Is there a 'warm-up' time on solar panels?

Arqane

I was reading a Yahoo article on the solar roads they're trying to come up with. I'm pretty skeptical because there are a ton of hurdles to overcome, even though as a land-use concept it's good. Apart from dealing with the actual material problems for roads, the main thing I could think of would be the horrible angle and shading issues that you'd have. I can't see the average insolation on roads being much more than 2-3. Between the low elevation, trees often being planted by roads, and hills that aren't facing south, you're going to get a horribly low amount of sun compared to any southern-facing roof on a building.

Plus there's the cars going over it that shade the "panels". But that led me to a thought that matters for more than just the roads. Do panels instantly generate energy when the sun hits them, or is there a little lag while they power up to their potential? For the solar road, if a heavy stretch of road has a car that runs over it every 3 seconds covering it and there's any lag period before it hits full power, you'll get little to no power. But it also effects things such as cloud cover, branches being blown that cover panels for a short while, birds flying over or landing on panels, etc..

So does anyone know the physics behind or or have a good real-world example of any lag effect, either to power up the cells or as they power down?

waynefromnscanada

Re: Is there a 'warm-up' time on solar panels?

When sun hits a solar panel it produces instantly, when the sun doesn't, neither does the panel. There is no lead time. In fact, as the sun or anything else heats a solar electric panel, it's output goes down. With that in mind, when pavement gets so hot it will "fry an egg", you can be sure a solar panel will do the same thing, and it's output, if the panel survives that heat, will be drastically reduced. Not to mention of course the requirement for such "road" panels to be stronger than concrete to survive what vehicles will do to them - - - In my opinion, one of the most idiotic ideas ever hatched! Sounds like a hold over joke from April 1st.

Arqane

Re: Is there a 'warm-up' time on solar panels?

Yeah, I was pretty skeptical, too. As a comment, I put down that attaching solar panels to lamp posts on the side of the road would probably get you as much energy for a much lower cost.

Still, even though the speed could obviously be traveling at nearly the speed of light, are you sure there is no lag in the production of electricity? Even for a fraction of a second? There's no lingering energy between the heat, or the electrical load balancing, or the magnetic field?

So basically if you connected a light bulb on a circuit to a solar panel with no capacitors or storage, as soon as you cover the panel will the light go out?

vtmaps

Re: Is there a 'warm-up' time on solar panels?

Arqane wrote: »

Still, even though the speed could obviously be traveling at nearly the speed of light, are you sure there is no lag in the production of electricity? Even for a fraction of a second?

Well sure there's a lag, if you're in a physics lab and are concerned with the speed of light. As a practical matter, there is no lag.
There may be a lag in the transmission of the power through a charge controller or inverter, but that is not caused by the panel's lag.

--vtMaps

Arqane

Re: Is there a 'warm-up' time on solar panels?

Well, I figure it might be worth testing in real-world conditions. There are lots of factors involved where it might benefit to spread the sunlight out a little differently. If you had 2 identical panels with a certain amount of sunlight and alternately shaded them, in a perfect scenario you would always get the same energy no matter which one was being exposed to the light. But since it's not that simple, you may end up with less power if there actually is something in the process that takes time to fully energize the system. On the other hand, you'll likely end up with slightly more power because each panel would have time to cool down so you wouldn't lose power due to excess heat.

With all the different factors that go in to it, in actual practice, you might be able to find some efficiency gain.

PNjunction

Re: Is there a 'warm-up' time on solar panels?

At the non-practical levels you are talking about, marketing departments and solar funding schemes for unrealistic projects that will never see the light of day (pun intended) might look into it.

The only warm-up time ever encountered in solar on a practical level was from the old thin-film panels that used CIGS technology (not every thin film uses this). Long gone now, but hyped every now and again.

mike95490

Re: Is there a 'warm-up' time on solar panels?

Yes, there is a warm up period in solar panels, but just not what you are thinking of. Photon comes in, knocks an electron loose, you have power at the speed of light.

