Morningstar’s SunSaver MPPT solar controller with TrakStar Technology™ max panels

South Africa

On the Morningstar’s SunSaver MPPT solar controller with TrakStar Technology™, can I use 2 x 200w Tenesol panels?

Morningstars string calculator says the panels are a 'Optimal Configuration'.

But my supplier (whom I trust, he is cautious and has saved me some expenses to date) says:

If you connect these two panels in Parallel, the total voltage will be 24.4v and that is not sufficient to charge a 24volt bank of batteries.

In Series, the current may bump up to 16.67amps and that is too high for this 15amp controller. I am not saying that it will, but it can certainly go that high, especially if the battery voltages are low.

It is not good to push equipment at its limit, the components will eventually get too hot and burn

He uses a Watt / Volts to get the 16.67amps.

So if anything goes wrong, the 5 year warranty will be voided, unless he is over cautious and the product can actually handle it.

Batteries: 24v 102ah batteries.
Panel Minimum power: 195W
Maximum power: 205W
Voltage at max. power Vpm (V): 26,7V
Current at max. power Ipm (A): 7,5A
Open circuit voltage Voc (V): 32,9V
Short circuit current Isc (A): 8A
Temp range: Lowest 5deg celcius, highest 45deg celcius.

Do I trust MorningStars string connector, or do I trust the local supplier.

BB.

Re: Morningstar’s SunSaver MPPT solar controller with TrakStar Technology™ max panels

Using the MorningStar string calculator for 0C min and 35C max temperatures... Your Voc-cold is ~71.60 volts.

The MS MPPT 15 controllers max array input voltage is 75 volts--So, if you don't see much below 0C, the controller should be fine.

Current wise, the controller can take very high input current/power and will limit its output to 15 amps maximum--So, you will not over stress the controller for that reason (in fact, you can connect this (and many other) MPPT controllers directly to a higher voltage battery bank and they will down convert to a lower voltage battery bank just fine--Just need a fuse/breaker on the Vpanel input for safety/protecting the wiring in the case of a short/failure).

Power wise, you can "cost effectively" power the controller with upwards of:

15 amp * 29 volts battery charging * 1/0.77 panel+controller derating = 565 Watt array "cost effective" maximum array

And a few times a year during the middle of a clear/cool day, it may clip the output current to ~15 amps--But that is fine and you will not lose very much solar production.

If you want to add more panels now or later, there are several 30 amp MPPT controllers out there (MorningStar, Rogue, Midnite) that would also be very good choices.

-Bill

South Africa

Re: Morningstar’s SunSaver MPPT solar controller with TrakStar Technology™ max panels

Thank you BB.

These panels are to provide power for lights, but reading here about MPPT controllers, I need to replace the Phocos CML20 for I seem to not get the max I can get from these panels. Can re-use the Phocos elsewhere.

I hear you re. the other controllers, man I hear you, but I am now so 'gatvol' (have had enough) of these panels, I want to burn them. :grr
Whichever way I turn, I am stuck. If I go bigger, then I need to mix and match panels, plus more costs ito cables, installation ...

But, if my calcs below are right, the controller is the best fit for these panels, then maybe I have the final match. This is what my calcs are saying:
Attachment not found.

BB.

Re: Morningstar’s SunSaver MPPT solar controller with TrakStar Technology™ max panels

I did not mean to poke you with a stick...

I know it is frustrating trying to mix/match equipment and not spend too much time+money doing it. Sometimes, you just make the best of a bad situation and move on.

-Bill :-)

South Africa

Re: Morningstar’s SunSaver MPPT solar controller with TrakStar Technology™ max panels

Not a all, you gave the best advice by far and if I was not stuck with the panels, I would have taken your advices.

As you say, make the best ... there comes a time where one has to sign off on a system, and that time is now way overdue for me on this lights system.

You said:

this (and many other) MPPT controllers directly to a higher voltage battery bank and they will down convert to a lower voltage battery bank just fine

I presume you meant:

this (and many other) MPPT controllers directly to a higher voltage array and they will down convert to a lower voltage battery bank just fine

BB.

Re: Morningstar’s SunSaver MPPT solar controller with TrakStar Technology™ max panels

BB. wrote: »

(in fact, you can connect this (and many other) MPPT controllers directly to a higher voltage battery bank and they will down convert to a lower voltage battery bank just fine--Just need a fuse/breaker on the Vpanel input for safety/protecting the wiring in the case of a short/failure).

No--I actually intended to type this (poor grammar aside).

Many (most, all, some?) good quality MPPT controllers, because they can "control" their output current (and total power transfer) are able to connect directly to a larger (and higher voltage) battery bank and "down convert" to the lower voltage/higher current to charge/maintain that 2nd battery bank.

Solar panels are current mode devices (the available output current is proportional to the amount of sunlight hitting the panel). We are used to connecting solar panels (current source devices) directly (or through a PWM type charge controller) to a battery bank because the solar panels will ultimately limit the maximum current feeding the battery. So (with in reason), it is perfectly save to connect a 20 volts 10 amp solar panel to a 12 volt 100 AH battery bank (and use some sort of charge controller to prevent over charging of the battery bank).

