Side by Side Mono-crystalline verse Poly-crystalline Solar Panel Comparision

Mono or Poly-crystalline?

UPDATE June 2015:  See my review of the next generation Polycrystalline solar panels.  Unless we see this type of improvement with mono panels, these panels are the way to go period.


This is always an interesting choice that people have to make.  I will discuss the pro's and con's of each type of solar panel for a location in Southern Ontario. I compare my installation - Poly-crystalline Panels with one 265 W Silfab MONO panel.  Individual results may vary.  We are just a microfit customer trying to help others in the Province to have the best and up to date information so that the consumer can make the best educated choice.  We have no allegiance with Heliene, Flexible Solar or anyone for that matter.

Introduction:

I have spoken about getting the highest ROI on your investment before in my opening blog (see Dec 2013). If you have a very limited roof area, then you may get a higher ROI and income by using higher capacity panels which are the mono type.  With no roof area limitation, then poly might be your best choice. Presently, poly-crystalline panels appear to be the best choice for me.  You will pay a high penalty for little benefit to get 10-20 Watt more per panel using mono panels.  I believe that in the past, there was a bigger difference between the two.

Simply put, both work.  Mono crystalline cells use more expensive refined silica.  Poly-crystalline panels use a lower cost silica and look a bit different than mono.

You can check on line what is a mono and what is a poly-crystalline solar panel and what is the physical differences.  It has been reported that Poly-crystalline panels work better in low light situations, off axis production and in hotter climates.  Though-out the winter months you will experience at least 30-40% over cast days with some intermittent sun light.  Panel orientation is not relevant when the day is over cast.  The clouds act as a big soft-box and spread the light every where evenly.  Our testing confirmed these assumptions.

Discussion:

Poly-crystalline panels are increasing in output as the years progress.  You can get 260 W poly's verse 280 W mono's.  Because Mono panels can cost 20-25% more than Poly, Poly will win on the best ROI.  That makes the cost of that small incremental difference of 10 or so watts very high. Panel orientation, south or the angle of the sun of your roof is of much more importance.  Unfortunately we can not change the angle of our roofs.

There is another consideration for mono.  You just might like the look of mono panels better.  You might also like the look of black panels better.  Black panel backing is a great thing to have in winter but gets hotter in summer.  Over all I stuck with the blue panels but it is a personal thing.  My wife likes the blue.

Getting a quality installation is extremely important as it will add  significant value to your property at re-sale due to the income generating ability of the panels.  The Flexible Solar people did a great looking job for us. They don't cut corners and use or offer the best materials for long life project.  Remember that solar panels perform poorly at higher temperatures.  They do great in the cold and not so great in the summer.

Comparison:

We removed one of our poly panels and installed a 265 W mono from Silfab.  We have a 9.9 kW system so we are under 10 kW rule.  So far I have learnt or confirmed this:

1. Low light and early morning light:  Winner goes to poly panels.  I have 250 W Poly panels making more than the mono who should be making the most as it is rated 6% higher by the manufacturer.

2.0 Overcast and over head:  Winner Goes to polycrystalline.

3.0  Bright sun both do well.  Mono does perform well under bright sunlight.  Problem is that this May -2014, we have had very few days with full sunlight.  Winner goes to polycrystalline.  You may see different results from different manufactures.  Perhaps some manufacture's MONO will do better.  Look at the STC and PTC ratings of the panel and the tolerance:  A +1-4% is much better than a +1%.  IMHO, all panels should have a +2-4% tolerance like our poly panels do.

Testing Conditions: - Almost equal to Standard Testing Conditions -STC

On the 19 May 2014 we had a very good solar day.  No visible clouds at solar noon. Temperature around 20 C with a small wind. reported 13 kph.  System would not peak showing that we have high level light scattering occurring.  The angle of the sun hitting the panel nearly a perfect 90 degrees.  Solar harvesting in AM 46 kW hr and 88 kW hr total for the day.  That is best for May to date.  Based on these very sunny conditions, all of my Poly-crystalline panels worked better than the mono when adjusted to equal rating.  We are comparing 250 W poly, 300 W poly and 265 W mono.

