Recommended panel angle (single axis tracking)

[CasaDelGato]

I've been looking around to find the "optimum" angle to mount my panels at. This assumes a single axis tracking system.
Most of the sites I've looked at seem to recommend about a 40deg angle for my area (Greenbank, WA), to optimize for max total year power output.
BUT it looks like they are all assuming a very simplistic power model, i.e. power/sqft of sunlight is the same year round. (assuming panel is perpendicular to the sun.)
In the winter, sunlight is significantly weaker after going through more atmosphere.
It would ALSO be nice to be able to factor in standard cloud cover history data. (2 months of glorious sun mid-summer, down to almost complete overcast mid-winter.)
Anyone know of a place that does the more complete analysis?

[russ]

Use PV Watts to play around and see. THe link is on the forum (main) page on the right hands side. It won't load for me right now.

You can make various adjustments and find the best combination

[Sunking]

Unless you have restricted space I suggest you DO NOT USE a tracker. They are expensive, prone to high failure rates, and 90% of the time it is less expensive to just use a few extra panels on a fixed tilt with no reliability issues. You can even use a racking system to adjust tilt angle as the seasons change.

[CasaDelGato]

Use PV Watts to play around and see. THe link is on the forum (main) page on the right hands side. It won't load for me right now.

You can make various adjustments and find the best combination

Yeah, that site seems to be broken. I'll take a look if it ever comes back...

[CasaDelGato]

Unless you have restricted space I suggest you DO NOT USE a tracker. They are expensive, prone to high failure rates, and 90% of the time it is less expensive to just use a few extra panels on a fixed tilt with no reliability issues. You can even use a racking system to adjust tilt angle as the seasons change.

Note that I am a "tinkerer" and any tracking I do will be built by me, and mostly scrounged. So price will be relatively low. (I try for decent reliability though, as repairs are a PITA.)
Though looking at current panel prices, I will have to decide how much my time and effort are worth vs just buying more panels.
I am in a somewhat restricted space in that my panels MUST be on a tower. (surrounded by trees) So making the tower larger isn't really an option.

[CasaDelGato]

Yeah, that site seems to be broken. I'll take a look if it ever comes back...

Ok, by going through http://gisatnrel.nrel.gov/PVWatts_Viewer/index.html I was able to get the calculator to work.
Using the default PV array (since this is just for aiming comparisons, size is irrelevant) I find that about 30 deg tilt is optimum.
Fixed - $330
1-axis - $410
2-axis - $426

Definitely shows that 2 axis is just not worth it.
For a Fixed array to put out the same power as a 1-axis array, means it would need to be 1/3 larger. That is significant.
For me, it will depend on if the value of my time/effort is worth the lost output over the lifetime of the panels.