Which Type of Solar Panel is best: Mono-crystalline or Poly-crystalline?

Which type of Solar Panels to use- Mono or Poly-crystalline?

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 some one 265 W Silfab MONO panel.  I updated this review in May 2014 after installing the test Silfab panel.

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.  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.  Polycrystalline 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 is believed 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.

I am gathering data on how and when the east and south facing panels turn on in the am as the sun slowly moves to an easterly rising location from its 21 December position. This helps to show how a south facing panel with the sun coming from the SSE to East reacts to the early morning sun compared to an east facing panel.  I can see a small but important improvement in the east's panel output over that of the south facing panels.  As of 21 January, south still out performs east by about 40%.  I move the east panels to track to the west and it is about 18% less than south at this time of year.  This changes to neutral and then to + 20% as we enter March.  Unless you move your panels, south is almost always the best orientation to use.

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.

Comparison:

Update: Mayv2014 preliminary

We remove one of our poly panels and installed a 265 W mono from Silfab.  So far I have learnt this:

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

2.0 Overcast and over head:  Goes to polycrystalline.

3.0  Bright sun both do well.  Mono does perform well under bright sunlight.  Problem is that this May we have had very few days with full sunlight.  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 degress.  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.

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. 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.

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 250- 255 W panel.  It is a very poor 265 W panel.  That is because some manufactures and Silfab is not the only one over rate the performance of their panels.  I have had days where 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 than the 265 W mono.

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 keep 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.

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 a panel 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.  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.

FYI the backing of the panel is critical to ensure long life of the panel and 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.  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.

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.

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.

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.  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.

Our recommendation:  Heliene 60 or 72 Cell polycrystalline panels.

Kirk is a retired Professional Engineer with experience in the Electrical Utility sector.

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.

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