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Solar Panel Temperature Affects Output

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#1 Strider167

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Posted 24 January 2014 - 08:25 AM

Solar Panel Temperature Affects Output – Here's what you need to know

Solar panel temperature is one of the important factors that affects how much electricity your panels will produce. It's ironic – but the more sunshine you get, the hotter the panels get and this in turns counteracts the benefit of the sun.

In some cases the heat factor can reduce your output by 10% to 25% depending on your specific location.

Of course, not all solar panels are affected by heat equally and luckily some do much better at coping with the heat than others. Here's what you need to know.

 

If you look at the manufacturer's data sheet you will see a term called "temperature coefficient Pmax". For example the temperature coefficient of a Suntech 190 W (monocrystalline) solar panel is –0.48%. What this means is that for each degree over 25˚C … the maximum power of the panel is reduced by 0.48%.

So on a hot day in the summer – where solar panel temperature on the roof might reach 45˚C or so – the amount of electricity would be 10% lower.

Conversely, on a sunny day in the Spring, fall, or even winter – when temperatures are lower than 25˚C – the amount of electricity produced would actually increase above the maximum rated level.

Therefore, in most northern climates – the days above and below 25˚C would tend to balance each other out. However, in locations closer to the equator the problems of heat loss could become substantial over the full year and warrant looking at alternatives.

Note:For those of you who want to use their solar panels to charge their RV or boat batteries – you'll will need to make sure that the voltage produced by your panel (under high heat scenarios) will be sufficient to recharge your battery – so it's best to order higher voltage solar panels to offset the temperature losses – and also keep the panels clean for maximum output.

 

Some Solar Cells Respond to Temperature Changes Better than Others

The solar panel temperature affects the maximum power output directly. As solar panel temperature increases, its output current increases exponentially while the voltage output is reduced linearly. Since power is equal to voltage times current this property means that the warmer the solar panel the less power it can produce. The power loss due to temperature is also dependent on the type of solar panel being used.

Typically, solar panels based on monocrystalline and polycrystalline solar cells will have a temperature coefficient in the –0.44% to -.50% range.

 

Amporphous Silicon does a bit better. For example, the Sanyo HIT hybrid cells and bifacial cells, which consist of a layer of monocrystalline silicon covered with a thin coating of amorphouse silicon have a lower temperature coefficient of –0.34% - making them another good choice for people looking for high efficiency solar panels in areas closer to the equator.

The best so far in terms of dealing with high temperatures are the Cadmium Telluride solar panels – with a temperature coefficient of –0.25%. However, while they are good with dealing with temperature changes – they are not as efficient at converting sunlight into electricity.

Newer technologies such as CIGS and some of the 4th generation solar cell technologies being developed show show promise of also being less affected by the temperature – but we have to wait until their datasheets are published to know for sure.

 

Possible Solutions?

Because of the problem of loss of electricity as a result of heat buildup – most installers make sure it is possible for air to flow above and below the solar panels to help keep them cool.

-Try to use light colors under the panels.

-Stay away from black back panels.

-Water cooling - Run your potable water under the panel (maybe in line with solar hot water system) with a heat exchanger.

 

 

Keep the lights on

 


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#2 dustybookend

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Posted 24 January 2014 - 09:15 AM

Note:For those of you who want to use their solar panels to charge their RV or boat batteries – you'll will need to make sure that the voltage produced by your panel (under high heat scenarios) will be sufficient to recharge your battery – so it's best to order higher voltage solar panels to offset the temperature losses – and also keep the panels clean for maximum output.

The above is 100% misinformation and should be ignored.
The panel nominal voltage should be the same as the nominal battery voltage.

#3 Strider167

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Posted 24 January 2014 - 09:54 AM

Note:For those of you who want to use their solar panels to charge their RV or boat batteries – you'll will need to make sure that the voltage produced by your panel (under high heat scenarios) will be sufficient to recharge your battery – so it's best to order higher voltage solar panels to offset the temperature losses – and also keep the panels clean for maximum output.

The above is 100% misinformation and should be ignored.
The panel nominal voltage should be the same as the nominal battery voltage.

 

A charge controller, or charge regulator is basically a voltage and/or current regulator to keep batteries from overcharging. It regulates the voltage and current coming from the solar panels going to the battery. Most "12 volt" panels put out about 16 to 20 volts, so if there is no regulation the batteries will be damaged from overcharging. Most batteries need around 14 to 14.5 volts to get fully charged.

 

So this being said you can use 12v, 24v, 48v or more and the controller will put out what the right charge is for the battery and keeping in a good state of charge. Any good system will have a charge controller.

 

A good controller to get is a Maximum power point tracking (MPPT), More on these later.


Edited by Strider167, 24 January 2014 - 10:33 AM.


