I'm confused by the sizing of the inverter and figuring out how to wire the panels to maximize efficiency of the inverter.

Do you know of any articles or documentation that make this perfectly clear?

For example, what I'm looking at now is the 165w Mitsubishi panels. 24v each. Imp 6.83a. (specs here: http://global.mitsubishielectric.com/bu ... tions.html )

On the sizing tool, I select the 165w panels, 32f and 95f degrees (should this be winter average high temp during the day? Or as low as it could get during the day during the winter - same with summer?).

I'm shooting for 18 panels. So, as I see it, 165w X 18 = 2970w. Does this mean there's no reason to really go for an inverter over 3kw? I'd probably want to oversize it a bit in case I add more panels later. So in the sizing tool I selected the Xantrex GT3.3 (240v).

Am I reading this correctly (this page is extremely hard for a newbie to understand), where for 18 panels my options are either 1 string of 18 panels (which shows 594.53 max volts/max temp...getting close to the inverter max of 600Vdc), or add more panels and make it two strings of at least 11 panels each (in order to get the min Vmp above the 195Vdc inverter minimum)? In this scenario, is there any way that the 18 panels could realistically produce more than 594.53 watts if wired in one string?

I guess this is starting to make sense. I still don't understand the relationship between temperatures and voltage/current, etc.

Ha ! Would any of us be here if this stuff was easy. At least the industry all speaks the same language, Peak Volts, Max Power...... all mean the same thing from one major mfg to the next.

At colder temps, you get your max voltage, as panels heat up, their efficiency drops, and their voltage goes down.

As the light falling on the panel becomes more direct and perpendicular to the panel, it generates more amps, while the voltage is mostly set by the temperature.

To fully decide how to adjust your panel/inverter loading, take about 20 - 30% off the wattage spec from the mfg. That will be fairly close to the output you will realize. If you will be in a situation where you have a bright snowfield in the winter, and your panels face east, then you will approach your peak voltage output. A MPPT style inverter should shave some volts off that, to get the panels into their max wattage range.
During the "core" hours of the production day, the panels will be warmed by the sun, and will not be at their cold output voltage, unless they are frozen somehow. Black glass in sunlight gets hot, even in winter.

Posting your specifics here could yield lots of advice

I believe he lives around the City of San Mateo, CA (10-15 miles south of San Francisco)--possibly up in the hills (little cooler and, depending on the area, some more wind and fog--depends if he is in a sheltered valley or on the ridge line).

To answer the question... the low temperature is the lowest temperature you would expect to see with good light (even under light overcast too). This gives you the voltage that the inverter should never exceed (600vdc for the Xantrex GT inverter series).

If the panel temperature ever drops below 32F (or whatever is the exact string = 600 VDC) while under some sun, you run the chance of damaging the inverter (and this would not be covered under warranty).

The high temperature limit is really just temperature at which the voltage of the panel falls to that below what the inverter requires. No damage will happen... But, for example, if you have 95F as your maximum, and you get 5 days of 100F+ temperature, it is possible that your inverter will cut-out and not generate power during this period of hot weather. Not great, but not the end of the world either.

-Bill