Recommend an MPPT?

[stevesgonewalkabout]

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.

This is exactly what I'm trying to do right now (on my phone). 
- I've found the $100 MPPT (linked above),
- a $170 panel with 230 watts I'm finding hard to locate?
- the mounting brackets can be bought for $15
- cables / connectors - these have me stumped. 

If I could find the above items I would go for it. If not I'm going to have to pay the extra for a  kit 200w with 20amp PWM for $310. 

Unfortunately I've simply run out of time.

 

[jimindenver]

You don't have to do a 230 watt panel. The Eco-w will easily handle a 250-270w panel if you can find a good deal.

Where are you looking in general if I may ask. (I'm pretty good at finding them)

 

[stevesgonewalkabout]

You don't have to do a 230 watt panel. The Eco-w will easily handle a 250-270w panel if you can find a good deal.

Where are you looking in general if I may ask. (I'm pretty good at finding them)

Hey Jim 

I'd love the help searching the but I just ordered a 200 watt kit off amazon  at $360 with tax and postage it's well over what a more savvy person could have built the system for, but I really need this installed. Once it's on the van I'll forget about the cost anyway

 

[jimindenver]

Steve

Part of the equation I talk about is what is available. Out of a number of options you found one that fills your needs now. That's all that matters. There is an advantage in that you can easily add a 12v panel or two or.... and not have to have them perfectly matched up. That can save you a lot of money if you ever wanted to expand.

 

[akrvbob]

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As you can see, point #1 above definitely applies to small installations on a van. Without any details, I can't really comment, it's pretty vague.

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. If we were at the tropics where there is no winter then this would be a good reason to choose PWM. But I doubt anyone here is, we all go through winter when it is plenty cold for maximum value of MPPT. Fortunately, that's when we need extra power the MOST!! Power production drops like a rock in the winter!! The days are short and the sun is low, that means little power. Summer is the opposite, long days give you lots of power!! The sun is very high and a good angle to the panels=lots of power.  

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. That's all a great theory for sunny days in the summer, But I can testify that it isn't all sunny days in the summer!!!!!!  

Guess what, rainy days happen on a regular basis! After a week of rain, you're going to be really glad to get 100% and not flush 36% down the toilet!!!!!! Or if it's stormy, and you get three hours of sun every day for a week, again, you'll be really glad to get 100%, not 64% on those few hours of sun. Then, ALL winter, I want 100% all day because I need it!!!

**** Plan and BUY for the worst weather--not the best. ****
**** Plan and BUY for the worst weather--not the best. ****
**** Plan and BUY for the worst weather--not the best. ****

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).  I respectfully disagree, based on 6 years of depending on solar. I began with a 50 watt panel that cost $350--and a MPPT controller. I'm up to 580 watt, and still a MPPT controller.  Why do I insist on MPPT? 

A group of us were in Flagstaff and we got 16 straight days of rain, we never saw the sun!!! Everyone ran out of power--BUT ME! Why? Am I magical?

**** I always Plan and BUY for the worst weather--not the best. ****

More important are the battery management features of the controller and overall efficiency of your electrical system.This I agree with totally!! Most people compare a $50 PWM to a $300 MPPT like the Blue Sky 30001 and say, "I'm not paying an extra $250 for MPPT!!!!" You're buying a whole lot more than MPPT. You're buying a 5 year warranty, American made, by a company that will really back it up and take care of you!! Call and ask a question and you might well talk to the owner or the EE who designed it and know everything abut it. More than anything your buying information about your system and control over it in many extra features that if you learn and use them could double the life of your battery. Without buying anything else you can set the absorption voltage and the time it holds it. In batteries like a $300 Lifeline, that's critical to getting your moneys worth out of it.

That $50 PWM will cut the life of your Lifeline AGM in half because it will never be charged the way it wants.!

Keep doing that and you'll beg to get a $300 Blue Sky!!
Bob 

 

[jimindenver]

I agree that temperature compensation is key to a hands off system. The thing is you have to know what the temperature compensation is going to decide to do. My Morningstar's temperature compensation follows Lifelines specs until I would need it the most. In extremely cold and hot situations it can't be made to follow Lifelines specs and I will have to either manually set the controller or disconnect the solar for the duration. I can tell you that the Eco-worthy is a lot easier to reset than the Morningstar.

One feature the Morningstar has that the Eco-w needs is a voltage sense line. Without it the controller senses the voltage through the lines to the battery and if they are a bit to thin, too long or a connection is weak, there will be voltage drop. A PWM controller will simply drop out of bulk and absorb too quick. A MPPT controller will be affected in Bulk too because it uses the battery voltage to decide what to do.