A salesman told me an MPPT charger triples solar panel output?

[goboatingnow]

The 3x statement is right where PV voltage is much higher then the battery. This tends to be the situation today with higher voltage series strings panels. I’ve seen Voc s approach 80v or more these days !

[tomtriad]

How do you know when a salesman is lying? Their lips are moving...

[MVDarlin]

I replaced my flexible 100 watt rated solar panels (almost worthless) with hard glass 150 watt panels from Amazon. Boy, what an improvement. About $150 each. I love the Victron controllers with Bluetooth connection to my cell phone for monitoring. I use 2x 100v/30 amp Victron mppt controllers for 7 panels, 4 connected to one controller, 3 to the other. to operate AC freezer, refer and TV with inverter connected to house bank and house DC needs. I plan to replace my 8 AGM type 31 batteries with 2 100 amp lithium this winter for the next efficiency improvement. My boat is in the Sea of Cortez on a mooring ball with plenty of sunlight most days. The $3,000 solar system allowed me to move off the dock, saving $800 per month moorage fees. I recovered the cost of the system in 4 months. I also have another panel connected to my skiff and windless batteries.

[Kinkircating]

Originally Posted by MVDarlin

I replaced my flexible 100 watt rated solar panels (almost worthless) with hard glass 150 watt panels from Amazon. Boy, what an improvement. About $150 each. I love the Victron controllers with Bluetooth connection to my cell phone for monitoring. I use 2x 100v/30 amp Victron mppt controllers for 7 panels, 4 connected to one controller, 3 to the other. to operate AC freezer, refer and TV with inverter connected to house bank and house DC needs. I plan to replace my 8 AGM type 31 batteries with 2 100 amp lithium this winter for the next efficiency improvement. My boat is in the Sea of Cortez on a mooring ball with plenty of sunlight most days. The $3,000 solar system allowed me to move off the dock, saving $800 per month moorage fees. I recovered the cost of the system in 4 months. I also have another panel connected to my skiff and windless batteries.

Thank you for this real world example. It confirms what I had originally thought, but I’m still trying to understand this more clearly. So couple of questions for you, would you say that universally rigid panels are going to be more efficient than whatever the latest and greatest flexible panels would be?

For example reading about the new HH boats they are advertising (4000W) of flexible solar panels basically covering every square inch of the coachroof. I’m questioning how effective this set up would actually be because of a couple of reasons. First they are glued to the roof without any air gap underneath, as they heat up in the direct sunlight they will become less efficient. Second the shading issue, unless you are at anchor and have the boom tied up out of the way you’ll always be shading a large number of the panels. I’ve see first hand how this can reduce efficiency by 70%. The third being a wildcard of how many individual controllers are set up to combat the shading issues.

Anyway my thoughts when looking at this type of set up was that a 4kW array of flexible panels set up in this manner is probably less efficient than a 2.5kW solar array of rigid panels positioned outboard of the boom/shading in raised panels with individual controllers. Then you have to consider the useful life is 3-5 years vs 25 years for a rigid panel.

Anyway I’m kind of hoping I’m wrong in how I’m thinking about this and it is just better to wallpaper the roof, but my engineering background tells me it’s probably not the optimal route to go.

[fxykty]

Originally Posted by Kinkircating

Thank you for this real world example. It confirms what I had originally thought, but I’m still trying to understand this more clearly. So couple of questions for you, would you say that universally rigid panels are going to be more efficient than whatever the latest and greatest flexible panels would be?



For example reading about the new HH boats they are advertising (4000W) of flexible solar panels basically covering every square inch of the coachroof. I’m questioning how effective this set up would actually be because of a couple of reasons. First they are glued to the roof without any air gap underneath, as they heat up in the direct sunlight they will become less efficient. Second the shading issue, unless you are at anchor and have the boom tied up out of the way you’ll always be shading a large number of the panels. I’ve see first hand how this can reduce efficiency by 70%. The third being a wildcard of how many individual controllers are set up to combat the shading issues.



Anyway my thoughts when looking at this type of set up was that a 4kW array of flexible panels set up in this manner is probably less efficient than a 2.5kW solar array of rigid panels positioned outboard of the boom/shading in raised panels with individual controllers. Then you have to consider the useful life is 3-5 years vs 25 years for a rigid panel.



Anyway I’m kind of hoping I’m wrong in how I’m thinking about this and it is just better to wallpaper the roof, but my engineering background tells me it’s probably not the optimal route to go.

