Solar panel downside

[Robin2]

From my limited experience with my solar panels there seems to be one downside that I have not seen mentioned elsewhere.

 

I think it is generally accepted that when a battery is being charged the initial charge settles on the surface of the plates raising the apparent voltage and you have to leave the batteries disconnected for several hours to allow that charge to diffuse into the plates by which time the voltage will have fallen to the "proper" level for that state-of-charge.

 

Without solar panels the batteries get partially depleted over night and when you start the engine to charge them they can take a good current for a reasonable period of time which makes good use of your charging fuel.

 

However when you have solar panels they will have put a little bit of charge into the batteries by 9am and in the course of doing so will have raised the voltage on the battery plates considerably more than tiny improvement in SOC would justify. Then when you run the engine the batteries only accept a much smaller current which significantly increases the fuel cost per amp-hour.

 

Has anyone else noticed this?

[jelunga]

Not this but I have a feeling that when the battery is being charged by both the solar panel and either the engine or mains charger then the voltage of the solar panel makes the other methods think the battery is more charged than it is. I intens to put a switch in the solar panel circuit so that when other means are charging the battery I can switch off the solar panel.

 

Gibbo, any comments please? Remember I have the Heart invertor-charger.

[Ex- Member]

From my limited experience with my solar panels there seems to be one downside that I have not seen mentioned elsewhere.

 

I think it is generally accepted that when a battery is being charged the initial charge settles on the surface of the plates raising the apparent voltage and you have to leave the batteries disconnected for several hours to allow that charge to diffuse into the plates by which time the voltage will have fallen to the "proper" level for that state-of-charge.

 

Without solar panels the batteries get partially depleted over night and when you start the engine to charge them they can take a good current for a reasonable period of time which makes good use of your charging fuel.

 

However when you have solar panels they will have put a little bit of charge into the batteries by 9am and in the course of doing so will have raised the voltage on the battery plates considerably more than tiny improvement in SOC would justify. Then when you run the engine the batteries only accept a much smaller current which significantly increases the fuel cost per amp-hour.

 

Has anyone else noticed this?

 

Not being technical I'm not sure how much this would affect the charging. However if you're using solar and getting some charge at 9am and it's a nice day, then why run your engine unless you have to cruise or you're short of power.

 

 

[Gibbo]

Has anyone else noticed this?

 

No. No one will notice it. Anyone who does notice it, is imagining things.

 

Not this but I have a feeling that when the battery is being charged by both the solar panel and either the engine or mains charger then the voltage of the solar panel makes the other methods think the battery is more charged than it is. I intens to put a switch in the solar panel circuit so that when other means are charging the battery I can switch off the solar panel.

 

Gibbo, any comments please? Remember I have the Heart invertor-charger.

 

The Hearts don't use any of the clever tricks that some other chargers use. It will not notice and it will not affect what the Heart does.

[jelunga]

Great. Thanks. It still does help me get it charging at acceptance for longed then. Tried telling mr heart it was a cool gel not a cool wet. No real difference. Batteries are carbon fibre containing Elecsols. The onlmy way is to starf an equilising charge and then terminate when smartgauge says 100 and E03s keep flashing.

No. No one will notice it. Anyone who does notice it, is imagining things.

 

 

 

The Hearts don't use any of the clever tricks that some other chargers use. It will not notice and it will not affect what the Heart does.

 

Error. Should read " still does NOT"

 

Error. Should read " still does NOT"

[Robin2]

No. No one will notice it. Anyone who does notice it, is imagining things.

 

 

I would very much appreciate it if you would explain where my understanding is faulty.

 

Not being technical I'm not sure how much this would affect the charging. However if you're using solar and getting some charge at 9am and it's a nice day, then why run your engine unless you have to cruise or you're short of power.

 

My panels are meeting my demand during the day time but they are not producing enough extra to cover the night time electricity use.

[WotEver]

I would very much appreciate it if you would explain where my understanding is faulty.

http://www.smartgauge.co.uk/surf_chg.html

 

T.

[Gibbo]

I would very much appreciate it if you would explain where my understanding is faulty.

 

Pick a number, let's have 65...