But in 5 minutes, the sun has warmed up that nice cool panel. Warm panels produce less voltage than cold panels. That causes all sorts teeth gnashing and hair pulling, as the record morning cold temperatures have to be used in open circuit panel voltage calculations, so frosty morning high voltages don't fry things. When panels warm up after a bit, the voltage drops and things get back to normal.

niel

Re: Is there a 'warm-up' time on solar panels?

you guys talking about the speed of electricity got me thinking about it more than i ever have. some answers found say the speed of light and some say less and i'm wondering if anybody has actually confirmed the speed or not. many view this like dominoes falling from one end to the other with electrons, but i'm thinking this is a false way to view it. why? because electricity isn't just pushing its way out as it is also being pulled from the other end simultaneously. how can one say the electric in say 10ft of wire takes half the time as a length that is 20ft long when both ends go + or - at the same time? this makes me believe it is in tandem and does not flow quite like water from one end to the other. yes, each electron does move from 1 atom to the next, but it does not push the electron from that next atom as that electron leaves simultaneously as the one previous to it does. to better illustrate my thoughts on this with dominoes it would be as a long string with dominoes attached to it. when it is pushed on one end it is pulled from the other at the same time making the speed, no matter how long it is, to be that which it took from one domino to the next or in reality one atom to the next.

now i don't know what the actual speed of one electron traveling from one atom to the next is, but i suspect that speed is the speed no matter the length of wire. anybody hear of tests actually conducted along these lines?

john p

Re: Is there a 'warm-up' time on solar panels?

You have to admit solar panels embedded as roadway would make for interesting wet weather driving..,, It would create a new vehicle dance craze ,, ""The solar shuffle"".

inetdog

Re: Is there a 'warm-up' time on solar panels?

niel wrote: »

you guys talking about the speed of electricity got me thinking about it more than i ever have. some answers found say the speed of light and some say less and i'm wondering if anybody has actually confirmed the speed or not. many view this like dominoes falling from one end to the other with electrons, but i'm thinking this is a false way to view it. why? because electricity isn't just pushing its way out as it is also being pulled from the other end simultaneously. how can one say the electric in say 10ft of wire takes half the time as a length that is 20ft long when both ends go + or - at the same time? this makes me believe it is in tandem and does not flow quite like water from one end to the other. yes, each electron does move from 1 atom to the next, but it does not push the electron from that next atom as that electron leaves simultaneously as the one previous to it does. to better illustrate my thoughts on this with dominoes it would be as a long string with dominoes attached to it. when it is pushed on one end it is pulled from the other at the same time making the speed, no matter how long it is, to be that which it took from one domino to the next or in reality one atom to the next.

now i don't know what the actual speed of one electron traveling from one atom to the next is, but i suspect that speed is the speed no matter the length of wire. anybody hear of tests actually conducted along these lines?

The electric current in a wire is defined in terms of the number of electrons passing through a given cross section of the wire in one second.
Any particular current can be carried by moving a large number of electrons at a relatively low speed or a smaller number at a higher speed. An ammeter cannot tell the difference...

If you can estimate the number of free (conduction) electrons in the metal, you can figure out what the individual electron velocity will be for a given current.
It will be very small compared to universal metrics like the speed of light.
On the other hand, the time it takes for close to the steady state current to flow when a voltage is suddenly applied to a length of wire will be a multiple of the time it takes for light to travel from one end of the wire to the other.

niel

Re: Is there a 'warm-up' time on solar panels?

inetdog,
so you contend that it goes from one end to the other, but you have not put forth any proof that it is one way or the other. by your contention that the moment a circuit is complete that it shall start at - until it reaches +. i say the instant it was a complete circuit that it did not flow from - to + in the conventional way you are depicting it in, but was uniformly spread out. it wasn't just the push of electrons as there was a pull at the same time. the slowdown is not that it had to go from 1 end of the wire to the other, but that there was a slowdown from 1 atom to the other.

