Solar Performance in the Med

[noelex 77]

Solar panels only have a relatively narrow range of Vmp. Providing the solar controller can work within the range, and this range is above the battery voltage, there is no advantage moving to higher voltage. Unfortunately, the only way of creating higher voltages involves placing more solar cells in series, which increases the shading problems.

Originally Posted by sdj

edit: Voc must be matched to controller-input-max, only so you don't burn the controller out. There is no complicated maths about it.

No, this is very dangerous. Please do not do this.

Voc will be exceeded in cold temperatures and solar levels above 1000 per square metre. Most controllers can protect themselves from excessive current, but will be instantly, and permanently damaged by an input voltage above the maximum rating. You must select a controller with a input voltage comfortably above the Voc rating of the panels.

[sdj]

Originally Posted by noelex 77

Solar panels only have a relatively narrow range of Vmp. Providing the solar controller can work within the range, and this range is above the battery voltage, there is no advantage moving to higher voltage. Unfortunately, the only way of creating higher voltages involves placing more solar cells in series, which increases the shading problems.

No, this is patently incorrect. The entire point of the MPPT controller is to FOLLOW the constantly moving Vmp from the panels under varying lighting conditions. If the panels had a narrow Vmp range, there would be no need for any Vmp power point tracking.

Originally Posted by noelex 77

No, this is very dangerous. Please do not do this. .... Voc will be exceeded in cold temperatures and solar levels above 1000 per square metre. Most controllers can protect themselves from excessive current, but will be instantly, and permanently damaged by an input voltage above the maximum rating. You must select a controller with a input voltage comfortably above the Voc rating of the panels.

Choose a PV arrangement with high as possible Voc that does not exceed the controller input max-rated voltage.

[conachair]

Originally Posted by sdj

If the panels had a narrow Vmp range, there would be no need for any Vmp power point tracking.

Watch the input voltage of a decent MPPT regulator, it doesn't vary much, a few hundred mV can make a significant difference to the power going into the batts.

[sdj]

Originally Posted by conachair

Watch the input voltage of a decent MPPT regulator, it doesn't vary much, a few hundred mV can make a significant difference to the power going into the batts.

Such a casual observation isn't useful.

Under constant and bright solar conditions, yes the input voltage will seem to remain in one place, but if you were designing the system on paper, how would YOU have known that voltage in advance, and HOW would you build a non-mppt system that would use the chosen voltage? Nice to be able to observe it in hindsight, but not possible to select it beforehand.

The real magic of MPPT is under low-light conditions, where a low PV volts PWM system will simply go to sleep, and so will your MPPT system if the Voc is too low.

Unsubscribing

[noelex 77]

Solar panels can still deliver reasonably high voltages at low light levels. However, they cannot deliver any significant current, hence there is no useful power that can be extracted.

Below is a photo showing the output of my (previous) “12v” solar panels. The photo is blurry because the light levels are so low, nevertheless the panels can still produce 18v but with no useful current.

The same wattage of solar panels connected in series would produce more voltage, and less current, but low voltage is not the issue. The solar panel voltage is well above the battery voltage without resorting to series connection even at low light levels.

[skenn_ie]

Choose a panel that has an MPPT slightly above the float-charge Voltage of your battery pack. The situation of needing to match battery voltage to panel voltage WILL change, with better charge controllers. Flyback converters convert electrical energy into magnetic energy, then back into electrical energy. The output voltage is determined by the load, not the input voltage, hence it is determined by the battery voltage, the input voltage now being largely irrelevant.

[StuM]

Originally Posted by sdj

Unsubscribing

Thank you.

[conachair]

Originally Posted by sdj

Such a casual observation isn't useful.

Not a casual obervation but from logging data to a database for many days.

Unsubscribing

Best idea you've had so far about solar.

[CatNewBee]

Main reason for using MPPT and high voltage panels is the smaller current between the panel array and the controller, that means less voltage drop and less losses, smaller, cheaper and more convenient cabling etc., while the high current path from the controller to the battery is very short and can be done with thick adeqate cables. This alone makes a MPPT setup more efficient, besides the effects, that hot solar panes yeld less voltage than cold, and if the difference between Vmp and Vabsorption (not Vfloat) is not sufficient, there will be no significant charge current.

If you have AGM batteries, you need to charge up to 14.8V, with a voltage drop of 0.5V.. 1V along the connections and the long cabling and degraded output voltage due to heat, a 32 cell panel may become inefficient even in bright sun.

So go for 36 cell panels with PWM and at least 40 cell panels with MPPT.

32 cell panels work ok only with floaded lead acid batteries, they need lower absorption voltages, are happy with 14.2V.