However, you cannot connect a 24 or 48 volt battery bank to a 12 volt battery bank--It is almost like a dead short on the higher voltage battery bank, and the weakest link/component will fail (with lots of smoke and fire).

A MPPT charge controller is capable of current limiting its output (safely/reliably). So you can connect the solar panel input (of, for example, the Morningstar MPPT 15 amp controller) to a 24 or 48 volt battery bank and charge a 12 volt battery bank just fine.

Just like the AC transformer in a car battery charger limits the AC current/power when charging a 12 volt battery--The MPPT controller also limits the current/power from the higher voltage battery bank when charging the lower voltage battery.

It is the (typically) buck mode switching regulator in the MPPT controller (and the negative feed back circuitry/computer control) that allows this to work just fine.

Vs a PWM controller which is (more or less) nothing more than a simply on/off switch (no current limiting ability between Vpanel input and Vbatt output.

The MS 15 amp MPPT controller was specifically designed for down converting 24/48 volt battery bank to 12 (or 24) volt battery bank for charging/maintaining the lower voltage battery bank (say you had a 24 volt battery bank and wanted a 12 volt battery for HAM radio).

-Bill

South Africa

Re: Morningstar’s SunSaver MPPT solar controller with TrakStar Technology™ max panels

Ok, so in a nutshell, if you have a 24v main bank, and a 2nd 12v battery that you also want to keep charged, you can do that with a MPPT controller, T&C's apply, right?

Do you agree with my calcs for the load on the 2 panels and the MS 15 amp MPPT controller?

I really do not want to spend one more sent on this unless it will work. :-)

BB.

Re: Morningstar’s SunSaver MPPT solar controller with TrakStar Technology™ max panels

Yep... Just a DC to DC charge controller that happens to also be a MPPT solar charge controller.

What size battery bank are you looking at? 204 AH @ 24 volts?

With a 400 watt array and 5-13% rate of charge:

• 400 watts * 0.77 panel+controller derating * 1/29 volts charging * 1/0.05 rate of charge = 212 AH @ 24 volt maximum battery bank
• 400 watts * 0.77 panel+controller derating * 1/29 volts charging * 1/0.10 rate of charge = 106 AH @ 24 volt nominal
• 400 watts * 0.77 panel+controller derating * 1/29 volts charging * 1/0.13 rate of charge = 82 AH @ 24 volt minimum "cost effective" for size of array

For heavily cycled batteries, I would suggest 10%+ rate of charge.

For lightly cycle batteries and/or if you have lots of sun, then less than 10% can be OK. (i.e., weekend operation, charge during day, discharge at night).

-Bill

PS: Note in my post #2 above, I forgot to fix my equation--It was missing a "1/" term for calculating the size of a solar array based on MPPT charge controller ratings.

South Africa

Re: Morningstar’s SunSaver MPPT solar controller with TrakStar Technology™ max panels

Excellent.

To sum up then:
a) 24v 204ah battery bank, if heavily cycled, could be an issue for usage is every day.
b) Use a 24v 102ah bank which will charge better, but do not exceed the magic 25% DOD.
c) And before the battery bank exceeds 25% DOD, build another switchover box to swap back to utilities power. :-)
WAY cheaper than more panels / batteries or regularly replacing batteries in the event of maximum lights used for extended periods.

Thank you again BB, it is nice to get realistic expectations here, rather than as before where you THINK you get it, but missed a little calc. :-)

Lessons learned in all of my experiments, for the next newbie:
Number 1: Reduce your load first. That is the easy part!
Number 2: Do NOT buy panels and then try and work it back, you will be disappointed. :-)
Number 3: Decide on the right controller for your reduced load, then get the panels to match the controller.
Number 4: And do NOT buy panels now with intention to get more later ... it WILL bite you ... but, you can be lucky. :-) (read rule 4 again ...)

BB.

Re: Morningstar’s SunSaver MPPT solar controller with TrakStar Technology™ max panels

You can discharge more than 25% per day--It is just you will have less storage for "bad weather" and the batteries will not last as long if they cycled more deeply.

http://www.solar-electric.com/deep-cycle-battery-faq.html

Battery cycle life on the left, depth of discharge on bottom.



If the battery lasts 2,000 cycles with 25% discharge per day, and 1,000 cycles with 50% discharge per day... You can do deeper discharge with 1/2 the battery cost and 1/2 the life... I.e., $300 worth of batteries for 5 years and $150 worht of batteries for 2.5 years.

The cost for batteries will be pretty much the same. And if there is a mistake and you kill the batteries, you will only have 1/2 the batteries to replace (save money). And if you discharge during the day (workshop lights, etc.), you really do not need as large of battery.

-Bill

Cariboocoot

Re: Morningstar’s SunSaver MPPT solar controller with TrakStar Technology™ max panels

Note also that the deeper you discharge a battery the more you have to recharge it. So if the array is balanced for an average 25% DOD it will not necessarily work for recharging in a single day at a greater DOD.