i'm going to use another example of what i'm saying. many have seen wooden blinds in shutters with the individual slats connected with a piece of wood 90 degrees from the slats. (you regulate how much light comes in with them.) now if you were to move that connecting piece say from top to bottom, disregarding the pull of gravity, the top would represent the push of the - polarity and the bottom would represent the pull of the +. the shade does not flow from top to bottom as it is instantaneous due to an equal push in 1 direction and a pull from the other. the push would go downward on the top at the same time the pull is going downward from the bottom. the flow you talk of is an illusion as it is really simultaneous as i'm depicting. any resistance that would slow it down is just like moving the shutter downward slower and is not really from the top to bottom of the shutter, but rather the time of 1 slat to the next slat which happens to be the same as 1 end to the other. am i confusing you as this is difficult to explain. i'm not saying you can't slow it down, but it is not from one end of the wire to the other like water flow in a pipe as it is from 1 atom to the next with all moving at the same time. if it were to flow then closing that wooden blind would also be like dominoes and go one at a time.

BB.

Re: Is there a 'warm-up' time on solar panels?

The speed of a pulse of light through a vacuum is around 1.017 feet per nano seconds. Electric pulse is a little bit slower (depends on insulation type and such).

Another interesting question is how fast does an electron move (on average) through wire... And that is surprisingly slow, and the electrons travel very little distance in a 1/60th of a second (AC power line frequency):

http://amasci.com/miscon/speed.html

And about AC... how far do the electrons move as they vibrate back and forth? Well, we know that a one-amp current in 1mm wire is moving at 8.4cm per hour, so in one second it moves: 8.4cm / 3600sec = .00233 cm per second
And in 1/60 of a second it will travel back and forth by .00233cm/sec * (1/60) = .0000389cm, or around .00002"

There are just so many electrons in a wire, that it takes very little movement of that huge number to produce useful current flow.

Think of it like water--The speed of sound through water is much higher than air, but the average rate of flow is not very fast.

-Bill

Cariboocoot

Re: Is there a 'warm-up' time on solar panels?

You know guys, the OP's question was answered back at post #2.
Really wandering off down the esoteric path of the theoretical here. I wonder if that path will be paved with fragile, slippery, paid-for-by-tax-dollar PV's?

BTW it turns out the speed of light is no longer constant either.

pleppik

Re: Is there a 'warm-up' time on solar panels?

niel wrote: »

i'm going to use another example of what i'm saying. many have seen wooden blinds in shutters with the individual slats connected with a piece of wood 90 degrees from the slats. (you regulate how much light comes in with them.) now if you were to move that connecting piece say from top to bottom, disregarding the pull of gravity, the top would represent the push of the - polarity and the bottom would represent the pull of the +. the shade does not flow from top to bottom as it is instantaneous due to an equal push in 1 direction and a pull from the other. the push would go downward on the top at the same time the pull is going downward from the bottom. the flow you talk of is an illusion as it is really simultaneous as i'm depicting. any resistance that would slow it down is just like moving the shutter downward slower and is not really from the top to bottom of the shutter, but rather the time of 1 slat to the next slat which happens to be the same as 1 end to the other. am i confusing you as this is difficult to explain. i'm not saying you can't slow it down, but it is not from one end of the wire to the other like water flow in a pipe as it is from 1 atom to the next with all moving at the same time. if it were to flow then closing that wooden blind would also be like dominoes and go one at a time.

What you're really asking about is how does a signal propagate along an electric wire.

It's a lot more complicated than you probably expect, and depends a lot on the properties of the wire. But because we use wires to carry a lot of different kinds of signals (cable TV, phone, etc.) over very long distances, this has been studied very extensively.

But to keep it simple, let's think of just a big loop of wire. To start with, the wire isn't connected to anything and has no voltage or current. (In the real world, a loop of wire is also known as an antenna, so it will actually have some voltage from passing electromagnetic signals, but I'll ignore those.)

Now imagine that you connect both ends of the wire to a battery or other power source. As soon as you make that connection, a voltage signal starts propagating along the length of the wire at a significant fraction of the speed of light (the exact speed depends on the physical properties of the wire).

