help me buy a MPPT controler & size my system

mraroid

Hi...

I am a nob. I tried to do my homework. Am I on the correct path?

My small PV system is used to power some fans in my greenhouse. The PV array is a total of 120 Watts, 12V, and 8 amps. All the PV collectors are the same. The 8PV collectors I used are from this kit:

http://www.sunforceproducts.com/product_details.php?PRODUCT_ID=29

(Costco has the best price I found @$270, but you can also find this kit on Amazon for just a little more)

I am using two 6V lead acid golf cart batteries I bought at Costco. Here are the battery specs:

GC2 product Blk/Blk:
Amp-Hour at the 20 hour rate: 225Ah
Minutes at 75 amps: 110 minutes
Minutes at 25 amps: 447 minute

I have been shopping for a MPPT charge controller. I am open to recommendations. The one I found is made by Morningstar and is called the SunSaver MPPT:

http://www.mrsolar.com/pdf/morningstar/Morningstar%20SS%20Duo.pdf

Its operating range for 12 volts is up to 200 watts (my system is 120 watts), and it amp rating is up to 15 amps (my system is 8 amps). It looks to be about right, with even a little room to grow (but I do not expect to - the 8 amps works for me). While this looks like it would do the job, I am new to this and open to any suggestions.

I found a big difference in pricing. I looked at Mr Solar, Sunelec, and Alt E Store. This is what I found:

Mr Solar:

$216.00 plus $16.02 shipping, total $232.02

Alt E Store:

$232.75 plus $18.00 shipping, total $250.75

Sunelec.com:

$260.00 plus $34.23 shipping, total $294.23

So a big price spread. Over $60 price difference. And one place wanted $16.02 to ship and another wanted over $34 dollars???--- but used the same shipping method. I guess it pays to shop.

I have read about Solar Guppy's free software that will interface with this unit, and I have read that a remote sensor might be advantageous (??)
So, here are my questions:

1) Can someone recommend a different MPPT controller to me, other then the one I found? Or is this about the only small one around?

2) Where can I get the best price for stuff? I would buy in a brick and mortar store if one were in my town and the price was less then the Internet. I am in Portland Oregon. I do not know where to shop.

3) Are four 6 volt batteries (2 each wire in series) a correct load for my baby system, or can I run with just two 6V batteries (wired in series).

Thanks!

jack in Portland Oregon

Cariboocoot

Re: help me buy a MPPT controler & size my system

There really isn't a reason to have an MPPT controller on a small system like this. I'd suggest you save your money there and add some more PV. 120 Watts isn't really enough for a 225 Amp/hr battery.

BTW, the charge controller you linked to is a PWM unit, not an MPPT.

Take a look at this site's host company, Northern Arizona Wind & Solar (NAWS):
http://store.solar-electric.com/

You can look up lots of stuff there, all good quality at reasonable prices, and compare to any local suppliers you have.

For instance their price on the SunSave Duo is $157.30 http://store.solar-electric.com/modubachco25.html

niel

Re: help me buy a MPPT controler & size my system

as cariboocoot said, with my additional comments.

why pay $4.50 per watt for junky pvs when you could've bought larger quality pvs for far less per watt?

if you're stuck with those little pvs then the sunsaver mppt (not duo) would work well if you place your pvs 2 in series and then paralleled the 4 of strings of 2. this gives around a 24v to be downconverted by the controller to 12v output. just paralleling them won't work as well as i recall they have a slightly lower vmp than most quality pvs have.

good luck in mounting 8 smaller pvs.

try not to insult our host by listing all of the competitors without even considering our host.

Cariboocoot

Re: help me buy a MPPT controler & size my system

Niel; unfortunately the OP has already bought the amorphous panels. That money is gone.

