Charge Controller Choice

[MBJ]

Hey yall,

I am installing a 1.8 KW system with Renesola 300w panels. 2 strings of 3 wired in series. The panels are about 200 feet from the house, so I have a combiner at the panels and then run 6 gauge wire to the house. I am trying to decide between the midnight 150 and the midnight 200 for the charge controller. At normal temperatures the VOC will be 134 volts, on the coldest possible day in Southern Ohio (-22F) the Voc will be 156.6 and enter HyperVoc mode on the charge controller (if its a 150). Any time under 7 degrees fahrenheit the controller will go HyperVoc. The battery bank is 48 volt lead acid (2 strings of 8 six volt batteries) (360AH). The inverter is 2000w Cotek. I would just bump up to the midnight 200, but I've heard that the larger the difference between the battery bank voltage and the charge controller voltage, the harder the controller has to work.....and consequently, run fans and make a lot of noise. So, do I go with the 150 and not worry about the few winter days or times when it goes HyperVoc? Or do I go with the 200?

Thanks!

-Matt

[littleharbor]

The charge controller will lose a minimal amount of efficiency with higher voltage. You really will benefit from keeping the voltage high due to the distance between panels and batteries. Your open circuit voltage looks fine for 99% of the time the system is running. You'll lose very little output due to hyper voc. Your Vmp on a warm day with your 3s2p will be more in the 105 volt range. Still going to need appropriately sized wire.
To answer your question I would stay with the 150. One thing to consider with the 200 is the smaller max output which is in the 76 amp range. The 150 has a max amp rating of 93 I believe.

[Yet another Yeti]

You might consider to change to 3 strings of 2 panels in series
during the winter months .

Overall 2 panels should supply the charging voltage + 2 to 7 volts ,

since these 300w modules usually have a Vmp of around 32 to 36 ,
and your brand seems to produce 45 Vmp ,

thus 64 V and even 2*44 V from the PV should be enough
to at least deliver 55 V for bulk and float charge .


The inverter works much harder to convert from 134 V down to
55 V , than from 90 V down to 55 V .

[littleharbor]

.

(Quote) Yet another Yeti,
The inverter works much harder to convert from 134 V down to
55 V , than from 90 V down to 55 V .(Quote)





It's a charge controller we are talking about here, not an inverter.

The 134 and 90 volts you are referring to are open circuit voltages. This isn't what the CONTROLLER is stepping down. The Vmp. the controller is dealing with would be something just over 70 volts for two panels in series and something just over 105 volts for three in series. Of course, in cold climates these numbers are going to be a bit higher. As far as the CONTROLLER working "much harder", you are wrong.

Two 24 volt nominal panels in series yields a 48 volt nominal output. This makes no sense when using a MPPT controller in a 48 volt system regardless what time of the year it is.

[Yet another Yeti]

The Rene Solar might be even a 72-cells large panel ...

MODERATOR: He/She has been warned previously about running amok at the keyboard without any clue as to the accuracy of the output.

All postings by Yeti are suspect as to safety and accuracy.

That should make it more a 36 or 48 Volt module ....

Found it on ebay , if allowed ,
advertised as "24" Volt panel .. :
https://www.ebay.com/p/renesolar-300...-mc4/678617131

[littleharbor]

The Rene Solar might be even a 72-cells large panel ...

That should make it more a 36 or 48 Volt module ....

Found it on ebay , if allowed ,
advertised as "24" Volt panel .. :

https://www.ebay.com/p/renesolar-300w-grade-c-poly-solar-panel-72-cell-24v-ul-ce-listed-mc4/678617131

72 cell panels are 24 volt panels. You're pretty new to this solar thing aren't you?

[SunEagle]

The Rene Solar might be even a 72-cells large panel ...

That should make it more a 36 or 48 Volt module ....

Found it on ebay , if allowed ,
advertised as "24" Volt panel .. :

https://www.ebay.com/p/renesolar-300w-grade-c-poly-solar-panel-72-cell-24v-ul-ce-listed-mc4/678617131

On average a "cell" will generate about 1/2 volt. A 72 cell panel on average will have a Voc = 36V rating but in practicality the Vmp is lower and the panel falls into the 24V category.

[MBJ]

Thanks for the responses everyone! I'm gonna order the 150 today.