48V Solarpanel for boat with 12V systems..

[Franziska]

Hi,

I might have the option to get some excess 48V solar panels from a shore based installation project for a very good price.
They are ok for road side mounting, so resistant to heavy saltwater spray in winter.

As our array onboard is fairly old I am considering them as a budget replacement.

What I do not want to change though due to our limited budget, is any of the onboard consumers and also preferably not the batteries.
I would consider to get a new controller and or converter though (recommendations?).

The current installation is completely 12V.

If we where to replace batteries in 2-3 years I could change storage to 48V, but due to safety concerns I prefer not to and have as few 48V lines as possible on board.

Is there a good way to use these panels under the above circumstances?
Has anyone done this?
How did your panels last?

Thanks Fran

[mbartosch]

Originally Posted by Franziska

Hi,
I might have the option to get some excess 48V solar panels from a shore based installation project for a very good price.

The current installation is completely 12V.

Is there a good way to use these panels under the above circumstances?

It is quite uncommon (i. e. inefficient and potentially dangerous for some electronics) to directly attach solar panels to the boat's electrical system.
48 V panels are perfectly OK as long as you attach them to the solar panel input of a suitable solar charge controller, preferably a MPPT controller. A solar charge controller will convert the varying input voltage of the panels to system voltage, an MPPT controller additionally finds the optimum "power point" the solar panels deliver and optimizes power output significantly compared to (cheaper) PWM controllers. In general, the more difference between panel voltage and system voltage, the more useful a MPPT controller will be.
Typically the controllers need to be configured properly to match battery type.

There are a lot of manufacturers producing such controllers, personally I like the Victron MPPT controllers: https://www.victronenergy.com/solar-charge-controllers

If there are multiple 48 V panels, you can connect them in parallel and use one single charge controller for them.

Make sure that all cabling and charge controllers are dimensioned properly. And do not forget properly fusing the cables near the battery according to cable cross section.

[Franziska]

Thanks.

We have already solar and we would not consider an installation without MPPT.

The question is more aiming towards the best option to handle the voltage difference.
For which you pointed me in the right direction with Victron.

Is there any reason which would 12Volt more desirable? They tend to be much more expensive...

[Bleemus]

Originally Posted by Franziska

Is there any reason which would 12Volt more desirable? They tend to be much more expensive...

From my understanding the Victron controllers prefer higher voltages in order to maximize MPPT output.

[mbartosch]

Originally Posted by Franziska

We have already solar and we would not consider an installation without MPPT.

The question is more aiming towards the best option to handle the voltage difference.

The voltage difference is actually required for most MPPT to work!

The typical MPPT controllers actually only work if the input (panel) voltage is higher than the system voltage. For a 12 V system the panels should produce at least 20 V to actually allow the MPPT controller to do its job.

The MPPT controller specifies the maximum input voltage, for the smallest Victron MPPT that's 75 V. This means you can use any panel voltage between about 20 V and 75 V maximum with this controller properly, they will produce 12 V (subject to charging profile) at the output.

[mbartosch]

... or do you mean voltage difference between different panels on the input side...?

If you connect panels in parallel, all panels must have the same rated voltage.

If this is not the case, say the old panels output 36 V and the new 48 V you will need at minimum two (MPPT) controllers, each for one "voltage group" of panels. Both can be programmed identically, as they will work with either input voltage.

[Franziska]

Actually I am looking at two of the big model 250+ modules of these:

https://www.solardirectgroup.com/MOD...SDM_5_190+.pdf

They have 3 blocking diodes per panel.
So effectively they should behave like 6 smaller panels when it comes to shading.

I need to correct myself though, they are not 48v as you can see in the spec.
Rather 31v to 37.6v.

Still, if understand you right the Victron should be able to transfer this into the 12v battery bank.
Wrote an email to Victron to get confirmation.

The main reason we are considering these panels is that we may be able to get them for a good price.

[john61ct]

The solar panel voltage has nothing to do with the output voltage.

Just get the right controller to suit.

Victron mppt gives a lot of flexibility, recommend SmartSolar series.

I prefer 1:1, but if you put multiple panels per SC, they should match each other.

[john61ct]

For best shade handling, one 75/15 per panel. Maybe $120 each?

75/10 I think you have to buy dongles so no cheaper.

If you're sure no shading issues, then could parallel to a single 100/20 but...

[john61ct]

They don't maximize wattage per available area though. Sunpower cells are much more efficient.

[john61ct]

Use the VoC rating when matching to SC's max voltage spec, and leave 10-15% headroom for reflective/cold conditions.

[Franziska]

John,

you're a star as ever.
They say there are 3 bypass diodes per panel in there.
So, each panel should behave roughly as 3 smaller ones when it comes to shading. Is that correct?

Further sunpower panels might be more efficient, but at a big extra cost, no?
We are on a budget and have enough space for the two big panels.

[john61ct]

Originally Posted by Franziska

John,

you're a star as ever.
They say there are 3 bypass diodes per panel in there.
So, each panel should behave roughly as 3 smaller ones when it comes to shading. Is that correct?

Further sunpower panels might be more efficient, but at a big extra cost, no?
We are on a budget and have enough space for the two big panels.

Yes the efficiency per sq.ft. issue is just one to be aware of.

The internal diodes mean that shading on one string will still leave maximum 50-60% output rather than in effect none.

But putting both panels on the one SC will mean the MPPT algorithm will be jumping around, less efficient than 1:1, non-shaded panel output undisturbed.

Cheapest 1:1 would be 2x 75/10 plus one dongle shared, or even borrowed just for customizing settings.

The blueSolar line's getting cheaper now smartSolar is out.

Buy the dongles later for full real-time monitoring.

[wrwakefield]

Franziska,

We added 2- 165 watt 30+ VDC new panels last year.

We also have a 12 VDC house battery bank.

MPPT controllers set the output voltage required for the batteries, so no worries. You just need to size the controller[s] to match maximum DC voltage and amperage from the solar source[s] being regulated.

Our needs were best met using a Victron MPPT 75/15 [Max DC volts/Max amps] with built-in bluetooth on each individual panel. [Note: No bluetooth dongle needed on these new models from Victron. Bluetooth is used for programming and monitoring using the free Victron app on smartphones and/or tablets.]

Other capacity controllers are available.

Best wishes with your project.

Cheers! Bill

[john61ct]

What's with all the strikeout font?