If you plan on 50% DOD daily (even as a max) you will not only sacrifice battery longevity but also you should have a much larger array to bring the batteries back up.

With a 'balanced' 25% DOD/ 10% peak current system if you go to 30% or 40% DOD you may need to conserve power for a day or two to bring the batteries back up to full or run the generator to Bulk them.

Inevitably some 'tweaking' of a system is needed after it is installed and usage patterns become apparent. People who give themselves no margin for error end up disappointed with the performance of their system.

South Africa

Re: Morningstar’s SunSaver MPPT solar controller with TrakStar Technology™ max panels

BB, it makes a lot of sense. Will have to play and see what happens in the real world. I have access to cheap UPS batteries, but if that was not the case ... :-)

As this man says:

Cariboocoot wrote: »

Inevitably some 'tweaking' of a system is needed after it is installed and usage patterns become apparent. People who give themselves no margin for error end up disappointed with the performance of their system.

Been there, done that ... scars, T-shirts, shorts, tekkies, golf balls ... dunnit all, with me getting the wrong end of the stick. :-)

My margin is to be able to auto switch back to the utilities if the batteries cannot be fully re-charged in +-5 hours on a cloudy day if the usage was well managed the night before. If is was badly managed, well then grid here we come.

Saving is over a year by being off the grid with lights for as many months as possible and then some more. :-)

South Africa

Re: Morningstar’s SunSaver MPPT solar controller with TrakStar Technology™ max panels

The real saving is in winter, for summer is a bonus. Let me ask a question from another perspective:

Lets say you have been given the following as a present:
- 2 x 200w Tenesol panels
- MS 15a MPPT controller
- Inverter that has 94% efficiency on 24v
- 102ah batteries (as many as you need for a balanced system)
- And as many LED lights as the system can supply power for at night

How many watts for how many hours would you expect to get from the above parts in a balanced system, to maximize the ROI on 4 hours daylight per day?

Cariboocoot

Re: Morningstar’s SunSaver MPPT solar controller with TrakStar Technology™ max panels

South Africa wrote: »

The real saving is in winter, for summer is a bonus. Let me ask a question from another perspective:

Lets say you have been given the following as a present:
- 2 x 200w Tenesol panels
- MS 15a MPPT controller
- Inverter that has 94% efficiency on 24v
- 102ah batteries (as many as you need for a balanced system)
- And as many LED lights as the system can supply power for at night

How many watts for how many hours would you expect to get from the above parts in a balanced system, to maximize the ROI on 4 hours daylight per day?

Easy.
400 Watt array: end-to-end 800 Watt hours AC around here (4 hours sun). Kiss it goodbye in Winter.
Expect 13 Amps peak charge on a 24 Volt system, works well with the MS 14 MPPT.
Enough to charge 204 Amp hours @ 24 Volts around minimal 6% rate (okay for no-load charging).
At 25% DOD (all nighttime use as per above) maybe 1kW hour AC to work with (+/-).

On the whole not a totally unreasonable system, but would be better with either less battery or more panel because the margin for error is pretty small. One of those cases where you must ask "what happens if I run out of power?"

South Africa

Re: Morningstar’s SunSaver MPPT solar controller with TrakStar Technology™ max panels

Cariboocoot wrote: »

On the whole not a totally unreasonable system, ...

4 hours sun is my benchmark for Cape Town's winter on a non-rainy day. Rainy days, as we have now, can be for a week. :-)
These are the weeks where I save the batteries for when the utilities, and they are warning us the grid is near max (WOW!!! SURPRISE!!!), tend to fail.
Utilities is called Eskom, nickname of Eksdom ('Ek-is-Dom' - I am dumb/stupid.)

One MS15 MPPT controller to be ordered then ... we need to do this experiment. :-)

Cariboocoot wrote: »

... but would be better with either less battery or more panel because the margin for error is pretty small. One of those cases where you must ask "what happens if I run out of power?"

Easy.
Switch back to the grid and if no grid, still easy ... romantic candlelight for SWAMBO ... and if the candles are finished ... time for bed. :-)

South Africa

Re: Morningstar’s SunSaver MPPT solar controller with TrakStar Technology™ max panels

Straight from Morningstar tech department, confirming all that has been said here. Man, I am impressed with them! They always come back.

... if you wire in series, the controller will work fine.

Although at peak output from your panels (which depending upon your location can be very rare) may produce over 15A, this is no problem for the SSMPPT controller. I understand and you are correct that all things being equal it is best not to push components to their operating limit. However, we designed the SSMPPT controller to operate at full output power (we have already taken into account the stress of running at full power indefinitely).

Using the two panels in series will not void your warranty. This controller is able to self-limit how much power it pulls from the solar panels so that if the panels ever had the ability to produce more than 15A, the controller will simply adjust so that it only pulls 15A from the panels.

It is actually fairly common practice to slightly oversize the solar array with an MPPT controller, as would be the case in your system.