MPPT vs PWM cotrollers?

[Axel_G]

It depends on the temperature you are operating the solar panels at.

The optimum (with maximum power output) output voltage for solar panels goes down as the temperature goes up.
So in Florida at Noon with the sun burning the panels they will only deliver just the 14V to charge your batteries. In this situation the MPPT will just add to the losses in the system and be meaningless. Here the PWM is the better choice.
At morning in some cold region they will deliver above 18V. In this situation the MPPT will actually be able to improve the battery charge current by the 30% advertised.

Typically in colder situation you are trying to get out every bit of energy, so the MPPT makes sense and you will be able to recharge the batteries faster when the sun comes up. But at noon with high temps there will not be a big difference.

Axel

[GTom]

I am afraid I won't see Florida temps along the West coast of UK. To overcome the voltage issue, I'd use building blocks like these:
- 200W panel (Vp>18V) wired to a victron 15A controller

- or 2x100W panels in series, wired to a victron 15A

To find the sweet spot, it seems to be a matching game between controllers and panels. Overall, I aim for 300-400Wp, which means the voltage necessary for mppt will be there and I don't need to waste one full panel worth of power on controller efficiency.

[FionaJC]

I had 100W panels with a PWM controller into a 220A bank. Every winter the batteries would be dead by the spring. I had to use a petrol 2Kw Genny to bring them up each week by charging at 20-40A for 6 hours. They never charged (51.802924 1.024397). The charge was never more than 13.5V 3A in the summer.
I changed the PWM to MPPT and the solar was delivering 17.8v. The MPPT controller dropped this down to 13.5v and chatrged at 3A This winter I added more solar to 150W. the charge is now at 3.5A and we are getting to spring with two fully charged batteries. First time ever. The old one was aSteca Solsum 6.6 Solar Charge Controller, the new one is Epever Tracer 2210A 20A MPPT Solar Charge controller. Here is a review from a guy I know, this is what convinced me to change and to decide on the model. He has doone loads of vis=deos on PWM and controllers that claim to be MPPT.

https://www.youtube.com/watch?v=zTBrktPQdCM

.

[conachair]

Originally Posted by GTom

I am afraid I won't see Florida temps along the West coast of UK. To overcome the voltage issue, I'd use building blocks like these:
- 200W panel (Vp>18V) wired to a victron 15A controller

- or 2x100W panels in series, wired to a victron 15A

To find the sweet spot, it seems to be a matching game between controllers and panels. Overall, I aim for 300-400Wp, which means the voltage necessary for mppt will be there and I don't need to waste one full panel worth of power on controller efficiency.

It's the power that tails off with temperature, not voltage. (I think!!)

Mppt finds the sweet spot for you, that's the whole point of them - Maximun Power Point Tracking. They adjust the voltage to around Vp to get the best out of the panel by trial and error. Aren't most '12v' panels VOC more like 21v anyway? So no need for serial & the losses from shading, my 2 x 100W are in parallel, switching in and out the MPPT you can see the controller pulling the panel voltage down varying around 18v to find the max power over half a minute or so before it settles down.

[sailorchic34]

Originally Posted by conachair

It's the power that tails off with temperature, not voltage. (I think!!)

Nope, Voltage falls as temperature rises, roughly 1V per 20C rise, over 20 C. (20C being an international recognized standard temperature which panels are listed at) It's why a 12V panel's output voltage is so much higher. They allow for the voltage sag with high temperatures, so the voltage is normally over 14V under all conditions.

The temperature indicated is cell temperature and not air temperature.

For the higher latitude sailor, MPPT will give more bang for the buck. For the folks closer to the equator it's less of an increase in efficiency.

Myself I use a PWM as it's cheaper and being a poorer sailor, PWM is enough. Plus the added boost from a MPPT controller only really happens during bulk charging, Acceptance charging is standard PWM.

So if your batterys are mostly charged by 11 am, that is switched over to acceptance, then MPPT is not doing a lot for you. That is a PWM controller would also bring the batteries up, just a tad slower.

It does help more during partly cloudy conditions. Also not all MPPT controllers (and PWM controllers for that matter) are the same as they vary as to how often they check or calculate the MPP of solar output.

[conachair]

Originally Posted by sailorchic34

Nope, Voltage falls as temperature rises, roughly 1V per 20C rise, over 20 C. (20C being an international recognized standard temperature which panels are listed at) It's why a 12V panel's output voltage is so much higher. They allow for the voltage sag with high temperatures, so the voltage is normally over 14V under all conditions.

The temperature indicated is cell temperature and not air temperature.

For the higher latitude sailor, MPPT will give more bang for the buck. For the folks closer to the equator it's less of an increase in efficiency.

Myself I use a PWM as it's cheaper and being a poorer sailor, PWM is enough. Plus the added boost from a MPPT controller only really happens during bulk charging, Acceptance charging is standard PWM.

So if your batterys are mostly charged by 11 am, that is switched over to acceptance, then MPPT is not doing a lot for you. That is a PWM controller would also bring the batteries up, just a tad slower.