Flexible panels are thought to be less long lived than solid panels: myth or reality? They are certainly more expensive per W.

Just like yachts with teak decks, HH cats are sold to new owners and not with care towards future 2nd hand owners. 10 years from now we’ll hear whether their panels are still working to their specs.

[noelex 77]

Originally Posted by fxykty

Flexible panels are thought to be less long lived than solid panels: myth or reality?

It is certainly a reality with the current panels. Whether they can solve these problems in the future remains to be seen.

Solar panels integrated with boat structures, such as those encapsulated within a hard top, maximise the area available for solar collection and are visually pleasing, but I think the panels are going to be very difficult to replace when they fail. Given the limited cooling I suspect their lifespan is not going to be long. Perhaps just long enough to cover the warranty period?

[PaulCrawhorn]

There are top quality semi-flex panels made in Europe

cost 10x more per watt plus need to be professionally installed by authorized shops.

They still won't last on average, half as long as rigid framed units

But looking better, getting more kW of power, better sailing performance is worth it to those with bigger boats and deeper pockets.

Someone with a 1970's 30-footer, less likely.

[SunPoweredYachts]

The advantage of an MPPT controller, over PWM, increases the greater the difference between the voltage of the solar panel(s) and the voltage of the battery bank.

Going off rated numbers, which will vary with performance during the day, the MPPT will take the higher voltage of your panel, 34.3V, and drop it down to charge your 12V nominal battery (will vary, but let's say 13.5V), it then takes the difference 20.8V (34.3V-13.5V) and turns it into "extra" (or better to say "useable") amps. So 375W / 13.5V = 27.03A

A PWM controller will take your higher voltage and drop it down but does nothing with the difference, hence the gains of an MPPT over a PWM.

Another way to think of the power is breaking it down into two stages, with an MPPT:

1- solar panel to controller (higher voltage, lower amps) - 34.3V and 10.63A
2- controller to batteries (lower voltage, higher amps) - 13.5V and 27.03A

With a PWM

1- solar panel to controller - 34.3V and 10.63A
2- controller to batteries - 13.5V and 10.63A

So in this case you will get 2.5x more useable power from an MPPT over PWM. Also when the question posed was "When I asked how many amps per hour can this panel generate, he told me 30 amps." it needs a little clarification and would be the amps from an MPPT controller to the battery.

[Na Mara]

This seems like a good thread to ask this question in as I notice others have made the points about shading and so on.

I read this article and it matches something that Jeff and PYS was saying on one of his videos about it being best to have one controller per panel. According to the article, with series connected panels the current is constrained to the lowest current in any of the panels in the series, while with parallel connected panels the voltage is constrained to the lowest voltage over any of the panels. Either way, if you have dissimilar panels and/or severe shading of any of the panels, you will be taking an efficiency hit in the real world as power is volts multiplied by amps. In the examples in the article the efficiency hits are of the order of 40% and 10% respectively for series and parallel connected systems of dissimilar panels. And this is before the inefficiencies that arise from an MPPT controller having to pick the optimal power point from multiple (potentially one from each connected panel if they are variously irradiated) optimal power points.

This seems to be the argument behind the advice from PYS and others to go with one small, cheap mppt charger per panel on sail boats, rather than parallel or series coupling panels to a single big charge controller. At 90 euro a pop for Victron's smallest charger, that seems like a legitimate strategy or have I missed something?

I would like some answers to this as I am ordering the parts for this in the next month or two and I am doing a 750W solar system comprised of 300W semiflex glued down and 450W of rigid panels aft that is comprised of 10 panels ranging between 114W and 55W. If I go with the advice from PYS and what is implied by the above article then that is 10 victron 75/10 charge controllers at 900 euro rather than a single/pair of larger controllers for around the same money. No difference in price, but a big difference in installation practicalities and wiring.

[SavMel]

It is important to differentiate the two functions an MPPT Charge Controller performs. The first is the Maximum Power Point Tracking (MPPT) function. The second is the Charge Control function.

MPPT is the act of forcing the solar panel to operate at its maximum power point. The power output from a solar panel is not directly proportional to the voltage of the panel or the current of the panel. It is a function of the two, and the maximum power point (where you get the most power output) is at the knee of the red PV curve, as illustrated below:

(Image stolen from Electrical Academia website.)

