In over my head

[eastTn noob]

Hey yall, I have a few questions so I'll try one at a time. I have all victron controls (250/100 mc4ve.can charge controller) (multiplus 24v/3000va/70a inverter/charger) 20 Trina solar 260w/30.6v/8.5a panels. 2 eco-worthy dual axis trackers that will hold 5 panels each. Less than 3000w load on 2 24v 200ah lifepo batteries. Now the question, how many panels do I need, and how should they be wired? Thanks in advance for any help!

 

[Hedges]

Get the PV panel specs Voc, Vmp, Isc, Imp from label, also max fuse.
From data sheet, get temperature coefficient of Voc.

Look up coldest temperature ever recorded for your location.

For the charge controller, get MPPT max/min voltage, MPPT start voltage, max allowed PV voltage.
(Minimum voltage may be a function of battery voltage, like 5V higher)
Get max PV input current and max PV short-circuit current.

Links to all data sheets will make it easier for us to help you. But we'll try to have you get the data and calculate string lengths.

You have 20 panels, and trackers to hold 10 of them. Think about where they can mount without getting shade from each other or anything else.

Come up with an estimate of your kWh/day consumption for various months.
The 10 panels of fixed orientation could be tilted to maximize summer or winter production as needed.

 

[eastTn noob]

Get the PV panel specs Voc, Vmp, Isc, Imp from label, also max fuse.
From data sheet, get temperature coefficient of Voc.

Look up coldest temperature ever recorded for your location.

For the charge controller, get MPPT max/min voltage, MPPT start voltage, max allowed PV voltage.
(Minimum voltage may be a function of battery voltage, like 5V higher)
Get max PV input current and max PV short-circuit current.

Links to all data sheets will make it easier for us to help you. But we'll try to have you get the data and calculate string lengths.

You have 20 panels, and trackers to hold 10 of them. Think about where they can mount without getting shade from each other or anything else.

Come up with an estimate of your kWh/day consumption for various months.
The 10 panels of fixed orientation could be tilted to maximize summer or winter production as needed.

Thanks for the response, I will gather the information I have and reply.

 

[eastTn noob]

Ok,panel info. VOC 38.2 ISC 9A VMP 30.6 15a max fuse. Bought them used from santan solar so no data sheet, sorry. -20F record low temp
Charge controller- 245v start 250v max battery +5v min max pv input 250v 70a short circuit. 3 pairs mc4 connector for total of 90a input.
Have figured 2500wh daily. Thanks again.

 

[Hedges]

38.2 Voc x 5s PV string = 191 Voc per string

250V max PV input / 191Voc = 1.308, that's 30% headroom so no worries about cold. If that had been 16% or less, then calculations using temperature coefficient from a Trina data sheet would indicate if it was still safe.

9A per string, should be OK to parallel 2 strings into one input. No fuses needed. Other 2 strings into the other two MPPT inputs.

20 x 260W = 5200W (STC), expect maybe 70% of that under typical best conditions, 3500W.
Check an insolation calculator website, maybe 2 effective hours in January, 7 effective hours in July.
7000 Wh on a sunny winter day, 24,000 Wh in summer. Tilt for winter sun could balance those more. Or maybe you want A/C in the summer.

Seems like plenty for your 2500 Wh requirement.
Just need enough battery for nights and cloudy days.

Really, just 200W average load, 24 hours/day?
Unless you live in a tent with only refrigerator and radio, most of us manage to use much more.

 

[eastTn noob]

38.2 Voc x 5s PV string = 191 Voc per string

250V max PV input / 191Voc = 1.308, that's 30% headroom so no worries about cold. If that had been 16% or less, then calculations using temperature coefficient from a Trina data sheet would indicate if it was still safe.

9A per string, should be OK to parallel 2 strings into one input. No fuses needed. Other 2 strings into the other two MPPT inputs.

20 x 260W = 5200W (STC), expect maybe 70% of that under typical best conditions, 3500W.
Check an insolation calculator website, maybe 2 effective hours in January, 7 effective hours in July.
7000 Wh on a sunny winter day, 24,000 Wh in summer. Tilt for winter sun could balance those more. Or maybe you want A/C in the summer.

Seems like plenty for your 2500 Wh requirement.
Just need enough battery for nights and cloudy days.

Really, just 200W average load, 24 hours/day?
Unless you live in a tent with only refrigerator and radio, most of us manage to use much more.

Thanks for the information, any kind of math just becomes a jumble of numbers in my mind. On the load, I used a off grid worksheet to get that number using the electrical appliances that we have. It may end up slightly higher but we have wood heat, gas range, gas w/h ,all lighting is low voltage (12v) through a separate system. So,I should wire them in series in groups of 5?I assume the 10ga wiring will be fine? Thanks again.

