250 watt panel with Morningstar SunSaver MPPT 15 AMP controller

[solar.t]

Hi,
Trying to keep costs down could a guy get away with the configuration of a 250 watt panel using a Morningstar SunSaver MPPT 15 AMP controller (model SS-MPPT-15L)?
The battery bank is two Trojan T105s. 3-4 hours charging at 15 AMPS would be plenty for my needs.
Thanks.

[Sunking]

Problem is the maximum panel input for the Sunsaver MPPT is 200 watts with 12 volt battery, and 400 watts @ 24 volt battery. At 250 watts you crossed the line to a 20 amp controller. At 250 watts with MPPT controller is 19 to 20 amps

[solar.t]

Problem is the maximum panel input for the Sunsaver MPPT is 200 watts with 12 volt battery, and 400 watts @ 24 volt battery. At 250 watts you crossed the line to a 20 amp controller. At 250 watts with MPPT controller is 19 to 20 amps

Wouldn't the 250 watts only be under optimum conditions?
Is it hard on the controller to have more watts coming into to it than it was rated for or can the controller handle it?

I don't know if there are any good quality ones in 25-30 amp range.I don't really need the full 20 amps and it looks like a pretty big price jump to go to the next level of 45 amp MPPT controller.

[Sunking]

Do you have the panel already. If not use a 200 watt panel.

[solar.t]

Do you have the panel already. If not use a 200 watt panel.

I have the panel already.

[Sunking]

I have the panel already.

OK you can try the a 15 model, but it is outside my comfort zone. Hopefully the controller will pull down the Vmp to limit the current without shutting down or damage. I have never pushed a controller beyond 10% and you are up to 25%.

[solar.t]

OK you can try the a 15 model, but it is outside my comfort zone. Hopefully the controller will pull down the Vmp to limit the current without shutting down or damage. I have never pushed a controller beyond 10% and you are up to 25%.

I wonder if it really is 25% more. Isn't there a derating that will reduce the current before it reaches the controller? And thanks for your replies.

[solar.t]

After refining my search terms I found the answer from Morningstar. Not only is it acceptable to have a higher wattage input from the array than the specs call for Morningstar recommends doing so. An informative read.

http://www.morningstarcorp.com/en/support/library/MPPT-Primer2.pdf

Q5. Can I use a 240 Watt (60 Cell / Vmp 30V) PV module with a SunSaver MPPT™
controller?

Yes. Even though the SunSaver MPPT™ controller in a 12V system is nominally rated for a 200W PV array, you
can use a larger PV module e.g. a 240W PV module.

• For 12V systems the SunSaver MPPT controller is an acceptable option due to its ability to convert the
module voltage down and charge a 12V battery very effectively.

and more .......


Some of the benefits in exceeding the nominal wattage ratings of an MPPT controller include:

• Effect of maximum charging power limit of a Morningstar TrakStar MPPT controller on an oversized
array:
o Better production early and late in the day.
o Operates at maximum power rating getting full charging potential of MPPT controller more
often.
o Better production during low solar insolation periods (cloudy weather).
o Limits the maximum charging current.

• Viable reasons for using an array rated for a wattage greater than the controller maximum:
o Daily maximum power levels may typically be lower than STC rated power of the solar modules.
Tilt, azimuth angle, time of day or year, weather, climate, dust, pollution and other
factors reduce output power of the array leaving some unused controller capacity.
o Energy harvesting during lower power production periods (cloudy weather) is often more
valued than during times when the array can operate at full power (sunny weather).
o Ability to use larger array sizes for more options to better match strings for the array.
o Using fewer, but high power, modules instead of several smaller ones is more cost effective.
o The availability and lower cost of 60 cell modules (Vmp~30V) from the Grid connected solar
market.
o More consistent levels of charging current (running controller at maximum levels more
consistently).

