Instant benefit from replacing Solar PWM with MPPT controller?

[Suijin]

The there are 24”x60” panels that are 160 watt so I’d start with replacing your panels.

[FionaJC]

As an Electronic Engineer I did lots of calculations and maths. At the end of the day its not an exact science because of shadows, guano, dirt angle of sun etc. I have had a cheap PWM with 200W for 10 years and every winter my batteries die due to my bilge pump. I have used the SWAG approach (scientific wild arsed guess)

This autumn I changed the batteries, replaced two damaged panels and went to MPPT with a decent Epever controller. I have now added Wifi and a logger. I know that I had 3Kw of power and they charged at a higher amperage under MPPT than PWM as I have a rough idea what I get at what time of year.

My batteries remained fully charged even though we have had snow. Forget the calculations, the change was worth the expense. I usually stop sailing in October and start again in march.

Do your research, watch lots of YouTube, don't pay over the odds and dont buy too cheap otherwise you do what I did and bought twice.

[FionaJC]

Originally Posted by sailorchic34

Oh good lord.

I am with you all the way on this for many reasons, we are both engineers, w e make assumptions in our simplified factual explanations, but as women our opinions are 75% less effective, You were being empirical and I was being apocryphal.

Its like asking how wet is a damp piece of string. - Answer ? It Depends.

I originally went PWM due to cost. MPPT is better but was much more expensive.

Where Sailorchic is they have sunshine, where I live we have winter darkness and low sun horizon.

Can I suggest you see how it goes and if stuck for a birthday present you ask for an MPPT controller. I paid £41.53 for a 20A controller ( I want expansion head room).

[sailorchic34]

Engineers use WAG in calculations all the time.

I do agree that MPPT does deliver more amps then PWM. No question there. My only point is it is sometimes cheaper to just add one more 100 ish watt panel, which for a nominal $100 will provide 4.75 ish ah during the peek 5 hours of sun. That is a bit more then twice what a good MPPT controller will do.

OK I know there are cheap MPPT controller out there. But for bang for the buck three 100 watt panels will provide more ah then two 100 watt panels with mppt and do it for the same or less $$$

That is assuming someone with two 100 watt panels. If your using 24v panels then your going MPPT anyway. (unless you have a 24V system).

For me it made sense to use 100 watt panels. First mine are mounted so they can pivot up and down, which is handy when the boat flops with the tide and lighter and easier to girl handle and position then the larger 200-240 watt panels.

If my controller dies I can connect my 12v panels direct to the battery's with a disconnect and still charge the batteries. OK technically you CAN connect 24v panels to partly discharged 12v battery's direct too. But you have to keep an eye on the voltage much closer, so the batteries don't barf and die.

[BruceS]

Now give us similar graph for Dec in the N Hemisphere....
There is a stage in the morning and evening when MPPT won't do any charging when PWM will.
On the other hand at present I have 105v VOC strings ..... try that on a PWM.......
There is NOT a simple answer....

[svlamorocha]

Originally Posted by john61ct

Watts per hour is commonly used to define watt-hour

That may be as common as ignorance. "Per" as in "kilometers per hour" means "divided by". The dash in "watt-hour" means "multiplied by". Those are different things.

[44'cruisingcat]

Originally Posted by 48d north

As we are also putting new 100w panels on our boat this season we appreciate all the treads that have been cropping up lately with this topic. And we especially appreciate sailorchic's responses in lay-person's terms as I struggle with putting solar on a sailboat. (We use alternative energy at home, much easier). In speaking with 2 well known manufacturers of solar kits it was strongly recommended that we stay with a PWM controller because the cost of a MPPT did not start to payback till we were well over 400w and to just add another 100w panel to the set up if we needed. How does that sound sailorchic? Thanks OP for your questions to get this going.

Adding more solar panels is probably the most cost effective way to increase power collection, but on a boat there are space limitations.

[StuM]

Originally Posted by GTom

This one was measured and posted by Maine Sail

Charging LiFePo4, which can take all the current you can throw at them. The optimum case to demonstrate the supeiority of MPPT.

Where you are using solar during the day for charging FLA and to power variable house loads, you will very rarely see anything like that improvement.

[StuM]

Originally Posted by FionaJC

This autumn I changed the batteries, replaced two damaged panels and went to MPPT with a decent Epever controller. I have now added Wifi and a logger. I know that I had 3Kw of power and they charged at a higher amperage under MPPT than PWM as I have a rough idea what I get at what time of year.

My batteries remained fully charged even though we have had snow. Forget the calculations, the change was worth the expense. I usually stop sailing in October and start again in march.

Again, an indication of the variable advantage of MPPT. In a cold climate Vmp will be higher and you will see a much larger gain from MPPT than you would in the tropics.

To reiterate.

YMMV dependent on a number of factors, To just claim x Watts increase from y Watts of nominal power is absolute nonsense without taking a number of factors into account is nonsense.

[StuM]

Originally Posted by sailorchic34

Engineers use WAG in calculations all the time.

Good engineers use the correct units.

[StuM]

Originally Posted by sailorchic34

I do agree that MPPT does deliver more amps then PWM. No question there. My only point is it is sometimes cheaper to just add one more 100 ish watt panel, which for a nominal $100 will provide 4.75 ish ah during the peek 5 hours of sun. That is a bit more then twice what a good MPPT controller will do.

Now on that we are 100% in agreement!

[sailorchic34]

Originally Posted by svlamorocha

That may be as common as ignorance. "Per" as in "kilometers per hour" means "divided by". The dash in "watt-hour" means "multiplied by". Those are different things.

Per CAN mean divided by, but it may also be used to mean "for each" as well.

[FionaJC]

Originally Posted by StuM

Good engineers use the correct units.

But they simplify for non-engineers who would otherwise be confused.

[sailorchic34]

Originally Posted by StuM

Good engineers use the correct units.

You mean like feet, inches, BTU"S and fathom?.

Not everyone speakie di engineering, Let alone with a southern accent.

[StuM]

Originally Posted by svlamorocha

That may be as common as ignorance. "Per" as in "kilometers per hour" means "divided by". The dash in "watt-hour" means "multiplied by". Those are different things.

Ashley, the dash in watt-hour doesn't mean anything and it is not a recognised unit name.

The correct forms are "Watt hour" and "Wh". Note the upper case "W" and lower case "h".

For those who are still unsure about the appropriate units, you may like to peruse:
http://www.cruisersforum.com/forums/...ml#post1933764

Read the whole thread if you want to waste a couple of hours seeing how difficult it has been (and apparently still is) for some here to grasp the simple basics.