 

[Hedges]

I think the PV panels would wire in series strings of 5.
You can get MC4 extension cables and cut in half to make pigtails that go in SCC, or in junction box if there is a longer home run made of other wire. Where two strings are connected in parallel, 5s2p, you can either get MC4 "Y" connectors or have two pigtails spliced together.

10 awg is allowed for about 30A, actually rated 40A so even derated for temperature or 75 degree terminals it is enough for either single string or two strings in parallel.

Unfortunately, "MC4" aren't all compatible. Only Stabuli actually makes MC4. All the others, may or may not mate to those or other brands reliably; we've had many rooftop fires in the US. Only same brand, or pairs of brands tested together for UL listed, are allowed. Use at your own risk. Some people say to cut off existing connectors and install all new ones of a single brand. The ones I have been OK.

At least if you put all these on ground mounts, a burnt wire is less likely to mean a house fire. Also, RSD (shut down per panel) not required. I think avoiding RSD also means SCC should be mounted somewhere other than the house. RSD is fireman safety.

 

[eastTn noob]

I think the PV panels would wire in series strings of 5.
You can get MC4 extension cables and cut in half to make pigtails that go in SCC, or in junction box if there is a longer home run made of other wire. Where two strings are connected in parallel, 5s2p, you can either get MC4 "Y" connectors or have two pigtails spliced together.

10 awg is allowed for about 30A, actually rated 40A so even derated for temperature or 75 degree terminals it is enough for either single string or two strings in parallel.

Unfortunately, "MC4" aren't all compatible. Only Stabuli actually makes MC4. All the others, may or may not mate to those or other brands reliably; we've had many rooftop fires in the US. Only same brand, or pairs of brands tested together for UL listed, are allowed. Use at your own risk. Some people say to cut off existing connectors and install all new ones of a single brand. The ones I have been OK.

At least if you put all these on ground mounts, a burnt wire is less likely to mean a house fire. Also, RSD (shut down per panel) not required. I think avoiding RSD also means SCC should be mounted somewhere other than the house. RSD is fireman safety.

Okay, thanks so much for your time and patience. I'm going to get to work on this tomorrow. I'll post again when operational or I have a problem.

 

[Hedges]

Double-check voltage and polarity of PV strings with DMM before connecting to inverter or SCC.
(be careful not to touch the probes, which bring out contact beyond the touch-safe connectors.)

 

[eastTn noob]

Double-check voltage and polarity of PV strings with DMM before connecting to inverter or SCC.
(be careful not to touch the probes, which bring out contact beyond the touch-safe connectors.)

I have 5 of my panels on the south facing roof, checked voltage and polarity. Both good (140v on overcast day) my new question is should I get an arc when the battery cables are hooked to the inverter? (I'm currently working on the 2 trackers)

 

[Hedges]

Battery cables to inverter, 48V battery to 0V capacitor will have a capacitor charge surge.
With lead-acid we've generally ignored that. Lithium internal resistance is several times lower, current several times higher. It tends to trip BMS, burn contacts, blow fuse.

Look up "precharge" on the forum. Some sort of resistor to limit current before closing switch or connecting cables.

 

[sunshine_eggo]

38.2 Voc x 5s PV string = 191 Voc per string

250V max PV input / 191Voc = 1.308, that's 30% headroom so no worries about cold. If that had been 16% or less, then calculations using temperature coefficient from a Trina data sheet would indicate if it was still safe.

9A per string, should be OK to parallel 2 strings into one input. No fuses needed. Other 2 strings into the other two MPPT inputs.

99.9% certain this is a single tracker MPPT unit. The strings are paralleled at the unit. I would expect that 4 parallel strings need fusing.

 

[eastTn noob]

99.9% certain this is a single tracker MPPT unit. The strings are paralleled at the unit. I would expect that 4 parallel strings need fusing.

In line on all 4 pos cables? 30a?

 

[Hedges]

You're probably correct.
If it is this one, 35A or 70A total short-circuit current, and 30A per MC4 input, suggests all paralleled.

https://www.victronenergy.com/upload/documents/Datasheet-SmartSolar-charge-controller-MPPT-250-70-up-to-250-100-VE.Can-EN.pdf

In line on all 4 pos cables? 30a?

Yes, or in a combiner box.

The in-line MC4 fuses aren't touch-safe when opened, but the MC4 are touch-safe, so disconnect in appropriate order.