The voltage gradient starts pushing current along the wire, and the current creates a magnetic field. But a changing magnetic field creates an electric field (aka voltage) in the opposite direction, reducing the amount of current which flows. As the current gets closer to its steady-state level, the magnetic field changes more slowly, allowing the voltage to get closer to a consistent gradient. Eventually (meaning very very fast), the current and voltage gradient are basically constant and you have reached steady state.

Exactly how fast this happens depends on the material and configuration of the wire, and also the insulation around the wire (different insulators have different properties in electric and magnetic fields).

niel

Re: Is there a 'warm-up' time on solar panels?

i am familiar with the subject matter having a degree and being a ham operator. first of all dc has no frequency. i am debating that the electric has the potential to be faster than most think because it does not flow like water with 1 atom bumping into and pushing the next. if you had a wire extending from here to the moon and back you are saying it would take a split second to reach from - to +. i say the whole thing is nearly instantaneous due to the pull from the + at the same time as the push from the -. the time limiting factor is not from one end of the wire to the other, but rather from 1 atom to the next and note that the electron in that next atom is simultaneously moving in tandem and never being hit or pushed by the previous to make it move. if i'm wrong then there would be a difference between the wire going to the moon and back compared to the wire just going 2ft from - to +. how can anybody say there isn't any instantaneous flow at the + from its pull when the - has it's push no matter the length of the wire from one end to the other? by instantaneous it is only limited by the time of going from 1 atom to the next as all electrons are jumping at the same time.

Cariboocoot

Re: Is there a 'warm-up' time on solar panels?

In physics terms it is not instantaneous because nothing is. In real-world terms it is instantaneous because there's nothing that can measure the time differential as any such device would operate under the same conditions and be subject to the same "lag".

Not the same as with bouncing a signal off a satellite in orbit and getting it back to Earth at the receiving station. Especially when you add in the modems and VOIP equipment.

niel

Re: Is there a 'warm-up' time on solar panels?

that is why i said nearly instantaneously and i did define what that time represented. my point is that i contend it to be the same for a 2ft piece of wire as it is for a 400,000 mile piece of wire time wise.

Cariboocoot

Re: Is there a 'warm-up' time on solar panels?

niel wrote: »

that is why i said nearly instantaneously and i did define what that time represented. my point is that i contend it to be the same for a 2ft piece of wire as it is for a 400,000 mile piece of wire time wise.

I agree.
Doubtful that even the most rabid physicist would say otherwise.

vtmaps

Re: Is there a 'warm-up' time on solar panels?

niel wrote: »

by instantaneous it is only limited by the time of going from 1 atom to the next as all electrons are jumping at the same time.

No, they are not all jumping at the same time. As "pleppik" pointed out "As soon as you make that connection, a voltage signal starts propagating along the length of the wire at a significant fraction of the speed of light".

The electrons will not start jumping from one atom to the next until that signal reaches them. It will take longer for current to begin flowing through the entire length of a 400,000 mile long wire then it will through a 2 ft long wire.

Cariboocoot wrote: »

In physics terms it is not instantaneous because nothing is. In real-world terms it is instantaneous because there's nothing that can measure the time differential as any such device would operate under the same conditions and be subject to the same "lag".

Physicists measure the time differential with real-world equipment... that's how they know there is a speed of light. For a classic example, check out the Michelson-Morley experiments (wikipedia) of more than a century ago.

--vtMaps

vtmaps

Re: Is there a 'warm-up' time on solar panels?

Arqane wrote: »

I was reading a Yahoo article on the solar roads they're trying to come up with.

Solar roads, if feasible, will exacerbate the draining of energy from the sun:
http://nationalreport.net/solar-panels-drain-suns-energy-experts-say/

--vtMaps

Cariboocoot

Re: Is there a 'warm-up' time on solar panels?

vtmaps wrote: »

No, they are not all jumping at the same time. As "pleppik" pointed out "As soon as you make that connection, a voltage signal starts propagating along the length of the wire at a significant fraction of the speed of light".

