Originally posted by Naptown
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I promise I understand how an MPPT works in the most intimate detail. I used to design DC-DC converter. And I also understand the algorithm part of an MPPT.
Small offgrid panels use 36 cells for 12V and 72cells for 24V battery that is to be able to compensate for high temperatures in hot climates.
Mppt will be most effective in cold and sunny days and not as effective in hot summer days. With a 36 cell panel and 12V Lead Acid battery the average gain over a year compared with an PWM controller is not higher than 15% will wary a bit with location (climate).
Those 15% can be also obtain using a simpler and less expensive PWM controller and a solar PV panel that is 15% larger.
Notice I use % so the size of the system is irrelevant. A larger MPPT controller will also be more expensive.
How is 1$/Watt way off for solar PV panels ? Maybe very small solar panels cost a bit more but I think 1$/Watt is a good average price for PV panels.
As for your example 100W panel example
A 12V battery dose not usually have 12V during charging it will be quite a bit more (13 to 14.4V) depending on the charge rate and SOC of the battery.
Also that 17V at max power point is calculated for cells with 25C temperature it will be quite a bit lower in the summer.
For small offgrid systems you usually have the panels quite close to the controller and batteries (usually mounted on the roof or somewhere quite close) so there are almost no savings on copper. Plus at high voltage difference between PV and battery the MPPT (DC-DC converter) will get quite inefficient dissipating even more heat and reducing the life of the MPPT controller even more (mostly the electrolysis will fail).
An PWM dose not get that hot and it dose not need electrolytic so it can last as much as the solar panels over 25 years where MPPT will be changed quite a few times adding to the cost of operation.
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