Am I right or am I wrong

[Snowynorth]

From reading, I understand that I should stay back 15% from maximum inverter PV impute. Where we are -40 in winter is not all that uncommon. I am understanding that I should stay another 15% back from max PV v for winter. Am I understanding this right?
Ya I know it sucks to be me in winter. But then it's not +125 to 130 f in summer either, and that doesn't suck.

Please let me know if I'm on or off base. Thanks

 

[Rednecktek]

You've got the right basic idea, just off a little on the details. Because of the low temperature voltage boost that panels experience the rule of thumb is 15-20% fudge factor based on about -20F which MOST of the time is plenty of headway. On the data sheet/plate for panels should be a temperature coefficient rating or something like that so you can calculate what the voltage boost is based on your area. For -40 (C or F since they're the same for you in Antarctica*) you really need to do the math to figure out a more exact amount of voltage boost to keep below the max VoC limit of the SCC.

The other factor is that it's just good practice to not run devices at 100% load all the time, so under-volting your array helps prevent burnout from constant heavy loads and helps the longevity of the device.

So yes, for most people who have at least 2 seasons (Summer = Warm Rain, Winter = Cold Rain here in Seattle) doing the 20% is usually plenty of fudge factor to account for cold temps AND longevity.

Where you are you'll probably have to get more exact with the math.

*I'm assuming you're in Antarctica and not trying to mount panels to my wife's feet if you're experiencing -40 temps.

 

[Snowynorth]

You've got the right basic idea, just off a little on the details. Because of the low temperature voltage boost that panels experience the rule of thumb is 15-20% fudge factor based on about -20F which MOST of the time is plenty of headway. On the data sheet/plate for panels should be a temperature coefficient rating or something like that so you can calculate what the voltage boost is based on your area. For -40 (C or F since they're the same for you in Antarctica*) you really need to do the math to figure out a more exact amount of voltage boost to keep below the max VoC limit of the SCC.

The other factor is that it's just good practice to not run devices at 100% load all the time, so under-volting your array helps prevent burnout from constant heavy loads and helps the longevity of the device.

So yes, for most people who have at least 2 seasons (Summer = Warm Rain, Winter = Cold Rain here in Seattle) doing the 20% is usually plenty of fudge factor to account for cold temps AND longevity.

Where you are you'll probably have to get more exact with the math.

*I'm assuming you're in Antarctica and not trying to mount panels to my wife's feet if you're experiencing -40 temps.

Actually not far from you in Alberta. We had some brutal cold this December some below -45 before the Windchill.
Can you say "feels like -60" ha. Thanks for the info. Knowing not guessing is in order.

 

[Supervstech]

Panels should have a variance figure for VOC below standard per degree C below 25C then you calculate the variance to your max below, which would be 65C degrees.

Solar panel maximum voltage calculator - How to work out the max voltage

To get the maximum solar panel voltage you should expect from your solar panel, use our solar panel maximum voltage calculator.

gold-coast-solar-power-solutions.com.au

 

[rmaddy]

From reading, I understand that I should stay back 15% from maximum inverter PV impute.

No. This is not true. It's common to over panel by adding more wattage than the maximum.

Where we are -40 in winter is not all that uncommon. I am understanding that I should stay another 15% back from max PV v for winter.

It's important to avoid going over the max PV input voltage which is based on the Voc of the panels. For -40º you should be 20% below, roughly. But you can calculate the exact value based on the max PV input voltage of your solar controller, the Voc of your panel arrangement, and the temperature coefficient Voc of your panels. This will be a value somewhere near -0.3%/ºC.

 

[HRTKD]

From reading, I understand that I should stay back 15% from maximum inverter PV impute. Where we are -40 in winter is not all that uncommon. I am understanding that I should stay another 15% back from max PV v for winter. Am I understanding this right?
Ya I know it sucks to be me in winter. But then it's not +125 to 130 f in summer either, and that doesn't suck.

Please let me know if I'm on or off base. Thanks

Victron has an MPPT calculator that lets you plug in your PV panel specs and your temperatures. It will tell you if you are too close to the limit of the Max PV Input Voltage on days when the temperatures hit rock bottom.

MPPT Calculator - Victron Energy

MPPT Calculator - Victron Energy

www.victronenergy.com

 

[Snowynorth]

Panels should have a variance figure for VOC below standard per degree C below 25C then you calculate the variance to your max below, which would be 65C degrees.

Solar panel maximum voltage calculator - How to work out the max voltage

To get the maximum solar panel voltage you should expect from your solar panel, use our solar panel maximum voltage calculator.

gold-coast-solar-power-solutions.com.au

Thanks that math is within in my scope. I'll read and get it right. The Victron calculator too. I'm not going to take any chances, I'll stay below what the calculations tell me. With 500v max pv impute I should be able to do it without too many strings.

 

[Abodyofscience]

For components that heat up while delivering power [just like humans] I guess wind chill also matters.

