# Heat in solar panels...

#### Externet

Joined Nov 29, 2005
2,023
Good day.
Sun does warm up solar panels, no doubt. Ambient too. But is heating only product of the solar radiation + environment or the panels themselves add warm up by the current produced ?

In other words; a solar panel that has reached its temperature plateau under the sun while disconnected (no current flowing); It will increase its temperature when connected to a load and current flows, right ?

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#### drjohsmith

Joined Dec 13, 2021
675
I would say
that the cell will self heat , due to current,
BUT the size of the cell,
means the heating from the sun is many orders of magnitude greater,

Also the current flowing from a cell is very low,
my array peaks out at 700 volts DC, for 6 KW,

#### DC_Kid

Joined Feb 25, 2008
963
Any generated heat has to go somewhere. Heat always makes object (mass) temp rise. How much so depends on many factors.

If the object is at a high temp, say 300F by absorbing light and UV energy (aka converting Rf into heat), and then the panel itself generates a smidge more heat, the temp will rise to some # just above 300F. This of course all without any heatsink going on from changing wind (airflow).

#### Ian0

Joined Aug 7, 2020
7,463
I'd wondered that as well.
Bizarrely, my SPICE model which consists of a current source in parallel with a string of diodes does precisely the opposite.
When off load, the current from the current source flows through the diodes. When there is an external load, very little current flows through the diodes.

As a solar cell is about 20% efficient, the current flowing in it represents a fifth of the energy from the sun, so I suspect the difference may be quite small.

#### drjohsmith

Joined Dec 13, 2021
675
I'd wondered that as well.
Bizarrely, my SPICE model which consists of a current source in parallel with a string of diodes does precisely the opposite.
When off load, the current from the current source flows through the diodes. When there is an external load, very little current flows through the diodes.

As a solar cell is about 20% efficient, the current flowing in it represents a fifth of the energy from the sun, so I suspect the difference may be quite small.
I can tell you one thing about a PV array
On a sunny winter day, when air is around freezing , they are very efficient.
on a sunny summer day , they are VERY hot, and in efficient,

ie today, mod winter but sunny, I was generating 4 Kw mid day
middle of summer, I can only get about 5 Kw,

#### DC_Kid

Joined Feb 25, 2008
963
I can tell you one thing about a PV array
On a sunny winter day, when air is around freezing , they are very efficient.
on a sunny summer day , they are VERY hot, and in efficient,

ie today, mod winter but sunny, I was generating 4 Kw mid day
middle of summer, I can only get about 5 Kw,
4kw winter, 5kw summer, that means more efficient in summer?
What about the rest of the system stuff, like controllers, wires, etc. Colder temps on them make them waste less?

#### Ian0

Joined Aug 7, 2020
7,463
ie today, mod winter but sunny, I was generating 4 Kw mid day
middle of summer, I can only get about 5 Kw,
I was told that it was due to the air being clearer in the winter.

#### DC_Kid

Joined Feb 25, 2008
963
I was told that it was due to the air being clearer in the winter.
??
colder and clearer winter sky, means less output?

#### BobTPH

Joined Jun 5, 2013
6,518
Look at the energy in and out. With no electrical load all of the energy must go into heat. With a load, some of it goes to the load, so there ought to be LESS heating. Am I missing something?

Bob

#### Ian0

Joined Aug 7, 2020
7,463
Look at the energy in and out. With no electrical load all of the energy must go into heat. With a load, some of it goes to the load, so there ought to be LESS heating. Am I missing something?

Bob
That's what my SPICE model says, but I'm not sure I believe it.

#### DC_Kid

Joined Feb 25, 2008
963
Look at the energy in and out. With no electrical load all of the energy must go into heat. With a load, some of it goes to the load, so there ought to be LESS heating. Am I missing something?

Bob
With a panel facing the sky, some of the panel is not PV at all. Some incident energy is reflected, some absorbed by non PV parts of the panel. Ambient air temps make the panel hot in summer, even with no load.

With no load, the PV wastes all of the energy that converts via PV process? I thought PV's make volts, and to get power transfer you need a load (amps).

#### BobTPH

Joined Jun 5, 2013
6,518
With no load it does not convert any energy, just like a battery does not convert any energy with nothing connected.

Think of a solar hot water hearing panel with a flow of water to a tank. When the water us flowing, heat us removed from the oanek and transferred to the tank. If the flow stops, the panel will certainly get hotter.

Bob

#### drjohsmith

Joined Dec 13, 2021
675
Re the temperature.
Panels have an efficiency that drops off with rising temprarure.
So my panels , when winter are running at maximum efficiency.
In summer , air is "hot" ,sun has more energy as nearer , better angle , but panels are now very hot . Efficiency drops .

#### Ian0

Joined Aug 7, 2020
7,463
In summer , air is "hot" ,sun has more energy as nearer ,
Pedantry corner:
Perihelion is on 4th January, so sun is only nearer In the summer if you live in the Southern Hemisphere.

#### BobTPH

Joined Jun 5, 2013
6,518
Re the temperature.
Panels have an efficiency that drops off with rising temprarure.
So my panels , when winter are running at maximum efficiency.
In summer , air is "hot" ,sun has more energy as nearer , better angle , but panels are now very hot . Efficiency drops .
I hate to tell you this, but the sun is not closer in the summer.

Is the sun closer in the summer?

Bob

#### drjohsmith

Joined Dec 13, 2021
675
I hate to tell you this, but the sun is not closer in the summer.

Is the sun closer in the summer?

Bob
You are of course right, ish,
as the earth tilts, when the sun is further away in winter, by a portion of the earths diameter
but, any way , it was bad English , as the earth is not in a circular orbit of the sun anyway

the sun mainly in the winter is on more of an angle to where I am
much lower in the sky
so going through much more of the atmosphere,
and the same square meter of radiance of the sun is spread over more of an area of the earth due to the angle,
Obviously all changes as the day progresses,

but we diverge

In winter,
panels are receiving a lot less solar energy,
and air is a lot cooler,
Sun and air resulting in the panels running at high efficiency

In summer
panels are receiving maximum solar energy
but air is hot
sun and air result in the panels running in efficiently

Back to the OT
Id say the heating form the current is minimal compared to the amount of energy absorbed as heat from the sun,

#### BobTPH

Joined Jun 5, 2013
6,518
Back to the OT
Id say the heating form the current is minimal compared to the amount of energy absorbed as heat from the sun,
All of the heat cones from the sun. The current does not produce extra heat. If you read my other posts, the current actually removes heat from the panel, just like water would if you were using a solar hot water panel.

Bob

#### Ian0

Joined Aug 7, 2020
7,463
All of the heat cones from the sun. The current does not produce extra heat. If you read my other posts, the current actually removes heat from the panel, just like water would if you were using a solar hot water panel.

Bob
That must be true, otherwise energy out would exceed energy in, and we’d all get banned for discussing an over-unity device!
Is it something similar to the Peltier effect?

#### BobTPH

Joined Jun 5, 2013
6,518
I am basing my contention on nothing but energy conservation.

Bob

#### Ian0

Joined Aug 7, 2020
7,463
If you take a boring old 1N4001 and connect it to a power supply, there is a Voltage across it and a current through it, and it gets warm due to the power it dissipates V x I.
The solar panel has a silicon diode, and connected to a power supply in the dark, current would flow and power would be dissipated just the same.
Place it in the sun, the voltage across the diode is the same polarity, the current flow is in the opposite direction, therefore the power is negative.