RV Question about solar panels, controllers, and batteries

[Dave in AZ]

But if the solar panels create power whether or not it is needed (they have no indicator of load need), they create power 100% of the time they are in the sun. If that power cannot flow into the battery, it MUST be dissipated as heat somewhere, whether that it in the controller,

Your understanding of electricity is wrong. Your use of terminology is wrong, and show you don't understand the basic physics. You keep using the word power as a synonym for electricity or voltage, it is not. Power is a defined term. If you don't have an electrical current to a load, then there is zero power.
Electric power is the rate of transfer of electrical energy within a circuit.
https://en.wikipedia.org/wiki/Electric_power

Something sitting in the sun, heating up and having electrons kicked up and down, but no current flowing to a load, is the exact same as a dead fish sitting in the sun--zero power generated.

 

[datdude]

I said as much Dave. I am not an expert and that s why I am trying to get smarter about this stuff. I prebeat that horse for you, so no need to keep doing it.

But I don't think you can say no "power" is created. It is released as heat. A loaded PV will run cooler than an unloaded PV, Why is that if it is not because the "power" created in the panel is moving elsewhere?

 

[Dave in AZ]

I said as much Dave. I am not an expert and that s why I am trying to get smarter about this stuff. I prebeat that horse for you, so no need to keep doing it.

But I don't think you can say no "power" is created. It is released as heat. A loaded PV will run cooler than an unloaded PV, Why is that if it is not because the "power" created in the panel is moving elsewhere?

The panel isn't creating power.
Photons in the sunlight carry energy. If panel is connected to a load, the photons get converted to a current that carries that energy away to a load, where work is done and heat produced.

With no load connected, the absorbed photons just convert to heat the panel, same as a rock sitting in sun.

Whatever, my point is, you kept making statements that are false assumptions. Like almost every sentence in the post I responded to, is not true, and you state them like truths, not questions. I see you're trying to understand, your inaccurate phrasing just irked me.

I'll let you get back to it, there isn't really an open question here to be helped with.

 

[datdude]

Photons in the sunlight carry energy. If panel is connected to a load, the photons get converted to a current that carries that energy away to a load, where work is done and heat produced.

With no load connected, the absorbed photons just convert to heat the panel, same as a rock sitting in sun.

Whatever, my point is, you kept making statements that are false assumptions. Like almost every sentence in the post I responded to, is not true, and you state them like truths, not questions. I see you're trying to understand, your inaccurate phrasing just irked me.

I'll let you get back to it, there isn't really an open question here to be helped with.

Did you see post 20? "And for everyone's benefit, everything I say should be considered as much a question as a statement lol."

 

[datdude]

The panel isn't creating power.
Photons in the sunlight carry energy. If panel is connected to a load, the photons get converted to a current that carries that energy away to a load, where work is done and heat produced.

With no load connected, the absorbed photons just convert to heat the panel, same as a rock sitting in sun.

Whatever, my point is, you kept making statements that are false assumptions. Like almost every sentence in the post I responded to, is not true, and you state them like truths, not questions. I see you're trying to understand, your inaccurate phrasing just irked me.

I'll let you get back to it, there isn't really an open question here to be helped with.

So voltage increases, but current doesn't, so no power, right? Perhaps I should have called it energy or something else, but you cannot really turn off PV in sunlight to the best of my knowledge. If the layers are exposed to sun, then will convert the radiation into voltage, am I understanding that correctly?

 

[corn18]

So voltage increases, but current doesn't, so no power, right? Perhaps I should have called it energy or something else, but you cannot really turn off PV in sunlight to the best of my knowledge. If the layers are exposed to sun, then will convert the radiation into voltage, am I understanding that correctly?

Voltage in the form of potential energy. But not power.

 

[datdude]

Voltage in the form of potential energy. But not power.

So are you saying that an unloaded (disconnected) panel and a loaded panel should be the same temperature?

 

[Mattb4]

So are you saying that an unloaded (disconnected) panel and a loaded panel should be the same temperature?

You need to understand energy transfer. The sun provides the energy. We average this at highest production to be 1000w per square meter of area. Solar panels take some of that energy and convert it to electrical power (the amount they can utilize is called efficiency). Thus if you have sunlight of 1000w per sqm energy striking the panel, and let's say 200w of electrical load on the panel, the amount of energy left that could be turned into panel heat is now 800w.

So no, a loaded panel will not get as hot as a unloaded one sitting in the sun. Nor can a unloaded panel receive more energy than the 1000w it is being struck by. The amount it will heat up will depend on the amount of wattage it absorbs minus the amount that gets reflected or radiated away.

