Solar....how much wattage is enough

[WotEver]

9 hours ago, reg said:

I hope you are aware that Pragmatic answers spoil debates

So good...

2 minutes ago, reg said:

I hope you are aware that Pragmatic answers spoil debates

You said it twice!

[rusty69]

1 minute ago, WotEver said:

So good

Solar, and Thanks for All the Fish! 

[reg]

6 minutes ago, WotEver said:

So good...

You said it twice!

No my tablet has decided to post it twice, don't know how and don't know why, and won't let me delete the ****** thing. It's a well known fact that undersized batteries overcharged by oversized solar arrays will dramatically affect your android keyboard (but only if you use factor 3)

Edited May 28, 2018 by reg

[WotEver]

3 minutes ago, rusty69 said:

Solar, and Thanks for All the Fish! 

I’m on my third pangalacticgargleblaster now, so don’t start...

[reg]

Just now, WotEver said:

I’m on my third pangalacticgargleblaster now, so don’t start...

Wouldn't even attempt to type that with my android keyboard, all hell would break loose and my mppt would explode. 

 

Hope this helps the op, if they haven't lost the will to live. 

[Richard10002]

2 hours ago, Richard10002 said:

Horace, I have 490W of solar panels, and a 40A Tracer BN MPPT controller and am at the point where I need new batteries. My power useage is about 100Ah per day, and I have the means to charge by engine or generator in the winter or if there is no sun.

 

What range of battery bank sizes would my panels be OK for?

 

Horace?

[Alan de Enfield]

3 minutes ago, Richard10002 said:

 

Horace?

[Horace42]

46 minutes ago, Dr Bob said:

1 hour ago, Horace42 said:

Horace, I totally disagree with what you are saying.....although as I dont understand a word of what you are saying .....I may be wrong (but I'm not)!

You said previously "when the MPPT controller tries to match the instantaneous output of your panel to your instantaneous demand."

I dont think you understand it properly the MPPT controller doesnt try and match anything. It tries to put power in until it cant - because the batteries cant take it and then goes into float. Nothing to do with balancing anything.

I do not understand your expanation. Please try again. 

 

You are welcome to totally disagree, but why? "although as I dont understand a word of what you are saying .....I may be wrong (but I'm not)!"---

How do you know you are right if you don't understand what I am talking about - implying also that what I say is wrong - and especially saying so in 'public'.

Be that as it may, you are close to the truth about me not understanding the MPPT controller. I do not know the finer points of the inner workings.

But outwardly, as you say, it stops charging and goes into float when the battery is fully charged.

I guess it knows when the battery is fully charged by sensing the voltage.

But in order to charge the batteries it must have enough 'volts' from the solar panel to push the current through the batteries, and in bright sunshine, I guess some form of voltage regulation or current limiting to protect both batteries and panels from overload.

The 'matching and balancing' bit comes from the instantaneous random load causing a voltage drop at the battery, whereby the MPPT senses this and responds accordingly - and depending on inner resistance characteristics - current will flow to the devices connected connected to the batteries.

In principle the MPPT controller works much the same way as the engine generator controller.

Either way, the battery must supply all the power when the sun is not shining or the engine not running.

 

 

 

[nb Innisfree]

Roof size is irrelevant if a tree anology is used. A tree solves its problems by having a vast surface area of leaves in relation to its footprint {ignoring roots) If a suitable framework resembling a large tree's network of radiating branches with many, many solar panes attached could be secured to the roof then solar power generation in the winter would easily exceed usage. The framework would need to be made from a very light material (magnesium?) There could be a problem extinguishing a fire if it ignited from the intense heat generated and the problem of bridges would also need addressing but I'm sure there is a whizz kid somewhere on the forum that could solve these little wrinkles. 

 

Calling Professor Bizzard, calling Professor Bizzard... 

 

 

Edited May 28, 2018 by nb Innisfree

[reg]

2 minutes ago, nb Innisfree said:

Roof size is irrelevant if a tree anology is used. A tree solves its problems by having a vast surface area of leaves in relation to its footprint {ignoring roots) If a suitable framework resembling a large tree's network of radiating branches with many, many solar panes attached could be secured to the roof then solar power generation in the winter would easily exceed usage. The framework would need to be made from a very light material (magnesium?) There could be a problem extinguishing a fire if it ignited from the intense heat generated and the problem of bridges would also need solving but I'm sure there is a whizz kid somewhere on the forum that could solve these little wrinkles. 

 

Calling Professor Bizzard, calling Professor Bizzard... 

 

 

Your not treating this seriously are you. 

[WotEver]

29 minutes ago, Horace42 said:

I guess it knows when the battery is fully charged by sensing the voltage

You guess wrong

30 minutes ago, Horace42 said:

... current limiting to protect both batteries and panels from overload.

