I have found that the Unisolar panels give you 90% power when the sun is at a 45* angle to them (because of the rough textured Lexan surface), so all you have to do is use locally bought aluminum "L's" and 1/4" bolts of various kinds. You figure out the average sun angle and true south, and bolt them in place. Unbreakable, so no worry about hail and vandalism damage.
Glass panels only bring in 10% power at that angle (because of the smooth reflective surface) so must be tracking for efficiency (or a lot more panels), and that adds to the cost by up to double for full auto tracking with manual control for hail threat to the glass. The efficiency gain of full tracking for glass panels is 40% over seasonally adjustable fixed. Try to seasonally adjust your roof angle for the direct roof mount glass panels you see! Basically, with low angle roof mounting, you have to double the glass panels you would need with a full tracking system.
With the Unisolar at fixed you get 90% of a tracked glass panel system of equal wattage, so you save a substantial amount. I have both type systems, so I know.

Bump for real progress toward CO2 pollution> 90% reduction, and mitigation of AGW before self sustaining methane releases can happen and cause a true ELE.

I have found that the Unisolar panels give you 90% power when the sun is at a 45* angle to them (because of the rough textured Lexan surface), so all you have to do is use locally bought aluminum "L's" and 1/4" bolts of various kinds. You figure out the average sun angle and true south, and bolt them in place. Unbreakable, so no worry about hail and vandalism damage.
Glass panels only bring in 10% power at that angle (because of the smooth reflective surface) so must be tracking for efficiency (or a lot more panels), and that adds to the cost by up to double for full auto tracking with manual control for hail threat to the glass. The efficiency gain of full tracking for glass panels is 40% over seasonally adjustable fixed. Try to seasonally adjust your roof angle for the direct roof mount glass panels you see! Basically, with low angle roof mounting, you have to double the glass panels you would need with a full tracking system.
With the Unisolar at fixed you get 90% of a tracked glass panel system of equal wattage, so you save a substantial amount. I have both type systems, so I know.

To reduce CO2 by 90% in a decade, everyone must go to green power. Non-CO2 polluting power, and non-CO2 agricultural practices.:GEEK:

The glass panel vs. Tefzel Unisolar panels was actual readings from the system ammeters when my glass panels had to be in fixed position while the sunseeker unit was repaired.
One inch hail will break the glass panels and destroy them if the sunseeker points straight up to the brightest point in the sky. I believe they have to be at at least a 30* angle from flat to resist the hail. That is why we needed to buy a manual-controller for the full tracking Wattsun/Astropower array. This put the total mounting cost close to equal the panel cost (and the panels were bought on sale).
The Tefzel is similar to Lexan in unbreakability, and fixed latitude mounting was easy and cheap compared to the tracking needed for glass panels. Real Goods put the efficiency loss with fixed glass panels at 40%. The Unisolar panels are not a magnet for dust and snow, and show great performance in cloudy and partial shade conditions, compared to the glass crystalline panels. The glass panels show less input when dusty, and the unbreakable plastic panels self clean as well as the glass.
As far as the hail hitting the junction boxes, it would have to be blowing at a 30* from vertical or more angle, also ruining the JBs on the Astropower panels.
Cost analysis: Full tracking 600 watt array self installed with wiring to controller---$7,000, or $11.67 per watt for 100% efficiency and emergency manual control necessary. Fixed Unisolar mounting and wiring to controller, 424 watts for $2,100, or $4.95 per watt at 90% efficiency for this location, net equivalent $5.45/watt.
Every location and situation is different, of course. If I had a 15/12 roof facing south and enough fixed glass panels to make up for the 40% efficiency loss, the easy mounting and necessary wiring and electric for code to the controller, I would have spent a total of $9K at most. So it is close, anyway. With a lower pitch roof, more glass panels would have been necessary. The Real Goods efficiency calculation is for fixed average sun angle south (-40% from full tracking). Going from the say 15/12 to a 6/12 roof south mount would mean about 20% more cost, or about $11k, for the same net electricity. Big hail blowing hard against the 6/12 mounting would destroy the panels, too.
Other factors in favor of the unbreakable panels are resistance to rock vandalism, and blowing broken branches.
The decision of panel type is all dependent on location and building characteristics, along with estimated electrical use needs.