These testing conditions are similar to that of the STC or standard testing conditions.  We were lucky as our roof reaches perpendicular to the sun on the 22 May and we got these results on the 19 May.  These panels did not give STC results but rather PTC or PVUSA standard testing results.  STC is at 25 C so these conditions were even better at 20 C.

Several of my poly panels harvested the same as the 265 W mono with no adjustment based on there STC ratings.  All panels were performing closer to their PTC rating and not their STC rating.  Winner goes to polycrystalline hands down.   All of Heline's 72 cell polycrystalline 300 W panels exceeded the 265 W Mono by 5%.. Several of our 250 W CG poly panels equalled the Mono panel.  In addition, the mono panel had not yet had time to burn in.  The Mono panel did work well, but not as well as I expected because of its higher nameplate capacity.  Mono did show more harvesting over the week than my 250 W poly panels but IMHO it should have harvested more.  That could be due to the fact that my 250 W poly panels for the most part do better than the 250 W rating which is expected to decrease annually by 1/2%.

4.0 Comparison between Silfab's mono and our 60 cell CG panels and our 72 cell Heliene panels.  Panel monitoring is a bit addictive.  You must resist using the instantaneous number and wait for the Solar Edge monitoring system to fully report at the end of the day.  The 265 W mono Silfab would be a  good 255 W panel.  It is a very poor 265 W panel. You must be the judge in this matter. That is because some manufactures and Silfab is not the only one over rate the performance of their panels.  I have had days where some of our 250 W CG poly panels produce more than the mono or very close to the mono.  We hope to try the Heliene's mono panels rated at 17.5% efficiency.  My heart skips a beat when you see the power rating of their 72 cell poly panel.  It is a bit unfair as it does have 20% more cells but the numbers do speak for themselves.  The performed on a watt by watt comparison a bit better (5%) than the 265 W mono. Don't mis-interpret what I am saying.  The weekly summary showed that the Mono did in fact do better than the 250 W Poly panels but it IS rated 15 W higher.  It could be in the nature of the beast.  Perhaps Poly due to their intrinsic design have a 1-4% rating naturally.  This means that some panels will be closer to 262 W and others closer to 250 W.  We do see that there is a range of outputs per panel.  You win with the higher performing panels and you still win with the 250 W performing panels.  I have yet to test the two when the temperature hits the high 30's C.  Poly should win as all other indicators have been proven to be true.  Your ROI is just better with poly panels.

5.0  Mono offers higher outputs and better efficiency and the chance to have the backing in Black.  As temperature does effect performance significantly, we kept to the white backing.  You many choose mono over poly if you have a limited roof area as you can get more watts per square foot or you just like the look of mono over poly.  All in all, poly panels are the better choice in a warmer environment for max ROI.  I am not including the SunPower panels in this discussion as it is something you have to pay too much for and most of us can not even get them.  The funny thing is that SunPower take these great panels and sell them with a String inverter system with no optimizers, thus IMHO it appears to nullify the basic design feature of their panels.

6.0  Silfab also use the lower cost PET backing material verse the better backing material used by Heliene and CG.  You can see my posts on suitable panel backing materials.  Personally I would stay away from PET and request Tedlar or Kynar backing be used.  I got the Silfab to replace one of my panels that was producing 30% lower than expected.  Heliene suggested (it is a CG panel) that perhaps one of the diodes was not working.  I tried to check the diode and found what appears to be a loose connection at the back of the panel.  I need to replace the battery in my Multi Meter to check the diode.  The connection may have been all that was wrong.  I will re-install the panel to check it out in the near future. I took the panel outside in the sun and it read 37 V DC showing that all cells are now working.  I still have to check which diode is not  working.

FYI the backing material used for a panel is critical to ensure long life of the panel as it's purpose is to seal it from moisture and oxygen attack.  There is a link on one of my posts showing cracking problems with someone's (?) PET backing panels.  People understandably are using lower cost materials to help them save money.  These materials however must last for a very long time: - 20-50 years.  It is the yellowing of this white backing that reduces the panel's output over its life time.

This is important: Solar Harvesting is a long term investment and you must use the best materials available so that you don't have to replace your panels early.

