Solar panel question...

[myke232]

I want to build a 400 watt system like Will has shown here:

RV Solar Power Blue Prints

Building a vehicle mounted solar power system? Let me help.

www.mobile-solarpower.com

He suggests using 4 100 watt panels. Can I use 2 200 watt panels and get the same results?

 

[JoseAgustinV]

In short therms its the same, but usually the 200w panels has pretty similar voltages compared to 100w panels, and you can add more watts with panels in series without exceeding the the voltage ranges of the SCC.

Also, you have to consider what is the minimum voltage range of your SCC to work properly.

 

[MisterSandals]

That Renogy has an unusually low input voltage which CANNOT be violated:

Max. Solar Input Voltage : 25V

This is why Will has 4x 100w tiny solar panels in parallel. I am a huge fan of using big cheap panels but if you are set on this SCC, you'll have to pay close attention to panel Voc.

 

[myke232]

That Renogy has an unusually low input voltage which CANNOT be violated:

Max. Solar Input Voltage : 25V

This is why Will has 4x 100w tiny solar panels in parallel. I am a huge fan of using big cheap panels but if you are set on this SCC, you'll have to pay close attention to panel Voc.

Would something like these work?

https://www.continuousresources.com...200w-36-cell-12v-nominal-solar-panel-5-busbar

The specs say Voc: 24.335V

 

[JoseAgustinV]

Would something like these work?

https://www.continuousresources.com...200w-36-cell-12v-nominal-solar-panel-5-busbar

The specs say Voc: 24.335V

I can't see the max voltage of the renogy SCC, it just says max voltage = 25V but im not sure which voltage is that on solar panels to compare, i think you could get 2 of these panels then connect in parallel to avoid exceeding the max voltage, but let some1 more experienced to answer.

 

[MisterSandals]

The specs say Voc: 24.335V

No. If it gets colder than 25 deg C, the voltage will increase above the rated Voc. Its something like .2v increase per degree so it would not take much to let the magic smoke out (voltage limits are among the strictest in this sport).

 

[MisterSandals]

Can I make an out of the box suggestion?
Get a separate solar charge controller, something like the Victron 75/15 for $80. That would handle 2 of the 200w panels nicely.

To futureproof, you could get the amazing Victron 100/30 (i have this, its awesome, bluetooth makes it a breeze and fun). Its $225-ish on amazon but worth every penny.

Look on craigslist for some big cheap panels. I know you are likely space limited on your RV (i have 2x 165w panels on a 25' using my Tetris-fu). Maybe you have room for couple bigger panels or a single monster panel.

 

[myke232]

No. If it gets colder than 25 deg C, the voltage will increase above the rated Voc. Its something like .2v increase per degree so it would not take much to let the magic smoke out (voltage limits are among the strictest in this sport).

What is the number/spec that I would need the panels to be to fit within the Max. Solar Input Voltage of 25V?

Get a separate solar charge controller, something like the Victron 75/15 for $80. That would handle 2 of the 200w panels nicely.

To futureproof, you could get the amazing Victron 100/30 (i have this, its awesome, bluetooth makes it a breeze and fun). Its $225-ish on amazon but worth every penny.

Sounds like a good idea. So there no limit on how large the solar charge controller can be in relation to the panels, right?

I like the Renogy one because it looks fairly straightfoward to install as you don't have to wire it to the ingintion, so I think I could handle it. I wonder if this dc-dc charger needs to be wired to the ignition?

https://www.victronenergy.com/dc-dc-converters/orion-tr smart
https://www.victronenergy.com/uploa...Smart-DC-DC-chargers-isolated-250-400W-EN.pdf

 

[MisterSandals]

What is the number/spec that I would need the panels to be to fit within the Max. Solar Input Voltage of 25V?

How cold is the coldest sunny day your panels will be used? That will determine how close to 25v you should get. And, if cutting it close, you should find out the actual panel thermal coefficient.

Have you looked at the Victron Orion (dc to dc, solar too?)? I am not familiar with it but suspect its first rate.

(Sorry, you are ahead of me already!)

 

[MisterSandals]

Do a search on this site for “orion”, lots of results and discussions.

 

[myke232]

How cold is the coldest sunny day your panels will be used? That will determine how close to 25v you should get. And, if cutting it close, you should find out the actual panel thermal coefficient.

