I’m adding two additional 12 Volt solar panels to my RV for a total of 600 Watts. I will be wiring the panels in Series. The output from the controller will be feeding a 300 AH 12 V Lithium Battery capable of 200 Amps Continuous Charge.
Living just above the 49th Parallel, we do not get direct sun. What is the likely-hood I would ever see the full 600 Watts at any given time.
The panel Specs are:
Output Power of 200 Watts
Short Circuit Current of 9.62 Amps
Rated DC Voltage of 20.8 Volts
Open-Circuit Voltage of 24.4 Volts
Module Efficiency of 21.5%
I have been told that typical Ohms law does not apply in a solar panel setting (600/12=50 Amps). Therefore, I’m wondering what is the appropriate size MPPT controller, required in my situation (100/30 or 100/50).
I have read, should the 3 panels actually output 600 watts at any given time, a 30 Amp MPPT Controller will cut off any potential greater than the Controllers 30 Amp Output.
If the panels never generate the full 600 watts due to location, conditions, etc… would I get any benefit from installing a 100/50 MPPT Controller?
As all Controllers have a built in safety factor (read 25%) a 100/30 could potentially put out 33 Amps.
The imporannt value is the Voc at low temperature. Usually PV panels generate higher voltage at lower temperature. If you put 4 panels with Voc 24.4V in series, they are likely reach out higher than 100V, which will destroy a MPPT 100/xx. wiht 3 panels in sieres, there should be enough heeadroom to 100V, but check in MPPT calculator.
If you panel is not listed, you can enter the parameters, but you need the temperture voltage coefficient.
According the output amperage:
The MPPT will drive the panels in a power point where they will not execced the MPPTs output rating. The same happens, whenn battery is at 100% SOC and the MPPT throttles the panels to serve current power demand or even to 0W.
No, it won’t. The Victron 100/30 will shut down for any input voltage over 100, and won’t give any more current than 30A. However, this being said, it IS possible to connect more solar on the input than would give the rated current - up to the max Isc limit.
Use the MPPT calculator to set the size of your MPPT.
The mppt calculator has a button to allow 130% overpaneling. Anything above this overpaneling is at your risk, but when panels are situated or fitted in non-perfect manner then its up to you to decide if anything above 130% is suitable.
Ps overpaneling is the wattage of array going into the mppt above its given max input wattage.
Voltage limit is a hard limit and remember to allow temperature coefficient for cold temps.
I don’t know if it was just to scare us technicians but in the Victron Professional training Guy says quite boldly that over voltage WILL destroy the MPPT.
Over voltage CAN destroy an MPPT. What happens is that there is an N Channel FET on the PV input of the MPPT. Once an over voltage situation occurs, this FET is turned on, shorting the PV input. The intention is to protect the MPPT internal circuit. However, if there is too much current available, then this FET will melt and go short circuit, thus rendering the MPPT unit inoperative.
Whilst you can overpanel to a certain extent, You CANNOT over voltage the unit at all. You need to make sure that at the coldest operating temperature, the Voc of the array is <95% of the MPPT’s rated voltage. Panels produce more voltage when cold.
Each MPPT spec has a MAX input current, you also need to make sure that you do NOT exceed that, otherwise internal damage can occur whilst the MPPT is doing power sweeps to determine the max power operating point.
I hope that this explains the safety requirements for correct operation, and only exceed those limits at your own risk - and that of the MPPT going smoke.
Wiring is series has an advantage as it’ll reach +5 V above battery V earlier in the day compared to wiring these panels in parallel.
Assuming an absorption V of 14.4V, the MPPT could theoretically output ~42A into your battery. Hence the suggestion to go for the 100/50.
If the maximum charging capability is not required because of low cycling or other factors like it’s mostly cloudy and the panels won’t reach their maximum available power, you could easily go for the 100/30. The batteries will get charged with a max of 30A. Which at 14.4V = 432W. In this case you would ‘lose’ the theoretical 168W available in your 3 panels. This is called overpaneling and is safe to do.
The nominal rating of a solar panel has been standardised for illumination at 1000W/m^2 and 25C.
Even at 49N, you will get to 1000W/m2 in summer. In the tropics we can get to about 1360W/m^2 on a good day. your 12v panels probably have a Voc of `20.5V, so 3 in series will get to 61.5V. plus a bit for low temperatures - so they fit with any controller with adequate current. The 75V controllers only go to 15A, but you need more than that, so a 100/30 or 100/50 is the available choice.
Thanks Skipper, I wonder if I would even experience that 168 watts lost, that you mention. Low Cycling is a very high probability, events of clouding and shading are often experienced too. In the past we had two 12v Lead Acid Batteries and just the 200 Amp Portable Suitcase and the batteries never got below 3/4 charge. Within a day (2 max) they would be back to full charge.
We do most of our camping in Provincial Parks which are very tree covered. The 3 panels would be lucky to see full sun at the 49th parallel for more than a few hours a day. I have a 200 Watt Suitcase as well and we are constantly moving it to stay in line with the sun best we can.
Two of the three panels on the trailer are parallel to the length of the trailer and located at the front. The third panel is mounted at the rear and adjacent to the length. Does the change in direction of the rear panel effect the performance of the three, when wired in series?
Yes totally agree the 100/30 are 100/50 are the choices in a Series wired array. Here in Canada I’m looking at approx $100 difference (taxes in) in price between the two controllers. Based on Skippers feedback, does it make sense to spend $100 more to potentially pick up 168 watts if even possible.
With all the partial shading and low light conditions that we potentially experience, which wiring array (Parallel or Serial) make more sense, BUT the issue would be replacing the 10 Ga PV wiring in the front wall of the trailer with 8 Ga (assuming that would be required for Parallel). This task would require extensive work.
If wiring in Parallel, am I correct to assume 100/50 is my only choice.
You want to wire in series. The MPPT’s don’t work well at low voltage. If you have partial shading on one module, there are internal bypass diodes to make the series connection work. 10AWG is perfectly adequate for a series connection.
Not sure I would get partial shading on just one panel at any given time. As the sun moves (trailer doesn’t) through out the day, the exposure on each of the three panels will likely change as well.
One thing I forgot to ask, If the 100/30 to 100/50 upgrade costs $100 and we were to gain lets say 25% of the 168 watts lost, would the the right choice be to spend the extra $100 and pickup the 42 watts. The big question I have is, with the 600 watts of panel in my configuration, will I even see 432 watts (max of 100/30)
If I install a 100/30 Controller now, Will the Victron app tell me if I reached the 100/30 limit (432) at peak (sun) on any given point in a day.
If so, I can replace the 100/30 for a 100/50 and see what I truly lost.
If In my situation, there was a real likely-hood I would see at least 432 watts in my area with the 600 watts of paneling, I would without issue spend the extra $100
With 600W of panels I would be surprised if you don’t see peaks of 500 - 550W regularly. You should get to the 600W. Depends if you have inclined or flat mounting. Being able to tilt the modules towards the sun when parked will help a great deal.
Yes, the Victron app will tell you the history - this is retained in the MPPT unit. History gives you yield, max power and voltage together with max / min battery voltage for each day for the last 30 days. I would go for the larger controller, this will run cooler.
I will not use the 100/30 mppt with 600w potential solar input power on a 12v battery as you could exceed the ISC of 35A. I would definitely use the 100/50 bit more money for future expansion