higher voltage MPPTs are more efficient?

[scrubolio]

I'm a total noob, and would appreciate any comments on this.

I am figuring out which charge controller to use and came across these two from Victron.

Smartsolar MPPT RS 450/100 versus Smartsolar MPPT 250/100 Tr. (both spec sheets are attached below)

For example when I use the Victron MPPT calculator with REC Alpha Alpha Pure Series 405 watt panels (spec sheet attached below)

The MPPT RS 450/100 can handle a max of 8s2p = 16 panels

The MPPT 250/100 Tr can handle a max of 4s9p = 36 panels

Questions/comments/issues:

1. Can someone please explain to me why the MPPT 250/100 is able to intake so much more power but can only output 100 amps? And why is this beneficial or not beneficial versus the MPPT RS 450/100 which uses less than half the panels yet can output the same 100 amps?
2. Is the MPPT 250/100 not as efficient at converting the power?
3. Running wires, fuses, fuse holders, etc for 8s2p seems to be a lot less work than 4s9p and much cheaper. after listing out all the additional parts necessary, the MPPT RS 450/100 comes out to being cheaper.
4. Any other comments would be much appreciated.

Thanks for the help.

Spec sheets and more are attached below:

REC Alpha Pure Series 405 watt


MPPT RS 450/100 spec sheet (middle column), w/ MPPT calculator screenshot


compared to MPPT 250/100 Tr spec sheet (right most column), w/ MPPT calculator screenshot

 

[Bud Martin]

How did you come up with using thirty-six 405W panel configured as 4s9p for the 250/100?
405W x 36 = 14580W of power.

The RS 450/100 has dual MPPT inputs, so 8s2p per MPPT input? How does it come up with 8s2p?

 

[Doggydogworld]

The 450/100 has two MPPT inputs. Each can handle 20A short circuit current. Isc for your panels is 10.30, so two in parallel would be 20.6A, more than the limit. Thus you end up with 8S1P on MPPT1 and 8S1P on MPPT2.

The 250/100 can handle up to 70A Isc. I don't understand why it says 9P is ok. That's 92.70A Isc, way above the spec. 4S6P should be the max.

4S6P is still 24 panels vs. only 16 for the 450/100. Higher current capability offsets the lower voltage. But I don't understand why their calculator says 4S9P is OK.

 

[Ellcon123]

You haven't stated battery voltage? That will determine overall power. If you had a 100A DC output model using 48V then max power is nominally 4800W. Anything over 5000W of solar is wasted.

 

[sunshine_eggo]

I'm a total noob, and would appreciate any comments on this.

I am figuring out which charge controller to use and came across these two from Victron.

Smartsolar MPPT RS 450/100 versus Smartsolar MPPT 250/100 Tr. (both spec sheets are attached below)

For example when I use the Victron MPPT calculator with REC Alpha Alpha Pure Series 405 watt panels (spec sheet attached below)

The MPPT RS 450/100 can handle a max of 8s2p = 16 panels

The MPPT 250/100 Tr can handle a max of 4s9p = 36 panels

Questions/comments/issues:

1. Can someone please explain to me why the MPPT 250/100 is able to intake so much more power but can only output 100 amps? And why is this beneficial or not beneficial versus the MPPT RS 450/100 which uses less than half the panels yet can output the same 100 amps?

MPPT have limits and a goal with their design. The 250/100 (I have one) has a 250Voc limit a 70A Isc limit and a 100A output limit. The circuitry and components used define these limits. It's intended to be used as a typical off-grid MPPT. Staying under the Voc and Isc limits, one could hang about 13kW of 6S 60 cell panels; however, the MPPT would never output more than 100A.

The 450/100 is designed for high voltage/low amperage strings and would be the ideal choice for long PV wire runs. It has a 100A output and 2X 450Voc/20A PV inputs. Staying under the Voc and Isc limits, one could hang about 14kW of 9S 72 cell panels; however, the same 100A limit applies.

1. Is the MPPT 250/100 not as efficient at converting the power?

No. This isn't about efficiency. It's about design intent. They are intended for different uses.

1. Running wires, fuses, fuse holders, etc for 8s2p seems to be a lot less work than 4s9p and much cheaper. after listing out all the additional parts necessary, the MPPT RS 450/100 comes out to being cheaper.

Depends on the length of run and the components selected. MC4 fuses can just be used in each string, require no holders and are relatively inexpensive, or maybe you want to do a combiner box.

1. Any other comments would be much appreciated

To answer your Subject question, "no."

Higher MPPT voltages typically result in LOWER efficiency. Datasheets list a maximum, but the parameters are never specified, so it can be misleading. Fortunately for inverters, a little more is known. When you see an INVERTER efficiency of 95% max, what that typically means is that the inverter is 95% efficient at about 30% of rated power. Below that, the efficiency tapers off dramatically. My Quattro 48/5K is only about 65% efficient at 100W. It also tapers off to about 85% at max continuous.

