thinking about going mppt...

[birdhouse]

hello all-
i've been debating about getting into a solar mppt controller for my off grid system.  problem is, my panels are somewhat of a mishmash.  this is all for a 24v bank. 
i've got:
two- evergreen 195w 18.? Vmp wired in series for 36.? Vmp 390w
two- of the same as above, but with cracked glass that's been repaired with clear-cote ~90w each
two- sun brand 245w 30.7? Vmp wired each on their own wires to bank. 

question: can all of these panels run on one charge controller without reducing output of certain panels because of the wattage/voltage mismashes? 

i'm guessing the answer is no, one controller won't do it.  if this is the case i may just run the non-cracked evergreens (390w) on a morningstar sunsaver 15 because it would be right at the max the controller could handle, and it's cheap by comparison. then continue to run the other panels off my ts-60.   

any other thoughts/recommendations on controllers/solutions that don't break the piggy bank yet get my oddball array all on mppt? 

thanks for any replies!

adam

[DamonHD]

Do you have to do it all at once and all on one controller?

For example the Morningstar SS-MPPT-15L that I have can handle 400W @ 24V which could do all your Evergreens at a pinch I think.  I have a horrible mix of paralleled panels on my Morningstar which is probably not maximally efficient, but at least your Evergreens may be reasonably matched.

Then, if you like it, you could do something separate for the rest; in the mean time you'll have a hybrid system with intermediate efficiency.

Rgds

Damon

[birdhouse]

damon-
i'd prefer to put it all on one controller like a ts-60 mppt, but i'm pretty sure some of my panels would drag the others down in that scenario. 

 i'm leaning towards using the sunsaver for my two good evergreens for now.  its a bummer that controller doesn't max at 500 watts for 24v.  then i could get two and use the other for my pair of 245 watters. 

i wonder what would happen if i series wired one of my 245w 30.7Vmp panels with one of my broken glass evergreen ~90w 18Vmp and plugged that into a sunsaver?  or could i do two sets like that and parelell the sets into ts-60/45 mppt? 

thanks!
adam

[DamonHD]

It would be common to have multiple strings even on a single MPPT inverter if panels are not perfectly matched, eg for me because I have some facing east and some west.  So I don't think that having separate controllers is *that* big of a deal, and does give you some fallback if something blows up!

Don't mix different panel types or positions (or brokenness) in series, whatever you do; you'll get the output dragged down to the weakest in the circuit.

All IMHO.

Rgds

Damon

[richhagen]

I've thought about Mppt.  I would love to get one, but the Outback FM60 is about $509 (U.S.$), and a Morningstar TS-60 is about $190 ( I actually have a few Trace C-40's in my system which run about $119, but the different Amperages make the comparison more confusing.)  Since I have yet to fill my roof with panels, I could alternatively purchase $320 more in solar panels. Although I would shop for a low price per watt, I could probably add another 120 Watts even if I had to buy four smaller panels for my 48V system, effectively more if I used it as a part of a string of larger panels, currently about $1.38 per Watt plus shipping which would depend on whether I could pick them up, and how big the order was. 

The question is whether that power from the panels is greater in the long run than the difference in power I would see if I bought the Mppt controller instead.  I think that if I were to load the mppt up to capacity it probably would be, but even then, I have panels on my roof that were built in the 80's, and I've only had half of one panel go dead on me from all of the panels I have installed on my roof's over the years.  I'm not sure how long mppt controllers last, but I suspect that solar panels will last a multiple of that on average.  I guess the right approach would be to figure out what you need your system to accomplish, and then figure out the minimum cost option to get there for the long run, although I really do not know how reliable mppt controllers have proven to be relative to their non-mppt counterparts.

[rossw]

I've thought about Mppt. 

My experience shows MPPT stretches your production hours and optimises output wherever possible. I'd say around 30% increase in kWh over time. Lets be conservative and say 20%.

If your PV array is small enough that 20% additional panels is less than the cost of the MPPT, that's probably cheaper.
If your array is like mine, and 20% more panels would be 3 or more times the price of the MPPT, then it's a no-brainer.