It doesn't look like NAWS has much to worry about from competition, judging by those prices!

mraroid

Re: help me buy a MPPT controler & size my system

BB. wrote: »

Niel,

I think that "insult" was a bit harsh for a first time poster in this thread...
http://forum.solar-electric.com/showthread.php?p=55491#post55491
Perhaps drop that part---Marc did mention NAWS in his post.... It is not always obvious to new posters that NAWS is a store and hosting this site (depending on how much reading they have done before hand).

-Bill

Apologies to all I have offend. I am a *total* nob and know nothing. I have already bought the PVs and a inverter. I liked the idea of being able to gather stats with the software from Solar Guppy so I would not have to buy the hardware display.

Part of this baby system is a learning tool for me. Sort of like going to solar install school. I realize now that I could have saved some money and bought PVs, then each and every piece. But to a nob, a turn key solution sometimes gets to you.

I will price hardware at this forum's site. I just thought this was a solar forum. I thank the sponsor that fund this forum and will try to toss them some of my business.

I also believe MPPT is way over kill for my small project. But this is a learning tool for me so I want to use it to gather benchmarks. Can I mix and match my PV and high end ones?

Can I post a photograph on this site, or just links to flicker pages? I have a connector that looks like a radio connector from USA auto from the 1960s car radio. I wonder if it is also now used in the solar industry.

Thanks again to the sponsors who make this forum possible.

Sincerely,

jack

mraroid

Re: help me buy a MPPT controler & size my system

Cariboocoot wrote: »

There really isn't a reason to have an MPPT controller on a small system like this. I'd suggest you save your money there and add some more PV. 120 Watts isn't really enough for a 225 Amp/hr battery.

How many watts do you suggest? Can I mix 24V PVs with my 12V ones?

BTW, the charge controller you linked to is a PWM unit, not an MPPT.

My bad. I am intrerested in the MPPT charge controler.

Take a look at this site's host company, Northern Arizona Wind & Solar (NAWS):
http://store.solar-electric.com/

Thanks Will do.

mraroid

Re: help me buy a MPPT controler & size my system

niel wrote: »

why pay $4.50 per watt for junky pvs when you could've bought larger quality pvs for far less per watt?

As the saying goes niel, when ever you start a new project, the first thing you do is go out and buy all the wrong stuff. I am trying to ask questions and fix this now.
[QUOTE}
if you're stuck with those little pvs then the sunsaver mppt (not duo) would work well if you place your pvs 2 in series and then paralleled the 4 of strings of 2. this gives around a 24v to be downconverted by the controller to 12v output. just paralleling them won't work as well as i recall they have a slightly lower vmp than most quality pvs have.[/QUOTE}
I only understood about 1/2 of what you said niel. Are you saying wire 2 PVs in series, then wire 4 in parallel?

good luck in mounting 8 smaller pvs.

With the enclosed hardware, they mounted quite easy on the roof. I use stanless hardware to bolt them down.

try not to insult our host by listing all of the competitors without even considering our host.

I did not know. I found how to find the host's store and will look and try to toss them some of my business.

Thank you for letting me know.

jack

niel

Re: help me buy a MPPT controler & size my system

Cariboocoot wrote: »

Niel; unfortunately the OP has already bought the amorphous panels. That money is gone.

It doesn't look like NAWS has much to worry about from competition, judging by those prices!

i wasn't complaining in my reference to our host because of what he already bought, but he listed competitors with prices for the controller he is considering to buy. we are somewhat flexible and i think we can forgive you, but talk of a slap to naws when they provide the very forum he's on. there's nothing wrong with shopping if you like, but don't lay out the details of your shopping as you could just have generalized and only listed a few prices without dealer names as those dealer names were not that important in your quest for an answer to a system question.

niel

Re: help me buy a MPPT controler & size my system

mraroid wrote: »

As the saying goes niel, when ever you start a new project, the first thing you do is go out and buy all the wrong stuff. I am trying to ask questions and fix this now.

I only understood about 1/2 of what you said niel. Are you saying wire 2 PVs in series, then wire 4 in parallel?

With the enclosed hardware, they mounted quite easy on the roof. I use stanless hardware to bolt them down.

