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Old 05-07-2017, 02:03 PM   #1
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Solar panel users--

Is anybody using monocrystalline solar panels???? Are you satisfied with their performance when they are subjected to shaded or dirt conditions?

Presently I have 4 each 150 watt polycrystalline solar panels mounted onto my rear hardtop. They perform well and satisfy all my expectations providing 24 amperes charging current to my batteries when away from our dock. But poly panels are outperformed by mono panels and of course, monos have their own issues.

When I first installed my panels some 3-4 years ago my reasoning at that time led to the poly over the mono primarily because the current from a mono is reported to drop to nothing if any part of the panel is shaded or dirty (think gull poop).

OK, with all that history stated, I am thinking of adding another two panels from Hetech onto the top of my new hardtop that covers the helm. The unit costs difference between similarly rated panels is about 10% which is not much considering I am only looking to add 2 panels. Further, the cost impact is offset by their higher efficiency.

I am looking for user feedback to help me make a decision should I move ahead with a purchase.

Thanks--
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Old 05-07-2017, 03:06 PM   #2
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I have (2) 330 watt mono Kyocera panels. Have not previously had anything else to compare them to. My mast forward stay goes over them, as well as an antenna or two depending on sun angle. I have been overly impressed with output particularly on cloudy days. I have exceeded max output by 12% several times. Again having nothing else to compare them to, I don't know how much can be contributed by the way manufacturers rate them. With the cheaper manufacturers boasting a bit vs. quality manufacturers using more real life ratings.
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Old 05-07-2017, 03:43 PM   #3
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I have (2) 330 watt mono Kyocera panels. Have not previously had anything else to compare them to. My mast forward stay goes over them, as well as an antenna or two depending on sun angle. I have been overly impressed with output particularly on cloudy days. I have exceeded max output by 12% several times. Again having nothing else to compare them to, I don't know how much can be contributed by the way manufacturers rate them. With the cheaper manufacturers bosting a bit vs. quality manufacturers using more real life ratings.

Thanks Scott--

But back to your panels, 330 watts at what output voltage? The panels I am looking at range at 30-36V for those over 150 watts. For that reason, I intend to stay with the 18V panels. Not sure if MPPT controllers offer internal inverters to process a voltage change to that needed for 12V battery banks.

Now of course there are many advantages going to a higher voltage panel especially dealing with wire loss but the cost of wire vs controller is another matter. I did consider using MPPT processing when I first installed my panels but I found adding another panel (great if you have room) was less expensive route than getting the performance benefits from MPPT.

I am leaning towards going mono this time. The prices I have are very attractive although my quotes are from February. Kyocera panels have excellent history but are too expensive for me to consider.
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Old 05-07-2017, 04:46 PM   #4
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Jinko.
Worlds largest panel manufacturer
Salt mist corrosion resistant frames.
10 year warranty
Very cost effective.

I have 9 X 260w 12v running through a midnite classic150 mppt
10 months full-time live aboard on the hook with mostly domestic appliances.
Genset rarely used
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Old 05-07-2017, 04:52 PM   #5
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330 is at 40 volts, open voltage is 49. My mppt controller handles all the conversations and multi stage charging. If only coastal cruising in US etc, I probably wouldn't have gone solar. But being in the Caribbean long term, the payback is much faster.
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Old 05-07-2017, 05:30 PM   #6
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At 600 watts heading to 900 watts you definitely want an MPPT controller. Check the specs. You will need one of about 90 amp rating and a nominal 12V (three step charging) output voltage. They aren't cheap at that rating, about $1,000.

But you will pick up about 15% more amps to your batteries. You must be using PWM controllers now. They just waste the voltage between 13 and 17, the typical Vmp.

Also consider wiring pairs of panels in series to produce a nominal 24V. That will save conductor size or reduce voltage drop.

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Old 05-07-2017, 06:03 PM   #7
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We went with the outback flexmax 80 for those reasons
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Old 05-07-2017, 06:50 PM   #8
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At 600 watts heading to 900 watts you definitely want an MPPT controller. Check the specs. You will need one of about 90 amp rating and a nominal 12V (three step charging) output voltage. They aren't cheap at that rating.

