Solar controller MPPT or PWM

[Top cat]

I see that makers of MPPT controllers claim up to 30% more output for a given panel. Is this difference actually achieved in practice on systems up to 200W 12V ? or is this marketing hype ? Given that an MPPt controller costs about £50 more would I be better spending a bit more on a larger panel and using a PWM controller ?

 

Top Cat

[blodger]

My understanding is that the potential gains are lowest if you are using 12v nominal panels, better for 24v and a neccesity for anything above.

The chaeper MPPT controllers usually are not so you may as well get a good spec MPW.

You have to pay seriously more for a good MPPT.

I prefer 12v panels for boats & sheds and am with you in thinking more panels rathen than trying to squeeze more out of the panels with an expensive MPPT.

However, many do not see it that way so it's a case of personal experience/choice

[Ally]

I'd agree. Unless you are rolling in money, chose a good PWM, a Steca or similar. The cheaper MPPT's are less likely to give you any gain to speak of, over a PWM, and if you are connecting to expensive equipment that has, say, a Victron inverter or similar in the systems, how would you feel if a cheap MPPT took that out? Go for a good name in either, then it's really down to funds. We use PWM on our own boat completely successfully...a good one.... and it gives us all the info we need too.

Just my personal thoughts.

[Guest]

Interesting _ I'm finally getting around to ordering solar and I was seriously looking at a Steca controller.

[Justme]

I dont think its just the cost difference in the controller you need to account for.

 

12v nom panels tend to be more costly per watt than panels designed for house use. Then work out the cable costs for low voltage & high voltage installs as you can save quite a bit especially if the panels are not very near the controller. Smaller array fuses s,witches or breakers for the low amp higher voltage install.

 

Factor all that in as well & I bet the total installed premium for mppt is not £50.

[jenlyn]

I have two I dont use. 10 amp ones. PM me for price if wanted.

[Guest]

I have two I dont use. 10 amp ones. PM me for price if wanted.

Steca??

[jenlyn]

Yes, steca 1010 with the digital readout

[Guest]

Yes, steca 1010 with the digital readout

Cheers, better specd. than I was looking for.

[MtB]

I have discovered another advantage of a PWM over a MPPT.

 

With my Tracer MPPT, if the batteries it charges actually get badly discharged, it stops working! I arrived at Aldebaran the other day to find the Tracer auxiliary display blank and the Tracer MPPT appearing totally dead with no lights whatsoever. A bit of testing with the meter showed the solar panel producing 17v but the Tracer output zero. Battery voltage was 0.16v.

 

I assumed the Tracer had died and replaced it with a cheap PWM controller I had in the van. This worked and rapidly put some charge in the batteries. While I was waiting I jury-rigged up the tracer with a spare solar panel to a spare reasonably charged battery I happened to have lying around and it burst into life and actually worked perfectly.

 

I conclude at the Tracer MPPT won't charge a dead battery, whereas a cheap PWM will. This is a major reason to go PWM in my opinion.

 

MtB

 

Edited to clarify: I'd left the domestic isolator ON by mistake last time I left the boat and something (no idea what) appears to have drained the batteries faster than the solar could recharge them. Once the battery voltage fell too low the Tracer stopped playing.

Edited June 4, 2013 by Mike the Boilerman

[Justme]

MtB

 

Thats actually a very good reason to use a MPPT controller.

 

Keeping pumping energy in to a duff battery is a sure fire way to start a fire.

 

A good system will shut down if the system goes outside of safe limits.

[MtB]

MtB

 

Thats actually a very good reason to use a MPPT controller.

 

Keeping pumping energy in to a duff battery is a sure fire way to start a fire.

 

A good system will shut down if the system goes outside of safe limits.

 

 

Yes agreed, but my Tracer MPPT failed to detect a perfectly good battery seriously discharged.

 

Tracer MPPT controllers don't constitute, therefore, "A good system"

 

 

MtB

[matty40s]

S'ok mike has another boat.

