MPPT Controller Explanation For Dummies

[T1 Terry]

Well that's a scenario I hadn't considered, charging all day with solar, then more with a gen set after dark till it's finished off. I would have thought finishing off with solar was more practical/cost effective, expensive charging the last bits when you have to pay for the fuel.

T1 Terry

[noelex 77]

I am not sure where the generator came from. The idea is to avoid using one of those.

[T1 Terry]

Originally Posted by noelex 77

I am not sure where the generator came from. The idea is to avoid using one of those.

from this

The value of MPPT comes when you are consuming more than you can produce with a PWM controller.

The only way an MPPT controller would not drop back to PWM mode is if the Ah used greatly exceeded the Ah produced by the solar and the MPPT controller, this would then need to be supplimented by generator charging wouldn't it?

T1 Terry

[noelex 77]

Unfortunately solar production is not constant, it varies with the seasons and locations and from day to day.
Like many boats relying on solar for much of the year we produce way more power than we can use. At this time of year MPPT is of no value.
During winter our production falls. Regulation is wasting power so we try to avoid regulation during the more marginal times. If we get close to regulation we will run the the water maker a bit longer, or back up the computer etc

During this time many boats manage their batteries in the 50-90% SOC, in a similar way to generator only equipped boats that tend to use the 50-80% band to avoid excessive regulation.(the slow charging rate of solar means higher SOC are more usable, with little or no regulation)

Solar production falls away near the end of the day which means as the batteries are nearing a higher SOC the available charging current is reducing naturally. High SOC are not unusually with minimal management.

The amount of power we can use is governed by the amount we can produce and while the extra 5-15% is only a small addition it is nevertheless valuable. This does not apply to everyone and for many yachts their money would have been better spent elsewhere. However the availability of good PWM regulators is decreasing and if you want good and versatile battery management options especially with data on solar production there are fewer non MPPT controllers that are suitable, especially for larger arrays.

[T1 Terry]

To me, if you are relying on the extra you may get from an MPPT controller over a PWM controller, you have a seriously under sized system. For the 5% to 15% to be a make or break means there is no margin in it for poor solar days, you could never catch up a bad day resulting in constantly under charged batteries and the resultant damage that would cause.
I understand the using the solar while it available on diversionary loads, but it would need to be very finely scaled to still leave enough extra to achieve the finish off charging required by lead acid batteries. It's one of those things we do with the lithium systems, in motorhomes we heat the water for the nights shower or make a loaf of bread etc, a water maker on a boat switched on by a high voltage cell would have the same effect. It surprises all new lithium battery users just how much faster their batteries charge without changing anything in their charging system, I think the money would be better spent in that direction than on an MPPT controller, better value for money.

T1 Terry

[goboatingnow]

Terry, I think some of the logic of your analysis is faulty.

Very few solar installations on boats are self sustaining, A lot of solar installations exist to top-up other charging methods, ie teh user cannot exist over a period of time solely on solar.

With that in mind, therefore , if you have a large >100W system, and the load is demanding less then the panel capability, then tracking the power point is a waste of time and a bit of wire is the best controller!. ( often called panel mode)

However, in the reversed situation, where the load is demanding more then then panel is capable of producing, in ALL does cases voltage conversion is a benefit ( ie static Vmp) and active tracking adds a little to that.

PWM is not a 'technique' , all it is , is connecting the panel to the battery, you could do the same thing with a voltmeter. The PWM part only plays a part in preventing high Vo ( operating) as the current falls. Below the absorption point, PWM is just a 'wire', with all the loss of efficiencies that 'can' occur with mismatched Vmp to Vo issues.

Arguing that you dont need all the power in the panel and hence dont need mppt, is a bit perverse.

Note , I take no part in the money v mppt argument, marine mppt pricing is merely 'new tech' & 'marine' market price setting.!!!


dave

[sailorboy1]

All this money talk! There are more things to consider as a practical matter.

Depending on the panels and controller quality the upgrade to MPPT doesn't necessary cost much as far as system total. When I did mine the price difference was $112 more to go the MPPT route and use higher voltage larger panels. And I bet a lot of that $112 would have been lost in mounting hardware to use 2 smaller panels instead. And the MPPT gave me a lot more programming and monitoring ability.

[Mystic38]

agreed..

when space is at a premium you can only fit what you can fit..at that point MPPT will give you more charging capability. period.

In my case, space (size) limited to a single 130W panel.. max charge current with MPPT went from 7.3A to 9.2A... about a 25% improvement, and took the entire system from "barely adequate" to "plenty with reserve"..

3 weeks in Georgetown and never started the engine once. To me, thats a success.

Originally Posted by Don L

All this money talk! There are more things to consider as a practical matter.

.

