Solar Panel recommendations please

[MisterSandals]

.26kwh = 260wh
I think this is an AC device so you will need an inverter which will have about 15% loss:
260wh x 1.15 = 299wh

Your 16 cells at 3.2v and 25ah
16 x 3.2 x 25 = 1280wh

At 100% efficiency, you can power your CPAP 1280 / 299 = 4.28 days without recharging.

 

[Mark_B]

Well, that is fantastic news. Thanks so much for the equation.
The next factor is that it will run on 12 volts. And I have another 12v LifePo4 battery bank, so I can still make this one 24v.
Is there a way to figure out what the consumption would be using the 12v input?
Something like the killowatt meter?

 

[MisterSandals]

Is there a way to figure out what the consumption would be using the 12v input?
Something like the killowatt meter?

You could use a DC clamp meter to test the momentary consumption (use rate). Or use a Hall sensor (ferrite ring around a wire) or shunt (inline resistive sensor) with its own monitor to keep track of charge inflow and load outflow for state of charge (and likely momentary use) info.

 

[Mark_B]

An 4P8S 25.6v battery bank is a good power reserve.
A Victron 100/50 is a nice meaty SCC (i have an 100/30 and its great).

How much will it handle? Lets do some math.

You seem to be undecided for panels so lets find some big cheap ones on craigslist (phoenix?):

SOLAR PANELS 330 watts - electronics - by owner - sale

AXIpremium HC BLK 330watts 120 cell monocrystalline High performance solar module German engineered – made for America Axitec-Soft-Grip-Seam aluminum frame Soft Grip Higher stability and easier...

phoenix.craigslist.org

330w for $165 - looks great!

Lets arrange an array to stay below 100v for your SCC.
Solar panel Voc: 40.49 (shown in 4th pic)

We can put 2 of these in series for 81v. This is very good, gives us a little leeway for cold weather which can increase the voltage. 2 in series is 660w.

660w / 25.6v (battery voltage) = 25 amps

2 panels in series connected to 2 panels in parallel would give 1320w and would use your SCC nicely near its charging limits. To be honest, 2x of the 330w panels would make a nice backup system in itself. If you want the max, 4 panels in a 2S2P config is the max usable.

So, locate some panels and see how the Voc works out for building an array to work within 100v SCC and maximize the 50amp (if you want to maximize that is).

Come back when you locate some panels, check back in with a few if you want opinions or want to check the math or array config options.

I snagged some panels yesterday. I picked up 4 of these brand new Grade B panels at about $150 each, made by Mission in TX.

Did I push the limit on my Victron 100/50 too much on these? I hope to build a frame and mount these in the next week.

Specifications:

Rated Power: 385W
Open circuit voltage (VOC): 48.5 V
Max power voltage (VMP): 40.8 V
Short circuit current (ISC): 9.99 A
Max power current: 9.43 A
Maximum system voltage: 1500V UL certified
Fuse Rating: 20 A
IP67 Junction Box with bypass diodes and standard solar connectors

 

[MisterSandals]

Did I push the limit on my Victron 100/50 too much on these?

Yes, the Voc for 2 of those will exceed the 100v input max if the temp drops jus a couple degrees below 25 deg C.
Best you could do is run all 4 in parallel but thats 40amps.
Your connectors and wiring from panels will need to handle this.

 

[Hedges]

I snagged some panels yesterday. I picked up 4 of these brand new Grade B panels at about $150 each, made by Mission in TX.

Did I push the limit on my Victron 100/50 too much on these? I hope to build a frame and mount these in the next week.