It does help more during partly cloudy conditions. Also not all MPPT controllers (and PWM controllers for that matter) are the same as they vary as to how often they check or calculate the MPP of solar output.

Stand corrected about voltage, ta.

temperature-affect-solar-panels-20687.html

Typically, silicon solar cell power output drops about 0.4 percent with every degree Celsius (1.8 degrees Fahrenheit).

The temperature refers to the actual material temperature, and not the air temperature, so on a sunny day it's not that unusual for a solar panel to reach 45 degrees C (113 degrees F). That means a panel rated for 200 watts at 20 degrees C (68 degrees F) will only put out 180 watts.

Still plenty voltage, but loosing some power.

Must be a lot of solar to hit absorption by 11am

IS there that much cost difference between 3 stage PWM & the likes of the Victron?

[Canibul]

Nice timing on this thread. I am in the process of deciding what I want to replace my aprox. 700 watts of solar with. I am looking at the semi-flex 100 and 120 watt panels. I already have a nice Outback MPPT so wasn't really planning to replace that, just the panels. I am curious as to the best way to go, spend more on high end panels, or go with the $150 cheapos and just plan to replace them more often. This approach actually seems to have some merit, depending on which parameters are most important. I will be replacing 1/4" plywood with something to attach the flex panels to. I am considering a method that leaves the underside of the panels largely exposed to open air, vs gluing them to panels of some kind. Like the plastic cardboard type panels.
In the FAQ's on one of the flex panel sites I was reading, the manufacturer recommeded PWM chargers over MPPTs because the MPPTs continue to use the cells even after the battery is charged ( according to them) and this keeps the heat high on the solar cells, and shortens their life. Perhaps this might explain the apparent popularity of the discontinued solar panels on aluminum backing. Aluminum is a great thermal transfer medium.

[john61ct]

Total power produced increases with lower temperatures, some panels go **over** Voc rating on clear cold days with reflected light.

So 75/15 don't put more than 65W.


If you want multiple panels per SC whether in series or parallel, put the groups on either side, so at least one group gets no shading.

A setup where a SC's group is split across the middle, so one side or the other is shaded will lose **a lot** of power output.

Ideal as I said is one MPPT SC per panel if you can swing the pricing / panel matching.

The MPPT advantage is greater with 40+ volts, and that's also where you can find the $/watt bargains. If you stick to nominal 12V (18-21Voc) panels, supercheap PWM SCs like $12-25, may be the way to go, just carry spares 8-)

[DreaminFred]

True, so far I was mostly looking at full panel+controller+etc sets, but Ebay&Amazon are full of MPPT controllers 40A<200$, this one apparently getting nice reviews. Maybe worth If I pick the parts myself...[/QUOTE]

Many of the controllers on EBay marketed as MPPT aren't. Watch the videos on Youtube that test the inexpensive "MPPT" controllers. Beware of "reviews" if there are fewer than a number you wouldn't personally fake to sell thousands of $50 items.

China makes nice looking labels and faceplates that may not have any relationship to the product inside the package.

F

[john61ct]

Yes for a good MPPT buy from trusted channels.

The supercheap PWMs it doesn't matter long as it works.

Kits are usually poor value

[GTom]

Originally Posted by DreaminFred

Many of the controllers on EBay marketed as MPPT aren't.

These weren't even labelled as MPPT . Anyway, it is quite clear now that I'll pick the parts individually. As for panels probably any rigid 160-200W would do (I know quality flex panels are a completely different story).

@Fiona: Thank you for the report on the Epever, I see those getting mostly good reviews on caravanist forums, I saw one account complaining about radio reception (should be FM-Stations, which are VHF frequencies!). Any disturbances there? Although the 20A controller is quite small, maybe shouldn't be an issue... More worrying was this old post, regarding the actual capability of MPPT operation. However, your (and quite a few customers at Amazon) experience definitely supports its superiority above MPV, meaning the issue is gone.

The Epever datasheet says 20mA self-consumption, Victron claims 10mA - this doesn't seem to be a significant difference (<<1W). Efficiency in a boat-environment/partial shading is an open question.

[GTom]

(sorry, PWM instead of MPV )

[nic26]

Originally Posted by Mike OReilly

My understanding and my research found that MPPT was generally superior to PWM. This left me wondering why anyone buys PWM. The price difference for the small controllers I was looking at was small, approaching insignificant.

Can you tell us what you found? On Amazon i.e. I find normal PWM ones for 12 Euros while the MPPT ones start at about 60 Euros.

[john61ct]

A €12 SC is not normal, it is super cheap, to be skeptical about.

Not to say may not be fine, but as I said carry spares.

A proper MPPT like the Victrons discussed above will extract more power from even low-voltage panels, 10-15+%. Lots more the higher the voltage.

[Capella]

Please do not take offense, but if you are considering "saving" $100 by using PWM when outfitting your multi-thousand dollar boat, you might as well give up now. MPPT is just so much better that there is no argument. Are you also going to photocopy charts, and use your phone GPS for navigation?

Regards Michael