Are these panels suitable for 12v battery charging?

[Mikeincairns]

Hi. I am a newbie to solar (but with good background in electronics).
I am building a "hobby" system just to learn. Will not be using this in real-world.

I have been given some free panels - SRP Model BBPV-250W. Specs are -
Vmp (voltage at peak power) 47.2V
Imp (current at peak power) 5.30A
Why is the Vmp rating so high for this panel??

I realise this Vmp is much higher than I have typically read about in blogs.
Can I use this panel with a 12 solar controller and charge a 12V battery?
I have a cheap 40A MPPT charger so I think it should work.

Any suggestions, advice, comments, warnings?
Much appreciated

[Bala]

The specs for the charge controller will have maximum input v.

[Mikeincairns]

Thanks for your post Bala. I know what you are saying but interestingly the charge controller (cheap Chinese brand) has no Vmax rating.

It does however say "Solar panel voltage: 12v with 18v panel, 24v with 36v panel". But I'm not so worried about maxing out the controller. I have already connected the panel and it didn't blow up!!.

I was really just trying to learn & understand why the panel has such a high Vmp (47.2 V) ? ...and how such a high MPP of 47.2 V will be relevant when charging a 12 V system. Everything I read about 12V systems have panels at 18V or so.

I have a feeling this type of panel would be better matched to a 48V system? I suspect the panels came from a grid-tied system so they might operate at a higher voltage.

But will it work successfully on a small-scale 12 v battery system???

[Bala]

Are you in Cairns Qld?

Yes most likely a grid panel at that w and v.

The charge controller input will determine if it will work with 12v. I suppose it either will or it will burn.

Most cheap mppt controllers are not mppt, they are PWM.

I have pwm controllers that would work with that panel @12v and then a Redarc Dcdc charger MPPT controller on my Ute that has a max v input of 28v.

[bcroe]

Typically a panel will generate some 0.5V per series cell at Maximum Power Point. Open circuit
may rise to 0.6V, no current, higher with lower temp. High voltage will be wasted on a PWM
controller, and they typically will not tolerate much excess voltage. An MPPT controller will efficiently
transform the input voltage to that needed, but still has an input voltage limit. Bruce Roe

[bob-n]

"I was really just trying to learn & understand why the panel has such a high Vmp (47.2 V) ?"

There are many different uses for panels. Some use them to generate 240VAC. In those uses, a higher-voltage panel is preferred because it will have lower current for the same power, and require less copper connecting the panel to the inverter.

"...and how such a high MPP of 47.2 V will be relevant when charging a 12 V system. Everything I read about 12V systems have panels at 18V or so."

In simple terms, the higher the input voltage to output voltage ratio, the harder it is on the electronics. For the same power, you need larger capacitors, larger inductors, and larger semiconductors. That's a broad generalization, but gives you an idea why people try to stay at a reasonable ratio of input to output.

[Mikeincairns]

Thanks everyone. I summarise from your advice, that this CAN work but would not be ideal. Probably need a really good quality MPPT charge control to cope with the large input-output difference.

[Mike90250]

Morningstar makes some quality MPPT controllers, as does MidnightSolar and Victron

[secessus]

It does however say "Solar panel voltage: 12v with 18v panel, 24v with 36v panel".

Can you post the model number or pic of the controller? That language suggests it's PWM or simpler.

MPPT doesn't have to cost much or be NASA-grade: a real 40A MPPT (Chinese) can be had for $130 if you sniff around and are ok with slow shipping. Victron are nice (and good-looking) and will cost about 2x as much. Morningstar are very nice and will cost about 3x as much. Horses for courses. If you are super geeky (and I mean that in the best possible way) there are folks on YT who are building their own MPPT controllers.

I live offgrid and everything I own and do is is powered by 570w of panel fed to a 40A Chinese mppt (4215BN), and stored in golf cart batts. My setup won't win any style points or inspire Instragram post but it works 100%.

[Mikeincairns]

All great advice. Thanks everyone for your time and effort to post. Yes - I discovered that I was scammed with the $50 charge controller. After testing I discover that it is PWM (even though it has MPPT written on the box and the device). It's going back to the supplier!