Buy right, install right, and I don't see why the MPPT would be substantially less reliable than the panels.

[birdhouse]

thanks for the replies!
so the consensus sound like i can't hook different panel wattage panels in series to mppt, unless i want the lowest panel to drag down the highest panel.  can multiple modules of various size/volts be paralleled to a single mppt controller without some dragging the others down? 

IE: 390w @ 36Vmp on one set of wires to controller
490w @ 30.7Vmp on another set of wires to controller and
180w @ 36Vmp on the last set of wires to the controller

would this equate to approx 1060w @ 32/33v as far as what the controller thinks it is seeing?? 

right now, all i've got hooked to my controller is my wind turbine and 390w worth of evergreens.  the controller is a ts-60 (non-mppt) running in dump mode with a custom made 50 amp (@29v) dump load.  i've seen my wind turbine put out over 600 watts, so that controller is about maxed out with what i've got hooked to it. 

so i need another controller to bring the other 670w worth of solar panels into my system.  that's why i was looking into mppt.  problem is, one new controller doesn't sound like it will do my mismatch of panels in mppt form. 

so i was thinking about using a new sunsaver 15 mppt from morningstar to run the 390w 36Vmp worth of evergreens.  then maybe put the turbine on a new ts-45 non-mppt and have it be the only dumping controller.  then put the 490w 30.7Vmp panels and the two broken glass evergreens on my original ts-60 non-mppt. 

this way i'd have some mppt, my turbine on it's own dump controller, and the other 670w worth of panels on a pwm ts-60.  this involves buying two new controller, and including the display ect. would probably run me 600 bucks or so. 

sorry for the long winded response, but you see the dilemma i'm in!

is there a simplier way that still involves some mppt??? 

thanks!
adam

[rossw]

thanks for the replies!
so the consensus sound like i can't hook different panel wattage panels in series to mppt, unless i want the lowest panel to drag down the highest panel. 

For the purposes of clarity, it doesn't "drag down" the highest panel, it "limits the entire string to the CURRENT of the lowest rated panel". So it's not so much "dragging down" the bigger ones, than just not letting them deliver the current they could.

can multiple modules of various size/volts be paralleled to a single mppt controller without some dragging the others down? 

IE: 390w @ 36Vmp on one set of wires to controller
490w @ 30.7Vmp on another set of wires to controller and
180w @ 36Vmp on the last set of wires to the controller

would this equate to approx 1060w @ 32/33v as far as what the controller thinks it is seeing?? 

It's much more complicated, unfortunately. What will happen basically is that the mppt controller will do a "sweep". It will try pulling a range of currents from your group of panels. As the current changes, so will the voltage. Thats how they work. What the MPPT does though, is find the point at which it gets the maximum *power*.
Example - hypothetical values:
30V @ 10A is 300W.
35V @ 9A is 315W
40V @ 7A is 280W

The MPPT controller would settle on close to 9A from the panels to get the most *POWER* out to deliver to the batteries.

With 2 or 3 (or more) dissimilar arrays, the curve probably won't be a single nice curve - it may (and probably will) have several peaks.
The peak power for one string may be at a different point to the peak power for another - and which is best across the whole lot of them may vary depending on temperature, illumination and other factors. It is likely there won't be any one point where all the arrays are performing anywhere near their optimum.

so i need another controller to bring the other 670w worth of solar panels into my system.  that's why i was looking into mppt.  problem is, one new controller doesn't sound like it will do my mismatch of panels in mppt form. 

so i was thinking about using a new sunsaver 15 mppt from morningstar to run the 390w 36Vmp worth of evergreens.  then maybe put the turbine on a new ts-45 non-mppt and have it be the only dumping controller.  then put the 490w 30.7Vmp panels and the two broken glass evergreens on my original ts-60 non-mppt. 

this way i'd have some mppt, my turbine on it's own dump controller, and the other 670w worth of panels on a pwm ts-60.  this involves buying two new controller, and including the display ect. would probably run me 600 bucks or so. 

sorry for the long winded response, but you see the dilemma i'm in!

is there a simplier way that still involves some mppt??? 