For max power output, you want your panels to operate at this point on the curve at all times. Note that this curve is also a function of the irradiance of the panel, so the MPP (the knee of the curve) will move based on how much sunlight the panel is receiving, and obviously the amount of power you get is a function of the irradiance as well.

The second function of the MPPT Charge Controller is the charging function. Most modern MPPT Charge Controllers run complex charge algorithms. I've seen up to 7-stage adaptive charge functions in these units. Most units are able to be custom programmed. Programmable parameters can include bulk voltage, absorption voltage, absorption time, float voltage, and various current limits. I've selected the charge algorithm and various parameters to safely and properly charge a lithium battery bank on board our boat.

These two functions are accomplished through power electronics in the MPPT Charge Controller.

For the MPPT function: One buck converter forces the panel to operate at the maximum power point. Control circuitry on this buck converter continually zeroes in on the maximum power output by perturbing the operating voltage and observing the effect on current. Multiplying the two together results in the power output. If the adjustment caused a higher power output, the controller keeps adjusting in that direction (say, voltage up). If the adjustment caused a lower power output, the controller adjusts in the opposite direction (say, voltage down).

The power output of this first stage is dumped into a DC-link capacitor internal to the MPPT Charge Controller. That DC-link capacitor will be at the MPP voltage (the x-coordinate from the knee of that red curve). For some of my panels, this is at 36-ish volts when fully irradiated. Obviously, you can't simply connect that to your 12-v battery bank. (This would drag the panels down to the voltage of the battery bank, thus pulling them away from their maximum power point.)

For the Charge Controller function: Another converter pulls power from the DC-link at whatever voltage it happens to be at from the MPPT function hardware. It bucks down that voltage to the set points programmed into the charge algorithm. It is also the hardware (and control software) that enables you to set various voltage set points, time limits on the various charging stages, and current limits.

Long and nerdy post, but hopefully this helps explain the two different functions of an MPPT Charge Controller.

[Na Mara]

Originally Posted by SavMel

Note that this curve is also a function of the irradiance of the panel, so the MPP (the knee of the curve) will move based on how much sunlight the panel is receiving, and obviously the amount of power you get is a function of the irradiance as well.

Great post SavMel! The quoted section grabbed me as with multiple diverse panels variably irradiated - as is typical on a sailboat - all parallel connected to a single MPPT charge controller the MPPT will have multiple optimal voltages to choose from. Any it chooses will maximize the output from one of the panels at the expense of the failing to do so for the others. Is that not correct? In which case, 1 controller per panel should be best for maximizing output from diverse variably irradiated panels like those on a sailboat.

[donradcliffe]

You cannot put all three panels in parallel and expect an MPPT controller to work its magic. You need to put the two 17 volt panels in series and then parallel that circuit to the 34 volt panel.

[Pete7]

Not sure I would want to do 9 MPPTs, you would be forever updating the software

Could you join the panels of equal size into say 2 or 3 strings? larger Victron MPPTs would be cheaper too.

Pete

[smac999]

if the panels are facing the same angle and can't shade 1 at a time then you can combine some of them in sets. but for example you have a port and stb panel on a dodger and the boom moves back and forth across them, you'd want 2 controllers.

[SavMel]

Originally Posted by Na Mara

Great post SavMel! The quoted section grabbed me as with multiple diverse panels variably irradiated - as is typical on a sailboat - all parallel connected to a single MPPT charge controller the MPPT will have multiple optimal voltages to choose from. Any it chooses will maximize the output from one of the panels at the expense of the failing to do so for the others. Is that not correct? In which case, 1 controller per panel should be best for maximizing output from diverse variably irradiated panels like those on a sailboat.

Thanks! Your point is correct. To achieve the highest output from an array with different types of panels and different shading across the array you really need an MPPT for each panel. This however can become impractical if you've got, say, 9 different panels. At that point, you've got to look at the trade offs. 9 MPPT Charge Controllers would be expensive, mounting locations become sparse, and wiring could get hairy. How much extra power will you get from having an MPPT per panel, and is that worth the cost (thinking in terms of $$/Watt here)?

In a case like this, I would probably try to parallel panels (or series strings of panels) with a similar Vmmp parameters (found on the data plate of the panels) and shadings. This would provide an acceptable (to me) compromise that lands that $$/Watt metric in a range that I'm okay with. Trade offs are everywhere, and to each their own!