 

Start at 65% SOC at 5 O'clock in the morning. Sun rises, solar panels start to put a little bit of power into the batteries. Battery voltage rises slightly. 9 O'clock comes, batteries have increased to 68% SOC. You start your engine and the alternator kicks in putting in as much as either it can produce or as much as the batteries will accept (it doesn't matter which).

 

Now do the same thing, but switch the solar panels off so they do nothing. Start the engine at 9 O'clock and the charge rate will probably be a tiny bit higher, simply because the batteries are starting from 65% instead of 68%. When you get to 68% stop the engine.

 

Now restart the engine. Is this starting point of 68% somehow different from the starting point of 68% in the first example? If it is then you can expect a different charge rate from the engine. But how can it be different?

[Paringa]

My Steca charger stops putting anything in from the panels when an alternative charging method comes into play, engine or mains charger. I just leave it all to get on with it now and just keep an eye on the Smartgauge for battery state.

[Robin2]

Pick a number, let's have 65...

 

Start at 65% SOC at 5 O'clock in the morning. Sun rises, solar panels start to put a little bit of power into the batteries. Battery voltage rises slightly. 9 O'clock comes, batteries have increased to 68% SOC. You start your engine and the alternator kicks in putting in as much as either it can produce or as much as the batteries will accept (it doesn't matter which).

 

Now do the same thing, but switch the solar panels off so they do nothing. Start the engine at 9 O'clock and the charge rate will probably be a tiny bit higher, simply because the batteries are starting from 65% instead of 68%. When you get to 68% stop the engine.

 

Now restart the engine. Is this starting point of 68% somehow different from the starting point of 68% in the first example? If it is then you can expect a different charge rate from the engine. But how can it be different?

 

I understand what you have said, but I wonder if it is applicable to the situation where the battery is subjected to a "high" voltage low current charge in the phase that you describe as 65% to 68%. My suspicion is that the solar panels make the battery appear to be as charged as if the engine provided the 65% to 68% charge but they have actually not put anything like as many amp-hours into the battery.

 

My Steca charger stops putting anything in from the panels when an alternative charging method comes into play, engine or mains charger. I just leave it all to get on with it now and just keep an eye on the Smartgauge for battery state.

 

My point is not about competition between the two charging sources while the engine is running - rather it is about the effect the solar panels have in the period before you start the engine.

[Gibbo]

... where the battery is subjected to a "high" voltage low current charge...

 

This is the root of your confusion. If you put a high voltage on a battery, the battery will dictate a high current. If you have somehow got a low current going into a battery then either you have a low voltage or the battery is fully charged.

 

You can control the voltage across the battery or you can control the current through the battery. You cannot control both. You control one, the battery dictates the other.

 

Therefore a high voltage, low current charge simply isn't possible unless the batteries are full anyway.

[dor]

OK, this is what happens on my boat. Let's say that in the morning my batteries might be reading over 13 V because the solar panel is charging them. They are still far from fully charged. I start the engine and it starts charging at a current I would expect from the state of charge - say 50+ amps. In other words the voltage applied by the solar panel is not affecting the alternator charging. When the alternator has raised the voltage to about 14V the solar panel controller (std, not MPPT) cuts off the panel so no charge is fed to the batteries from the panel. This is the same as it would do if left for several days and fully charged the batteries.

 

I know what is happening as I have lots of ammeters & voltmeters - my wife thinks I am obsessed by meters. The ammeter on the solar panel is very useful for knowing just how much I am getting out of my panel. The main ammeter will tell me exactly how much is going into or out of the batteries.

[Robin2]

This is the root of your confusion. If you put a high voltage on a battery, the battery will dictate a high current. If you have somehow got a low current going into a battery then either you have a low voltage or the battery is fully charged.

 

You can control the voltage across the battery or you can control the current through the battery. You cannot control both. You control one, the battery dictates the other.

 

Therefore a high voltage, low current charge simply isn't possible unless the batteries are full anyway.

 

Ah ... but a solar panel is bit like a constant current source ...

 

OK, this is what happens on my boat. Let's say that in the morning my batteries might be reading over 13 V because the solar panel is charging them. They are still far from fully charged. I start the engine and it starts charging at a current I would expect from the state of charge - say 50+ amps.