For the power levels you're talking about, you MIGHT do some research of something like this item on ebay: 220840808084
For around $40 it claims MPPT, not sure if that one is 10A or 15A, but you might find that at those prices, one per string is viable.

[ghurd]

For the power levels you're talking about, you MIGHT do some research of something like this item on ebay: 220840808084
For around $40 it claims MPPT, not sure if that one is 10A or 15A, but you might find that at those prices, one per string is viable.

Sorry, that company is known to be ungood...

http://fieldlines.com/board/index.php/topic,144207.0.html

[birdhouse]

ross-
thank you so much for your detailed explanation!  that is just the kind of info i was looking for!  with so many different panels producing different Vmp's and wattages, it sounds like my array would kinda "confuse" a single mppt controller, making it settle on one peak for a while, then switch to another peak ect.  never finding "the" sweet spot, because there is no absolute sweet spot with my hodge podge of panels.     did i get that right?   and if so, do you think even with the constant sweeping/changing of peaks, i'd still see increase with persay a mppt ts-60?? 

i do like the idea of finding small mppt controllers at a reasonable price and run much of my panels on their own mppt controllers.  this makes much sense, though finding reputable companies making such things for a decent price may prove to be a struggle. 

ghurd-  thanks for steering me clear from those jobbies!!

thanks again!
adam

[rossw]

ross-
thank you so much for your detailed explanation!  that is just the kind of info i was looking for!  with so many different panels producing different Vmp's and wattages, it sounds like my array would kinda "confuse" a single mppt controller, making it settle on one peak for a while, then switch to another peak ect.  never finding "the" sweet spot, because there is no absolute sweet spot with my hodge podge of panels.     did i get that right?

Thats about it.

   and if so, do you think even with the constant sweeping/changing of peaks, i'd still see increase with persay a mppt ts-60?? 

I think that an MPPT, even not operating at the "sweet spot", would provide more output than simply running the panels directly to your battery bank. Probably better than a PWM controller would manage too. But not sure that the cost/performance ratio would be great.

i do like the idea of finding small mppt controllers at a reasonable price and run much of my panels on their own mppt controllers.  this makes much sense, though finding reputable companies making such things for a decent price may prove to be a struggle. 

I know another bloke who "traded" panels with someone else so they both ended up with "similar" panels. You might be lucky enough to find someone to swap with, but it's probably a bit of a stretch.

Smaller, cheaper controllers should address your problems - to a point - one thing that still concerns me would be if they all had slightly different settings, you might have one decides your batteries are ready to go into absorb or float, while another is madly still trying to dump in bulk charge. With modest panels, that may not be a problem.

ghurd-  thanks for steering me clear from those jobbies!!

Yeah, thanks mate, I meant to say "the usual disclaimers, I have no association with them, know nothing about their product etc".
I just can't believe there are not decent, smallish controllers around at low cost - they're not THAT complicated!

[offgridonmountain]

Hi folks,new guy here (long time reader,first post)

I have 600 watts in solar with a Morningstar MPPT 45.It's an excellent charge controller and does a good job here at my off grid homestead.

Yesterday I was looking at the remote meter and I had a thought about the cost effectiveness of MPPT.I grabbed my old casio calc. and played

with figures for a while. I used to be under the impression that (with some exceptions) you had to have at least 500 watts in solar to make an

MPPT charge controller cost effective,but what I came up with is that it's closer to 900-1000 watts.Given that in my observations,MPPT on average

is gaining me about 1.25 amps gain per 100 watts.All of this is figured with a .77 derating in panels from their labeled output.The exceptions

to this cost effectiveness (or lack thereof) would be a set number of panels due to space constraints(like an rv or boat),or the need to wire panels in series

to gain a high enough voltage/low enough current to make a long wire run to the controller without spending a fortune in copper wire.

This is considering the cost of my panels at $2 a watt and my controller was ~$380 .

So as dissapointing as it seems because the Morningstar MPPT 15 and other MPPT charge controllers  in it's class are such nice,attractive products,

Without those exceptions in play,MPPT charge controllers are not cost effective  unless you are working with a 24v battery bank and above 900 watts in solar.