Thank you for letting me know.

jack

yes, put 2 pvs in series and do that 4 times so you have 4 sets of 2 in series. once that is accomplished then parallel all of the series strings so that the + output leads are together and the - output leads are together.
i can't draw this out on the pc i'm on and to be honest i wouldn't know how to go about it as my pc skills are semi lacking so maybe somebody could illustrate the arrangement for you.

very good on having them mounted.

see post 8 for added on letting you know and now that you know then you should at least put them into the equation too to be fair.

Cariboocoot

Re: help me buy a MPPT controler & size my system

mraroid wrote: »

How many watts do you suggest? Can I mix 24V PVs with my 12V ones?

Not on a 12V system without separate charge controllers. You need to down convert the 24V panels to 12V, and that requires MPPT.

My bad. I am intrerested in the MPPT charge controler.

What controller you get depends on what batteries you get and how much panel is needed to recharge them. Not a very finite answer, but it's the right one. MPPT controllers are costly, but have much more flexibility over PWM controllers, including the ability to down convert and limit output current.

I think I'm going to start recommending limits on 12V systems. You see a lot of people posting around here with massive 12V battery banks (often with totally insufficient PV) and it just doesn't make sense. If you really need whopping great amounts of Watts every day, you should go up in Voltage. Trying to charge a 1000+ Amp/hr battery bank from 12V becomes an exercise in frustration, as the current levels involved are difficult to deal with, requiring multiple controllers and heavy wire. Plus, things run at the upper end of their capacity which creates more heat and less efficiency.

So you get to be the first one to hear my new rule-of-thumb about 12V systems: No more than two banks of 225 Amp/hr T105's. How's that sound? Works out something like this:

Usage = 225 Amp/hrs @ 12V = approximately 1.2 kW hours (at 100 Amp/hr discharge - nearly 50%).
Recharge = 22.5 Amps @ 14.2 Volts = 320 Watts = 400 Watts of panel.
Harvest = 1280 Watt hours per day (400 W @ 80% times 4 hours 'good' sun).

This seems to me like a reasonable maximum expectation for a 12V system. Yes you can go higher, but then so do the current issues.

westbranch

Re: help me buy a MPPT controler & size my system

Just be clear on Marc's first comment below,

IFF you have an MPPT Charge Controller, with 2 - 12 V panels in SERIES can you 'mix' them with a different 24 v panel, as this series configuration produces 24 V from 2 - 12 V panels.
If you were to do this, then you have to look at the Vmp to have it within 10% of the other panels for good results. Mix and matching always involves extra losses, the best way is to connect the same panels in an array.

You do not want to just add 12 V and 24 V panels together, hoping that the Charge Controller will sort out what is coming into it...

BTW '12' and '24 Volts' are the nominal voltages we talk about.
From your system manual " Open circuit measurement will read between 15 and 23.5 volts" This is normal for a 12 V panel.

HTH
Eric

niel

Re: help me buy a MPPT controler & size my system

westbranch,
he is not mixing and matching pvs as this is from his original post
"All the PV collectors are the same." they are all those little 12v 15w pvs and they are usually lower in vmp than most larger pvs if memory serves me correctly so if anybody knows what that vmp is (including you mraroid if you know) then please state it for me again.

Cariboocoot

Re: help me buy a MPPT controler & size my system

Neil; in post #6 mraroid did ask if he could mix 12V & 24V panels.
Eric; My response was based on that and his stated 12V system, hence the need for an MPPT controller if you try to use 24V panels with a 12V system, as opposed to connecting th 12's in series to make 24.

Don't you all just sometimes feel like your head is swimming in numbers?

niel

Re: help me buy a MPPT controler & size my system

my mistake then.
he would need to keep the imp close for series and i would advocate closer than 10%, but to each their own. newer pvs generally have higher imps, but depending on what the imp is on those little pvs there may be a match for them out there.
in paralleling you need the vmp close.

westbranch

Re: help me buy a MPPT controler & size my system

Niel and Coot, no problema guys.

all I wanted to make clear as he asked about mixing , was that it could be done - IF and only IF - (IFF) he had an MPPT CC.

