12V panels and batteries in a 24V system

[PaulLad]

Man this stuff gets confusing. I swear I saw one of Will's videos where he said you can't use 12V panels in a 24V system and then I also saw that if you are using 12V panels in a 24V system, you have to put them in series to get 40V minimum? Which is it? And does the same rule apply to batteries? Can I use 12V batts in a 24V system? If the answer is yes to either, are there downsides to using 12V components in a 24V system? Thanks.

 

[sunshine_eggo]

For PWM, panels must be suitable for battery voltage where Vmp is approximately 1.5X nominal battery voltage. Panels must not be in series unless that is needed to attain 1.5X target, e.g., 2X 12V in series for 24V system.

For MPPT, panels must be suitable for battery voltage where Vmp is at least 1.5X nominal battery voltage. Panels may be in series up to MPPT Voc limit allowing for cold temperature voltage effects.

All PV systems must supply sufficient voltage AT POWER to charge batteries. The 1.5X target ensures this is achieved in all conditions.

There are countless examples on this site of folks using 2X, 3X and 4X 12V to get 24V, 36V and 48V, respectively. The downside to this is that the 12V must be top balanced where they are all at the same voltage when system voltage is at the peak.

 

[Warpspeed]

And does the same rule apply to batteries? Can I use 12V batts in a 24V system? If the answer is yes to either, are there downsides to using 12V components in a 24V system? Thanks.

Most popular systems are 12v, 24v or 48v often made up by connecting 12v batteries in series (one, two, or four 12v batteries in series).
Or sometimes a larger number of individual low voltage cells connected in series to reach the required voltage.

Solar panels are usually either 12v or 24v and can also be connected in series to reach the required higher voltages.

 

[mikefitz]

, are there downsides

A 12 volt panel has maximum power at around 17 volts so will need a minimum of 2 in series in a 24 volt system. There is no technical disadvantage but larger domestic sized 24 volt panels are cost effective.
A 24.volt system with 24 volt batteries is preferred. Where 12v batteries are in series they can become out of balance with each other
Mid point balancer circuits can be used to restore balance .

 

[ledow]

Whatever battery you want to charge, the incoming charge voltage must be higher than that of the battery - often by a significant margin.

Your "12V" panel is probably giving out 14-19V at any point - because that's what it takes to charge a 12V battery.

To charge a 24V battery, that's obviously not sufficient. The voltage from the panels MUST be higher than the battery voltage in order to charge (simple physics).

So you can join two "12V" panels in series and this will give you enough to charge two 12V batteries in series (which is what a 24V battery basically is).

There are, however, limits - the controller charger will tell you what the maximum input it can take will be. It'll also tell you what the maximum battery it can charge will be (and that will often have to be selected by the charger for the right battery, e.g. 12/24/48V).

However, you also need to be careful to ensure that the individual panels are also able to connect in series (they will tell you what the most panels you can have in series will be) and that the current is within limits for the cables you're using.

It's definitely not a "this can't be done". It can, and it's very ordinary. You just have to know that your equipment is all capable of doing so and specified properly and fitted within specification. You can't just keep stringing dozens of random panels together on their original cables and feed it into any controller and expect it to charge a battery it wasn't designed for safely.

Check your equipment - all the panels I've bought tell you exactly what series/parallel configurations they support, all the controllers I've used tell you exactly what they expect for input voltage and output voltage for your battery, and all the batteries I've used will tell you what the minimum charge voltage and the most voltage they will safely accept is (and if they can be strung together in parallel and series configurations, and if so how many).

 

[PaulLad]

the controller charger

I assume you mean charge controller

the charger for the right battery, e.g. 12/24/48V).

I assume you mean charge controller

 

[profesor79]

The magic is in the charge controller. I have step-up (made by me) controller and from a 35VoC panel I am charging 48V battery. Most mppt will require at lest 5V more than battery voltage to start working as there is a voltage drop in DC-DC conversion line.

 

[DaddyBUDsDoorags]

I assume you mean charge controller

I assume you mean charge controller

Don't assume...there are combination chargers / controllers these days.
I'm more in the school of not combining different tools in the same bag...it all must be replaced if any portion of the unit fails.
I've seen some of these "guru's" touting these "all-in-one" units to people with more money than common sense...I think that degrades their credibility (in my opinion)