But you will pick up about 15% more amps to your batteries. You must be using PWM controllers now. They just waste the voltage between 13 and 17, the typical MPP voltage.

David
Yes, my controller is a ProStar 30 from Morning Star which must use pulse width circuitry. Although it does the job, you are correct stating they waste the energy that could be available from voltages above 13v with low batteries up to about 15 with fully charged batteries. The trade off that I made for the panels now on my boat was $300+ for a decent MPPT controller to gain that lost energy or just spend $150 for an extra 150 watt panel that results in greater total energy than I would have gained by purchasing the MTTP controller. Now that was a good decision IF and only IF there was available real estate which I had to accommodate that additional panel.

So now with my new hardtop............ie greater available real estate for more panels I have to do a new analysis pertaining to MTTP. As I type without going through panel V/I curves, the only outstanding benefit that jumps out is that I could add higher voltage panels using lighter gage wire and not be concerned with distribution losses. That can be a huge feature but it would only apply to new, higher voltage panels.

I looked at Jinko and they do have GREAT prices but one has to purchase 10 panels to get that pricing. Earlier today I sent a request to Hetech for a delivered quote for a pair of 150 watt mono panels.

We don't live on the boat so I recognize that additional panels may be an over reach. It would also require another 12v battery bank to store additional energy so I could operate everything other than my stove and hot water tank from batteries. If this was an entirely new system and not an addition to an existing system, I definitely would go to high voltage panels.

This is an interesting discussion
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Old 05-08-2017, 08:58 AM   #9
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I am going to spend more time weighing my options before making a panel purchase. Just looked at some MTTP controllers and their costs have plummeted from what was asked when I first installed my existing panels.

Higher wattage 36v panels with MTTP are an option because I can rewire my existing parallel panels ( 2 sets of twos) to series for 36v. More later--
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Old 05-08-2017, 09:35 AM   #10
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When you have room for more panels, adding panels is a cheap way to get more power. But on a boat you are almost always space constrained. You have a unique situation with new space becoming available, but I still expect the most long term value will come from getting the most output from your available space. That means using an MPPT controller.

You might consider using two smaller MPPT controller rather than one big one.

First, you can only really use a single controller if you can wire both the new and old sets of panels to have very close to the same Vmp. That's the voltage where the panels produce max output. If they don't match, you will be throwing away available power similar to using a PWM controller. With separate controllers for each set of panels, you can run each at its optimum voltage. And you won't be constrained selecting new panels based on the old panel voltages

Second, you can get better shade immunity with separate controllers for each set of panels. If you have a little shading over one panel on one set, the other set will keep cranking at full power and wont have to readjust to the shading.
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Old 05-08-2017, 11:08 AM   #11
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The attached document is from a presentation that will be given at the Grand Banks Rendezvous. It is a good primer for solar questions.
Attached Files
File Type: pdf Solar Presentation.pdf (2.30 MB, 136 views)
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Old 05-08-2017, 03:02 PM   #12
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You don't need new 34V panels to use a MPPT controller to reduce wire size. You just need to wire your existing panels in series/parallel to get that same input voltage to a MPPT controller.

I agree with twistedtree above. Using two controllers will limit shading effects. They will cost about the same as a single big one though.

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Old 05-08-2017, 05:23 PM   #13
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Bob, very nicely done presentation! Thanks for sharing.
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Old 05-08-2017, 07:49 PM   #14
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Bob, very nicely done presentation! Thanks for sharing.
+1

I know nothing about solar systems and that helped me a lot.
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Old 05-09-2017, 10:24 AM   #15
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Back to MTTP which I see has taken a price dive since I first installed my current panels. What have others experienced with their MTTP performance for 36 to 12 volts? Can you share their models along with amperage?

I just did some simple math using my 4 each 150 watt panels which most likely were rated at about 18V. So if the controller has an estimated 70% conversion efficiency to say about 13v, the charging current would be (4X150/13)X .7 = 32 amperes. Seems reasonable because my pulse width converter has its highest output at 24 amperes.