[FloridaSun]

Some of the benefits in exceeding the nominal wattage ratings of an MPPT controller include:

• Effect of maximum charging power limit of a Morningstar TrakStar MPPT controller on an oversized
array:
o Better production early and late in the day.
o Operates at maximum power rating getting full charging potential of MPPT controller more
often.
o Better production during low solar insolation periods (cloudy weather).
o Limits the maximum charging current.

• Viable reasons for using an array rated for a wattage greater than the controller maximum:
o Daily maximum power levels may typically be lower than STC rated power of the solar modules.
Tilt, azimuth angle, time of day or year, weather, climate, dust, pollution and other
factors reduce output power of the array leaving some unused controller capacity.
o Energy harvesting during lower power production periods (cloudy weather) is often more
valued than during times when the array can operate at full power (sunny weather).
o Ability to use larger array sizes for more options to better match strings for the array.
o Using fewer, but high power, modules instead of several smaller ones is more cost effective.
o The availability and lower cost of 60 cell modules (Vmp~30V) from the Grid connected solar
market.
o More consistent levels of charging current (running controller at maximum levels more
consistently).

THIS is why I have been so hesitant about upgrading my current TS-45 PWM to TS-MPPT-60... or 45? The ability to handle an oversized panel array is making me think a 45 would be better for me, matching it up with L16RE-Bs in the future with their 370Ah rating would give a near C8 charge ability for longer during the day while an MPPT-60 would have to match panel to battery and at times (cloudy) give a lower charge rate. In my location I have to deal with tropical thunderstorms, a regular, almost daily event in summer, morning sun and afternoon cloudy.
ah, no rush for me. I'm happy with my current 580W panels, 200Ah Batt. system for now but always thinking, always planning out my next project.
A question for the experts here... Do all MPPTs have oversize capability or is this only with the Trackstar system? Sure would be nice if CCs were rated to match available battery Ah (or even better, adjustable amp output)... like a TS-MPPT-25 for a 200-225Ah Batt. ...which morningstar doesn't sell.

edit: oh, poorly worded... Trackstar is patented but.. just what is the circuit that limits amperage? Does anyone make an 'add on' to do the job?

[solar.t]

Do all MPPTs have oversize capability or is this only with the Trackstar system? Sure would be nice if CCs were rated to match available battery Ah (or even better, adjustable amp output)... like a TS-MPPT-25 for a 200-225Ah Batt. ...which morningstar doesn't sell.

For what its worth from the end of the PDF file I posted a link to above:

Morningstar’s TriStar MPPT™ & SunSaver MPPT controllers are the only controllers that will always limit the
output current regardless of input power levels. Morningstar’s patented TrakStar Technology is capable of
limiting the output current, while other manufacturers’ MPPT controllers will operate above their maximum
current ratings at higher power levels.

Morningstar’s MPPT controllers can operate with an oversized array that is several times larger than the
maximum Nominal Solar PV ratings, while still limiting the maximum battery current to the controller’s
maximum current rating. Many other MPPT controllers on the market cannot react quickly enough for fast
changes in solar conditions. Even at the published maximum power levels, these controllers are known to exceed
their maximum output current ratings and can trip the overcurrent protection fault shutting off the controller
during high power conditions.

[Sunking]

THIS is why I have been so hesitant about upgrading my current TS-45 PWM to TS-MPPT-60... or 45? The ability to handle an oversized panel array is making me think a 45 would be better for me, matching it up with L16RE-Bs in the future with their 370Ah rating would give a near C8 charge ability for longer during the day while an MPPT-60 would have to match panel to battery and at times (cloudy) give a lower charge rate. In my location I have to deal with tropical thunderstorms, a regular, almost daily event in summer, morning sun and afternoon cloudy.
ah, no rush for me. I'm happy with my current 580W panels, 200Ah Batt. system for now but always thinking, always planning out my next project.
A question for the experts here... Do all MPPTs have oversize capability or is this only with the Trackstar system? Sure would be nice if CCs were rated to match available battery Ah (or even better, adjustable amp output)... like a TS-MPPT-25 for a 200-225Ah Batt. ...which morningstar doesn't sell.