 

Mine doesn't seem to be behaving like that.

[WotEver]

Ah ... but a solar panel is bit like a constant current source ...

[Gibbo]

Ah ... but a solar panel is bit like a constant current source ...

 

Re-read what I wrote.

[Justme]

Even if you were right the engine would be using LESS fuel per hour. Charging from the alt is not free, it puts a load on the engine that uses extra fuel to supply it. Reduce the load reduce the fuel.

 

As has been said the battery controls the V so even a PV array that could run at 20v wont when connected to a 12v battery.

(thats why we use MPPT controllers)

 

 

At the end of the solar day you might get a time when the alt shuts down as the PV could have a higher voltage set point than the alt. But you are still not using more fuel as the engine (which is on for the purpose of moving) will have less load so use less.

 

 

My system has shunts on all charge sources & loads. When I have a good strong PV charge (80amps) & the genny is running (so 100-120 amps from the charger) I can see a very very slight drop in the amps from the genny BUT the engine note also changes as its under less load. This only happens once out of bulk phase, during bulk the battery can accept all that I can supply & more. If the bank is nearly full & I have a good PV charge I would shut the genny off, just like you would on a boat with the engine if just running it for battery charging.

 

 

To turn off the FREE power source & leave the fuel guzzling one on is madness of the highest order. Let the PV reduce the load on the alt & save some fuel.

[OldGoat]

I wonder -

 

When batteries are charged at a very low rate (as one would with solar) the plates are subject to microscopic bubbles which raises the perceived voltage.

Thus the charging system will charge at a lower rate until the bubbles disperse.

 

Could this be the cause??

 

 

 

[Gibbo]

I wonder -

 

When batteries are charged at a very low rate (as one would with solar) the plates are subject to microscopic bubbles which raises the perceived voltage.

Thus the charging system will charge at a lower rate until the bubbles disperse.

 

Could this be the cause??

 

Eh?

 

Wrong way round. Low charge = no bubbles. Big charge = lots of bubbles.

[Robin2]

Re-read what I wrote.

 

This is the root of your confusion. If you put a high voltage on a battery, the battery will dictate a high current. If you have somehow got a low current going into a battery then either you have a low voltage or the battery is fully charged.

 

 

So how does the battery make the solar panel produce more than 2 amps even if the solar panel can supply it at 20v?

[Gibbo]

So how does the battery make the solar panel produce more than 2 amps even if the solar panel can supply it at 20v?

 

You're having a laugh right?

[Robin2]

You're having a laugh right?

 

No. I'm dead serious.

[Gibbo]

No. I'm dead serious.

 

I don't believe you.

[Robin2]

I don't believe you.

 

Let me try again...

 

Overnight the fridge laptop etc consume 30Ah. Before I got the solar panels the battery voltage at 9am was about 12.2 to 12.3 volts. The charge current from the alternator then started at about 40A and declined from that.

 

Early in the morning the solar panels produce, say, 2A most of which is consumed by the inverter but some goes into the battery - say 0.5A for an hour or so. That seems to be enough to raise the battery voltage to 12.6 / 12.8 volts and the alternator charge current starts at only 15 to 20 amps.

 

I am wondering if anyone else has experienced this, and if not, what might I be doing wrong.

 

An answer that takes more than 4 words would be much appreciated

[Gibbo]

An answer that takes more than 4 words would be much appreciated

 

I've learnt with you that an answer with more than four words confuses you.

 

The question has been answered.

[blodger]

Let me try again...

 

Overnight the fridge laptop etc consume 30Ah. Before I got the solar panels the battery voltage at 9am was about 12.2 to 12.3 volts. The charge current from the alternator then started at about 40A and declined from that.

 

Early in the morning the solar panels produce, say, 2A most of which is consumed by the inverter but some goes into the battery - say 0.5A for an hour or so. That seems to be enough to raise the battery voltage to 12.6 / 12.8 volts and the alternator charge current starts at only 15 to 20 amps.

 

I am wondering if anyone else has experienced this, and if not, what might I be doing wrong.

 

An answer that takes more than 4 words would be much appreciated

You have taken account that the panels during the day have input amp hours so maybe the batts are better than they were before solar with loads masking the true voltage at engine start up?