I  think any of the Morningstar PWM controllers are excellent and there are a bunch to choose from.

Please correct me if you think I've missed the boat,but that was my conclusion.BTW I started with a Ghurd dump controller and 160 watts of solar,thanks for having me.


Doug

[birdhouse]

doug-
yea, i totally hear what you are saying.  many variables go into the cost effectiveness of mppt.  last time i bought panels, the shipping was outrageous, but because i split the order with two of my neighbors, the panels ended up being less than a buck a watt delivered.  this would surely change the calcs on how cost effective mppt would be. 

also, since my only existing controller is maxed out, i need to buy another to get the rest of my panels online anyways, so that's where the mppt came up. 

voltage mismatch also plays some role.  IE: my two good evergreens are wired in series for 36+ Vmp which misses the boat by quite a ways for a 24v bank.  the highest my bank has hit is 31v while equalizing during the cold winter.  even then, i'm 5 volts off the peak that mppt could take advantage of.  not to mention in most mornings when the bank is 24.2ish, then i'm missing the boat by almost 12 volts.  this mismatch is why i've NEVER seen the full 390w going into the bank.  no, i don't have hardly any losses in wiring ect.  i wired these with #8 that goes about 15 foot to the controller. 

having passed the 1Kw mark in panels, i don't think i need any more for my needs at my ranch.  so i figured i could dial them in with some nice controller(s) to reap the most from them. 

i also agree that the morningstar pwm controllers are very well made, and easy to use.  my only beef with the pwm ts series, is when you switch from pwm to the dump mode, the voltage cutoff changes.  i used my ts-60 in pwm mode for over a year, and rarely had to add small amounts of water to my cells, then after a month of the same controller in dump mode, i had to add lots of water to my cells, and eventually backed the voltage off on the dip switches to keep water consumption to a minimal.  my dump is plenty large and a verified 50 amp worth of nichrome wire. 

just some thoughts
adam

[offgridonmountain]

Adam,

After being able to vent my Monday brain spasm on your thread because it was related(thank you).I figured on your issue a while and, thought maybe for
your 36 vmp panel sets,put together could feed a Rouge Power tech MPT-3024,a great machine built by a good guy in Oregon
http://www.roguepowertech.com/products/mpt3024.htm
It would leave you with ~300 watts lee way for any unforseen future add ons(like that pallet of unwanted panels someone dumps along side the road ).
A suresine 20l-24 or the prostar 15 could be used on the 30.7 vmp panels.Just an idea.Though I realize,unlike myself,not everyone is out to collect charge controllers
That is unfortunate about the ts60 not dumping when you want..If I had a wind turbine like that,I would think about one day getting the Midnite solar classic with the clipper
they are coming out with.It's the only MPPT charge controller that can track wind.Pricey though.
Or,instead I might build a monster Ghurd controller setup that would do what I wanted it to.
The wind issue agitates me because here on my ridge I have some of the strongest wind in the northstate,but My place is surrounded by tall ponderosa pines that have
all lost a top at one time from the wind.Every time I think about the cost of a tower,I think about how much solar that buys.

The other issue with MPPT(a positive one) is the entertainment value of watching it pull hard on a cold day when the batteries are low.especially when the panels are
exceeding rating due to edge of cloud effect.It's like watching the tractor pulls at the fair.I have my remote meter in the wall next to the kitchen table so I can watch it like a TV.

Have a good one

Doug

[birdhouse]

doug-
thanks for the link to the controller.  that's very reasonable at $325 considering the display is built in, and it comes with the remote temp sensor, and it comes with a five year warranty, and it'll handle 30 amps @ 24v and its made fairly close to where i live and...  wait, that's it... 

i think i may have to pick one of those up! 

i live in portland, OR but my ranch is outside of bickleton, WA.  sounds like you may be somewhat close by.  if you like watching the display on your mppt controller for entertainment, you'd love watching a turbine run!  my place also has many white and ponderosa pines.  made a scratch built 70' tilt up tower to get above them.  it wasn't terribly expensive.  it does pull through hard when the weather is so socked in that solar is all but useless!  many nights, i go to bed, turn off most of my loads, and wake to a fully charged battery bank! 

look like familiar landscape??



adam

[TomW]

Ahh, the 5 gallon pail. Indispensable in any location!

