Late this year I'll be adding the solar array on my new house.  The longer I wait the lower the prices will be.  Right now one can get poly panels for about $1.08/w (230w $248) @16% eff or mono panels for about $1.28/w (250W $320) @ 17.8% efficiency.  Somehow I feel the mono panel is the better deal but can I justify it economically?    Here is my attempt : I priced out a 22 panel system with each using 22 Enecsys micro inverters and  $1000 for racking.  $11694. for the mono,  $10110 for the poly then used the PTC rating of each and 95% efficiency for the inverters to calculate 4689 watts for the mono and 4339 watts for the poly.
$2.49/w for mono  and  $2.33/w for poly or mono costs about 7% more.  Now if I go back and add $3000 for installation labor to each I find that mono costs only 3.6% more than poly.  So mono clearly costs more per watt, where is the benefit.  The collection efficiency as I stated earlier is 17.8% for the mono and 16% for the poly doesn't that mean the mono will give 17.8/16 times the output under the same illumination?  11% more output is definitely worth paying 3.6% or even 7% more!

My conclusion is, the clear winner is the monocrystaline cells.
Am I wrong?  How or why? 

Well I was the victim of some "specsmanship". the efficiencies I used were 'cell efficiency' not module efficiency, the difference being in the glass. to correctly compare the Hundai modules being offered by DM solar the poly is 14.2% and the mono is 15.3% the difference is now much smaller but still 7.7% more output for the mono crystalline offering making it still the winner with just considering material costs. Adding installation costs and the facts that mono crystalline cells output degrades less over time and the output holds up better over temperature changes further tilt the choice toward mono crystalline panels.

I am currently monitoring three systems, two being monocrystalline and one polycrystalline, with collection efficiencies ranging from 13.9% to 18.1%. I am not sure of all the tradeoffs, but the energy produced seems to scale with the power rating, as shown at:
http://www.residentialenergylaboratory.com/comparison_of_pv_systems.html

So far, the only advantage I see for the higher efficiency panels is for applications that are space limited. There could be durability advantages for one type or another, but I have not seen differences in the literature for the different types of silicon solar cells.

Darn it Lee, but thank you. You are complicating my decision with facts. Another factor that might come into play is limitation of panel output under favorable conditions kike if a 250 watt panel was coupled to a 215 watt micro-inverter (Enphase) but since I'm planning to use the Enecsys 240 watt micro-inverter that's not a factor & in fact it should do real well with a 230 watt panel. So, you've changed my mind.

Liebler-

You mentioned "... the facts that mono crystalline cells output degrades less over time and the output holds up better over temperature changes..." You will need to do your own research on these areas, as I have not looked extensively into either of these issues. I do include some references at the web address that I provided that might help in that decision, but it was not my goal to make the decision between mono and polycrystalline. I did think that it was interesting that systems with very different conversion efficiencies performed essentially the same when normalized by their rated power. One thing that I need to add to the website is that system #2 is over a heated space, and it seems to shed snow more quickly, helping it out last month when we had a lot of snow.