What about the 3% or so cabling losses? That would put the voltage at 13.53v. How do we bulk charge at 13.95v much less 13.53v?
Salvo wrote: Come on, at least do the math right!
18V * (1 - 0.005 * (70-25)) = 13.95V
The PWM system is still looking good! It certainly not going to be much of a difference. In fact, the pwm system is using almost all power available from the panel. The system is operating at maximum efficiency.
pianotuna wrote: Hi all,
"The listed power of a solar cell is the power measured under ideal laboratory conditions, which prescribe a temperature of 25 °C (77 °F). However, on a typical hot summer day, it is not uncommon for a solar cell to reach a temperature of 70 °C (158 °F). A general rule of thumb is that the efficiency of a solar cell decreases with 0.5% for every 1 °C (1.8 °F) above 25 °C (77 °F). This means that on a hot summer day, the efficiency of a solar cell could drop as much as 25%."
Thanks for the link. I don't mean to be talking past your other comments but here is my assessment.
I don't know anything about the the Blue Sky 2000E. You might want to make sure you cannot meet your needs with panel(s) that work with that controller.
I believe you are in the same situation as cruz-in who also has a 230W panel. You should consider the SS-MPPT 15L for that panel as well. Chances are, you will seldom attain the 230W unless you are tilting your panels. This means that you won't waste much, if any, available panel power. In summer, the panels might not see 230 due to panel temp, even if tilted. In any event, the controller cannot be damaged according to the specs.
Come on, read the last line of the quote. 25% loss due to heating is possible. Their numbers of 25c to 70c would represent a 22.5% loss, which is indeed 13.95V. But the STATEMENT is a 25% loss. So my math is just as right as your math.
I was not going to mention this--but you did bump up to 18 volts when the discussion has been centered around 17 volts. If I do 22.5% loss at 17 the output drops to 13.175 volts. Meanwhile a 34 volt panel drops to 26.35 volts.
Salvo wrote: Come on, at least do the math right!
18V * (1 - 0.005 * (70-25)) = 13.95V
The PWM system is still looking good! It certainly not going to be much of a difference. In fact, the pwm system is using almost all power available from the panel. The system is operating at maximum efficiency.
pianotuna wrote: Hi all,
"The listed power of a solar cell is the power measured under ideal laboratory conditions, which prescribe a temperature of 25 °C (77 °F). However, on a typical hot summer day, it is not uncommon for a solar cell to reach a temperature of 70 °C (158 °F). A general rule of thumb is that the efficiency of a solar cell decreases with 0.5% for every 1 °C (1.8 °F) above 25 °C (77 °F). This means that on a hot summer day, the efficiency of a solar cell could drop as much as 25%."
In the OP of that thread, his MPPT system is delivering 102.8W from a 130W panel. Of course it wasn't delivering 130V at 50C, so it's hard to say just how efficient his controller is, but again, as Sal said, it is an early gen model.
I'd be interested to see if it holds up to some of the newer ones, is all.
Cheers,
Kendall
1986 Winnebago Chieftain 22RC
Our Camper (with no payments)
In the OP of that thread, his MPPT system is delivering 102.8W from a 130W panel. Of course it wasn't delivering 130V at 50C, so it's hard to say just how efficient his controller is, but again, as Sal said, it is an early gen model.
I'd be interested to see if it holds up to some of the newer ones, is all.
I'm sorry, but I cannot understand what you are intending to say, and I cannot find the 102.8 figure when I ctl-F for it in that link.
The posts are dtd 8/3/11, long before I began discussing this type of topic here in earnest. I will ask your indulgence in that I will not be reading that link in detail.
I would be happy to address your inquiry, but to do so in a reasonable manner, I will need a little more detailed info to proceed.
Product of the two is how I came up with the wattage.
Hope that helps
I appreciate it, but honestly I don't think there's much to discuss on this. Sal's controller may very well be up to par with a newer unit, but for now we just don't know.
If a newer unit CAN outperform Sal's, then the MPPT benefit that he has come up with (and I support) would have to be adjusted accordingly.
full_mosey wrote:
KendallP wrote:
full_mosey wrote: It is not that there is anything wrong with Sal's controller...