MPPT are most efficient at about 1.5X system voltage. For every system voltage increment, you see about a 1% drop in efficiency. Example:

48V max MPPT efficiency is about 72Vmp
At 120Vmp, -1%
At 168Vmp, -1%, etc.

In the case of long wire runs, the reduction in wiring losses more than offsets the efficiency losses.

So, if you're mounting on your roof or an adjacent ground mount, a 150/100 or 250/100 may be the more logical choice. If you're connecting to an array a couple hundred feet away, the 450/100 is likely the better choice.

 

[scrubolio]

How did you come up with using thirty-six 405W panel configured as 4s9p for the 250/100?

405W x 36 = 14580W of power.

The RS 450/100 has dual MPPT inputs, so 8s2p per MPPT input? How does it come up with 8s2p?

ahh yes the RS 450/100 has 2 trackers, so 8s2p per input with 2 inputs would be 32 panels. thanks for catching my mistake. so the potential panel count per controller is relatively the same based on their calculator. 32 panels vs 36

The 450/100 has two MPPT inputs. Each can handle 20A short circuit current. Isc for your panels is 10.30, so two in parallel would be 20.6A, more than the limit. Thus you end up with 8S1P on MPPT1 and 8S1P on MPPT2.

The 250/100 can handle up to 70A Isc. I don't understand why it says 9P is ok. That's 92.70A Isc, way above the spec. 4S6P should be the max.

4S6P is still 24 panels vs. only 16 for the 450/100. Higher current capability offsets the lower voltage. But I don't understand why their calculator says 4S9P is OK.

I think the calculator was going off of the Impp as opposed to the Isc. but going over a bit in amps seems to be "ok" based on Victron's own presentations (about 20-30%).

You haven't stated battery voltage? That will determine overall power. If you had a 100A DC output model using 48V then max power is nominally 4800W. Anything over 5000W of solar is wasted.

sorry, 48v battery bank.

So, if anything over 5000w of solar is "wasted" what is the point of connecting a potential 405w * 32 panels = 12,960 watts of panels? I understand those are under optimal conditions, but even if they output 7000 watts, isn't the extra 2000 watts just clipped off and wasted? I assume I'm thinking about the power curve wrong.

 

[scrubolio]

MPPT have limits and a goal with their design. The 250/100 (I have one) has a 250Voc limit a 70A Isc limit and a 100A output limit. The circuitry and components used define these limits. It's intended to be used as a typical off-grid MPPT. Staying under the Voc and Isc limits, one could hang about 13kW of 6S 60 cell panels; however, the MPPT would never output more than 100A.

The 450/100 is designed for high voltage/low amperage strings and would be the ideal choice for long PV wire runs. It has a 100A output and 2X 450Voc/20A PV inputs. Staying under the Voc and Isc limits, one could hang about 14kW of 9S 72 cell panels; however, the same 100A limit applies.



No. This isn't about efficiency. It's about design intent. They are intended for different uses.



Depends on the length of run and the components selected. MC4 fuses can just be used in each string, require no holders and are relatively inexpensive, or maybe you want to do a combiner box.



To answer your Subject question, "no."

Higher MPPT voltages typically result in LOWER efficiency. Datasheets list a maximum, but the parameters are never specified, so it can be misleading. Fortunately for inverters, a little more is known. When you see an INVERTER efficiency of 95% max, what that typically means is that the inverter is 95% efficient at about 30% of rated power. Below that, the efficiency tapers off dramatically. My Quattro 48/5K is only about 65% efficient at 100W. It also tapers off to about 85% at max continuous.

MPPT are most efficient at about 1.5X system voltage. For every system voltage increment, you see about a 1% drop in efficiency. Example:

48V max MPPT efficiency is about 72Vmp
At 120Vmp, -1%
At 168Vmp, -1%, etc.

In the case of long wire runs, the reduction in wiring losses more than offsets the efficiency losses.

So, if you're mounting on your roof or an adjacent ground mount, a 150/100 or 250/100 may be the more logical choice. If you're connecting to an array a couple hundred feet away, the 450/100 is likely the better choice.

Thank you for the detailed explanation.

I forgot about inline fuses, I was going to go with PV fuse holders but the inline ones will definitely cut down on wiring costs by a significant amount by fusing and parallel-ing the strings near the panels.

thus at 450V, the MPPT RS would technically be roughly -8% (~456v) efficient than an MPPT running at 72V.

how many panels are you running on your 250/100? Would it be wise to not "fill out" the MPPT with the max number of panels possible? I assume this would depend on one's location & panel setup.

to summarize (please correct me):

1. Longer length runs from MPPT to panels would benefit from a higher voltage MPPT
2. The most efficient would be shorter runs with an MPPT controller around 1.5x system voltage

Thanks again to everyone!