#4 dustybookend

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Posted 24 January 2014 - 11:12 AM

A charge controller, or charge regulator is basically a voltage and/or current regulator to keep batteries from overcharging. It regulates the voltage and current coming from the solar panels going to the battery. Most "12 volt" panels put out about 16 to 20 volts, so if there is no regulation the batteries will be damaged from overcharging. Most batteries need around 14 to 14.5 volts to get fully charged.
 
A good controller to get is a Maximum power point tracking (MPPT),


Now you are attempting to change the subject from panel to controller.

However your vague statement 'Most "12 volt" panels put out about 16 to 20 volts' is meaningless.

PV panel outputs of open circuit voltage, short circuit current, max power voltage and current are measured to international specifications.

Please do some research.

#5 Strider167

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Posted 24 January 2014 - 03:27 PM

OK...... The math.

 

In a solar cell, the parameter most affected by an increase in temperature is the open-circuit voltage. The impact of increasing temperature is shown in the figure below.

TEMPER.GIF

The effect of temperature on the IV characteristics of a solar cell.

The open-circuit voltage decreases with temperature because of the temperature dependence of I0. The equation for I0 from one side of a p-n junction is given by;

eq085.png

where:
q is the electronic charge given in the constants page;
D is the diffusivity of the minority carrier given for silicon as a function of doping in the Silicon Material Parameters page;
L is the diffusion length of the minority carrier;
ND is the doping; and
ni is the intrinsic carrier concentration given for silicon in the Silicon Material Parameters page.

In the above equation, many of the parameters have some temperature dependance, but the most significant effect is due to the intrinsic carrier concentration, ni. The intrinsic carrier concentration depends on the the band gap energy (with lower band gaps giving a higher intrinsic carrier concentration), and on the energy which the carriers have (with higher temperatures giving higher intrinsic carrier concentrations). The equation for the intrinsic carrier concentration is;

eq086.png

where:
T is the temperature;
h and k are constants given in the constants page;
me and mh are the effective masses of electrons and holes respectively;
EGO is the band gap linearly extrapolated to absolute zero; and
B is a constant which is essentially independent of temperature.

Substituting these equations back into the expression for I0, and assuming that the temperature dependencies of the other parameters can be neglected, gives;

eq087.png

where B' is a temperature independent constant. A constant ,γ, is used instead of the number 3 to incorporate the possible temperature dependencies of the other material parameters. For silicon solar cells near room temperature, I0 approximately doubles for every 10 °C increase in temperature.

The impact of I0 on the open-circuit voltage can be calculated by substituting the equation for I0 into the equation for Voc as shown below;

eq088.png

where EG0 = qVG0. Assuming that dVoc/dT does not depend on dIsc/dT, dVoc/dT can be found as;

eq089.png

The above equation shows that the temperature sensitivity of a solar cell depends on the open circuit voltage of the solar cell, with higher voltage solar cells being less affected by temperature. For silicon, EG0 is 1.2, and using γ as 3 gives a reduction in the open-circuit voltage of about 2.2 mV/°C;

 

 

(The panel nominal voltage should be the same as the nominal battery voltage.) This is the job of the Charge Controller.

 

 

Keep the lights on



#6 Paul

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Posted 25 January 2014 - 02:03 AM

Strider, where did you get the information in your OP? Is that your own writing, or is it from another source? If so, can you please quote the source? 


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#7 Strider167

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Posted 25 January 2014 - 08:51 AM

Strider, where did you get the information in your OP? Is that your own writing, or is it from another source? If so, can you please quote the source? 

Should have put them in....

http://www.solar-fac...emperature.html

http://pveducation.org/pvcdrom



#8 dustybookend

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Posted 25 January 2014 - 06:40 PM

Strider, if you understood your first post you should realise that since the adverse temperature coefficient is a fact of life, and since the difference between panel technologies is small, then there is nothing to be gained by considering it. Panels of the same nominal output and voltage will have similar o/c, s/c, Pmax characteristics so choice comes down to physical size and cost and perhaps how comfortable one feels with an unknown brand. Every panel I have seen has a white underside and of course should be mounted to permit air circulation.

#9 Paul

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Posted 25 January 2014 - 09:07 PM

Every panel I have seen has a white underside and of course should be mounted to permit air circulation.

 
That's one thing I still don't get here. When they mount solar panels on a roof, they mount them on frames that put them as much as 10cm - 12cm off the roof. WHY? I have no idea.

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#10 dustybookend

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Posted 26 January 2014 - 08:48 AM

 

 
That's one thing I still don't get here. When they mount solar panels on a roof, they mount them on frames that put them as much as 10cm - 12cm off the roof. WHY? I have no idea.

 

It may be just to simplify the mounting frame mechanics.
It may be to ensure a generous clearance for convection/conduction air currents. The panels can be mounted flush with or as a functional part of the roof but the underside temperature would increase significantly (per air temperature under normal roof)unless specific measures were taken to prevent it.





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