In the OP of that thread, his MPPT system is delivering 102.8W from a 130W panel. Of course it wasn't delivering 130V at 50C, so it's hard to say just how efficient his controller is, but again, as Sal said, it is an early gen model.
I'd be interested to see if it holds up to some of the newer ones, is all.
I'm sorry, but I cannot understand what you are intending to say, and I cannot find the 102.8 figure when I ctl-F for it in that link.
The posts are dtd 8/3/11, long before I began discussing this type of topic here in earnest. I will ask your indulgence in that I will not be reading that link in detail.
I would be happy to address your inquiry, but to do so in a reasonable manner, I will need a little more detailed info to proceed.
"Chances are, you will seldom attain the 230W unless you are tilting your panels. This means that you won't waste much, if any, available panel power. In summer, the panels might not see 230 due to panel temp, "
Concur completely....
you will also have more available power during the lower light periods of the morning and afternoon due to having the larger panel. So overall (throughout the day) a 230 watt panel will perform better than a 200 watt panel with this controller. Given the cost difference (actually in manny cases the 230 is cheaper than the 200) between a 200 and a 230, it seemed the 230 was the logical decision.
It is important to note, you will only waste watts when the panel operates above 200 watts. Which as mentioned on a flat mounted panel (or tilted one for that matter) is extremely rare.
By the way, with a little googling you can get a sharp 230 for much less than $500....
Product of the two is how I came up with the wattage.
Hope that helps
I appreciate it, but honestly I don't think there's much to discuss on this. Sal's controller may very well be up to par with a newer unit, but for now we just don't know.
If a newer unit CAN outperform Sal's, then the MPPT benefit that he has come up with (and I support) would have to be adjusted accordingly.
full_mosey wrote:
KendallP wrote:
full_mosey wrote: It is not that there is anything wrong with Sal's controller...
In the OP of that thread, his MPPT system is delivering 102.8W from a 130W panel. Of course it wasn't delivering 130V at 50C, so it's hard to say just how efficient his controller is, but again, as Sal said, it is an early gen model.
I'd be interested to see if it holds up to some of the newer ones, is all.
I'm sorry, but I cannot understand what you are intending to say, and I cannot find the 102.8 figure when I ctl-F for it in that link.
The posts are dtd 8/3/11, long before I began discussing this type of topic here in earnest. I will ask your indulgence in that I will not be reading that link in detail.
I would be happy to address your inquiry, but to do so in a reasonable manner, I will need a little more detailed info to proceed.
HTH;
John
Got it.
Let me restate my opinion.
Even IF one were to acquire the finest state of the art MPPT controller, one could hardly pick a worse panel than the 17.7Vmp. A 17.7Vmp panel is optimized for 12V PWM battery charging.
In order to hit the sweet spot of an MPPT controller in a 12V bank, each panel should have 24V(2x12V) or above.
There is a transition point between the 17.7Vmp and 24+Vmp where you must switch from PWM to MPPT. To put it another way, the panel's higher Voc will act as crossover point between 17.7 and ? where the panel will exceed the PWM controller's Voc limit.
Once you have exceeded the PWM 25Voc limit, you should start working towards the Voc limits of the MPPT as you select panels.
It is clear to me, that if you have enough money, a high voltage MPPT controller combined with high voltage panels is going to harvest the greatest number of amps for charging the battery bank.
Wiring in series is probably a poor choice--better to select panels that are already high in voltage with diodes between each cell.
In the real world 400 watts of solar derated by 25% to allow for panel heating may provide about 100 amp-hours per day for the RV to use in the summer time.
In those same conditions a pwm controller and 17 volt panels might not fare well at all.
PT, what are these real world conditions? This is important for comparisons.
I have no idea how my two 12v panels 210w total would have done last summer lying flat, but propped up facing South I was getting near 100ah on best days in August. Used a 16a PWM controller. Noon amps were 13amps. Was I not camping in the real world?
So-so days of 50ah being half the best days with 210w, then 420w should have no trouble getting 100ah on so-so days and near 200ah on very good days with 26 amps at noon in August with panels tilted up to the South but without any horizontal tracking.
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