Recommend an MPPT?

[stevesgonewalkabout]

Hey all,
I've done a quick search but I haven't come up with much. I need to order an MPPT tomorrow morning to have it delivered while I'm staying at a friends. 

I'm looking at this solar panel:
-Will this work with a 27V/210W Polysilicon panel. 

I'm trying to find a reasonably priced MPPT to work with it. 

I have found this:
Tracer MPPT Tracer1210RN Solar Charge Controller Regulator 12/24V INPUT 10A https://www.amazon.com/dp/B008KWPGS6/ref=cm_sw_r_cp_api_hpnrxbF8SVZDD


But with my total lack of knowledge about solar I'm getting confused here. 
It says it can take 100vdc, but max input 130 watt for 12v system. 

Can you guys let me know of a similar alternative if this isn't suitable for the panel above? 

Thanks in advance, this item is holding up the build on the van to no end!

 

[phillipaaron]

130watt @ 12v
260watt @ 24v

This controller would work. To calculate amount of amps to support is:
Watts / Volts = Amps
210w / 24v = 8.75amps is less than 10A so you're good.

 

[rvpopeye]

I have a Blue Sky but the Morningstar's look like my next one at upgrade time.

 

[BradKW]

I'm not sure if you've bought the panel yet, but if you stay with 12v panel(s) you won't need to spend the extra hundreds for MPPT, and instead will do just fine with PWM?

I believe most of the better known brands like Morningstar, Midnight, Outback, Xantrex all start around $500+

One exception that I'd looked at awhile back was Midnight's "The Kid": https://www.altestore.com/store/cha...30a-mppt-charge-controller-150v-black-p11138/
It's around $300...I thought it was interesting because its designed to be expandable with a 2nd unit.

But again, if you haven't bought a panel yet, it's likely that you'll end up saving a fair bit going with 12v ...Renology has some attractive panel/controller kits as well.

 

[amwbox]

Tend to agree with above. If you're system is low wattage, PWM should be fine. You start really getting MPPT benefits with larger arrays. Or if you use the higher voltage grid tie panels.

Morningstar is my preferred brand in any case. But you pay for it.

 

[jimindenver]

The Eco-worthy 20 amp MPPT controller is $102, I have used them for years. Simple, dependable, easy to use.

http://www.eco-worthy.com/catalog/worthy-mppt-solar-charge-controller-12v24v-p-182.html

 

[stevesgonewalkabout]

Thanks guys,

I really appreciate the replies. With such a short time frame it makes it very hard to get any research in.

I was looking at buying a second hand panel, so shying away from the 12v panels as I'm struggling to find them at a reasonable cost.

MPPT and 210 watt panel above is $230 or so, along with ancillary components which will add of course.

If the above MPPT will handle the 210 watt panel then I may go for it. Or move up to the 20 amp MPPT listed above.

This is my first build and there is an incredible learning curve to building a van conversion. All this advice really helps.


Note - the 20amp tracer MPPT is $100, so $30 more.

 

[akrvbob]

A general principle I live by is "Don't buy barely-enough". It'll be taxed and work hard and fail much sooner. That controller is ever so barley enough and with electronics that means heat and heat means a short life. Get the 20 amp MPPT at the minimum.

I'm a really big fan of Blue Sky. I have a 2000e and I really like it, but the newer 3000i gives you a huge amount of control over the charging right on the face of it. You can set the absorption voltage and the time it holds it without buying anything else. That's going to mean a MUCH longer battery life. I believe it will pay for itself in longer battery life.
Bob

 

[stevesgonewalkabout]

Thanks for the replies everyone, 




So there seems to be two options ways to go, pwm with 12v panel or the MPPT with a higher voltage panel. This is what I've come up with:







1. $100 MPPT 

MPPT Tracer2210RN Solar Charge Controller Regulator 12/24V INPUT 20A https://www.amazon.com/dp/B008KWPH12/ref=cm_sw_r_cp_api_x4trxbCDF6K5H



And 



$160 27v/ 210 watt solar panel. 

http://sacramento.craigslist.org/ele/5589874219.html



For a total of $260 





Or 



2. Pwm $50

P30L LCD 30A PWM Solar Panel Regulator Charge Controller with Digital Display and User Adjustable Settings https://www.amazon.com/dp/B00JMLPP12/ref=cm_sw_r_cp_api_17trxbDXWQ4DQ



and (for example) 

200watt 12v panel 

http://sunelec.com/solar-panels/sonali-200w-solar-panel-12v.html



For a total of $250


It seems the options are very similar in price, with the first option having a second hand panel. 