 

mppt all the way for me. 24 and 36v panels still available cheaper than 12v ones; and the performance is pretty impressive when you need to use heavy power draw, power tools, iron etc

[MtB]

S'ok mike has another boat.

 

mppt all the way for me. 24 and 36v panels still available cheaper than 12v ones; and the performance is pretty impressive when you need to use heavy power draw, power tools, iron etc

 

Iron???????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????]

[matty40s]

I wanted to spare paddyr the embarrassment of admitting the hoover use.....

[Top cat]

The kit I'm considering is all Victron which I hope is good stuff, at least their battery monitor is

 

The panel will mounted quite close to the controller and the batteries

 

The panels have a max power point of 18V and and open circuit voltage of 22V and a short circuit current of 8A

 

The PWM controller is rated at 10A and costs £33

 

The MPPT is rated at 20A and costs £89

 

I figure that if the 130W panel isn't enough I could add another if I go the MPPT route

 

So "IF" the two controllers are of similar quality is the claimed 30% improvement likely to be real given that the panel max power point is 4V above the battery charging voltage ?

 

I also have the choice between mono and poly crystalline panes, am I right in thinking that provided I can find room for the larger but cheaper poly crystalline panel that it should perform the same as a mono panel of the same nominal wattage ?

 

Top Cat

[Paul C]

Can't really compare a 10A controller with a 20A controller....

 

The 30% improvement isn't that meaningful now, but when conditions are poorer (eg cloudy, winter) then it really helps.

[smileypete]

I see that makers of MPPT controllers claim up to 30% more output for a given panel. Is this difference actually achieved in practice on systems up to 200W 12V ? or is this marketing hype ? Given that an MPPt controller costs about £50 more would I be better spending a bit more on a larger panel and using a PWM controller ?

 

Top Cat

 

PWM can work out better for smaller installs, domestic sized panels on 24V boats, and where roof space constaints mean 12V panels must be used anyway.

 

 

 

Yes agreed, but my Tracer MPPT failed to detect a perfectly good battery seriously discharged.

 

Tracer MPPT controllers don't constitute, therefore, "A good system"

 

 

MtB

 

Probably it's because the Tracer needs to see a healthy batt voltage to auto select the right charge voltage for 12V or 24V batts. More likely that it's powered from the batt side and not the solar side so won't power up til it gets 12V on the batt terminals.

 

You might as well say that Vaillant combi's don't constitute 'a good system' because they have more controls than an on/off button, or break down because they're installed by idiots.

 

cheers, Pete.

~smpt~

Edited June 4, 2013 by smileypete

[Justme]

The panels have a max power point of 18V and and open circuit voltage of 22V and a short circuit current of 8A

 

 

So "IF" the two controllers are of similar quality is the claimed 30% improvement likely to be real given that the panel max power point is 4V above the battery charging voltage ?

 

 

 

 

 

You will be loosing about 30 watts per panel with that 4v drop in voltage.

[George94]

It eventually got through my thick skull that PWM is appropriate when the panel voltage is not much above the battery voltage. Larger panels will have a significantly higher voltage than the battery, and that is where MPPT controllers make sense. They convert the excess voltage into extra amps.

 

Because larger panels tend to cost less per watt, and because for a given wattage you can use lighter cables when the voltage is higher, MPPT controllers offer cost savings elsewhere.

 

But it's a minefield matching panels with MPPT controllers. However many panels you choose, their voltage or wattage will slightly exceed the limits of your favoured controller, and you will have to go to the next size up, costing £hundreds more.

 

Happy the man who can make sense of all this.

[matty40s]

and you will have to go to the next size up, costing £hundreds more.

 

methinks you are eggs aggerating a bit, or you have been ripped off by smooth talking solar floating man.

[blodger]

 

 

You will be loosing about 30 watts per panel with that 4v drop in voltage.

 

The potential to loose 30w through a 4v drop is ameliorated by MPPT but I have not found it possible to to achieve a 30% return with MPPT on a modest 12v nominal installation over MPW

[peterboat]

I have discovered another advantage of a PWM over a MPPT.