I know that it is extreeeemely mind boggling at the start.... and even later at times...


cheers, As Nigel would say, more Vino Tinto por favor

EJ

mraroid

Re: help me buy a MPPT controler & size my system

One of my two kits is up on the roof and charging batteries. I can not return it to Costco. The second kit, while built and currently sitting in my living room, can probably be returned. I still have the box, and packing material. So, lets say Costco will give me my money back. What would you folks suggest I add to what is on the roof?

Reading what has been posted, I can mix a 24V PV panel with the 12V ones I have now? Niel says I can re wire my 12V panels in series to turn them into 24V panels? I am guessing this is better for some resion?

To recap:

I have this kit:

http://www.sunforceproducts.com/product_details.php?PRODUCT_ID=29

I own this inverter and planned to use it (to keep costs down, but open to other inverter suggestions):

http://www.blackanddecker.com/ProductGuide/Product-Details.aspx?ProductID=17929

I liked the MorningStar SunSaver MPPT because of the software Solar Guppy has for it. I have a old XP laptop I can toss at this project and I like the idea of gathering data. I can be talked into another MPPT charge controller. If I go over the 400 watts on the roof I can not use it.

I am using two 6V lead acid golf cart batteries I bought at Costco. Here are the battery specs:

GC2 product Blk/Blk:
Amp-Hour at the 20 hour rate: 225Ah
Minutes at 75 amps: 110 minutes
Minutes at 25 amps: 447 minute

Trying to understand all this stuff is like drinking for a firehouse. But if you post something, I can look it up and read, or go read a FAQ. I do not mind doing my homework, just direct me to something to read. I am trying to understand this as fast as I can.

Niel says I can rewire my 12V PV in series to turn them into 24V (if I understand you correctly). Cariboocoot says I might need a total of 1280 Watts on the roof? So, if I return the one Costco kit, that leaves me with 60 watts. So I am looking for at least 1240 Watts? Would this be in the form of two 24 V panes?

One note on battery drain. This system is to power fans in my greenhouse. My fans run 24/7. I suppose I can make them run only 12 hours a day if I need to shut them off and let the battery charge. But in a perfect world, I would like to leave them on 24/7.

Suggestions?

Thanks for the input so far.

jack in Portland Oregon

mikeo

Re: help me buy a MPPT controler & size my system

One note on battery drain. This system is to power fans in my greenhouse. My fans run 24/7. I suppose I can make them run only 12 hours a day if I need to shut them off and let the battery charge. But in a perfect world, I would like to leave them on 24/7

If it would work for you, just size your arrays to power your fans plus a little, and use a small battery bank, use a diversion load controller and run the fans only when the sun is shining.

Cariboocoot

Re: help me buy a MPPT controler & size my system

Yes you can wire 12V panels in series to make 24V. But any two in series should match each other exactly and together they should have a very similar Vmp to the 24V panels. How much tolerance is acceptable is debatable as Niel said. If you do go with a 24V array, you must use an MPPT controller to down convert Voltage for a 12V system. Otherwise you'll be "wasting panel"; a PWM controller will do it, but much of the power will go to heat when it's put to a battery with 1/2 the Voltage spec (resistance difference).

If you're only charging 225 Amp/hrs of battery you need about 400 Watts:
400W @ 80% efficiency = 320W divided by 14.2 charging Voltage = 22.5 Amps = 10% of battery's Amp/hr rating.

What I said was your daily harvest is likely to be 1280 Watt hours: 320W over 4 hours of 'good sun'. This is a good figure for a 12V system, but is dependent on having good exposure during peak sun hours and not suffering too much in losses to inefficiency.