I'm not sure... but the 100watt panels would be fine in any temp?

 

[MisterSandals]

I'm not sure... but the 100watt panels would be fine in any temp?

What is the temp coefficient?
What is the Voc?

 

[myke232]

What is the temp coefficient?
What is the Voc?

Thanks man.
I'm not really sure. I was just thinking that instead of using 4 100 panels it would be easier to use to larger panels, so that's why I was considering those 200w panels I linked to earlier.

Here are specs from a 100w panel from renogy...

 

[MisterSandals]

Without the thermal coefficient i could only guess. Based on below .3 to .5.
So using .4
25v-21.6Voc = 3.4v safety margin (danger margin?)

3.4/.4= 8.5 deg C
25(deg C)-8.5 = 16.5 deg C puts it at 25v

The Voc is rated at 25 deg C.

Does Solar Panel Temperature Coefficient Matter?

Your solar panel’s temperature coefficient has to do with the influence that the panel’s temperature has on its productivity. In this post, we will look at exactly what a solar panel’s temperature coefficient is and whether or not you should focus on it when planning your project.

www.google.com

>>
Most solar panels have a temperature coefficient of around -0.3% / °C to -0.5% / °C. For example, SunPower’s solar panels all have a temperature coefficient of -0.37% / °C.

 

[sYfte]

Get a separate solar charge controller, something like the Victron 75/15 for $80. That would handle 2 of the 200w panels nicely.

At 12V, 75/15s are only rated for 220W of PV, and my personal experience puts that closer to 200W. They would be adequate for a 24V system.

 

[myke232]

Can I make an out of the box suggestion?
Get a separate solar charge controller, something like the Victron 75/15 for $80. That would handle 2 of the 200w panels nicely.

To futureproof, you could get the amazing Victron 100/30 (i have this, its awesome, bluetooth makes it a breeze and fun). Its $225-ish on amazon but worth every penny.

How would the Victron 75/15, or even the 100/30 be able to handle 2 - 200 watt panels?
Isn't it 400w of panels / 12v battery bank = 33.3amps? So would I need a SCC that is rated for 40 amps?

 

[MisterSandals]

How would the Victron 75/15, or even the 100/30 be able to handle 2 - 200 watt panels?
Isn't it 400w of panels / 12v battery bank = 33.3amps? So would I need a SCC that is rated for 40 amps?

Yes, you are correct the 100/30 is better sized and that would maximize your 400w solar output. I have the 100/30 (bluetooth HIGHLY recommended!) and absolutely love it. I have 330w of panels connected and mostly see between 15 and 20 amps. Panels are flat on an RV roof.
A larger SCC will in theory, handle more amps, but so will a better quality SCC.

 

[myke232]

Yes, you are correct the 100/30 is better sized and that would maximize your 400w solar output. I have the 100/30 (bluetooth HIGHLY recommended!) and absolutely love it. I have 330w of panels connected and mostly see between 15 and 20 amps. Panels are flat on an RV roof.
A larger SCC will in theory, handle more amps, but so will a better quality SCC.

Cool, but wouldn't the SCC need to be able to handle 33.3 amps? And so I would need one rated at 40 amps?

 

[MisterSandals]

Cool, but wouldn't the SCC need to be able to handle 33.3 amps? And so I would need one rated at 40 amps?

No, the SCC will limit the output to its rating. It only NEEDS to be able to handle the input volts.

If you expect to run an SCC near capacity (amps specifically), i would suggest getting a top tier SCC to handle the heat.
Getting a larger (ya, more expensive) SCC should run a lot cooler.

 

[myke232]

No, the SCC will limit the output to its rating. It only NEEDS to be able to handle the input volts.

If you expect to run an SCC near capacity (amps specifically), i would suggest getting a top tier SCC to handle the heat.
Getting a larger (ya, more expensive) SCC should run a lot cooler.

Oh so it's ok to use the 100|30 then with 400watts of panels (they also have a 100|50).

Top tier as in victron?

 

[Forbisher]

Oh so it's ok to use the 100|30 then with 400watts of panels (they also have a 100|50).

Top tier as in victron?

Input your panel specs to check.

MPPT Calculator - Victron Energy

MPPT Calculator - Victron Energy

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