[s/v Jedi]

Originally Posted by Mystic38

agreed..

when space is at a premium you can only fit what you can fit..at that point MPPT will give you more charging capability. period.

In my case, space (size) limited to a single 130W panel.. max charge current with MPPT went from 7.3A to 9.2A... about a 25% improvement, and took the entire system from "barely adequate" to "plenty with reserve"..

3 weeks in Georgetown and never started the engine once. To me, thats a success.

There you go, another report of success and 25% improvement. Be prepared to be ridiculed or ignored by the naysayers though because they will not give up

[goboatingnow]

There you go, another report of success and 25% improvement. Be prepared to be ridiculed or ignored by the naysayers though because they will not give up

absolutely double

dave

[willardj]

I went ahead and put an mppt on my boat with our single 145w panel and have been quite happy with the results so far. 2 days ago when I finished getting it all together( the right way) I got a reading on my batt monitor of 10a.

[foggysail]

Originally Posted by goboatingnow

PWM is not a 'technique' , all it is , is connecting the panel to the battery, you could do the same thing with a voltmeter. The PWM part only plays a part in preventing high Vo ( operating) as the current falls. Below the absorption point, PWM is just a 'wire', with all the loss of efficiencies that 'can' occur with mismatched Vmp to Vo issues.

dave

Yes, in general I agree with your post. It is unfortunate however that the term PWM gets to be associated mostly with a buck converter which of course cannot output greater current than the input panels' output.

And yes, considering a buck PWM to be a 'wire' which is somewhat true as far as current transfer from a panel to a load is concerned with a plus for providing overcharge protection as you mentioned. All switch mode power conversion, flybacks, boost, bucks, bucks-boost use some type of PWM.

[hellosailor]

[chorus]
MPPT has become a magic buzzword and there are even totally bogus (not MPPT) units being sold on the web as MPPT. Caveat the unknown emptor, so to speak.

There are at least 3 different algorithms & logics used in MPPT controllers and among other things each maker can "poll" the solar panels and the battery at different intervals, adjusting the system more or less frequently. And apply different logic to what power they put out, i.e. pushing max amperage but "this much" more voltage than whatever the battery is at, rather than a simple 3-stage charging scheme.

I haven't seen anything that says any one scheme or maker is really a whole lot better than another, assuming you stick to the major brands, so capacity, price and warranty are the main comparison points.

The good news is that any MPPT controller will give you about 10% more effective power from your solar panels in most conditions. Whether that's worth your investment depends on your needs.

The bad news is that apparently 10-22% of the solar panels on the market, even from many brand names, are going defective and failing very early (2-5 years) as everyone has been cutting costs and outsourcing production. Article in the NYTimes earlier this week about this, so the great bargains in solar panels that everyone has been enjoying, may not be such bargains unless they're from a company that will be around to back up your warranty.

[goboatingnow]

Originally Posted by foggysail

Yes, in general I agree with your post. It is unfortunate however that the term PWM gets to be associated mostly with a buck converter which of course cannot output greater current than the input panels' output.

And yes, considering a buck PWM to be a 'wire' which is somewhat true as far as current transfer from a panel to a load is concerned with a plus for providing overcharge protection as you mentioned. All switch mode power conversion, flybacks, boost, bucks, bucks-boost use some type of PWM.

Yes but that has nothing to do with pwm solar regulators. There's no inductor and they are not buck or boost

Dave

[goboatingnow]

Originally Posted by hellosailor

[chorus]
MPPT has become a magic buzzword and there are even totally bogus (not MPPT) units being sold on the web as MPPT. Caveat the unknown emptor, so to speak.

There are at least 3 different algorithms & logics used in MPPT controllers and among other things each maker can "poll" the solar panels and the battery at different intervals, adjusting the system more or less frequently. And apply different logic to what power they put out, i.e. pushing max amperage but "this much" more voltage than whatever the battery is at, rather than a simple 3-stage charging scheme.

I haven't seen anything that says any one scheme or maker is really a whole lot better than another, assuming you stick to the major brands, so capacity, price and warranty are the main comparison points.

The good news is that any MPPT controller will give you about 10% more effective power from your solar panels in most conditions. Whether that's worth your investment depends on your needs.

The bad news is that apparently 10-22% of the solar panels on the market, even from many brand names, are going defective and failing very early (2-5 years) as everyone has been cutting costs and outsourcing production. Article in the NYTimes earlier this week about this, so the great bargains in solar panels that everyone has been enjoying, may not be such bargains unless they're from a company that will be around to back up your warranty.

Mppt has been around for nearly 20 years. It's cam provide anything uptp 25% boost which has been confirmed by several posters. With mismatched Vmp to Vo panels it can provide even more.

There are several mechanisms to track Vmp , most are based on the perturbate & observe method.


Dave