Forum Discussion
412 Replies
- Jeez Don, I would have hoped you knew more about solar and would know that video is bogus. I'll leave it up to you to figure out why.
pianotuna wrote:
Hi,
The video does the equivalent of a "perfect conditions" test. It shows about 20% gain. - There are a few that run that high voltage.
My point is that your were cherry picking with your proclaimed 0.2% difference in efficiency. As Wiz says, solar almost never outputs max watts. Low irradiation in the mornings and battery surface charge are the main factors that prevent max current when the batteries are at their lowest SOC.12thgenusa wrote:
How many folks are running an 85-v input? - Hi,
The video does the equivalent of a "perfect conditions" test. It shows about 20% gain.
Gathering real world data is good. But since conditions can't be duplicated it does remain some what anecdotal.
My real world measurements with 4 panels in series/parallel (fixed install, 256 watts total) show 17 amps of production at solar noon with clear skies in June and July (ambient 30 to 40 C) using a Blue Sky 3024di MPPT controller. The panels are 16.5 volts and input voltage to the controller is 33.
Charging starts 30 minutes after sunrise and ends at sunset.
I feel I got lucky. I wish there were an easy way for me to try PWM to see if results would be similar.
The solar system installed price was $2300.00. It has easily paid for itself. - JiminDenver said,
"I believe that as more of us use and report on our solar that we will find that there are different outcomes depending on our choices. Not that anyone is right or wrong as long as their needs are met but rather that a person looking to build can see the differences in the choices and build to their needs. "
Exactly! Real world data, collected in a well documented fashion, for realistic comparison. Things to consider; panel temperature, time of day, battery soc, elevation, panel type, install, etc. But many are not willing to put in the necessary effort. It's easier to just make claims that cannot be easily verified or dismissed. And then there are those who simply will not accept any amount of real world evidence, claiming it's purely anecdotal. Nevertheless, inquiring minds would like to know. CA Traveler wrote:
It sounds like you're trying to compare apples and oranges. Panel wattage is determined in lab conditions and have a variance. Real world conditions involve weather, panel pointing, wiring and controller losses, technology, etc.
It probably goes without saying, most reports on these forums are not exactly scientifically generated. And, yes, there are many variables to be considered. But on the other side of that same coin, it appears there are reports making, thus far, unsubstantiated claims. Add to this, marketing hype by those who marketeer electronics products. Phrases like "up to 50% more" need to be investigated further. Statements like "mppt always outperforms pwm" need to be taken with a rather large grain of salt, it seems, seeing as then the question arises, have those making such claims been diligent to do a scientific inquiry, themselves. And if so, have they been completely honest in their presentation of their findings?
I'm not anti-mppt. In fact, I think the technology is rather impressive. I'm just trying to get to the truth of the matter. Does mppt live up to all the claims? Does it perform better than pwm in all conditions and situations, once one considers heat, voltage, panel type, controller quality, etc.? And on a more personal level, will it give me the best performance when coupled with the particular 12v/140w panels I have? Moreover, when someone suggests I should wire my 12v panels in series and use mppt, do they, in fact, have real world evidence to support their suggestion, or just a belief?- Salvo said,
"You take a fairly large hit when going series. Look at the Rogue 3048 efficiency graph on pg. 43.
At 10A:
the 85V system is 93% efficient
the 51V system is 95% efficient
the 17V system is 97% efficient
That a loss of 0.4A when operating at 85V. 4% loss is significant. When on average, mppt is only 5% better than pwm, you're losing your advantage. I don't see it as a big deal to increase wire size for the 17V system to keep losses at 1%. RV cable runs are so short the cost is insignificant. "
I spent an extra $45 on cabling and connectors to go parallel, including 50' of portability. - I would say that depends on when and where he's getting that 48 amps
Weather, location, flat panels, Battery SOC
I know from my experience, that with flat panels, possiblity full output is not reached until late morning, by that time the batteries have been receiving a charge for several hours and in most cases won't pull on the solar that hard, the only way to see full power from the panels, is too run the microwave from the inverter while the sun is directly overhead
I have done this, but it is not my normal way off doing things
I have seen max controller output, when the morning was over cast or rainy and I did not run the generator and then the sun came out later in the day, the batteries were able to accept a higher charge rate and the sun was high and the sky was clear ..ie.. perfect conditions Salvo wrote:
You take a fairly large hit when going series. Look at the Rogue 3048 efficiency graph on pg. 43.
At 10A:
the 85V system is 93% efficient
the 51V system is 95% efficient
the 17V system is 97% efficient
That a loss of 0.4A when operating at 85V. 4% loss is significant. When on average, mppt is only 5% better than pwm, you're losing your advantage. I don't see it as a big deal to increase wire size for the 17V system to keep losses at 1%. RV cable runs are so short the cost is insignificant.
12thgenusa wrote:
I don't know about other controllers, but Rogue's published efficiency curves show that at a 20 amp output, 17-volt panels to a 12-volt system are about .2% more efficient than 34-volt panels, both right at 96%.
How many folks are running an 85-v input? I thought we were talking about series configuration to produce ~34v input. The greater the difference between input and output, the greater the inefficiency without question. The example was not comparing mppt to pwm, but series vs parallel using mppt. If the example given was truly 44-v input, that is about 1% less efficient than 34-v input.
If a person is only getting 48 amps out of a 960 watt system he has other problems.NinerBikes wrote:
24 V in parallel is 28 to 30V, not 36V.
With a 12V panel, you end up with 14.4 to 14.8V in bulk mode, out of 17.0V for the panel under full load, about 21 to 22 V open circuit.
With 24V panel, you end up 28 to 30 V Open circuit... check the panel specifications for Voc and Imp as well as Vmp... the ratio of the loss is less Voc to Vmp in a 24 volt system.
Depends on the panels. My "24-v" panels are 42Voc and 36Vmp.- You take a fairly large hit when going series. Look at the Rogue 3048 efficiency graph on pg. 43.
At 10A:
the 85V system is 93% efficient
the 51V system is 95% efficient
the 17V system is 97% efficient
That a loss of 0.4A when operating at 85V. 4% loss is significant. When on average, mppt is only 5% better than pwm, you're losing your advantage. I don't see it as a big deal to increase wire size for the 17V system to keep losses at 1%. RV cable runs are so short the cost is insignificant.
12thgenusa wrote:
I don't know about other controllers, but Rogue's published efficiency curves show that at a 20 amp output, 17-volt panels to a 12-volt system are about .2% more efficient than 34-volt panels, both right at 96%.
