View Full Version : so how much differenct does MPPT make?
July 25th, 2008, 17:12 PDT
Is there any way to figure out how much difference a MPPT controller would make?
July 25th, 2008, 18:47 PDT
not exactly, no. usually one can get about 10% current recouped that would've been lost. there are too many factors that can effect the amount of recouped current such as pv vmp and temperatures, wire resistance losses, and the dod on the batteries at the time to name a few.
July 25th, 2008, 18:52 PDT
since mppt takes advantage of the delta between the bat's max voltage (aprox 14.5V) and the panels max output voltage (often > 17V)
... it will be most benefitial when the panel is very cold (e.g. in the morning) OR when the bat. is very discharged (extreme case 10.5V). Here manufacturers claim around 30% difference.
My *guess* when comparing yearly averages (ceteris paribus) between mppts and PWMs would be <10%
... but you might want to wait for more opinions ...
July 25th, 2008, 18:59 PDT
The other major advantages...
1. Improved Hot weather performance with cool batteries (panel voltage falls with increasing temperature, battery voltage rises when cool). Vmp panel voltage no longer matters wrt to battery voltage.
2. High voltage panel strings with low voltage battery bus. Can greatly reduce the amount of copper required in the Solar Panel side of the installation.
3. Allows changes in battery bank voltage without having to rewire panels.
July 25th, 2008, 19:20 PDT
Anecdotally, I get about 10% when the batteries are in bulk charge. A bit more when they are low and it is cold. As the batteries come to absorb and float voltages, the advantage is lost. In short, by batteries get to float earlier in the day, or closer to float if there is less sun.
July 26th, 2008, 6:03 PDT
thank you all for convincing me that I don't really need one (at least until I can afford it :D )
so what about the external temp sensor? with my one battery & putting the controller right next to the battery in an insulated area, would it be better if I get a controller that will accept an external temp sensor or will the SunSaver 10 amp 12 volt solar charge controller be fine?
if it's going to save me some money in the long run (protect my battery), it may be worth the additional initial expense
I saw 'data logging' but now I can't find where (which model) to do more research. Any know where I might have seen that? I wish MorningStart had a comparison chart.
July 26th, 2008, 9:57 PDT
Fred, re the BTS (or RTS) , my experience is similar to what BB and Icarus wrote below... I have cool batteries and hot panels.
the BTS ( Bluesky) allows a higher charge voltage than the CC alone would as it is 3 feet above the battery and in much warmer air. the batt sits in an insulated 'external' room where the overnight floor level summer temps are about 3 - 6 Celsius while the CC temp only drops to about 10 C. I open the door to get the cooling bit the morning sun streams in and the 4 x 8 foot room warms up pretty wuickly, BUT the thermal mass of a large battery ( 1000 #) is much slower to change
ps forgot to add the daytime temps have been above 30 C while the batt temp remains in the teens... so a big MPPT gain
July 26th, 2008, 10:38 PDT
It doesn't get cold here - in 7 years, I've never turned the heat on, seldom close the windows for temp. (only for smoke, etc. as I live in a condo).
The battery will be in the back of my truck in a battery box in a insulated plywood 'power room' (just large enough for battery box & controller. The only thing that should affect battery temp should be the battery. It'll never get cold. Also, it shouldn't ever get too hot, no sun on it.
July 26th, 2008, 11:31 PDT
Also, the sunsavers have two battery choices - sealed & flooded, the prostar has three - gel, sealed, & flooded. If I'm using AGM, would it make a difference which controller for this.
July 26th, 2008, 14:02 PDT
The SunSaver MPPT has four modes (http://www.morningstarcorp.com/products/SunSaverMPPT/info/SSM_Manual.pdf) (PDF Manual)... Gel, AGM, Sealed, and Flooded cell...
The SunSaver MPPT can also be programed by a PC for different voltages/charging times/disconnect-reconnect voltage/etc.--if desired.
July 26th, 2008, 15:09 PDT
I keep trying to klick on 'message / reply' like email. Doesn't work!
I meant the non MPPT SunSavers as I've determined that I don't need the MPPT / can't have it. Now I trying to determine what I do need to have.
July 26th, 2008, 15:25 PDT
Yea... I thought you had ruled out the SunSaver MPPT--nothing like having a product line with one name and way different product in it...
July 26th, 2008, 16:06 PDT
Sorry Free... just my typing and clickig on spellcheck and not looking at the endproduct you get...
Before you get any AGM and CC you want to make sure that the CC can be set to the MAX voltage for that battery. They are all quite specific.
eg My AGM has a max voltage of 14.28 v, this comes from the 12 v battery actually being 6 - 2v cells and the specs are for each cell (as recommended by the local rep).
so pick a battery brand and see if each CC you like can meet the specs...