Think of it like a black object in the sun versus a white object. Why is the black object hotter? What happens to the temperature of a black object if you take some of the energy from it through convection?

The sun is the generator of all the energy and the solar panel just takes a portion of it and under load it supplies electrical power.

 

[datdude]

BTW, I was pointed to this thread and am reading it now, too. Very very similar question.

Does order actually matter?

So this may or may not be seen as a beginner question, but I have a feeling I'm trying to debunk a myth with MPPTs. My MPPT is a Li-time 30A controller, and it states that the MPPT must be connected to a battery before connecting it to solar. I have watched a couple videos now that also say that...

diysolarforum.com

 

[datdude]

You need to understand energy transfer. The sun provides the energy. We average this at highest production to be 1000w per square meter of area. Solar panels take some of that energy and convert it to electrical power (the amount they can utilize is called efficiency). Thus if you have sunlight of 1000w per sqm energy striking the panel, and let's say 200w of electrical load on the panel, the amount of energy left that could be turned into panel heat is now 800w.

So no, a loaded panel will not get as hot as a unloaded one sitting in the sun. Nor can a unloaded panel receive more energy than the 1000w it is being struck by. The amount it will heat up will depend on the amount of wattage it absorbs minus the amount that gets reflected or radiated away.

Think of it like a black object in the sun versus a white object. Why is the black object hotter? What happens to the temperature of a black object if you take some of the energy from it through convection?

The sun is the generator of all the energy and the solar panel just takes a portion of it and under load it supplies electrical power.

Thank you.

 

[corn18]

So are you saying that an unloaded (disconnected) panel and a loaded panel should be the same temperature?

No clue, don't care.

 

[RV8R]

Ok, guys, time for me to quit learning because he said so. Later.

I have only glanced at this thread, but I think you might be mixing up some terms;

Power
Work
Energy
Time

You can get meanings for those in reference to physics & electrical from the internet.

I believe a solar panel sitting in the sun ,,, much like a rock gains energy from the sun.

There are different types of energy ,,, a boulder on a mountaintop that is stationary still has “potential energy” as it could roll down the hill if persuaded. During the day it also assumingely will absorb the suns energy & retain it as heat.

If you have a question(s) here & really want to learn, all you have to do is ask. However, if you are not prepared to learn & use proper terminology YMMV here.

 

[datdude]

Solar power is not potential energy though. Potential energy must be stored and a PV cannot store the energy, so it is dissipated as heat, right? Energy conservation and all? It is hard to start learning new things without asking questions. I just think back and remember I would have felt like the biggest asshole if I had told all of the people I have helped teach cybersecurity to over the years that they were using the wrong words and needed to go educate themselves before I would help them. This is a DIY forum, not an we are all the experts and DIY learners are not welcome. I would expect this from Reddit, not so much this forum. Clearly I am in the wrong here and will see myself out.

 

[Supervstech]

Solar power is not potential energy though. Potential energy must be stored and a PV cannot store the energy, so it is dissipated as heat, right? Energy conservation and all? It is hard to start learning new things without asking questions. I just think back and remember I would felt like the biggest asshole if I had told all of the people I have helped teach cybersecurity to over the years that they were using the wrong words and needed to go educate themselves before I would help them. This is a DIY forum, not an we are all the experts and DIY learners are not welcome. I would expect this from Reddit, not so much this forum. Clearly I am in the wrong here and will see myself out.

I think where you are missing the point is wording.

PV is absolutely potential energy.

Until it is DRAWN by a load 9f some kind, it is just sunlight hitting a material.
The potential for energy transfer is present, but until a circuit is completed, no energy is produced.

The battery provides a specific voltage and current. When the battery is full, it slows and stops drawing current, the pwm controller limits voltage output to battery specifications.
If the battery gets disconnected from the controller, the instant voltage draw from the battery is gone, and voltage spikes up to PV voc output into the controller... some will display an alert some will function normally, some will burn up and fail.

Many controllers are multi voltage compatible. Without a battery, they have no idea what voltage to send out, and can be unpredictable, then when you reconnect the battery, they may send the wrong charge parameters, and destroy your batteries...

 

[Mattb4]

Solar power is not potential energy though. Potential energy must be stored and a PV cannot store the energy, so it is dissipated as heat, right? Energy conservation and all? It is hard to start learning new things without asking questions. I just think back and remember I would felt like the biggest asshole if I had told all of the people I have helped teach cybersecurity to over the years that they were using the wrong words and needed to go educate themselves before I would help them. This is a DIY forum, not an we are all the experts and DIY learners are not welcome. I would expect this from Reddit, not so much this forum. Clearly I am in the wrong here and will see myself out.