Specifications:

Rated Power: 385W
Open circuit voltage (VOC): 48.5 V
Max power voltage (VMP): 40.8 V
Short circuit current (ISC): 9.99 A
Max power current: 9.43 A
Maximum system voltage: 1500V UL certified
Fuse Rating: 20 A
IP67 Junction Box with bypass diodes and standard solar connectors

1540W (STC)

Into your 12V battery, 128A. Way over-paneled for a 50A charge controller.
You said you could make 24V. Then it would be 64A, or 55A as battery reaches 28V. That's reasonable.
Orient the panels in different directions to catch morning and afternoon sun. If a 90 degree angle between panels (e.g. 9:00 AM and 3:00 PM sun), then 0.7x as high a peak current, but more hours of charging.

With 4 panels in parallel, you should put a fuse in series with each. MC4 holders are available. 20A fuse as shown on label is good.
You can use two sets of "Y" connectors, join two pairs of panels in parallel, wire each pair separately back to the charge controller using at least 10 awg cables. 8 awg is also available.

Victron 100/50 data sheet says, "Max. PV short circuit current 60A" so you're good there.

 

[MisterSandals]

With 4 panels in parallel, you should put a fuse in series with each. MC4 holders are available. 20A fuse as shown on label is good.

Yes, good catch, i forgot to add this.

All good ideas.

The Voc of those panels is really unfortunate. If you could return those or get something better suited for input voltage it would make wiring a lot easier and cheaper.

Putting 2 panels eastish and 2 panels westish will widen your charging hours nicely as Hedges suggests.

 

[Hedges]

The Voc of those panels is really unfortunate. If you could return those or get something better suited for input voltage it would make wiring a lot easier and cheaper.

No need to return.

They're fine for a 24V battery.
Too low for single panel to charge 48V battery, too high to connect two in series with a 100V MPPT.

Only for a long run would wire cost matter.
The only issue appears to be that connecting four in parallel with "Y" connectors would exceed rating of MC4. So long as that is avoided, no problem using these panels.
I suggested two sets of 2 "Y" in order to use off the shelf stuff and not need a combiner or other weatherproof box.
My system, I have multiple MC pigtails coming from an outdoor electrical box, where the wires join to 8 awg wires run in conduit.

 

[Mark_B]

I think I could easily get the Victron 150/60. Would that eliminate all the concerns and let me go back to the 2s2p panel connection discussed prior? I shouldn't have trusted the salesman's off the cuff 'yes this will work for your controller' response. :\

 

[Mark_B]

All the suggestions are interesting btw. Makes me think more and understand a bit more.

 

[Hedges]

I think I could easily get the Victron 150/60. Would that eliminate all the concerns and let me go back to the 2s2p panel connection discussed prior? I shouldn't have trusted the salesman's off the cuff 'yes this will work for your controller' response. :\

Yes, that looks like a good fit, can charge either 24V or 48V battery with your panels 2s2p
Then no fuses, just a pair of "Y" connectors and 10 awg or larger cables.
(still not great for 12V battery)

 

[Mark_B]

Yes, that looks like a good fit, can charge either 24V or 48V battery with your panels 2s2p
Then no fuses, just a pair of "Y" connectors and 10 awg or larger cables.
(still not great for 12V battery)

Curious why you say not great for 12v?
The ad shows this:

Victron Energy BlueSolar MPPT 150/60-Tr (12/24/36/48V-60A)​

 

[MisterSandals]

(still not great for 12V battery)

Curious why you say not great for 12v?

I am curious too.
Because he is so over paneled? 1500w into a 12v battery is quite a bit. Will want to throttle down the SCC to reasonable charging amps.

But when the sun is shining, you will definitely be solar rich.

 

[Hedges]

Curious why you say not great for 12v?
The ad shows this:

Victron Energy BlueSolar MPPT 150/60-Tr (12/24/36/48V-60A)​

I snagged some panels yesterday. I picked up 4 of these brand new Grade B panels at about $150 each, made by Mission in TX.

Specifications:

Rated Power: 385W

1540W (STC)

Into your 12V battery, 128A. Way over-paneled for a 50A charge controller.

Because he is so over paneled? 1500w into a 12v battery is quite a bit. Will want to throttle down the SCC to reasonable charging amps.