Nice!

Tom

[offgridonmountain]

Adam,

That does look familiar,though I'm a ways to the south at the foot of Mt. Lassen in the State of jefferson(N. Ca,).

It would be great if you picked up the Rogue CC,It has been put through some hard testing by guys who test all the major manufactures.

That Rogue uses dynamic tracking and is probobly the most efficient out there.I dont know him personally ,but I watched Marc bring it to market to face

some hard core skeptics who came around to endorsing it.

What is your tower made from? It would work for my situation.I'm trying to push my self over the edge into wind(like when you were a kid going swimming)

If you look on a wind map,most of the numbers in the north state are like 1 and 2,maybe some 3's,but here on top of this ridge I am at "6".

I don't know what the numbers mean,but when I bought this place ,the wind had torn the siding off he buildings that had sat vacant for a few years.

View from my front window:

[ghurd]

Doug,
Class 6?  That means it gets really windy!
Is there ANY semi-clean shot through the trees?  Need both toward and away from the prevailing wind.
I'd look again, for something even close to almost decently OK.
In the right spot, even a starter 4' type windmill on a 20' pipe could make some real power when you need it most.
G-

[birdhouse]

doug-  this is cut and pasted from a previous debate from a new member wanting to use an old power pole for a tower.  i was trying to show how cheap a tower can be made...

i recently put up a 70'   4" tube guyed tower.  granted i scrounged as best as i could, welded as best i could, ebayed as best i could, and worked as best i could...  but that's pretty damned cheap!
   
pipe:                      $400  salvage 4" x .156 wall
rigging:                  $500
concrete:                $450
water jet cutting:     $100
misc welding stuff:   $100
primer/paint            $50

(all in USD)

so yea, that's $1600 total.  that will buy you a LOT of panels, but at your site, you may be surprised at the price per watt breakdown with even a 10' turbine.  the simple fact that they produce at night is a HUGE proponent for many.  i do it because i'm passionate about it, and it works, and when you're offgrid, everything helps! 

here's the thread to my build if you want to look into it in more depth. 
http://fieldlines.com/board/index.php/topic,145609.0.html

i sent rogue power an email hoping to score a dented and scratched edition for cheaper, but doubting that will happen.  either way, i've decided to buy one of their controllers.

thanks!
adam

[offgridonmountain]

Ghurd,

I've got a spot right over the house where the black oaks make a "U Shape in a 100' gap between ponderosas.The wind blows right through that gap.
If I look out my front it is the view in that picture,out my back 50' away is a 1/2 mile deep canyon.A 4 foot starter mill would be a good deal .

Adam,

I just pulled an old 25' power pole out of the ground that the previous owner had mounted a big 300 watt light on.I've been thinking about how to mount a
pipe to that.You know,I've got a lot of electrical ,mechanical,and hydraulic experience,and I don' know why,but a wind turbine build somehow worries me.
Like I'll get it built but never get it balanced properly.Ive built an excellent solar heated water system,and a good solar electric setup here on the homestead.
Like I said I just need to push myself over the edge.Thank you for showing me your setup,I will study it.

Ive go something out in the old shop that the old guy who died and left this place had stashed.It is an antique water motor(used for household power) and
I will be looking forward to showing you guys some photos of it maybe tomorrow.I wish I had the water to run it for grinding wheat.

Thanks again,

Doug

[birdhouse]

well, i've decided on a rogue power mpt 3024 unit after reading this thread on another forum:  http://wind-sun.com/ForumVB/showthread.php?t=4751 

the mpt 3024 controller has it's limitations, but for the money, and the features, i think it will suit me just fine.  i'm kinda excited to get some of my panels on mppt!  that will be a first for me. 

doug-  jump in head first on a turbine!  just do it one part at a time.  that's how i did mine and it took me almost two years to build, but hey, now it's done and pushing amps!  you have too good of a resource to not take advantage. 

thanks for all the comments/suggestions!

adam