You guess wrong again

31 minutes ago, Horace42 said:

... instantaneous random load causing a voltage drop at the battery, whereby the MPPT senses this and responds accordingly

Wrong again!

 

You’re on a roll here. 

[nb Innisfree]

33 minutes ago, reg said:

Your not treating this seriously are you. 

How dare you! 

[Tony Brooks]

36 minutes ago, Horace42 said:

But outwardly, as you say, it stops charging and goes into float when the battery is fully charged.

I guess it knows when the battery is fully charged by sensing the voltage.

 

But in order to charge the batteries it must have enough 'volts' from the solar panel to push the current through the batteries, and in bright sunshine, I guess some form of voltage regulation or current limiting to protect both batteries and panels from overload.

The 'matching and balancing' bit comes from the instantaneous random load causing a voltage drop at the battery, whereby the MPPT senses this and responds accordingly - and depending on inner resistance characteristics - current will flow to the devices connected connected to the batteries.

In principle the MPPT controller works much the same way as the engine generator controller.

Either way, the battery must supply all the power when the sun is not shining or the engine not running.

 

 

 

1. It should say "when it THINKS the batteries are fully charged" and as I told you all charge sources have a habit of getting it wrong. They tend to go to float too early. It may or may not monitor voltage rise but there is definitely a "time in absorption" calculation.

 

2. Panels can't be overloaded because as the amps they produce in any given light intensity rises the voltage tends to fall just like a battery charger or alternator regulator.

 

3. As I explained the control that protects the batteries is VOLTAGE regulation, nothing to do with current. Again as you have been told its the BATTERIES themselves that determine the current at any given voltage.

 

4. IF the MPPT controller is voltage regulating then any load applied that drops the system voltage will simply allow some or all the regulator output to flow to the load. However that load may depress the panel voltage so the controller stops regulating and so you are in effect into bulk charging until the load is removed. As you say just like an alternator regulator.

 

The advantage of MPPT over PWM is that to regulate the voltage a PWM controller keeps turning the charging voltage on and off very fast. The mark space ratio governs the effective charging voltage. A MPPT uses something akin to a switched mode power supply to convert the solar wattage into a wattage at charging suitable voltage so Watts at 20+ volts or more/far more voltage delivers more amps at charging voltage.

[Murflynn]

for those who complain that the fridge is the biggest drain on the batteries, and simultaneously claim that solar provides next to nothing over the winter months, may I suggest - buy a coolbox and keep it out of the sun in a sheltered place outside the cabin.  Beer, milk and butter will be kept adequately cool.

 

 

................... oh, and I am very disappointed to learn that my two mppt controllers are not intelligent, reacting to every little change in their environment.  I had fondly imagined that they were about to take over the world.  

 

as someone mentioned earlier - please do not feed trolls.

[Horace42]

2 hours ago, Alan de Enfield said:

That is totally incorrect.

 

You are working on the assumption that the solar panel controls the charge rate of the battery - false !!!

The charge rate reduces and the voltage increase as a battery gets to a higher SoC.

At (say) 90% SoC the battery(s) may only accept 5 amps - if your solar panel were to be putting out 50 amps, only 5 amps would be going into the batteries. It may take you 4 hours of charging to get to 90% SoC, another 4 hours to get from 90-95% SoC and a further 8 hours to get from 95-100% SoC as the current the battery(s) will accept falls lower and lower.

 

As a guide a battery can be considered to be fully charged when THE BATTERY has reduced the current it will accept down to 1% of the battery capacity. So for a 100Ah battery as it approaches 'full' it will only take 1 amp - irrespective if you try to force 10 amps or 100 amps into it.

 

You are posting rubbish and not only making yourself look silly, but trying to give those asking questions the wrong information which WILL cost them money.

 

I'll leave you to it now - I can do no more.

 

"that is totally incorrect.   You are working on the assumption that the solar panel controls the charge rate of the battery - false !!!"

 

I disagree with your comment.  I have said the MPPT controls the charge. And whatever the precise values it is set at, and assuming the sun is shining enough, it will deliver amps the battery until it is fully charged.
 

"You are posting rubbish and not only making yourself look silly"  

 

You are welcome to your opinion - but and that is all it is- and proves nothing one way or the other about choosing the correct solar panel.

That remark says more about you than me.

 

 As for spending money, it is surely for the OP to decide. What if the OP buys panels or batteries a bit too large - it is no big deal.  Better than being undersized.

Has anybody on this panel got oversized batteries or panels that they regret buying ? Please say so.

 

 

[Tony Brooks]

1 minute ago, Horace42 said:

"that is totally incorrect.   You are working on the assumption that the solar panel controls the charge rate of the battery - false !!!"

