Posted on 08/29/2023 3:36:17 PM PDT by Rebelbase
Hello, I have a technical question for 12V solar folks.
In the process of building an off-grid solar set up for my camper trailer. Just need enough juice to keep the fan running in the propane fridge and to power the blower on the propane heater plus the lights and water pump.
Going to do a 200 amp hour gel battery and two 100 watt panels. A couple of months ago I bought a new-in-box 100 watt panel at an estate sale that I was told was for a 12V system.
Reading the back of the panel I don't see 12V anywhere on the spec decal, which is below.
Here is the question, when I buy the second panel does it matter if the voltage specs do not match up perfectly?
I looked at the Renogy website and do not see the exact specs on their current inventory. I suspect this panel is several years old as it came from a well stocked prepper who passed a few months ago.
My answer is a gas generator.
Happy to help.
The RNG-100D-SS spec sheet says 12V right at the top.
You are good, it’s for 12v. They always put out more than 12 volts and your “charge controller” regulates the voltage down to just under 14 volts which is fine, this is what a car alternator charges the car system at. Generally it regulates it to 13.7 volts input to the battery. So you need a charge controller also to regulate your charging voltage.
If this panel was for a 24 volt system it would be rated at around 36-38 volts output into the 24 volt controller.
Type “RNG 100D” into Google and all kinds of stuff comes up.
In general you can put PV panels in parallel even if they're not identical, as long as they have similar voltage ratings. E.g. open circuit 19-23V, max power at 16-18V, that sort of thing. BTW, panels for a 24V system will typically have ratings about twice the above numbers.
I've mixed-and-matched over the years with good success. Just make sure the panels all work by themselves, before you parallel them with others. You don't want to put a dead/shorted panel in your system.
These need to be wired to the controller which will then connect to the battery. The battery is what puts out 12V, not the panels. In my very small radio battery system, I have two panels running into the controller. I’ve put a meter on them and I never get the exact same voltage coming out of the panels.
If you just by the same model panel then they are made to work together. They appear to be plug and play.
12V often isn’t exactly 12V. It’s usually higher and the charge controller puts in the voltage the battery needs to get it full. That’s definitely a 12V panel though and you will be able to add another later if you want and doesn’t even need to be the same model or brand.
LOL. I am getting one of those for extended cloudy days.
Having spent a couple of years installing solar panels, I can tell you that the voltage from both panels mentioned here is too high for direct charging of a 12V lead acid battery. Instead you’d want the panel to not be able to force more than about 14 Volts (similar to a car alternator). Anything above that starts to put the battery at risk of damage, unless limited to a very low charge rate.
So, you will need some type of regulator/charger, if you want to use those panels.
So I should be OK connecting another 12V panel that has slightly different voltage specs?
That is a 12V panel. Adding a panel has to be a 12V panel but doesn’t have to be exactly like the one you have.
If you connect them parallel the system will operate at the losest operating voltage of the panels.
If you connect them in series, the system will be a 24V system that will produce the lowest operating current of the lowest operating current of the panels.
The wattage will be the same of both wiring of the panels.
You don’t have a 12V panel, you have a panel that will be compatible with a 12V system.
You will need to place a charge controller in between your panel and your battery. That requires that your panel voltage be higher than your battery voltage.
You might want to reconsider your choice of battery, as deeply discharging any lead-acid chemistry battery (gels too) will drastically lower their lifespan. Look at LiFePo4 batteries - costs more, but gives you a much better result.
If you don’t need an inverter, and it sounds like you don’t, then you can stop there. Otherwise, a sine-wave inverter would give you some 60Hz power if you need it.
Oh yeah, the panels will feed into a charge controller before going to the battery.
“Here is the question, when I buy the second panel does it matter if the voltage specs do not match up perfectly?”
Nope, as long as you are running it through a charge controller this wont matter much as long as it is not rated at more voltage than the charge controller is rated. And aside from voltage, you have to be sure and have a charge controller than will handle as much or more than the combined amperage all the panels together will be putting to it.
The amount of storage battery doesn’t matter, but rule of thumb is the more storage you have the longer it will supply you until the inverter gets down to 10.5 volts and cuts it’s self off. But more also means it will take longer to charge it back up to full state again. So there is a balance that is of the most advantageous.
Only experimentation can give you an indication of you need more or less in storage and/or panels to maintain you demand at least 24 hours.
“Oh yeah, the panels will feed into a charge controller before going to the battery.”
Then you’re good, providing the panels like up with the controller specifications.
“So I should be OK connecting another 12V panel that has slightly different voltage specs?”
Yes, sorry replied about that question later here... :)
I may bite the bullet and go with LiFePo4.
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