Will this be enough to power your fans? You can answer that by running one through a Kill-A-Watt meter for a day and see what total usage you get in Watts. Multiply that by the number of fans, and you'll have your total power need for 1 day. If that exceeds the 1280 Watt hours then you'd need a larger system (more batteries, more panel).

And now I'm thinking we really should have some sort of basic solar power primer around here. But the last time I had an idea like that I found I'd volunteered myself to create the glossary!:p

And who changed the "smilies" 'round?

niel

Re: help me buy a MPPT controler & size my system

let's clarify this a bit. now with like pvs there is no problem for you to series/parallel them as they are exactly the same pvs. when you place a pv in series the voltages will add even if they are dissimilar vmp. for instance 17v+18v=35v. the problem for series is that you want the currents the same or it will try to default to the smaller of the 2 currents. now some will say keep that within 10%, but it should be the same imp.
now once you've got your individual strings you now need to parallel them. this is where you want the voltages the same and again everybody else gives a 10% on that, but the goal is really for the same vmp. each string should be the same voltage when combining in parallel or it will want to favor the lower of the voltages.
this all means that although mixing and matching can be done that care must be made in doing so to minimize loses and keeping compatibilities high.
btw, this means throwing a 16.5v pv in parallel with a 18.2v pv is not recommended. now if in series if you are trying to throw a 3a pv in series with a 4a pv that this is not recommended.
simplifying this you really want,
series=same imp
parallel=same vmp

you would have no issues doing series or parallel with identical pvs. now if you sent back the pvs you just bought you could keep the ones you have and have 2 parallel strings of 2 in series. in this case the voltage of each string is what you will want to match in getting more pvs to parallel with the ones you now have. if the vmp is for example 31v then you will need a pv or any combo of pvs (with the same imp in the series string) to parallel with your present pvs.
i have a feeling i may be confusing you here a bit so i'll stop for now, but before you commit to anything, run it past us for us to verify its workability.

tomba

Re: help me buy a MPPT controler & size my system

From one total noob to another, the best thing I did was go right past that 60W kit and buy the biggest 24V panel I could buy at the moment. I almost pulled the trigger on that SunForce thing. But you've got one and its fine for learning how things work. It will send current into a 12 V battery bank, its mounted and working. Great!

Costco has a great return policy, I'd take the unopened kit back. 300 bucks will go a long way towards a much better panel, or totally cover an MPPT controller.

I also went shopping there for 4x6V golf cart batteries and they didn't have them. Now I know I was quite lucky, the 180W panel would have been really undersized for a 230 AH 24V bank.

They will also accept your battery return, probably @100%. You can get a single 12 V Deep Cycle or Marine/Deep Cycle (at something like 90 AH and 115 AH) which would be better sized for your 60 W setup, but with plenty of room for more charging power. There's another 200 dollars saved.

$200+$300 = 175 W panel

When you decide you have seen enough of 60W charge and want to have more power, you should do as you suggest, get the MPPT controller, get a >100W 24V panel, and run that charger in tandem with the Sunforce charger which you already have. Once that's running you can see how you do with a single battery. You'll probably be doing great.

mraroid

Re: help me buy a MPPT controler & size my system

Thanks to all.... A update!

1) I have returned one kit at Costco and have gotten my money back.

2) I see now how importand my load mesurements are. I haev ordered a Watt meter. It should arrive in a few days. I can plug stuff into it and it will tell me watts used, amps, etc. It will display the usage for a hour, a week a month or a year.

Thank you Niel for that grat suggestion! When i get some hard numbers I will post that info.

Thanks to everyone for the support and help. I feel like things are starting to come together. That first kit was a waste of money. I should have done this from the get go.

Sincerely,

jack

niel

Re: help me buy a MPPT controler & size my system

i don't recall mentioning that, but it is a good idea to know your loads. dc loads will need a battery monitor and ac loads can have something like a kill-a-watt meter.

mraroid

Now I have some hard numbers

niel wrote: »

i don't recall mentioning that, but it is a good idea to know your loads. dc loads will need a battery monitor and ac loads can have something like a kill-a-watt meter.