Vendor calculators almost certainly oversize. I'm sure HD does for their bundled products.
You could ask for the vendor safety factor or their derating factor, based on expected product lifetime.
Very few people need a 50 year product lifetime.

 

[12VoltInstalls]

calculate the variance to your max

That was what I was going to post
Smart to not crowd the electrical demons that live in our equipment- that way they don’t know anyone else is around.

 

[Abodyofscience]

Re: variance. Assuming a normal distribution, you can dial up if you want 99% reliability, 95%, or 90%. The Zero Risk Bias is. . .well. . .it's a bias.

 

[Supervstech]

For components that heat up while delivering power [just like humans] I guess wind chill also matters.

Vendor calculators almost certainly oversize. I'm sure HD does for their bundled products.
You could ask for the vendor safety factor or their derating factor, based on expected product lifetime.
Very few people need a 50 year product lifetime.

I don’t think so… what makes windchill a thing is evaporation and “feeling” unless it’s raining, windchill wouldn’t be a thing to a panel.

 

[Ozark Tinkering]

I don’t think so… what makes windchill a thing is evaporation and “feeling” unless it’s raining, windchill wouldn’t be a thing to a panel.

So why bother with blowing fans across cooling fins?

 

[12VoltInstalls]

So why bother with blowing fans across cooling fins?

If windchill is a factor of concern then cooling fans are not needed lol

 

[Supervstech]

So why bother with blowing fans across cooling fins?

That is a factor of constant heat output transfer into a cubic foot of air per minute over surface area.

I do see your point, but there isn’t a heat engine producing in play with PV. And even with fans over a radiator… the temp will not drop below the temp of the air. The temp will drop faster, and any heat will be removed faster, but it will not drop below the actual air temp.

Windchill is a human feeling number. Nothing more.

 

[WYtreasure]

So why bother with blowing fans across cooling fins?

18.2 Heat Transfer From a Fin

18.2 Heat Transfer From a Fin

web.mit.edu

To aid in heat dissipation.

 

[Ozark Tinkering]

That is a factor of constant heat output transfer into a cubic foot of air per minute over surface area.

I do see your point, but there isn’t a heat engine producing in play with PV. And even with fans over a radiator… the temp will not drop below the temp of the air. The temp will drop faster, and any heat will be removed faster, but it will not drop below the actual air temp.

Windchill is a human feeling number. Nothing more.

I have to respectfully disagree. If that were the case it would be best practice to lay panels flat to the roof without an airspace behind them.
Generally speaking, solar panels are 36 degrees Fahrenheit warmer than the ambient external air temperature.
When solar panels get hot, the operating cell temperature is what increases and reduces the ability for panels to generate electricity.
I'd rather have a hot and windy day for disapating the buildup of absorbed heat from the sun for generating than a hot and sultry day without a whisper of a breeze.

 

[time2roll]

So why bother with blowing fans across cooling fins?

The fins will never cool below ambient. However they may cool from a higher temperature faster or shed more BTU with the fans blowing. The "wind chill" would be the equivalent temperature needed to shed the same BTU as not having the fans. If the device creating heat can be over chilled there would be a thermostat to turn the fans off. An automobile ICE engine has this function because it likes to run at about 200F.

For the OP: use one of the string calculators to verify the panel meets the specifications of the connected device at low tempuratures.

 

[Snowynorth]

The fins will never cool below ambient. However they may cool from a higher temperature faster or shed more BTU with the fans blowing. The "wind chill" would be the equivalent temperature needed to shed the same BTU as not having the fans. If the device creating heat can be over chilled there would be a thermostat to turn the fans off. An automobile ICE engine has this function because it likes to run at about 200F.

For the OP: use one of the string calculators to verify the panel meets the specifications of the connected device at low tempuratures.

My reference to Windchill was the cold we were feeling. Constantly hoping the furnace doesn't crap out :bad" and thinking of warm sun, palm trees and cold beer "good". . The references here to wind chill are interesting. I'll use the calculator. Thanks

 

[Supervstech]

I have to respectfully disagree. If that were the case it would be best practice to lay panels flat to the roof without an airspace behind them.
Generally speaking, solar panels are 36 degrees Fahrenheit warmer than the ambient external air temperature.
When solar panels get hot, the operating cell temperature is what increases and reduces the ability for panels to generate electricity.
I'd rather have a hot and windy day for disapating the buildup of absorbed heat from the sun for generating than a hot and sultry day without a whisper of a breeze.

You can disagree all you like.

The windchill temp will never be a calculation temp for inanimate objects. Certainly, windy air will cool a device faster than still air, but it will never cool below actual temp unless the device is wet… and below zero C, there isn’t much evaporation occurring… so, for the PV voltage calculation use ambient temp… not windchill.

 

[Ozark Tinkering]

You can disagree all you like.

Nope. I looked stupid enough the first time. Thanks.