best low light performance

Hi BFL13,

I just did email them.

Well the Mono has half an amp higher Isc Is that trivial? I don't understand MPPT. With PWM that half an amp would show up as their difference in max amps at high noon, and I would go for the higher Isc every time. But this is MPPT which makes amps out of thin air.

Does the chosen MPPT controller manual say anything about that? Would that company's tech support have any comment on which panel would be a better performer with that controller? You could email them.

Hi harold,

Did you not read Salvo's post about the Unisolar panels? Or perhaps you did not understand it?

HiTech wrote:

harold1946 wrote:

HiTech wrote:
Mine do the same.

Harold what do you have to back up your claim about efficiency beyond the standard test conditions of strong light? If we are talking efficiency, the relative efficiency from full sun to 50% or less light strength is what is interesting when discussing low light situations. Efficiency in full sunlight is interesting, but moot in low light discussions.

Jim

I have nothing other than the industry standard Tier rating, of which thin film is rated the lowest.
Do you have information to the contraty?

I saw nothing in there other than under standard lab test conditions, not low light.

Do you believe that efficiency would increase under low light or remain the same?

Hi BFL13,

My understanding is that MPPT is at best between about 96 and 98% efficient. I think it drops as voltage rises--but between 31.82 and 29.1 a pretty small range of difference. There would be lower line losses with the 31.82--but again a really tiny difference.

Low light curves not shown for the 245w Poly to compare with those shown for the 240 Mono.

However, note the combo that gets the watts ratings.
A. 31.82v / 7.70a
B. 29.1v / 8.26a

So which one can the MPPT do the most with for creating amps where 240/245w would get you approx 15amps if PWM 12v getting Isc as your rough target?

Does the MPPT like having the higher Vmp and to heck with the lower Imp, or is it the other way around? Or does it care? IMO this is important for how many amps you will get in whatever light conditions.

harold1946 wrote:

HiTech wrote:
Mine do the same.

Harold what do you have to back up your claim about efficiency beyond the standard test conditions of strong light? If we are talking efficiency, the relative efficiency from full sun to 50% or less light strength is what is interesting when discussing low light situations. Efficiency in full sunlight is interesting, but moot in low light discussions.

Jim

I have nothing other than the industry standard Tier rating, of which thin film is rated the lowest.
Do you have information to the contraty?

I saw nothing in there other than under standard lab test conditions, not low light.

harold1946 wrote:

pianotuna wrote:
Hi harold,

Thank you. But I still fail to understand you. And your answer is wrong. Amorphous produce more in lower light than either mono or poly

My question is

Mono or poly. Do not confuse the issue by mentioning Amorphous in any future answer.

I have no doubt you dont understand. :B
My answer is not wrong. How can a less efficient solar grid become more efficient under low light conditions? :@

Is it too confusing for you to understand that Amorphous is the least efficient of the three types?

I would love to see any references that state that Amorphous panels produce more under low light, or become more efficient.

Is there anything that proves solar efficiency is linear with light levels? Seems like a major assumption.

Hi,

I want the highest output at low light levels from the two panels below.

poly 245 watt

or

mono 240 watt

They will have their own controller. Once I walk the roof and measure I'll know how many panels I can fit. There is a possibility of adding one or two more as a "drop down" fastened to the rear of the RV--essentially increasing the total number of panels I can install.

The Unisolar system will remain as it is now on its Blue Sky 3024di controller.

More important than low light conditions is that the different panels have similar output voltage (Vmp) and current (Imp). You're not going to get much power out of an array having large differences in individual Vmp when in parallel, or Imp when in series.

Forget poly vs mono. Look at specs.

Sal

pianotuna wrote:
Hi Salvo,

I plan on populating the rest of my roof with either poly or mono panels. They are the same price, same size, and nearly identical wattage (5 watts difference on the rating).