 

[BradKW]

I would probably lean more toward something like this: http://www.amazon.com/WindyNation-2...ds_two_browse-bin:6907043011,p_89:WindyNation

1) Cables included
2) Amazon return and guarantee policies
3) qualifies for Prime, so free 2-day shipping is possible.

 

[ViaVacavi]

I just wanted to add something to the conversation. While MPPT is a great technology, it's largely misunderstood.

To really reap the advantages of MPPT, your panel voltage should be substantially higher than your battery voltage. Wiring 2 12v panels in series is almost a minimum requirement to start seeing any advantages. MPPT is also poor when solar cell temperature is high, as the voltage differential needed by MPPT decreases, and installations on a van can involve close clearances which impact cooling. Adding to that, MPPT controllers do use more power just to operate, which is insignificant on large systems, but have a larger impact on small systems. MPPT is great for large installations where large series arrays with higher voltage is used to combat cable losses and the panels have adequate cooling.

On small systems under 300 watts, and especially at 12 volts, there can be very little gain and even a loss of efficiency compared to PWM. Even in the most efficient conditions for MPPT on a low wattage system mounted on a van roof (without a decent inclination angle), I would be surprised if the efficiency increase wood leave the single digits.

The best way to maximize solar collection on a van is to have an adjustable mounting system, and facing the panels south, inclined to match your current latitude.

With the unique disadVANtages we have (improper inclination of the panel, inadequate cooling, low voltage strings and low capacity of the system), it makes much more sense to spend that extra money on making other areas of your electrical system more efficient (insulating your fridge, modifications that allow for natural draft to aide in cooling, LED bulbs, efficient ARM computers instead of power hungry x86 laptops that hog power, etc)

A decent and cheap pwm is really all you need with small systems that don't appeal to ideal MPPT conditions. And as Bob mentioned above, choosing a controller that lets you dial in your float, absorption, cutoff etc voltages should be high on your list, and there are many PWM controllers that would fit the bill

 

[29chico]

I would suggest that you get a controller that will play well with your batteries.  So check the charging voltage set points and make sure the stock settings for your prospective controller purchase has bulk, absorption and float voltages that will work well with whatever battery you are considering.  That or get a controller that allows you to set the charging voltage parameters.

Also, a controller that has the ability to have a remote temp sensor right on the battery, so that it can temperature compensate for varying battery temps will do a better job of correctly charging.

I would rather have a PWM charge controller with remote temp sensing than a MPPT controller that is incapable of properly temp compensating.

I like the Morningstar line of charge controllers, pretty good stuff across the line.

 

[akrvbob]

I basically agree with you, but I respectfully reach very different conclusions about a couple of your points and I'll tell you why in red after quoting you. 

To really reap the advantages of MPPT,  your panel voltage should be substantially higher than your battery voltage. That's very true, but nearly all 12 volt panels are 18 volts so if you're battery will only take 13 volt at that moment, the PWM controller is flushing 5 volts down the toilet. That's 36% of your power production and that is a terribly unacceptable amount. Whatever small amount of power the MPPT itself takes, is nothing compared to 36% waste.

MPPT is also poor when solar cell temperature is high, as the voltage differential needed by MPPT decreases, and installations on a van can involve close clearances which impact cooling.  I disagree, it's not poor when temperatures are high, it's just not as good. But, at the same time, it works exceptionally well when they are cool. Let's think about what that means:

1) In the summer, when you are probably producing more power than you need, MPPT is only doing an okay job. it still works, and is better than PWM, but not spectacularly well.
2) In the winter, when the sun is low and the days are short, MPPT works exceptionally well!!! When you need it most, it does it's best job!!!!