The MTTP size explodes to requiring a 40 ampere controller when considering a pair 330 watt 36 volt panels: (660/13)X.7= 35+.

This arrangement coupled with my existing setup without adding MTTP to it could provide in excess of 50 amperes of charging current.

A good way to gain crude knowledge of the MTTP's efficiency is by how hot it gets. Do you who have MTTP systems have a heating problem?
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Old 05-09-2017, 11:17 AM   #16
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I didn't quite follow your math on the above, but this is how I would do it on a theoretical basis. Both cases assume 150 watt, 12V nominal panels:

PWM Controller

You can look at the current vs voltage curve, but most panels put out essentially the same current from 12 to 17 volts. So pick the Vmp voltage which is about 150/17= 8.8 volts and assume it is the same as at the 13 volt charging rate. So that is 13 x 8.8 = 114 watts. PWM controllers have very little switching losses so the efficiency is 114/150= 76%. It will be worse at lower output voltages and better at higher.

MPPT Controller

These use a voltage converter which keeps the solar panel at its Vmp and converts the voltage down to what the battery needs. I am guessing that they are 90% efficient. So that the overall efficiency is, 90%. Compared to PWM converters they convert 90-76 = 14% more power from the panels to battery voltage.

How did I come up with 90%, pure guess. It would take an accurate voltmeter and clamp on ammeter to verify that figure from an actual installation.

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Old 05-09-2017, 12:38 PM   #17
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You can also limit shading by connecting the panels in parallel. The shaded panel will then not affect the clear panel.

Getting pretty far in the weeds with the discussion of panel inefficiencies in these small scale installations. The observable difference is minuscule. In a large scale array this would be a valid discussion.
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Old 05-09-2017, 04:39 PM   #18
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I didn't quite follow your math on the above, but this is how I would do it on a theoretical basis. Both cases assume 150 watt, 12V nominal panels:

PWM Controller

You can look at the current vs voltage curve, but most panels put out essentially the same current from 12 to 17 volts. So pick the Vmp voltage which is about 150/17= 8.8 volts and assume it is the same as at the 13 volt charging rate. So that is 13 x 8.8 = 114 watts. PWM controllers have very little switching losses so the efficiency is 114/150= 76%. It will be worse at lower output voltages and better at higher.

MPPT Controller

These use a voltage converter which keeps the solar panel at its Vmp and converts the voltage down to what the battery needs. I am guessing that they are 90% efficient. So that the overall efficiency is, 90%. Compared to PWM converters they convert 90-76 = 14% more power from the panels to battery voltage.

How did I come up with 90%, pure guess. It would take an accurate voltmeter and clamp on ammeter to verify that figure from an actual installation.

David

Hi Dave--

I took a simplistic assumption using the panel's peak power at a battery condition where its voltage was 13v and calculated from that the amount of current supplied to a battery. Next I adjusted that current (related to power, not voltage from the panel and multiplied that be an assumed efficiency of 70%. Nothing more matters because I am referencing power not panel output current. The panel's voltage/current is immaterial because I have assumed the panel is at its peak power point. The actual current entering a battery should be determined by the MTTP controller as a function of the battery's terminal voltage.

Now again, an MTTP controller is designed to transfer maximum power to the battery regardless of the battery terminal voltage (within a specific range of course) otherwise it is not MTTP.


EDIT: Just a couple of points. All solar panels behave as constant current sources...again over a range of output voltages....esentially you mentioned that above. Next if the transfer efficiency is as high as 90% of course the battery charge current would be greater. I seriously doubt without looking at various MTTP specifications if any of them can get much higher than about 75%
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Old 05-09-2017, 04:58 PM   #19
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WTF Is MTTP?

(I know what MPPT is.. and PWM... and other stuff too)
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Old 05-09-2017, 05:51 PM   #20
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WTF Is MTTP?

(I know what MPPT is.. and PWM... and other stuff too)
My Gosh.....your ARE observant!!! It was the result of my hurry up typing It should be MPPT

Tooo many darn acronyms in life all starting back in the Franklin Delano Roosevelt's administration
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