 

I disagree with your comment.  I have said the MPPT controls the charge. And whatever the precise values it is set at, and assuming the sun is shining enough, it will deliver amps the battery until it is fully charged.
 

"You are posting rubbish and not only making yourself look silly"  

 

You are welcome to your opinion - but and that is all it is- and proves nothing one way or the other about choosing the correct solar panel.

That remark says more about you than me.

 

 As for spending money, it is surely for the OP to decide. What if the OP buys panels or batteries a bit too large - it is no big deal.  Better than being undersized.

Has anybody on this panel got oversized batteries or panels that they regret buying ? Please say so.

 

 

[tree monkey]

1 hour ago, nb Innisfree said:

Roof size is irrelevant if a tree anology is used. A tree solves its problems by having a vast surface area of leaves in relation to its footprint {ignoring roots) If a suitable framework resembling a large tree's network of radiating branches with many, many solar panes attached could be secured to the roof then solar power generation in the winter would easily exceed usage. The framework would need to be made from a very light material (magnesium?) There could be a problem extinguishing a fire if it ignited from the intense heat generated and the problem of bridges would also need addressing but I'm sure there is a whizz kid somewhere on the forum that could solve these little wrinkles. 

 

Calling Professor Bizzard, calling Professor Bizzard... 

 

 

https://goo.gl/images/c3vvjC

 

[reg]

9 minutes ago, Horace42 said:

"that is totally incorrect.   You are working on the assumption that the solar panel controls the charge rate of the battery - false !!!"

 

I disagree with your comment.  I have said the MPPT controls the charge. And whatever the precise values it is set at, and assuming the sun is shining enough, it will deliver amps the battery until it is fully charged.
 

"You are posting rubbish and not only making yourself look silly"  

 

You are welcome to your opinion - but and that is all it is- and proves nothing one way or the other about choosing the correct solar panel.

That remark says more about you than me.

 

 As for spending money, it is surely for the OP to decide. What if the OP buys panels or batteries a bit too large - it is no big deal.  Better than being undersized.

Has anybody on this panel got oversized batteries or panels that they regret buying ? Please say so.

 

 

 

[Horace42]

13 minutes ago, Tony Brooks said:

1. It should say "when it THINKS the batteries are fully charged" and as I told you all charge sources have a habit of getting it wrong. They tend to go to float too early. It may or may not monitor voltage rise but there is definitely a "time in absorption" calculation.

 

2. Panels can't be overloaded because as the amps they produce in any given light intensity rises the voltage tends to fall just like a battery charger or alternator regulator.

 

3. As I explained the control that protects the batteries is VOLTAGE regulation, nothing to do with current. Again as you have been told its the BATTERIES themselves that determine the current at any given voltage.

 

4. IF the MPPT controller is voltage regulating then any load applied that drops the system voltage will simply allow some or all the regulator output to flow to the load. However that load may depress the panel voltage so the controller stops regulating and so you are in effect into bulk charging until the load is removed. As you say just like an alternator regulator.

 

The advantage of MPPT over PWM is that to regulate the voltage a PWM controller keeps turning the charging voltage on and off very fast. The mark space ratio governs the effective charging voltage. A MPPT uses something akin to a switched mode power supply to convert the solar wattage into a wattage at charging suitable voltage so Watts at 20+ volts or more/far more voltage delivers more amps at charging voltage.

Thank you very much for the detailed explanation.  Much more useful to me.  It would be nice to hear from the OP what happens next.

 

[Horace42]

4 minutes ago, tree monkey said:

https://goo.gl/images/c3vvjC

 

Roof size in my simplistic view relates to how much room you have to place panels and to some extent is a factor in choice of panel.

6 minutes ago, reg said:

 

For goodness sake please don't bury yourself on my account.

[system 4-50]

24 minutes ago, Horace42 said:

I have said the MPPT controls the charge. And whatever the precise values it is set at, and assuming the sun is shining enough, it will deliver ?? amps ?? the battery until it is fully charged.

can you fill in the presumably missing words to make it clearer what you are trying to say?

[reg]

22 minutes ago, Horace42 said:

For goodness sake please don't bury yourself on my accoun

Seems like something else you failed to understand. 

[WotEver]

42 minutes ago, Murflynn said:

as someone mentioned earlier - please do not feed trolls.

Yes, I’m guilty as charged and shall do my very best to stop. 

37 minutes ago, Tony Brooks said:

Yup. If it wasn’t so stupid it would be funny. 

[MtB]

4 hours ago, Horace42 said:

but to anybody trying to select a suitable solar panel - the battery size is important - and a balanced system cannot be properly designed without taking the battery size into account.

 

Could you explain what a 'balanced system' is in this context please?

 

I'm mystified. 

[WotEver]

34 minutes ago, tree monkey said:

https://goo.gl/images/c3vvjC