to get a high enough voltage to charge them.

Keep in mind if you have a 24v system with 24v batteries you will only have 24vdc output unless you convert it by:

• using a 24v to 12v DC - DC converter if you want to power 12v devices, or
• a 24vDC to 110vAC Inverter, if you want to power regular household devices.

 

[Al Slitter]

Thank you you explained this very well!

 

[MisterSandals]

using 2-55 Amp panels connected in parallel

I cannot get my head around this. What solar panels are 55 amps? And connecting them in parallel produces 110 amps.

How many watts are these panels?

 

[Haga7584]

He said 2 - 55watt solar panels, but then said 100amp panels later. I think he misspoke on the 100amp section and meant 100 watt panel.

 

[chrisski]

If you’re going to stay with 110 watts of panels, you probably need to an energy aduit and get the smallest inverter you can, but also look at things like idle amp consumption.

A decent inverter, the SAMLEX 1000 watt PST has idle amps is .8 amps at 12 volts. So the 12 volt inverter draws 10 watts whenidle, but the 24 volts inverter of the same model draws 12 watts idle. It’s a decent UL458 approved inverter.

Just don’t get any inverter, read the specs first. Especially dealing with 110 watts of panels. On top of that you mention the panels aren’t oriented good. A 10 watt draw is a big deal on your system.

Honestly not sure that second 55 ah battery is required. If you figure out how. Many AH your panels can make, may only be 20 or 30 ah at 12 volts, which is enough to charge one battery half depleted.

 

[Al Slitter]

He said 2 - 55watt solar panels, but then said 100amp panels later. I think he misspoke on the 100amp section and meant 100 watt panel.

I am sorry for the confusion. What I have at present is Two 55 Watts 12 Volt Poly Crystalline solar panels wired in Parallel.
The specifications on the back of these two identical panels are as follows:

Maximum Power 55 Watts
Operating Voltage 21.5 Volts
Short Circuit 3.28 Amps
Max Power Current 3.06 Amps
Maximum Voltage 18.0 Volts
Maximum System Volts 600Volts DC

I now see why the cofusion as I had stated Amps versus the 55 Watts.