Salvo wrote:

Here's some more corrections on the solar portion of the article.

1. Each cell generates approximately .5 watts, so you’ll need two cells to generate a single watt of DC.

Each cell generates about 0.5 VOLTS not watts. The 135W Kyrocera panel has 36 cells. Each cell produces about 3.75W.

2. Regarding PWM controller: Conversely, when the battery is fully discharged, the pulses of the battery stay "on" nearly 99% of the time.

When in boost mode, the PWM controller should be ON 100% of the time. The controller should not be switching.

3. While the PWM design is simple and rugged, there are some inherent flaws with the design. For one, PWM charge controllers are inefficient due to the fact that the controller connects the solar panel to the battery directly. This reduces the voltage developed by the solar panel from the nominal 17 volt output to the battery's voltage, which reduces the power available from the solar panel. Another inherent flaw with the design is that the pulses generated by the device can create interference in radios and TVs. This is due to the lower frequencies typically used in PWM charge controllers compared to the higher frequencies used in the MPPT controller.

The average efficiency difference (between MPPT and PWM) may be a mere 5%. That's a minor difference. You may be paying $200 more for a MPPT controller to get 5% extra current during boost stage. You can do lots better applying the $200 to purchase more PV panels.

When in boost mode the PWM controller switches remain ON. There shouldn't be any AM radio interference during boost. Depending on the PWM controller, you may see interference in absorption or float mode. I don't believe you'll ever see FM interference.

4. The pros of the MPPT charge controller are pretty significant. It can increase the charging efficiency of the system up to 20% and in some cases even higher.

You are doing your readers a great disservice here. ANY GAINS ABOVE 12% ARE TRANSIENTS. Compared to a PWM controller, average MPPT boost gain is around 5 to 10%. This is what the user will see over 99% of the time. Why even mention 20% gain when it's just a transient? Stating up to 20% gain (and sometimes more) is pure snake oil hype!

5. Cons of the MPPT controller include greater cost, at around $200, compared to a PMW controller, and greater physical size, but the pros associated with the unit's efficiency far outweigh the cons.

As mentioned above, if you apply the $200 extra cost for MPPT to buy more solar, you will come out way, way ahead.

Mello Mike wrote:



Thanks, Sal, for your thoughtful feedback. I'm glad you caught the volt/watt typo in the solar panel section. Thank you.

As for your MPPT comments. I'm a little confused. Is the efficiency gain for the MPPT controller 5%, 10%, or 12%? I've neither owned one nor used one so I'm relying strictly on those who have experience and knowledge with these charge controllers for this information. I've seen efficiency claims on some manufacturing websites that go as high as 30%! Do you have data that can back up your claim of just 5%? I ask only so that I can be educated on the matter and in turn so I can educate the readers of my blog. I have no hidden agenda and get no kickbacks from manufacturers for what I write.

MrWizard wrote:

what has Not been mentioned is the relationship of panel working voltage to pwm or MPPT

where MPPT shines is when using higher voltage panels and getting the benefit of the DC to DC conversion

using an older seimens 15.5 v panel is a perfect match for pwm and you get no gains using MPPT

16.5 and 17.5 seem to be the current norm vmp for 12v panels, the lower the voltage the smaller the MPPT increase/gain over pwm

you can feed a 19 vmp panel into a pwm controller but you will not get any conversion increase, it will be chopped down to 14+ for charging and you will actually lose some of the rated power power

where MPPT shines is in stacking higher voltage panels in series say 2*21.5vmp = 43v at 6 amps =258w into the MPPT controller then DC to DC conversion for more amps at 14v , (248÷14=18.43amps) that way getting more useable wattage from the panels to the batteries

if these same panels were used in parallel on low voltage pwm controller you would loose 30% of that power, it would be14v*12amps approx 168w charging

this over simplified without conversion losses , but thing is the efficiency gain or loss is determine by the vmp of the panels
the higher the vmp the better off the results using MPPT, panels can be series or parallel