My bad. It was a suggestion of Cariboocoot (thank you Cariboocoot!)

The tool arrived this morning. I would like to run two box fans. I would like to run them 24/7, but I can run them 12 hour on and 12 off and power up other fans from the power company. My fans stats are:

.75 amps
Fan low= 84 watts
Fan Mid = 92 watts
Fan High= 94 watts

I prefer to run my fans on mid to low, but never high.

Here again are my battery stats (two 6 volt golf cart led acid cell):

GC2 product Blk/Blk:
Amp-Hour at the 20 hour rate: 225Ah
Minutes at 75 amps: 110 minutes
Minutes at 25 amps: 447 minute

And I wanted to run Solar Guppy's software on a old XP laptop and use the SunSaver MPPT charge controller. I can buy 2 more golf cart batteries if I have to, but would rather not. They cost almost $75 each at Costco.

I have this on the roof, but I can remove it:

http://www.sunforceproducts.com/product_details.php?PRODUCT_ID=29

or, I can use it with future PVs. Can I post photographs here? I guess I can put in a link to flicker....

So....

In a perfect greenhouse world, I would prefer my PV system power up 184 watts 24/7 with a amp rating of 1.5 amps. But I can drop back and do 184 watts and 1.5 amps for 12 hours a day. I would rather over build my PV array rather than under build it so the batteries stay charged.

Suggestions welcome as to how to size the PV, and whether to bundle them with the PVs I have or not.

Thanks to all for lending your suggestions.

jack

mraroid

Re: help me buy a MPPT controler & size my system

tomba wrote: »

From one total noob to another, the best thing I did was go right past that 60W kit and buy the biggest 24V panel I could buy at the moment.

It is nice to know a nob like me might be able to pull this off. Thanks for the support. I think you are right about the 24V panels. Now I need some advice on sizing now that I know what my load is going to be.

jack

niel

Re: help me buy a MPPT controler & size my system

"In a perfect greenhouse world, I would prefer my PV system power up 184 watts 24/7 with a amp rating of 1.5 amps. But I can drop back and do 184 watts and 1.5 amps for 12 hours a day. I would rather over build my PV array rather than under build it so the batteries stay charged.

Suggestions welcome as to how to size the PV, and whether to bundle them with the PVs I have or not."

houston, we have a problem!!!

that 1.5a you cite is at 184w/1.5a=122.67v and not at 12v. 1 amp at 120v is 120w and an amp at 12v is 12w. and remember watts in must exceed watts out. 184w x 24hrs is 4416wh. there's no way possible a little pv system will hope to power these 2 fans running 24/7. if one would use about an extra 50% for losses and efficiency factors that 4416wh load now becomes a 6624wh load to be provided by pvs. if you average 4hrs of full sun per day (not counting cloudy, rainy, or snowy if applicable days) then you need at least 1650w in pvs. not practical to do for 2 120vac fans.
if you were to use 12vdc fans with low current draws it may be more feasible, but you may still need to have a much larger array depending on the actual draw going 24/7.

mraroid

Re: help me buy a MPPT controler & size my system

niel wrote: »

houston, we have a problem!!!

Wellllll....... Hummmm

OK. A little bit more math, but I do not think this will make any difference:

The amp rating I posted was on the tag of the fan. Using my handy dandy watt meter, I found actual numbers:

Fan low = 84 Volt amps, .71 amps
Fan mid = 90 volt amps, .76 amps
fan high= 96 volt amps, .83 amps

Let me ask this: How about powering up one fan for 12 hours a day? That would be 92 watts, 90 volt amps, and .76 amps. Would my batteries do that? And what kind of array would I need?

If that will cost me my first child, I do have a fall back.

I have some fans that can run off of batteries (D cells) or a wall wort. I have two of them in the greenhouse. I will measure them and post the results. So, in the conversion of AC to DC something is lost, correct? Would I make better use of my power if I just pulled a 12V lead off the fans? And not run them on AC?

