Matching solar voltage to battery voltage

[mrogers0924]

First post/question so if I missed this answer somewhere....anyway ...I've been reading for awhile now, but what still confuses me is whether it is necessary to "match" solar panel voltage to battery voltage.   I don't think you have to ( maybe wrong) but if you don't what are the loses?  I was thinking of buying a 24 volt solar panel, but what if I get 12 volt batteries?

If you don't match then there is some sort of transformer stepping from the controller to the battery.  So on a 12 volt battery you can then use your 12 volt devices directly.  If you "match" to a 24 volt battery you don't have to step down to the battery but you do from the battery to the device?  Which is worse??

Thanks in advance.

 

[DLTooley]

Better controllers will do this. The advantage is charging in low light conditions. I don’t know how much of a benefit it is.

 

[mrogers0924]

Hmmm, are you saying that higher voltage panels work better in low light? and its ok to have 24 volt panels with 12 volt batteries?

 

[wayne49]

The solar controller/charger steps the voltage down to whatever voltage is necessary for the current charging stage per battery type.
It is a non issue.

The panel voltages never match battery voltages. Different chemistry in the panels.

 

[DLTooley]

12v batteries always charge at 12v, actually a bit above. A good controller will step that down from a 24v panel setup. If the light is low enough not to generate a 12v charge the 24v will still charge. I can’t quantify that benefit and it is a question of mine.

In general, the 24v panel controller set up is an upgrade. Generally 24v panels are more expensive, but i imagine there might be some very good values used.

 

[mrogers0924]

The solar controller/charger steps the voltage down to whatever voltage is necessary for the current charging stage per battery type.
It is a non issue.

The panel voltages never match battery voltages. Different chemistry in the panels.

  Appreciate the reply, I feel more comfortable in making a purchase.  Was just wondering if there were any great loss differences between various voltage changes. Thanks again.

 

[mrogers0924]

12v batteries always charge at 12v, actually a bit above.  A good controller will step that down from a 24v panel setup.  If the light is low enough not to generate a 12v charge the 24v will still charge.  I can’t quantify that benefit and it is a question of mine. 

In general, the 24v panel controller set up is an upgrade.  Generally 24v panels are more expensive, but i imagine there might be some very good values used.

Thanks for the response.  I didn't know about the low light difference.  Just did some Googling.   I saw Bob on one of his videos had a mix of 24v and 12 volt running through separate controllers which got me on this thought tangent.

 

[B and C]

The controller you buy will determine which panels (and how many) you can connect. I am a big fan of MPPT controllers. These generally allow much higher panel voltages and convert the extra voltage into charging amps. The cheaper PWM controllers will not take the extra voltage coming into it and convert it to more charging amps. It just throws away the extra power as heat from the controller. I run two 100 watt panels in series and then parallel another two 100 watt panels in series.
They are connected to a 30 amp midnite kid with whiz bang jr controller into 350Ah of 12V agm battery.

You connect the controller to the battery first so the controller knows what it is supposed to be charging. Connect the panels last. If you want to disconnect the battery, you must disconnect the panels first. The battery is always connected first and disconnected last.

 

[mrogers0924]

Didn't think about it that way, was thinking "panels first", good info.  The "kits" I see on Amazon always include a PWM controller, so I guess I'm staying away from "kits"...which is true of all kinds of lumped together products...always trying to throw in the junk with the good stuff.  Thanks for the info.

 

[Freelander]

I just went through installing Solar on my RV, and 24v systems normally are for larger systems. Unless you have more than 400 watts 12v works fine. The advantages to 24v is you can use smaller wire and get more amperage on the same system.

And with an MPPT controller I can put more amperage into the batteries than the panel put out. 400 watts will put out unto 25 amps on 10 AWG wire.

 

[highdesertranger]

my panels are 80v and I charge a 12v battery bank with them. the controller regulates the out put of the panels. it's advantageous to use higher voltage panels with a MPPT controller. the MPPT turns the excess voltage into amps, well that's a simplified explanation.

may I suggest you study solar charging some more. ask here if you have questions. also you are going about this all wrong(don't worry everybody does). you need go about it in this order,

1. figure out your daily electrical useage.
2. size your battery according to #1
3. size your solar panel(s) according to #2

don't worry we will help you through this.

highdesertranger

 

[jonyjoe303]

The smaller panels are usually 21 volts, the larger ones are 36 volts. You can use either to charge a 12 volt battery with whatever controller you have. Any pwm or mppt controller will work with either panel. The only difference is amp output. Below are real world results that I got with different panels/controllers.

120 watt kycora (21 volt panel)
pwm controller = 6 amps
mppt controller = 6 amps

240 watt sharp (36 volt panel)
pwm controller = 7 amps
mppt controller = 12 amps

Your controller will have in the specs, what the maximum voltage of panel you can use, most can at least do a minimum of 45 volt panel, the high-end controller can do 150 volts.

 

[mrogers0924]

I just went through installing Solar on my RV, and 24v systems normally are for larger systems. Unless you have more than 400 watts 12v works fine. The advantages to 24v is you can use smaller wire and get more amperage on the same system.

And with an MPPT controller I can put more amperage into the batteries than the panel put out. 400 watts will put out unto 25 amps on 10 AWG wire.

Yep, I was thinking of going above 400 ...possibly push 1000, not sure, just thinking right now, thanks for the help

 

[mrogers0924]

The smaller panels are usually 21 volts, the larger ones are 36 volts. You can use either to charge a 12 volt battery with whatever controller you have. Any pwm or mppt controller will work with either panel. The only difference is amp output. Below are real world results that I got with different panels/controllers.

120 watt kycora (21 volt panel)
pwm controller = 6 amps
mppt controller = 6 amps

240 watt sharp (36 volt panel)
pwm controller = 7 amps
mppt controller = 12 amps

Your controller will have in the specs, what the maximum voltage of panel you can use, most can at least do a minimum of 45 volt panel, the high-end controller can do 150 volts.

There are so many different voltage specs....you are referring to the open circuit voltages I believe.   Took me awhile to realize that a 12 volt panel is just a rough approximation .....of enough volts to charge a 12 volt battery with a max OC Voltage but averaging around 17 ....lots to learn.  Thank you.

 

[mrogers0924]

my panels are 80v and I charge a 12v battery bank with them.  the controller regulates the out put of the panels.  it's advantageous to use higher voltage panels with a MPPT controller.  the MPPT turns the excess voltage into amps,  well that's a simplified explanation.

may I suggest you study solar charging some more.  ask here if you have questions.  also you are going about this all wrong(don't worry everybody does).  you need go about it in this order,

1.  figure out your daily electrical useage.
2.  size your battery according to #1
3.  size your solar panel(s) according to #2

don't worry we will help you through this.

highdesertranger

Thanks highdesertranger.  My brain likes to explore a bunch of variations and possibilities at once!  I've been going back and forth between a minimum configuration and a maxed out one.  Eventually I'll get to what Bob advises, and take a "baby step" and stop my analysis paralysis and just put something together.

 

[Larry-new]

The old financial adage of...It's not what you have, it's what you spend.... also works for power consumption.

Plan your usage...the higher draw items...microwave (if), and charging of various small items are best done while the sun is shining; the full batteries will then handle the lower constant draw of overnight items...fridge, furnace, etc.

As an added saving, and although my trailer lights are all LED, my main lighting is separate LED, USB charged. So's the water pump. So's the 4v. drill. So's the lithium jump starter/battery backup. Tablets and phone too, of course.

A cold night, and I'll unplug the freezer overnight.