Seems to me you could never get an MC4 fuse holder that forms a UL listed pair with the PV panel cables. Easier to accomplish with matching MC4 pigtails into a box.

 

[eastTn noob]

You're probably correct.
If it is this one, 35A or 70A total short-circuit current, and 30A per MC4 input, suggests all paralleled.

https://www.victronenergy.com/upload/documents/Datasheet-SmartSolar-charge-controller-MPPT-250-70-up-to-250-100-VE.Can-EN.pdf

Yes, or in a combiner box.

The in-line MC4 fuses aren't touch-safe when opened, but the MC4 are touch-safe, so disconnect in appropriate order.

Seems to me you could never get an MC4 fuse holder that forms a UL listed pair with the PV panel cables. Easier to accomplish with matching MC4 pigtails into a box.

Thanks again, I will check out precharge. And thanks to you sunshine eggo,you guided me back in February when I was still acquiring my equipment.

 

[pvgirl]

Just note with 20 230watt panels is most likely way too much for a 100a charger on a 24 volt system. You have 4600 watts of solar and maybe 2600 watts of change controller capacity. You might want to consider using less panels or another charge controller.

 

[sunshine_eggo]

Just note with 20 230watt panels is most likely way too much for a 100a charger on a 24 volt system. You have 4600 watts of solar and maybe 2600 watts of change controller capacity. You might want to consider using less panels or another charge controller.

Depending on absorption voltage, peak output of the 250/100 on a 24V system is 2900W.

If the goal is to get full harvest, yes. Additional controllers may be warranted. Use of 2 axis trackers will also render the 100A insufficient, but it will put out that 100A for a large portion of the solar day.

Victron is very liberal with their over-paneling allowance. One merely needs to respect the Voc and PV input current limit. When challenged they say this really doesn't matter that much if you don't care about reverse polarity protection.

The 250/100 has a 70A PV input limit (this is influenced by the MC4 connectors), so regardless of battery voltage, it can readily handle...

180Vmp * 60A = 10,800W (using 2X MC4 connectors at 30A limit each)

This may be useful in cases of inclement weather, poor insolation or opportunistic panel facing, i.e., E, S and W facing arrays.

Supporting data:

Matching solar modules to MPPT charge controllers - Victron Energy

Life used to be so simple; in a 12V battery system you took a ‘12V’ solar module, watched carefully that the maximum PV current would not exceed the charge controller maximum current and the system would work. Unfortunately due to the fact, that with PWM controllers the PV module is not feeding...

www.victronenergy.com

Limits to Oversizing a PV array

How to determine by how much you can oversize a PV array? This can be done with help from the spreadsheet tool. Here though is the manual explanation of how it is done.

There are two limits, when determining the maximum array size that can be connected to an MPPT:

1. The Maximum PV open circuit voltage (Voc at STC)
2. The Maximum PV short circuit current (Isc at STC)

Both values are specified in the datasheets of all our MPPT Solar Charge Controllers. Those two ratings of the PV array must not exceed these MPPT limits.

Note that these two maximum ratings must not be multiplied to determine the maximum installable peak power. Instead, each of them needs to checked by itself:

 

[Hedges]

Or different orientations for different strings, which are then wired in parallel.
Two strings SE, two strings SW, if they have about 90 degree angle between them, about 0.7 times the peak wattage.
That 4600W of PV would then be about a perfect fit for 2600W of SCC.

Oh, right. Trackers? They accomplish similar with more complexity, unreliability, cost.
The extra panels will be helpful on overcast days, anyway. But additional SCC if you want all power on sunny days.

 

[eastTn noob]

Or different orientations for different strings, which are then wired in parallel.
Two strings SE, two strings SW, if they have about 90 degree angle between them, about 0.7 times the peak wattage.
That 4600W of PV would then be about a perfect fit for 2600W of SCC.

Oh, right. Trackers? They accomplish similar with more complexity, unreliability, cost.
The extra panels will be helpful on overcast days, anyway. But additional SCC if you want all power on sunny days.

I'm hoping the amount of power I get will be sufficient. I'm going on with the 2 trackers and 2 sets of fixed. Only way to know. Once again y'all blow me away with your math skills. Thanks so much. Hopefully let you know by next weekend.

 

[eastTn noob]

Update, I now have 1 tracker assembled and operating for a total of 10 panels. 5 fixed, 5 on the tracker. Fridge has been running for 5 days and I still achieve float status by noon every day. Planning to have second tracker operational this week. I feel good about the system and the amount of power. I would like to thank you all again for the help and patience. Really don't think I could have done it without your assistance. Thanks Hedges, sunshine eggo, pv girl.