The electrons will not start jumping from one atom to the next until that signal reaches them. It will take longer for current to begin flowing through the entire length of a 400,000 mile long wire as it will through a 2 ft long wire.



Physicists measure the time differential with real-world equipment... that's how they know there is a speed of light. For a classic example, check out the Michelson-Morley experiments (wikipedia) of more than a century ago.

--vtMaps

Well I can see that 100-year-old research is bound to be more accurate than what was going on at a certain laser energetics lab of my acquaintance just 25 years ago.

Circuit = loop = atomic connection = simultaneous action for all intents and purposes.

niel

Re: Is there a 'warm-up' time on solar panels?

signal? what signal? dc has no signal or frequency. next you'll tell me there's little elves directing the traffic.

pleppik

Re: Is there a 'warm-up' time on solar panels?

niel wrote: »

signal? what signal? dc has no signal or frequency. next you'll tell me there's little elves directing the traffic.

The idea of direct current as having no signal or frequency is a useful engineering approximation, but it's not the real world. When you connect a DC voltage to a wire which did not previously have a voltage across it, there is indeed a signal. The signal is that you're going from zero voltage to some non-zero voltage.

It takes time for this signal to propagate along the wire, and the speed can be easily measured with an oscilloscope and a few minutes of time. Simply connect a DC source to a switch and a really long wire (no shorter than ten feet, and you can make it as long as you want), and connect another wire from the switch to the trigger input of the oscilloscope so that when you close the switch it triggers the sweep. The signal input of the oscilloscope goes between the ground of the DC source and the far end of the wire.

Then flip the switch and see what happens. Then get a longer wire and try it again. You will see that the voltage jumps some time after you flip the switch, and the longer the wire the longer the delay before the voltage jumps.

nsaspook

Re: Is there a 'warm-up' time on solar panels?

No need to get into a bunch of physics mumbo-jumbo but the energy of electriciy is not carried in the electrons (charge) of the wire. You can easily show that the kinetic energy carried by the elecrons as current is miniscule and is a material effect of the field energy that surrounds it from the source (a solar panel producing energy from photon caused charge seperation) to the load. The speed of electrical changes on that wire is mainly effected by the dielectric and conductor boundary those fields travel in and is usually a large fraction of light speed. Even a DC there is a 'surface charge' on the wire that sets up an electric field in conductors that combined with the magnetic field shows the direction of energy flow moving from the source on both sides of the wire to the load close to light speed even as current slowly flows in a loop in the circuit. Does all this matter in practice? No, but it's a good idea to understand the basic theory.

http://www.matterandinteractions.org/Content/Articles/circuit.pdf
http://www.ippp.dur.ac.uk/~davis/EnergyTransferElectricCircuits.pdf

waynefromnscanada

Re: Is there a 'warm-up' time on solar panels?

vtmaps wrote: »

Solar roads, if feasible, will exacerbate the draining of energy from the sun:
http://nationalreport.net/solar-panels-drain-suns-energy-experts-say/

--vtMaps

Hahaha This is an awesome "report". I'd love to post it on Face Book, but I know it would go viral and have half the country up in arms against anything solar and have some people so worked up they'd be going house to house destroying any solar panels they find.

PNjunction

Re: Is there a 'warm-up' time on solar panels?

BB. wrote: »

There are just so many electrons in a wire, that it takes very little movement of that huge number to produce useful current flow.

That's how I understood it. Instead of viewing it as a speedy road trip for the electrons, it is much more like those ball-bearing klackers hanging by strings. Very little movement (but yes, measurable current) except of course for the beginning and end bearings.

Related mind-trip on the slippery slope: Using a solar panel means that when illuminated, we are de-materializing the doped silicon right before our very eyes. Although that might take a million years to see any difference - or would that just be 20 years? Hope to live that long to see that!

Cariboocoot

Re: Is there a 'warm-up' time on solar panels?

PNjunction wrote: »

That's how I understood it. Instead of viewing it as a speedy road trip for the electrons, it is much more like those ball-bearing klackers hanging by strings. Very little movement (but yes, measurable current) except of course for the beginning and end bearings.