Getting more panel from your panels in the winter is reason alone to buy MPPT!!
Bob

 

[jimindenver]

There are two time MPPT helps. Early when the battery voltage is below 13.6v and a PMW controller is dumping voltage and power. There is also peak output. a 115W panel puts out roughly 6 amp at peak, two would be 12a. My 230w watt panel easily puts out 15a and often 16a at peak. Not only that but the lower the battery voltage, the higher the amps climb.

MPPT and PMW are options that need to be balance with many things as you work out your system. There is no right, only what is right for you.

 

[ViaVacavi]

Here is a copy and paste from Morningstar's own white paper on the subject (starting on page 9):
(white paper url: http://www.morningstarcorp.com/wp-content/uploads/2014/02/Morningstar-Corporation-Traditional-PWM-vs-TrakStar-MPPT-Whitepaper-March-2015.pdf )

-------------------------------------------------------------------
PWM Over MPPT:

The preceding discussion of PWM vs. MPPT may cause some to wonder why a PWM controller would ever be chosen in favor of an MPPT controller. There are indeed instances where a PWM controller can be a better choice than MPPT and there are factors which will reduce or negate the advantages the MPPT may provide. The most obvious consideration is cost. MPPT controllers tend to cost more than their PWM counterparts. When deciding on a controller, the extra cost of MPPT should be analyzed with respect to the following factors:

1. Low power (specifically low current) charging applications may have equal or better energy harvest with a PWM controller. PWM controllers will operate at a relatively constant harvesting efficiency regardless of the size of the system (all things being equal, efficiency will be the same whether using a 30W array or a 300W array). MPPT regulators commonly have noticeably reduced harvesting efficiencies (relative to their peak efficiency) when used in low power applications. Efficiency curves for every Morningstar MPPT controller are printed in their corresponding manuals and should be reviewed when making a regulator decision. (Manuals are available for download on the Morningstar website).

2. As explained in the Environmental Considerations section, the greatest benefit of an MPPT regulator will be observed in colder climates (Vmp is higher). Conversely, in hotter climates Vmp is reduced. A decrease in Vmp will reduce MPPT harvest relative to PWM. Average ambient temperature at the installation site may be high enough to negate any charging advantages the MPPT has over the PWM. It would not be economical to use MPPT in such a situation. Average temperature at the site should be a factor considered when making a regulator choice (See Appendix).

3. Systems in which array power output is significantly larger than the power draw of the system loads would indicate that the batteries will spend most of their time at full or near full charge. Such a system may not benefit from the increased harvesting capability of an MPPT regulator. When the system batteries are full, excess solar energy goes unused. The harvesting advantage of MPPT may be unnecessary in this situation especially if autonomy is not a factor.

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As you can see, point #1 above definitely applies to small installations on a van. 

Point #2 I guess can be hit or miss.  Part of it is the climate you're currently in.  Another factor could be poor cooling of the panels themselves - for example, a glued down flexible solar panel would dissipate heat poorly.  Conversely, driving down the road could cool the panels enough that climate isn't a big deal - but in that case you could be charging from the alternator anyways.

Point #3 above, I believe is the most misunderstood.  MPPT will be of little added benefit if you're generating much more power than you're using, since the algorithm is only active while in bulk charging mode.  If you're constantly in absorb mode, then there is no benefit at all over PWM.  Simply put, if you're spending even an hour or two per day in absorb mode, then at the end of the day it's a wash.  Sure, you collected power a little quicker and charged a little quicker in many instances - but if a cheaper controller would have got you to the same place by the end of the day by staying in bulk mode a little longer,  then nothing was really gained. 

All I'm saying is that the MPPT/PWM debate should be a lot lower on the list than most people put it.  On installations this small, the gain is pretty negligible, and even non-existent in many cases (especially where the system wasn't sized and matched correctly from the beginning, which many fall victim to).  More important are the battery management features of the controller and overall efficiency of your electrical system.

 

[Canine]

I tend to believe mppt is a lot like religion,it began when the first con man met the first sucker.Having found no independent source for unbiased information,I'm going to buy an mppt this fall and find out the facts for myself.Most of the studies I've seen are done by or paid for by a manufactor.At the moment,the only advantage I can see is the ability to use smaller wire for longer runs with higher voltage.Why would mppt work great with 1000 watts of panels and not work well for 200 watts of panels as some have implied?I may change my name to Didymus.