I will post that other fan data tomorrow.

Oh, and one quick question? Can I add the crummy PV panels I have on the roof now to the powerful new ones I am going to buy?

Thank you for your help. I am *really* learning a great deal.

jack

niel

Re: help me buy a MPPT controler & size my system

this you can figure out for yourself as 92w x 12hrs = 1104wh. add in the losses and efficiency factors at 50% more and we get 1104wh x 1.5 = 1656wh. i don't know how much solar insolation you get where you are or what the worst case scenario may be, but let's assume 4hrs/day. this means 1656wh/4hrs=414w of pv.

i do not know the vmp of your pvs, but i would guess it is most likely within the 10% tolerance range for most of the more current pvs. do not forget what was already posted in the thread for that doesn't go out of the window just because of your misconstruing the amps between ac and dc. many out there make this mistake and is a 10x factoring mistake.

mraroid

Re: help me buy a MPPT controler & size my system

I made a dash to the greenhouse to grab one of my 12V fans for testing. Here are the results:

12V Fan, high setting:

11 watts
16 volt amps
.13 amps
.69 P.F. (I do not know what P.F. stand for or what it means)

One of the big box fans (the kind that I quoted data for in a earlier post) puts out over twice as much air compared to one of the small 12V fans. But even if I use two of the 12V fans, that would be:

22 watts
32 volt amps
.26 amps

one box fan on low:

84 watts
84 Volt amps,
.71 amps

So I see a great savings here. Could I power up four 12V fans and not break the bank? I will go for two 12V fans if I can not. But if four are practical... Lets see, that would be:

44 watts
64 volt amps
.52 amps

I can always turn the fans off for 12 hours (or what ever) to give the batteries time to recharge. Hummm, I know how to work AC timers, I wonder if i can find 12V timers....

Thoughts?

jack

BB.

Re: help me buy a MPPT controler & size my system

PF = Power Factor...

For Basic AC Theory, Power is not Volts * Amps--Instead:

• Power=Volts * Amps * Cos Phase Angle between V&A
• PF=Cos Phase Angle
• PF=1.0=Cos 0 degrees
• PF=0.6=Cos 53 degrees
• PF=0.0=Cos 90 degrees

Based on capacitance and inductance of circuits, the current may lead (capacitive) the voltage or lag (inductive) the voltage.

So, if you have, for example, a big AC electric motor, it draws lots of current, but not "in phase" with the voltage--so there is "extra/excessive" current required for the motor to run, but does no work. From the wiring point of view, the wiring has to be heavy enough to transport the needed current to power the motor (PF less than 1.0).

For non-linear loads (CFL lamps, many computer power supplies), the "low average current" but with "high current peaks" can also be represented with PF too... The math is not as straight forward, but the end results is the same--Non uniform current spikes requires heavier wire/circuits to pass the "same amount of power".

Power factor

-Bill

stephendv

Re: help me buy a MPPT controler & size my system

mraroid wrote: »

So I see a great savings here. Could I power up four 12V fans and not break the bank? I will go for two 12V fans if I can not.

I think this is the best option. In its simplest form you could buy 12V PV panels and wire them up directly to the 12V fans without the need for batteries or charge controllers. The speed of the fan will be directly proportional to the intensity of the sun which may be just what you need in a greenhouse.

If you then wanted additional fans that were battery based then you could go for: 12V PV + PWM controller + 12V battery into 12V fan.

I would consider using independent systems, so you could have:
3 x 12V fans connected directly to 12V panels to give you good airflow when the sun's out.
Then an independent:
1 x 12V fan + battery + PV for day and nighttime use. So at night the 3 fans above would shut down, and the battery operated on would keep on running. If you size the battery correctly there'll be no need for timers since the battery fan will just run 24x7 and the other fans will provide you with boost power during sunshine. The sun will effectively be your timer