Solar Performance in the Med

[CatNewBee]

To come back to the initial question.

You can calculate in the Med panel nominal Wp *4 as medium Wh harvested per day. If you have 200Wp, you get 800Wh divided by 12V it will be around 66Ah, 300Wp will give you in average 100Ah per day.

There will be days with up to 50% more, but also days with much less.

[sdj]

Originally Posted by lawrence_craig

Here is 1 x 150W panel unshadowed at midday in Croatia.

Attachment 198415

The voltage differential between solar and battery is too low. See 12 vs 14 V. MPPT chargers cannot perform on such low differential.

This is the single most common mistake with solar installations. My guess is this is an older installation "upgraded" by adding a modern controller.

For 12V charging, you need at least 40V solar, and preferably higher. The closer you can get your solar open-circuit voltage to the max solar input voltage, the better.

In that particular case (with shading) you cannot reconnect the panels in series, so you will have to replace them with higher Voc panels or accept the situation.

[StuM]

Originally Posted by sdj

For 12V charging, you need at least 40V solar

You must be joking. That would mean that none of the systems on small cruising boats with one or two 12V nominal panels can work.

[sdj]

Originally Posted by StuM

You must be joking. That would mean that none of the systems on small cruising boats with one or two 12V nominal panels can work.

Leave it to the experts, mate.

[StuM]

Originally Posted by sdj

Leave it to the experts, mate.

Ok Mr Expert, please explain how you get 40V output from a single 150W 12V panel. (and don't tell me that all those small boat systems have a 40V Boost Converter).


And how about alternator charging. Does your alternator (assuming you have a boat and engine) put out 40V?

[sdj]

I already did, go and google it. Added to ignore list.

[StuM]

Originally Posted by sdj

I already did, go and google it. Added to ignore list.

Given his lack of any explanation in his previous posts in this thread, I'll take that as "I can't explain how to do that"

[CatNewBee]

Originally Posted by sdj

The voltage differential between solar and battery is too low. See 12 vs 14 V. MPPT chargers cannot perform on such low differential.

This is the single most common mistake with solar installations. My guess is this is an older installation "upgraded" by adding a modern controller.

For 12V charging, you need at least 40V solar, and preferably higher. The closer you can get your solar open-circuit voltage to the max solar input voltage, the better.

In that particular case (with shading) you cannot reconnect the panels in series, so you will have to replace them with higher Voc panels or accept the situation.

Your battery simply cannot absord more amps, she is almost full at 14.6V. Run some heavy loads and watch how solar amps jump.

[Catnut]

Hi, I am sitting here in Turkey, Marmaris, with 4 X 150W panels on 2 Victron MPPT controllers. the panels are flat mounted on an arch, I have house batteries of 800 Ahs, and am running a fridge, freezer & interior lighting.

I have partial shading at times from a lamp post and masts from other yachts,
and typically I get 2.20 kWh per day, the controllers switching into float by 15:30 ish most days,

Tony

[Franziska]

Stu,

interesting remark you make there. Beside what the other guy says/claims, do I understand you right that there are ways to "pump" higher voltage outputs into a 12V system?

The reason I ask is that commercial solar panel installations tend to use panels with 36V output which are produced in massive quantities and are way cheaper than the 12V panels most of us buy.

So, could these be sensibly be used to charge a 6x120Ah 12V bank?
Say as an alternative to 4x12V solar panel with total max output of approx. 650Watt?

Thanks for comments.

Originally Posted by StuM

Ok Mr Expert, please explain how you get 40V output from a single 150W 12V panel. (and don't tell me that all those small boat systems have a 40V Boost Converter).


And how about alternator charging. Does your alternator (assuming you have a boat and engine) put out 40V?

[StuM]

Originally Posted by Franziska

Stu,

interesting remark you make there. Beside what the other guy says/claims, do I understand you right that there are ways to "pump" higher voltage outputs into a 12V system?

The reason I ask is that commercial solar panel installations tend to use panels with 36V output which are produced in massive quantities and are way cheaper than the 12V panels most of us buy.

So, could these be sensibly be used to charge a 6x120Ah 12V bank?
Say as an alternative to 4x12V solar panel with total max output of approx. 650Watt?

Thanks for comments.

Yes, no problems using 36V panels with an appropriate MPPT controller.


The commonly used Victron 100/30 will accept up to 100V (and output 30A) while stepping the input voltage down to whatever is the most efficient voltage to charge the 12V batteries.



That's the way connecting 12V panels in series works. With 4 x 12 V panels in series, you will get 50+ V on a good day which an MPPT controller will step down to around 14 volts while boosting the current when charging a 12 V battery system.


The Victron 100/30 can safely handle the input from 2 x 36 V panels in series since their maximum voltage (Voc) is generally fairly close to 36 V (unlike 12 V panels which can put out 17V or more)





Putting a Boost Converter in the circuit however just adds another layer of inefficiency to no benefit.

[CatNewBee]

Originally Posted by Franziska

Stu,

interesting remark you make there. Beside what the other guy says/claims, do I understand you right that there are ways to "pump" higher voltage outputs into a 12V system?

The reason I ask is that commercial solar panel installations tend to use panels with 36V output which are produced in massive quantities and are way cheaper than the 12V panels most of us buy.

So, could these be sensibly be used to charge a 6x120Ah 12V bank?
Say as an alternative to 4x12V solar panel with total max output of approx. 650Watt?

Thanks for comments.

With an MPPT controller you can use any panels as long as their maximum voltage output Voc is lower than the allowed voltage input of the controller and the maximum current input / output is not overwhelmed by the panels Isc / Wp.

We use 96cell residential panels of 5x330Wp 60V with a MPPT controller 150/100 meaning 150V maximum input, 100A maximum output on 12V battery (in fact a lithium battery with 13.3V operating voltage) .

[StuM]

Originally Posted by CatNewBee

Your battery simply cannot absord more amps, she is almost full at 14.6V. Run some heavy loads and watch how solar amps jump.

No, the image show that the battery is at a low state of charge at 12V. The problem is that his solar is only putting out a few amps at 14.6 V . If that is in full sun, that says that there is almost certainly something wrong in the panel or in the connections between the panel and the controller.

[Franziska]

Thanks guys. That's very helpful to know!

[conachair]

Originally Posted by Franziska

The reason I ask is that commercial solar panel installations tend to use panels with 36V output which are produced in massive quantities and are way cheaper than the 12V panels most of us buy.

Any links to suppliers please?