I would not do it because you are just robbing Peter to pay Paul.

Using SolarT example. He has a 250 watt panel with a 15 amp current limit. With say a 5 Sun hour day the panel delivers 1 Kwh to the batteries. However if he had used a 20 amp controller he would have 1.25 Kwh, so he gets short changed. I understand over sizing a panel on a MPPT stretches harvest time, but but we are only talking sun minutes, not hours. Common design practice is to over size 10% PTC rating. SolarT is at 25% robbing himself, meaning he would get substantial more harvest if he used a 20 amp controller.

[FloridaSun]

Even at the published maximum power levels, these controllers are known to exceed
their maximum output current ratings and can trip the overcurrent protection fault shutting off the controller
during high power conditions.

Now that's a bit confusing to me. Does the controller shut down when overcurrent or continue to produce rated current? From all their other points it appears the CC will provide max amps when incoming watts exceed limit. If the controller shut off during mid day at overcurrent it would seem to negate any benefits.

[FloridaSun]

I would not do it because you are just robbing Peter to pay Paul.

Using SolarT example. He has a 250 watt panel with a 15 amp current limit. With say a 5 Sun hour day the panel delivers 1 Kwh to the batteries. However if he had used a 20 amp controller he would have 1.25 Kwh, so he gets short changed. I understand over sizing a panel on a MPPT stretches harvest time, but but we are only talking sun minutes, not hours. Common design practice is to over size 10% PTC rating. SolarT is at 25% robbing himself, meaning he would get substantial more harvest if he used a 20 amp controller.

Yes, having a too small CC would limit panel ability but I was wondering about keeping from exceeding C/8 charge while having panel capacity to produce during cloudy weather. Right now, 11AM DST, an hour before solar noon and all is clear blue sky... but more n likely by 1PM the thunderheads will rise and solar harvest goes way down and it's more than minutes, can continue for the rest of the day. Great for natural cooling effect but not so swuft for charging batteries if needed. When I was using cheapo chinesey MPPTs I never wanted to over rate them but... Morningstar... I might. Panels are cheap and I have room for them. (ha! hope they're still cheap when get around to next project!) I was thinking more of reliable all weather production than getting all the panels can produce.

hahaha! edit, it's 12 noon, 11AM solar time... my dyslexic ADD mind escapes me

[Sunking]

Now that's a bit confusing to me. Does the controller shut down when overcurrent or continue to produce rated current? From all their other points it appears the CC will provide max amps when incoming watts exceed limit. If the controller shut off during mid day at overcurrent it would seem to negate any benefits.

No it does not shut down, goes into current limit at 15 amps.

With a 200 PTC watt panel and 12 volt battery at peak production generates 15 amps on a 15 amp controller (max capacity). A 250 watt PTC panel should produce 20 amps at peak production, bu tif connected to a 15 amp controller will limit at 15 amps robbing you of 25%. With me so far?

What you gain putting a 250 watt panel on a 15 amp controller is a few more minutes of peak production at 15 amps around solar noon, bu tit will not make up for the total loss of loosing 25% for that precious noon peak production at 20 amps.

[FloridaSun]

No it does not shut down, goes into current limit at 15 amps.

With a 200 PTC watt panel and 12 volt battery at peak production generates 15 amps on a 15 amp controller (max capacity). A 250 watt PTC panel should produce 20 amps at peak production, bu tif connected to a 15 amp controller will limit at 15 amps robbing you of 25%. With me so far?

What you gain putting a 250 watt panel on a 15 amp controller is a few more minutes of peak production at 15 amps around solar noon, bu tit will not make up for the total loss of loosing 25% for that precious noon peak production at 20 amps.

but whatabout the max charge rate for an FLA batt. How does it affect battery health if exceeding C/8 for any length of time?