 

[jimindenver]

Three things about a MPPT controller.

The MPPT program only works in bulk because there is no other means of controlling it without losing the excess power like when the battery does it in PMW.

The bulk converter that takes the excess voltage and converts it to amps runs all the time even in absorb and float. When I run the A/C while in float the big system pushes 45a out of three panels rated for 8.6a.

Look at a schematic of a MPPT controller and you will find that they all use a PMW style of charging after the buck converter and MPPT program. The only difference is all of the panels watts are available.

On the heat thing. Usually by the time it is hot enough to even notice that the gap between PWM and MPPT has narrowed but PWM still doesn't catch up, you are likely in float and wouldn't notice. However if you were to take two batteries at 12v on two systems and charge them in the heat of the day, you will find that yes the MPPT system does lose a amp or so to the heat BUT the PWM system is still limited to 12v and dumping a third of its power. The MPPT system is gonna kick it's......

I am not here to argue it, only to try to help people understand and make a educated decision. In five years I have had people that have never touched the tech or had any idea what they were talking about tell me I was wrong. That's great for them but don't force others to be stubbornly stupid.

 

[ViaVacavi]

I tend to believe mppt is a lot like religion,it began when the first con man met the first sucker.Having found no independent source for unbiased information,I'm going to buy an mppt this fall and find out the facts for myself.Most of the studies I've seen are done by or paid for by a manufactor.At the moment,the only advantage I can see is the ability to use smaller wire for longer runs with higher voltage.Why would mppt work great with 1000 watts of panels and not work well for 200 watts of panels as some have implied?I may change my name to Didymus.

It'll work fine with your 200 watts, just less efficiently than it will with a higher power setup. Part of the efficiency differences between a low power and a high power solar setup are from the power required to run the unit being a larger percentage of available power, another part is the loss during the DC to DC conversion process, which becomes less efficient at lower currents.

 

[ViaVacavi]

Three things about a MPPT controller.

The MPPT program only works in bulk because there is no other means of controlling it without losing the excess power like when the battery does it in PMW.

The bulk converter that takes the excess voltage and converts it to amps runs all the time even in absorb and float. When I run the A/C while in float the big system pushes 45a out of three panels rated for 8.6a.

Look at a schematic of a MPPT controller and you will find that they all use a PMW style of charging after the buck converter and MPPT program. The only difference is all of the panels watts are available.

On the heat thing. Usually by the time it is hot enough to even notice that the gap between PWM and MPPT has narrowed but PWM still doesn't catch up, you are likely in float and wouldn't notice. However if you were to take two batteries at 12v on two systems and charge them in the heat of the day, you will find that yes the MPPT system does lose a amp or so to the heat BUT the PWM system is still limited to 12v and dumping a third of its power. The MPPT system is gonna kick it's......

I am not here to argue it, only to try to help people understand and make a educated decision. In five years I have had people that have never touched the tech or had any idea what they were talking about tell me I was wrong. That's great for them but don't force others to be stubbornly stupid.

It's all good, I'm also just trying to educate, which is why in l linked to a whitepaper from a very reputable manufacturer on the subject.

For what it's worth, I owned my own business in the Renewable Energy field for a number of years, and designed and produced a few lines of controllers for the wind industry (40kw and above), so I do have knowledge on internal workings of controllers

 

[jimindenver]

Why would mppt work great with 1000 watts of panels and not work well for 200 watts of panels as some have implied?I may change my name to Didymus.

Bob

I don't want to befuddle you again so I'll try harder this time.

MPPT works just as well on a small system as it does on a large one. The thing is the advantage provided may not warrant the extra expense of a MPPT controller while a extra panel would simply do more for you.

The argument is changing since MPPT controllers are getting smaller and less expensive and 24v panels are getting bigger and considerably less than 12v panels. Price out a pair of 115w 12v panels and a controller and compare it to the $170 I would pay for a 230w panel and a $102 MPPT controller. Then take into account the benefit early on and the three extra amps at peak.