question

sunshine avatar image
sunshine asked

advice re victron 12v system

Hello,

Looking to do the following on a cheap budget for a farm bound friend who is currently burning dinosaurs (geny) at a rate that makes me cringe.

120-130A/hr dc usage at 12V a day


so he likes 12v because he understands it so being a remote farm i want to keep it 12v nominal at the batts.


I can get 175w victron 12v panels locally too was going to wire 3 in parallel down to a dc breaker then to solar regulator. (will make leads esy to follow for him and ill use colour shrink on pv cables so he can easily identify the pos/neg of each panel should he need to remove one as result of damage.



so i was going for

3 x 175 victron mono panels Reference No. SPM041751200

bluesolar PWM yes PWM (remember cheap) sub tropical location too has display and charge his phone via usb thus (Saving $200 over the MPPT this covered the 3rd panel) I figured 525watts via PWM would outperform 350watts via MPPT.

800w victron inverter

360 a/h battery bank

12/30 victron charger

I know its only 3 days carry over only but he must run a stock pump for a few hrs every few days so ive added a victron 12/30 battery charger so when hes burning dinosaurs he can top up bank if required .


so thats back ground for you all

now to my question ... the PWM says 36 cell panels are best used but the 12v victron panels are 72 cell even though they are 12 v ??? are these still suitable ??


Am i silly to use the PWM ..after reading the white paper and everything else I could find it seems that 12v nominal systems are the go right up the 30A limit which will be right on for him. and as said the $200 saved has paid for the additional 175 watts.

cable runs all calculated for less than 3% voltage loss more like 1-1.5% as everything is pretty close together.


all fusing and breakers are dc rated so all covered on the saftey front.


Just that lingering 36 v 72 cell 12v panel question.


I could buy 2nd hand 24v pv panels and the MPPT but after many hre drive to set this up remote Id rather give him good new gear from victron and ensure I he has no issues.


thoughts


Future expansion is not and going to happen .... and 240v ac usage will always be kept to bare minium hence the smaller inverter.


Thanks for reading

victron products
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1 Answer
klim8skeptic avatar image
klim8skeptic answered ·

Hi Sunshine,

I have like a mobile beach shack (truck) that I have fitted out with solar, with a bit bigger array than you are anticipating.

About half of my consumption is for 12v appliances (TV, computer, stereo, lights, water pumps, tiny 10L HWS, phone/laptop/tablet chargers).

A have some 230v ac loads, refrigerator, tiny kettle, tiny hot plate, tiny skillet, microwave, clothes washing machine.

My goal was to us as much free energy (solar) before using LPG, or petroleum.

So far 16 months into my off grid lifestyle, I have not had to plug in, or top up. Gas usage has been 2 x 9kg bottles, mostly for cooking in winter, no petroleum (generator) so far.

My winter solar harvest/power consumption has been between 1.5-2.0 kWh a day (about 120-150 Ah@12v).

Summer solar harvest/power consumption goes up to 2.0-3.0 kWh a day. Extra power consumption over summer goes into the refrigerator, and 230v cooking. (No heating required from gas cooking over summer)

So I have said my system and arrays was a bit larger.

100/50 mppt with 4 x 190w panel. 2S x 2P. Flat orientation.

75/50 mppt with 3 x 190w panel. 3P. E/W orientation.

300 Ah lithium battery.

12/1600/70 multiplus.

A BMV700, Venus gx and a buttload of BMS/battery safety/monitoring stuff.


For your farmers project, I would advise a 100/50, with a full set of panels. Second hand panels are a bargain, just keep an eye on the condition they are in.

I would use an 800w multiplus over the inverter and charger combo, simply based on cost. (providing an 800w unit does what is required)(multiplus's can be a bit funny on generators though)



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sunshine avatar image sunshine commented ·

Thanks for your reply and your truck looks awesome.. on the panel array front did you fuse each panel within the string ..reason i ask is seems that if using a parallel connection of panels 3 or more would require individual fusing ..I was going to use mc4 branch connectors and bring all 3 panels down a to a dc rated 2 pole breaker..


going individual inverter and charger so he can use the charger on other things around the farm and its more geny friendly as you say.


still not sure about the victron 175w being 72 cells..

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klim8skeptic avatar image klim8skeptic ♦ sunshine commented ·

I have been crude with the 75/50 with the 3 x 190w panels. The 3 panels are paralleled on the back, front, and (not shown) cab of the truck.

They are not fused...or dioded...

The series fuse rating for each panel is 15A, well above the 2 x Isc rating of any panel. Should be safe in a failure event.


The SPM041751200 is a 36 cell panel. Blue Solar Panel.

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sunshine avatar image sunshine klim8skeptic ♦ commented ·

thanks mate i see its a 2 string panel of 36 cells.

I really want to give him 3 x 175w 12v panels but all my reading is saying 3 or more parallel panels require individual fusing so the mc4 branch adaptors cant be used. I have many small 12v systems on my property with 3-6 12v panles and ive never fused the panels (not saying this makes it right) just never had an issue I always put a dc 2 pole breaker before the regulator though.


whats your thoughts on just parallel the 3 x 12v panels into a 32A dc breaker then to reg.


I cant find the series fuse rating for the 175w 12v panel


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klim8skeptic avatar image klim8skeptic ♦ sunshine commented ·

but all my reading is saying 3 or more parallel panels require individual fusing so the mc4 branch adaptors cant be used.

It all comes down to the "series fuse rating" for the panel.

The SFR of panels is rated for panels short/reverse current fault capacity. Over the SFR capacity of a panel, the cells/interconnects/connecting cables will start to overheat/smoke/burn.

For a 3 parallel array, 1 panel could go faulty, and the other 2 panels could deliver current (Isc x 2) to it.


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sunshine avatar image sunshine klim8skeptic ♦ commented ·

I ended up going with 2 x 190w panels and will keep the string to the 2 panels for just over 20A @12v nominal . used a very well priced 30A victron PWM and will hook to a 270A/H batt bank . was able to use mc4 adaptors and 4mm .

this system with a 100-150A/h day production in south east Queensland should be more than enough for his lights /pump/inverter for tv set.


When he gets the dc fridge i will add another 2 panels and regulator and 2 more batts for the fridge alone.


2 smaller safer systems with independence from each other.

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klim8skeptic avatar image klim8skeptic ♦ sunshine commented ·

The PWM regulators have different requirements for panel Vmp and Voc. Just keep an eye on that.

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