 

With my Tracer MPPT, if the batteries it charges actually get badly discharged, it stops working! I arrived at Aldebaran the other day to find the Tracer auxiliary display blank and the Tracer MPPT appearing totally dead with no lights whatsoever. A bit of testing with the meter showed the solar panel producing 17v but the Tracer output zero. Battery voltage was 0.16v.

 

I assumed the Tracer had died and replaced it with a cheap PWM controller I had in the van. This worked and rapidly put some charge in the batteries. While I was waiting I jury-rigged up the tracer with a spare solar panel to a spare reasonably charged battery I happened to have lying around and it burst into life and actually worked perfectly.

 

I conclude at the Tracer MPPT won't charge a dead battery, whereas a cheap PWM will. This is a major reason to go PWM in my opinion.

 

MtB

 

Edited to clarify: I'd left the domestic isolator ON by mistake last time I left the boat and something (no idea what) appears to have drained the batteries faster than the solar could recharge them. Once the battery voltage fell too low the Tracer stopped playing.

Hi Mike interesting stuff I to have 2 tracers i suspect that they must require voltage to power themselves up? However for my panels they will have to stay, as it would mean redoing all the wiring etc and I would also lose a lot of power from the 30 v panels. I wonder however how much voltage they need to work/ mmmm

 

Peter

[smileypete]

The kit I'm considering is all Victron which I hope is good stuff, at least their battery monitor is

 

The panel will mounted quite close to the controller and the batteries

 

The panels have a max power point of 18V and and open circuit voltage of 22V and a short circuit current of 8A

 

The PWM controller is rated at 10A and costs £33

 

The MPPT is rated at 20A and costs £89

 

I figure that if the 130W panel isn't enough I could add another if I go the MPPT route

 

So "IF" the two controllers are of similar quality is the claimed 30% improvement likely to be real given that the panel max power point is 4V above the battery charging voltage ?

 

I also have the choice between mono and poly crystalline panes, am I right in thinking that provided I can find room for the larger but cheaper poly crystalline panel that it should perform the same as a mono panel of the same nominal wattage ?

 

Top Cat

 

First of all it's good to work out how much of a premium the MPPT will cost in terms of extra power output.

 

In full sun, when your batts are 12.8V and the panel is producing 8A the PWM controller will deliver about 100W (8A x 12.8V). When the batts are 14.4V the PWM will deliver about 115W (8A *14.4V) So the PWM will deliver between 100W and 115W say.

 

In full sun the MPPT will make use of the maximum power point of 18V and 8A and deliver about 145W (18V x 8A) when your batts can take it. So the MPPT will deliver up 30W to 45W more than the PWM.

 

Given a reasonable 10A PWM may be had for £20ish, in this case for now the extra £65 on an MPPT to get another 30W to 45W is costing £1.35 to £2 'per watt' (£65 / 30W or £65 / 45W)

 

As for PWM controllers a lot of the cheap PWMs are rubbish but here's a reasonable 10A PWM made Tracer/EP Solar:

 

http://www.ebay.co.uk/itm/10A-12-24v-EP-Solar-LS1024-Solar-Charge-Controller-/281116108436

 

Now turning to the panels themselves, if roof space is at a premium like on a typical narrowboat, usually the 12V panels on Ebay start around £1/Watt, but sometimes go for a bit less, eg:

 

http://www.ebay.co.uk/itm/80-Watt-Solar-Panel-PV-Monocrystalline-12V-80W-T-Power-Module-/370814420025

 

Overall it depends on how much roof space there is and the likelihood for future expansion. Sooo maybeeee if it's a typical narrowboat roof and power needs are quite modest, start off with a 130W Victron panel or 2x80W Ebay panels and a £20ish PWM as linked to above, and add another panel and possibly MPPT later too if needed.

 

cheers, Pete.

~smpt~

Edited June 5, 2013 by smileypete

[George94]

methinks you are eggs aggerating a bit, or you have been ripped off by smooth talking solar floating man.

 

 

A bit, yes.

 

But I have been trying to size up an array of around 800 watts, and have found it very difficult to determine which MPPT is best.