Potential energy the unloaded panel gets from the sun's energy is stored as heat. Walk out and put your hand on a unloaded panel in the sun and you can feel it. Heat is not convertible by the panel to electricity so it does not contribute to anything other than warming up the surroundings.

Electrical potential caused by the Sun's energetic particles causing electrons to be kicked from the silicon cell matrix however can be used to transfer power if a circuit and load is established. Energy conservation is that you can not get out more than the sun provides. So as I explained in my previous post any energy you transfer from the panel reduces the amount left to create effects like heating.

 

[datdude]

I think where you are missing the point is wording.

PV is absolutely potential energy.

Until it is DRAWN by a load 9f some kind, it is just sunlight hitting a material.
The potential for energy transfer is present, but until a circuit is completed, no energy is produced.

The battery provides a specific voltage and current. When the battery is full, it slows and stops drawing current, the pwm controller limits voltage output to battery specifications.
If the battery gets disconnected from the controller, the instant voltage draw from the battery is gone, and voltage spikes up to PV voc output into the controller... some will display an alert some will function normally, some will burn up and fail.

Many controllers are multi voltage compatible. Without a battery, they have no idea what voltage to send out, and can be unpredictable, then when you reconnect the battery, they may send the wrong charge parameters, and destroy your batteries...

Thank you for taking the time to explain this. I was thinking of potential energy like a pump back reservoir. Water is pumped back uphill at night when power is plentiful on the grid and is allowed to flow downhill during the day to turn hydro turbines. This potential energy is stored and as more water is added (rain) the potential energy increases because the reservoir itself is a large battery. So for me to learn, I tend to need to be able to relate these things back to other things I know about. Sometimes I need more help in these things and am trying to learn more.

 

[datdude]

Potential energy the unloaded panel gets from the sun's energy is stored as heat. Walk out and put your hand on a unloaded panel in the sun and you can feel it. Heat is not convertible by the panel to electricity so it does not contribute to anything other than warming up the surroundings.

Electrical potential caused by the Sun's energetic particles causing electrons to be kicked from the silicon cell matrix however can be used to transfer power if a circuit and load is established. Energy conservation is that you can not get out more than the sun provides. So as I explained in my previous post any energy you transfer from the panel reduces the amount left to create effects like heating.

It seems like the heat in that example is not stored (potential) because it is converted into heat immediately and dissipates. I am clearly not understanding that piece.

 

[Mattb4]

But the heat isn't "

It seems like the heat in that example is not stored (potential) because it is converted into heat immediately and dissipates. I am clearly not understanding that piece.

Sure it is. You can feel it can't you? If it was gone immediately the panel would not get hot. Does it dissipate due to transfer to the environment? Yes. Eventually all heat does this. But for a while it is stored. People use thermal mass to attenuate and store heat for longer periods. It don't generate heat but it slows transfer down.

ETA: There was a reason that back in NPS (Nuclear Power School) students referred to the course "Heat transfer and fluid flow" as "Student transfer and fleet flow". It was because it is a difficult thing for many to comprehend.

 

[upnorthandpersonal]

This is a solar panel:



It's based on the principle of the photo electric effect. A photon hits the P-N junction, which is essentially the place where two pieces of differently doped silicon meet. This interaction between the photon and the junction creates free electrons, which then transfer charge to the load if connected. If the load is not connected, the electrons don't go anywhere and eventually recombine.

Therefor, if there is no load, all the energy that could be extracted and turned into heat in the load now stays in the panel. In other words, yes, temperature of the panel is different when there is a load compared to when there is not. However, it can only get so warm as this is directly related to the amount of incoming sunlight, and even then only 20% or thereabout is converted to begin with (panel efficiency), so there could be a 20% difference at most.

P.S.: @datdude : welcome to the forum. Don't let a few people discourage you from interacting and asking questions.

 

[datdude]

Sure it is. You can feel it can't you? If it was gone immediately the panel would not get hot. Does it dissipate due to transfer to the environment? Yes. Eventually all heat does this. But for a while it is stored. People use thermal mass to attenuate and store heat for longer periods. It don't generate heat but it slows transfer down.

ETA: There was a reason that back in NPS (Nuclear Power School) students referred to the course "Heat transfer and fluid flow" as "Student transfer and fleet flow". It was because it is a difficult thing for many to comprehend.

Thanks, I have had exactly zero training on this stuff, not that it shows. So even some of the most basic terminology is missing for me. I have spent my career working with utilities. I have a very high level understanding of generation, transmission, and distribution systems and how to protect them. I do not have experience at the engineering level with them. I break them or secure them, I do not program them or understand their intricacies.