 

[sunshine_eggo]

Thank you for the detailed explanation.

I forgot about inline fuses, I was going to go with PV fuse holders but the inline ones will definitely cut down on wiring costs by a significant amount by fusing and parallel-ing the strings near the panels.

thus at 450V, the MPPT RS would technically be roughly -8% (~456v) efficient than an MPPT running at 72V.

Your operating voltage on a 450Voc unit is likely to be no higher than 380V, so your 8% calculation is likely closer to 5-6%.

how many panels are you running on your 250/100? Would it be wise to not "fill out" the MPPT with the max number of panels possible? I assume this would depend on one's location & panel setup.

I'm only partially deployed, but this will be a 3S6P array of 330W panels. I will likely eventually expand to include two 3S strings of 285W panels with one facing due East and a second due West (same Voc/Vmp as 330W, lower current). This will result in a 3S8P array totaling 7650W against the MPPT's max output of 5800W.

to summarize (please correct me):

1. Longer length runs from MPPT to panels would benefit from a higher voltage MPPT
2. The most efficient would be shorter runs with an MPPT controller around 1.5x system voltage

Yep.

 

[cs1234]

@scrubolio

Please be careful hooking up a string of panels at 200-400vdc. Make sure you familiar with DC ARC faults and DC cabling and fusing requirements first.

 

[Charleswgibbs]

So, if anything over 5000w of solar is "wasted" what is the point of connecting a potential 405w * 32 panels = 12,960 watts of panels? I understand those are under optimal conditions, but even if they output 7000 watts, isn't the extra 2000 watts just clipped off and wasted? I assume I'm thinking about the power curve wrong.

Having a higher powered array, even if peak power is wasted, will output max power for a longer period of time, so in total more kWh a day even though the peak is being clipped.

If your max charge rate is 5000w but you have 7000w of potential panel output you'll reach 5000w earlier and maintain it longer than if you only had 5000w of output. It will also bring in more on days with bad weather compared to a smaller array.

 

[sunshine_eggo]

Having a higher powered array, even if peak power is wasted, will output max power for a longer period of time, so in total more kWh a day even though the peak is being clipped.

If your max charge rate is 5000w but you have 7000w of potential panel output you'll reach 5000w earlier and maintain it longer than if you only had 5000w of output. It will also bring in more on days with bad weather compared to a smaller array.

clipping:

Solar Charge controller, how many amps?

I want to install 600 watts of solar on my van. After performing a basic calculation of 600/12 = 50, it seems that I would need at a minimum a 50 amp charge controller. I am a little confused as I am looking at starter kits from Grape solar and Rich solar 3 X 200-watt panels with only 40 amp...

diysolarforum.com

 

[SignatureSolarJames]

Higher DC differential= more losses

best efficiency: low voltage by about 2%

Other things to consider: wire loss, Wire cost, the need for durn combiner boxes. my opinion is 500V/450v or bust

 

[cs1234]

Give me 450-500vdc or give me death!

Don't forget to pick up one of these, they are only $3.

 

[Bud Martin]

BTW, I notice something about the spec of the 450/100 and 250/100.
The 450/100 shows start-up Voltage of 120V and MPPT Voltage range of 80 ~ 450VDC
The 250/100 shows start-up Voltage of 245VDC and does show MPPT Voltage range, the 245VDC stat-up does not look right at all.

 

[sunshine_eggo]

BTW, I notice something about the spec of the 450/100 and 250/100.
The 450/100 shows start-up Voltage of 120V and MPPT Voltage range of 80 ~ 450VDC
The 250/100 shows start-up Voltage of 245VDC and does show MPPT Voltage range, the 245VDC stat-up does not look right at all.

It says "maximum" implying it won't start at 246-250V

SmartSolar standard MPPT criteria:

+5V above battery to start
MPPT throughout the operating range provided PV is +2V above battery.

 

[Bud Martin]

"The 450/100 shows start-up Voltage of 120V and MPPT Voltage range of 80 ~ 450VDC"
So what is this 120V start-up Voltage is referring too? I thought for this one it needs 120V from PV to get the MPPT to startup then once it starts the PV Voltage can go lower than the start Voltage.
I know Victron and most SCC only need to see +5V above the battery to start.

 

[sunshine_eggo]

"The 450/100 shows start-up Voltage of 120V and MPPT Voltage range of 80 ~ 450VDC"
So what is this 120V start-up Voltage is referring too? I thought for this one it needs 120V from PV to get the MPPT to startup then once it starts the PV Voltage can go lower than the start Voltage.
I know most SCC only need to see +5V above the battery to start.

Sorry, I was just responding to the 250/100.

The 450/100 criteria are different than the Blue/SMartSolar units. Much higher Voc to start, maintains MPPT down to 80V. Possibly won't charge at all below 80Vmp.