This chart show the daily output of 3 different solar panels. 300 W  Poly- from Heliene, 265 W Mono from Silfab, and 250 W CG Poly panels.  Can you find the 265 W Mono Panel?  A 265 W panel should produce 6% more than the 250 W Poly panels.  Likewise, the 300 W Poly panel should produce 13 % more than the Mono Panel.  

The Mono Panel produced 1.8 kWhr

What you see then, all the 250 W poly panels should have produced 1.69 kW hrs.  All except 2.20.11 which has a known problem are exceeding that value.  Accordingly, based on the 265 W Mono, all of the 300 W Heliene Poly panels should be less than  2.03 kW hrs.The fact is they are producing 2.125 kW hrs, much more than an equivalent Silfab 72 cell Mono based on this testing.  Also the Mono panel is not yet burnt in, so we are seeing the good side of this panel.  The Silfab panel is 2;20;19  These results were taken on a good sunny day without visible clouds when the sunlight was perpendicular to the panels based on the time of the year.  The Heliene 72 cell panels are 5% over and above this 265 W  Mono panel.  It is all about ROI and Poly is winning here.  If the Mono is really a 255 W panel, then poly is still the clear winner.  I would like to have other manufacture's Mono panels to test, but we are not going to buy their panels just to test them.  It is always best to get a random panel test.  A single panel taken from a larger order would do the job well.

August 2014 Update: The mono panel is producing some where around 255-260 W panel as compared to the 250 W poly panels.  Rating is poor to fair.  If it performed at 265 W I would give it a good rating.

For us, Poly-crystalline panels win over mono-crystalline because we have a good roof area and are most interested in ROI.  If we didn't have a 10 kW limitation, then it is quite likely that high output mono would be the way to go.  The best would be SunPower Mono but you can't get them or the price is way too high.  All of these things can change over night.  Many times products are prices not on cost but on how much one can get.  That is why we must always look at ROI.  Pay strict attention to quality build and quality long life components.  Look at the type of backing being used.  Stay away from PET backing and stick with Tedlar and or Kynar.

Thus we have verified that Poly-crystalline panels do a bit better than Mono-crystalline panels in all conditions.

What about the ROI?

Based on our one day test, I calculate that we would lose the output of two panels over twenty years using the Silfab panel verse our Polycrystalline panels on a 10 kW system.  There is no reason to believe that the panel will produce more power and it is likely to produce less power as it burns in.  All of the poly panels have been burnt in for months.  We harvest about $150-160 per panel per year.  Losing two panels because some one wanted to make more money would have cost us over $6000 over 20 years.  IMHO, panel manufacturers need to under rate and not over rate their panels.  They need to make money so charge accordingly.  Panels will lose about 10% over 20 years, so starting at +3-4% is a good way to rate the panel.  You will sell more panels under the 10 kW microfit limitation any way.  That IMHO is a no brainer.

Our recommendation:  Heliene 60 or 72 Cell polycrystalline panels.  Note:  We have not yet tested the Heliene 60 cell mono but make the inference that they are identical minus the 12 extra cells.  Heliene have NOT over rated these panels making them the best buy for the microfit program.

Kirk is a retired Professional Engineer with experience in the Electrical Utility sector.  We have no connection with Heliene, Silfab or Flexible Solar.  We just believe that an informed consumer is the best consumer.  Your results may vary from ours. All monitoring results were obtained from SolarEdge panel monitoring reported data.

More information:

If you are interested in installing a Microfit or Fit solar panel system, I strongly recommend giving Steve a call at Flexible Solar Solutions in Windsor, Ontario serving Southern Ontario.  They are the best and most honest microfit solar panel installers that I have had the pleasure of working with.  They will give you a straight analysis of your roof and what you can expect to earn.  Don't forget to tell them that Kirk sent you.  See my first post for more information on going Solar.

We expect to earn $6500-7500 per year depending on the weather for 20 years.  That should work out to us having an extra $100,000.00 income for our retirement over and above your system costs.  At that point we grid tie and earn the going rate of power which just might be very close to what we are currently being paid.

IMPORTANT UPDATE:  See my review of Canadian Solar's next generation poly panels

 Steve at Flexible Solar Serving Southern Ontario 519-962-9218