July 26th, 2008, 16:39 PDT
That the license on my motorcycle. Was to be FreeBird, but that was taken. It was cold back than so decided on FreeBrrd. Lynyrd Skynyrd, Freedom and bird since it was a NightHawk.
I'm planning on going with a Deka 8A24. Haven't seen much in specs on it. I will do research.
On that topic, I may not be able to order everything at once. Need to order as much as possible while I have an address to ship to so I'm thinking that if I had to, I could leave off the battery and still put everything together and see if it all worked - pretty much - just when the sun is shining. Than drop in the battery when I get it a couple of weeks later. Rather have someone else receive a battery than solar panel ;) I could even pick the battery up locally, I saw a MK distributor in Sacramento, must be one in the SF Area.
July 26th, 2008, 16:52 PDT
looks like max charging voltage for Deka AGM is 14.4 to 14.6 volts at 68°F.
MorningStar SunSaver Flooded PWM is 14.4.
So that's it. Doesn't need to match the kind of battery really. Needs to match the charge voltage the battery wants.
I'm not used to getting to stick with what I picked out in the first place. I always shop, research, find something a little better, raise the price, shop more, and on, and on... End up with nice stuff, but broke!
Thanks again all.
July 26th, 2008, 21:04 PDT
the sunsaver has a sensor built into the cc and it can't attach to the battery where it is needed. no you don't have to have mppt either as this pwm cc can fit the bill for about the same price and does offer an external bts that i recommend that you get to monitor the temps. http://store.solar-electric.com/c12.html
you can also get something like the morningstar prostar as i belive it too can have a bts.
July 27th, 2008, 4:11 PDT
Is there any way to figure out how much difference a MPPT controller would make?Nigel's (nigtomdaw) recent post on this very topic may be useful reading. See http://www.wind-sun.com/ForumVB/showthread.php?t=3188&highlight=MPPT
Jim / crewzer
July 27th, 2008, 7:52 PDT
other thing with the remote temp sensor is that I can mount the controller where I can see it
as just a price comparison:
Xantrex C12 12 Amp $88.00
Xantrex Battery Temperature Sensor $24.65
ProStar 15 15 Amp $101.20
Remote Temperature Probe $28.16
Xantrex C35 35 Amp $98.00
Xantrex Battery Temperature Sensor $24.65
BlueSky MPPT 2512i 25 Amp $189.05
BlueSky Temp Sensor $30.40
I could physically fit 3 of the Kyocera 65 panels, but than I'd have no place to put my solar oven when is use so I'll never expand to over 2 so not need over 7 Amp
I like the light controller option. That could turn the fans off in the middle of the night when they aren't really needed.
but now crewzer's got me back to looking at MPPT :D
July 27th, 2008, 8:07 PDT
so what is SC-View?
July 27th, 2008, 8:15 PDT
It's a free PC program to monitor a MorningStar Sunsaver Mppt Charge Controller. One needs a rs232 to modbus converter, MorningStar gives them out free for the asking.
July 27th, 2008, 8:27 PDT
You don't know how much I hate computers. I started working on them before Windows came out. I'd get so much more done if I didn't start the day on a computer. Now I'll probably get the Morningstar MPPT just so I can hook up the computer to it. Got to quit reading other stuff on this forum. Never should have gotten a laptop. It's just so much more reasonable to keep in touch via email than long distance phone. and I've got a website that I need to keep going (motorcycle race stuff).
At least I wont have enough power to use the laptop very long without going to the library. Think the new one only runs on battery for 4 hours or so :D
July 27th, 2008, 8:31 PDT
That's better than a digital display. Cool!
Is MorningStar MPPT the only one with something like that?
July 28th, 2008, 11:02 PDT
Looks like I'm talking to myself here ;)
So if you were going to add $100 (in my situation, with my setup), would you put it towards the MPPT (Morningstar SunSaver MPPT 15 Amp & RTP instead of the Xantrex C12 & BTS or ProStar 15 & RTP) or towards a panel with a bit more output (Kyocera 85 instead of the 65)?
I'm going to purchase this all in about two weeks so than I won't have any more decisions to make :D
thank you all
July 28th, 2008, 12:37 PDT
I'd suggest the MorningStar Sunsaver Mppt ...
July 29th, 2008, 10:52 PDT
just to clarify to you and anybody else that when i refered to the sunsaver cc that i was refering to the straight pwm sunsaver line and not the new sunsaver mppt cc. they may have confused things to some that are not aware by calling the new mppt cc a sunsaver. i make the assumption that anybody just saying sunsaver is refering to the straight pwm line unless the mppt is specified.
as to what is best for you will be your decision as anything over a straight pwm cc (bz cc's being a bad exception) and the numbers of originally stated pv watts is an improvement. you will ultimately decide how much you can spend or will spend in the future and on what as it is your balancing of budget and needs.
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