*You probably won't be happy with a PWM and nominal 12 volt panels in difficult low light conditions. You might do better with a 24 volt panel and pwm or with MPPT.*
This is TOTALLY backwards. MPPT will never out perform a PWM in low light conditions.
Also, MPPT is NOT a better performer than PWM for <600-800 watts of panels.
Thirdly, if you know there will usually be shaded or possibly low light conditions, ANY advantage to the MPPT will likely be lost.
While using 24v panels can help, I dont really see a huge advantage with a system <600 watts.
HIGH QUALITY PANELS ARE CRITICAL. My Renogy panels on a cloudy day wil significant tree cover, were still kicking out ~1.5 amps of their rated 5.25 max
Per MorningStar tech books::
Below is information from MorningStar's site about their own MPPT vs PWM controllers.
"1. Low power (specifically low current) charging applications may have equal or better energy harvest with a PWM controller. PWM controllers will operate at a relatively constant harvesting efficiency regardless of the size of the system (all things being equal, efficiency will be the same whether using a 30W array or a 300W array). MPPT regulators commonly have noticeably reduced harvesting efficiencies (relative to their peak efficiency) when used in low power applications. Efficiency curves for every Morningstar MPPT controller are printed in their corresponding manuals and should be reviewed when making a regulator decision. (Manuals are available for download on the Morningstar website).
2. As explained in the Environmental Considerations section, the greatest benefit of an MPPT regulator will be observed in colder climates (Vmp is higher). Conversely, in hotter climates Vmp is reduced. A decrease in Vmp will reduce MPPT harvest relative to PWM. Average ambient temperature at the installation site may be high enough to negate any charging advantages the MPPT has over the PWM. It would not be economical to use MPPT in such a situation. Average temperature at the site should be a factor considered when making a regulator choice (See Appendix).
3. Systems in which array power output is significantly larger than the power draw of the system loads would indicate that the batteries will spend most of their time at full or near full charge. Such a system may not benefit from the increased harvesting capability of an MPPT regulator. When the system batteries are full, excess solar energy goes unused. The harvesting advantage of MPPT may be unnecessary in this situation especially if autonomy is not a factor.