It is hogwash to think that I don't understand or can't tell the performance of my self installed solar electric systems.
The Real Goods Solar Living Sourcebook has explained reflective losses of glass panels along with "The Independent Home" book. That is where the 40% figure comes from, and verified by my own measurements. My full tracking 8 panel array is the equivalent of 11 of the same panels fixed at the average yearly sun angle south.
My ammeters are Trace (Xantrec) and with their charge controllers. That is where my personal measurements came from.
Reflective loss of glass is also explained in the book Earthship (and in most physics textbooks).
As far as glass panel resistance to hail, look at what the warranty says about angle of mounting. They will not guarantee against hail damage unless panels are set at a minimum angle, generally at least 30* to the ground.
Unisolar are just one that uses a textured surface to capture more sunlight, and there are others that are unbreakable, too.
The lesson is: if you go solar, look at the warranty and performance figures for the various panels in various mounting situations. Look at the mounting costs, and other installation costs for self-install, code compliance, etc. Read the Solar Living Sourcebook and other books on solar electric system installation. Don't fall for the sales pitches of various solar electric profiteers.

The problem with flat glass panels is reflectivity and power loss when the sun is not straight on. They are variable with individual manufacturers and types.
The 10% power with the sun at a 45* angle to the panel refers to my Astropower multi-crystalline flat glass panels.
The hail resistance of straight on 1" at 52mph is not adequate for many areas. Here we get up to 1.5" hail hitting at up to 90 mph. This is common for Colorado and much of the plains, and other areas. Some areas get hail up to over baseball size!! The Tefzel and Lexan will not break, while tempered glass will. The Unisolar's backs are sheet stainless steel, which most glass solar panels do not have.
My main worry is that I could be gone (away from my manual control) when a hailstorm hits my glass panels, destroying $4K in panels, and my main system for 220VAC and the well pump would need generator charging until replacement panels could be purchased, shipped and installed.
Another worry is that if one of the two tracking motors quits or the sunseeker malfunctions like twice before, I will have to manually set it at average sun angle south and lose 40% of my main system electricity.
If my house was bigger with a bigger roof facing south at a 15/12 angle, I could have fixed mounted 4 more Astropower panels at an extra cost of 1600 for the panels and 600 for a through the roof required GFI box, and got a little more electricity. That is 2,200 plus simpler mounting costs of 1K, total 3.2K. My full tracking pole mount system was 3.5K.
So the most efficient thing to do is design your house with the front roof section facing south at the average sun angle, and big enough for the amount of panels you need, which can then be cheaper tempered glass mono-crystalline type, or the more expensive solar panel roofing shingles which don't need a mounting system and attach directly though the sub-roofing and to the plywood or OSB structure.

Cloudy day performance of Unisolar versus glass panel Astropower type. At noon on a cloudy day my front 18 amp system (@24VDC) read 4 amps or 22% power. My Unisolar garage system which is 18 amps @ 12VDC measured 7 or 39% power.
Also when the sun is going down it hits trees for partial shading. With the tracking panels point straight on, but partially shaded, the reading is 4 or 22%.
The Unisolar panels which are at a 50* angle to the sun at this time, and partially shaded, still put out 6 amps or 33% power. When the glass panels had to be fixed for sunseeker repair, at the same angle as the Unisolar and same time---they read 0. Just before at 45* and no shading from the trees the Unisolar read 16.2 (90%), and the fixed glass read 1.8 (10%).
The Trace controllers read in amps to tenths. Easy math, although the angle was an experienced estimate, verified with a compass, so could have been + or - 2*.
Of course, we are thrilled with our Unisolar panels, but are not sales people for them. Glass panels take up a much larger market share and have a lot of sales people and middle man/installer profiteers. Even Unisolar, you have to shop around for the best deals including shipping.
Mounting is something that can be costly. From previous posts you can see the difference in the mounting costs. Also, later posts show how this can be defrayed.
What I want to show is that with glass panels just mounted on your roof, flat with it on standard 3 to 5/12 roof pitches, are subject to large power loss, and in many areas, the threat of weather damage.