But when the sun is shining, you will definitely be solar rich.

Precisely.
At least 24V battery, then he can make use of all the PV. Otherwise (if 12V battery), half of it goes to waste (clipped by SCC) except on cloudy days or off-season.

 

[Hedges]

Will want to throttle down the SCC to reasonable charging amps.

If his batteries were AGM, would have to evaluate charge rate vs. amp hours, stay within whatever limit (0.1C, 0.2C?) desired.

He mentioned LiFePO4, which CAN take high charge currents, like 0.5C, but only under some conditions.

As SoC approaches and exceeds 90%, max allowed charge current decreases. I think switching from CC to CV can perform that function, but don't know how well it fits the specs for charge current (which only some battery vendors have published in detail.)

As temperatures get cold approaching 32F, or get hot, maximum allowed charge current also decreases.
If his batteries were 100 Ah, 60A charge current or 0.6C would only be appropriate for a narrow operating range.
If 280 Ah, 0.21C has a wider operating range, but still limited in both temperature and SoC before it causes accelerated degradation of battery life.

 

[MisterSandals]

He mentioned LiFePO4, which CAN take high charge currents, like 0.5C, but only under some conditions.

I needed to read from the top to refresh my memory on all this. So many threads (you too Hedges!).

All this power for a backup system! You're close to powering a smaller air conditioner while the sun is shining.

If Mark_B really gets addicted to solar like the rest of us, his SCC and array will take him to that next level for sure (its not often that a first system will scale up like his setup if he gets the 150/xx Victron with those big beautiful panels).

Still a shame like we see so often with 49 Voc not working perfectly with the Victron 100, 150, 250 voltage product lines.

 

[Hedges]

I needed to read from the top to refresh my memory on all this. So many threads (you too Hedges!).

You're right. Earlier postings identified battery, just 100 Ah as 24V bank.

Solar Panel recommendations please

So I am building 2 12v Lifepo4 battery banks with prismatic cells. I have a Victron 100/50 controller. I'm having a hard time having confidence as far as what total wattage I can set up. I like the mission panels. How many watts can I set up to match my controller?

diysolarforum.com

Check out the links to postings I provided here, on charge rate of LiFePO4

Wiki Entry Review: BMS

I would add mention that an active balancers primary advantage is the ability to move much more charge around than what a passive balancers "burn off" can accomplish.

diysolarforum.com

All this power for a backup system! You're close to powering a smaller air conditioner while the sun is shining.

I understand Victron SCC, together with a battery shunt and perhaps one more device, can regulate battery current to a targeted value while delivering all the current needed for other loads. That would be an ideal way to manage PV array oversized to battery charging requirements. e.g. always charge at 10A or 0.1C, while delivering as much as 60A to DC bus when loads draw 50A (to power that A/C?)

 

[MisterSandals]

I understand Victron SCC, together with a battery shunt and perhaps one more device, can regulate battery current to a targeted value while delivering all the current needed for other loads.

Actually its quite easy to set charging current on the SCC with just the app (no need for anything else).
It appears the charge current setting does not throttle the load output.

 

[Hedges]

Actually its quite easy to set charging current on the SCC with just the app (no need for anything else).
It appears the charge current setting does not throttle the load output.

"Load output", a port on the SCC?
That would be for limited current.

In general, an SCC might have 2kW of panels and DC connection to a battery.
The battery might have a 10kW inverter connected, drawing hundreds of amps at times.
SCC can't know how much of its output current is charging battery vs. being sucked up by the inverter unless battery has a shunt.

I understand Victron ecosystem supports this. I think it is a useful feature when PV array can deliver much more current than battery can accept.

 

[MisterSandals]

SCC can't know how much of its output current is charging battery vs. being sucked up by the inverter unless battery has a shunt.

You’re right, you are way ahead of me!

My SCC throttling was to not violate a BMS during a test (split port with very limited charge current).

I think we are beyond the OP’s backup battery for a CPAP scenario!