Related mind-trip on the slippery slope: Using a solar panel means that when illuminated, we are de-materializing the doped silicon right before our very eyes. Although that might take a million years to see any difference - or would that just be 20 years? Hope to live that long to see that!

This is correct.
If the electrons moved from atom to atom with the supposed time delay it would create a string of unstable element en route resulting in chemical change merely from electricity flowing through the wire. This does not happen.

Oh and that report about people thinking panels suck energy from the sun is from a hoax site. The shame is that it is so easy to believe such nonsense because of the appalling large number of people who would think things like that. Remember the so-called engineer at a certain utility claiming people with battery-backed solar could 'steal power' from the company? He meant 'steal profit' (by time shifting Watt hours) of course but you wouldn't want to say that in public 'cause you'd sound greedy. Sounding stupid is better, I guess. If I had known how easy and profitable that was I could have skipped the whole education thing and just declared myself 'king' and espoused nonsense on the 'Net with impunity.

nsaspook

Re: Is there a 'warm-up' time on solar panels?

PNjunction wrote: »

Related mind-trip on the slippery slope: Using a solar panel means that when illuminated, we are de-materializing the doped silicon right before our very eyes. Although that might take a million years to see any difference - or would that just be 20 years? Hope to live that long to see that!

De-materializing? Maybe a better word is redistribute. The photon energy doesn't cause the silicon or dopant atoms to move (there is stress from the electric field and heat that causes micro-fractures to the lattice that reduces output) as they are locked in the lattice structure by a high temperature diffusion process that as you say might take a millions years at the normal temperatures seen on a hot panel to redistribute those atoms. The charge carriers move freely but one charge carrier (electron/hole) from silicon is exactly the same as one from any other atom that the current flows in.

Kamala

Re: Is there a 'warm-up' time on solar panels?

To the OP,
There is not a "warm up time" for solar panels. There is some lag in their performance that is related to their temperature. This point was made earlier in the thread. Photovoltaic panels are, of course, routinely heated as a necessity of their function. That is to be bathed in the most glorious and intense sunlight as may be available. Unfortunately, as the source required for their production increases so does the deliverance of their performance decrease. Curious.

To the Moderators (current and former),
Are you now theoretical physicists?! I'm certainly not. And I cannot call any other posters on this thread otherwise or not. However, it is my understanding that the flow of electric current through a "good" conductor is less than but near to the speed of light. There is undoubtedly a long way to go from human experience to get anywhere near the speed of light. I consider all this talk of "pushing and pulling" an electron to or from one atom or another to be pish posh.

The Wikipedia definition of electric current (SI definition Ampere) is:
In practical terms, the ampere is a measure of the amount of electric charge passing a point in an electric circuit per unit time, with 6.241×10¹⁸electrons (or one coulomb) per second constituting one ampere

When I go to bed tonight, I'll turn off the light and be under the covers before the room goes dark.

K;)

BB.

Re: Is there a 'warm-up' time on solar panels?

Around 63.5 grams of copper is one Mole.

1 Mole of free electrons is Avogadro's constant or 6.02 x 10²³ electrons (making me write this on a phone).

there are about 100,000 Coulombs of free elections in that 2.2 Oz of copper.

There are very expensive particle accelerators that try to get electrons near the speed of light. That is quite difficult and takes a lot of energy to do that.

-Bill

john p

Re: Is there a 'warm-up' time on solar panels?

BB. wrote: »

Around 63.5 grams of copper is one Mole.

1 Mole of free electrons is Avogadro's constant or 6.02 x 10²³ electrons (making me write this on a phone).

there are about 100,000 Coulombs of free elections in that 2.2 Oz of copper.


There are very expensive particle accelerators that try to get electrons near the speed of light. That is quite difficult and takes a lot of energy to do that.

-Bill

It takes 1273 grains of coffee to make one average cup of coffee. Usings Nescafe constant ratio of free grains ............. This was checked by a Tibetan Monk last Ash Wednesday