adding panels

oglethorp · May 2009

I have 4 165s (sharp) 24v twins feeding 48v Apollo thru to 16 6v golf cart batts, to a MagneSine MS4448 inverter/charger 120/220ac. I need to add panels to increase possibilities. I have limited pewer useage. Batts are 6yrs old (bought used) and they are struggling but getting all i can out tof them.
I d like to add 4 more pannels and set them up the same way ,,, but(now the question),, Can I increase the size(wattage) to over 200 or more and still feed thim into the combiner box? I m a amature tring to not harm things but balance things out and get more power and faster charging of the bank. Plus I d like to add a 48v wind charger to help. Any advice would be greatly appreciated.
RSVP,,,
Oglethorp

icarus · May 2009

Re: adding pannels

It sounds like you have way too much battery for the amount of PV. The general rule of thumb is a Pv charging capacity of between 5-15% of ah capacity of your batteries. Sounds like you have over 1000ah (24v) of batteries and ~24 amps of charging, something in the range of 2% if I am understanding your numbers correctly. (By the way,, never trust my math,, it's horrible,,, but do your own to test my opinion!)

So if the charge controller has the capacity available there should be no problem adding the panels as you suggest assuming that they share similar Vmps. If they are more than about .25 volts different,, you will lose some capacity over all.

The same is said of the capacity of the combiner box.

As for the 48 vdc windcharger. Please find the wind energy threads in this forum,,, there are some pretty compelling arguments AGAINST small scale wind.

Welcome to the forum and good luck,

Tony

PS I also suggest that you read the following links to learn a bit more about your batteries and how to treat them. They will suffer (and probably have suffered) by not being fully charged all the time.

http://www.windsun.com/Batteries/Battery_FAQ.htm#Lifespan%20of%20Batteries
http://www.batteryfaq.org/

oglethorp · May 2009

Re: adding pannels

Sorry. I picked up these batts knowing they wouldn t last long. They (6v 235AH) 8 in seried do the 470AH. The pannels may be to much but now I have to replace the batts and with the juice off the pannels they struggle to get back up to full (in maine) on a decent sunny day. As the best anps from the charge controler may have been 12A at 50 something v MMPT. I ve struggled to get a grip on how to get the best comination. A solar electrician helped but is not responsible to the system, just helped buying the pieces.

icarus · May 2009

Re: adding pannels

I'm a bit confused.

It sounds like you are having trouble getting AmpHours into the batteries. As always it is much easier to get them out then to get them in.

Please list, the ah capacity of the batteries, the amp capacity of the controller, as well as you panel configuration as well as capacity.

So do you have TWO strings of 8 6 volt batteries,, each making ~470 ah each string? If not how are the 16 batteries strung together?

Tony

oglethorp · May 2009

Re: adding pannels

Sorry for the confusion. Still have alot to learn, but tring as well. System as follows;
16 6v golf cart batts,, 8 in series at 235 ah x 2 = 470 ah
4 165 sharp 24v , 2 series x 2 48vt. 4.73 amp x2 = 9.46anp +/-
Apollo T80
MagnaSine MS4448 Inverter/Charger. 120/240vac output
Mounted on a Midnite MNE-240 E-Pannel
How can I beef this system. I went big on the Apollo and the MagnaSine
but now I need to replace the batts and add panels ..Please advise
I do very much appreciate your patience.

BB. · May 2009

Re: adding panels

As Tony/Icarus has said... You have way too few solar panels... At the very least,

470 AH * 0.05 (min recommended charging current) = 24 amps

24 amps * 60 volts (max battery charging voltage) = 1,440 watts of solar panels

So--to properly charge that size battery bank, either get more panels, or at least top the bank off every few weeks with a genset (equalize--to equalize the cells and mix the electrolyte).

You have an 80 Amp Charge Controller--so, as long as you follow the rules for the Apollo charge controller (do not exceed the maximum open circuit voltage, do not exceed the maximum current/watts inputs)--just adding panels should be fine.

Older batteries can start to self discharge (still useful as storage batteries) and you may lose another 1-2% of battery storage per day--worst case (~5-10 AH per day for your battery bank).

Have you been monitoring the battery specific gravity?

Freas HD98C Precision Hydrometer Set

How to take Specific Gravity Readings
Trojan Batteries website

You can also use an accurate digital volt meter to estimate the current state of charge. Let the batteries "rest" for a few hours (no charging or discharging) and measure the voltage. Read the battery FAQ for care and feeding of your battery bank:

Deep Cycle Battery FAQ
All about deep cycle batteries

For your battery bank (48 volt bank; all voltages that follow assume the batteries are around 77F/25C):

49.68 ~ 80% state of charge
49.28 ~ 70% state of charge
48,24 ~ 50% state of charge
47.60 ~ 40% state of charge
46.32 ~ 20% state of charge
42.00 ~ 00% state of charge

You need to get your battery bank above 80% state of charge as soon as you can.

If the battery sites for more than a few hours or a day below 75% state of charge -- the batteries with "sulfate" (sulfates begin to harden) and permanently reduce the battery bank's capacity.

If you discharge on rare occasions to 20% state of charge--you will significantly shorten battery life.

Taking a battery to 0% state of charge will probably kill them (especially if they are older than a few years).

If you are properly charging your battery bank--you should be seeing ~56.8 volts every day. And once the battery bank is full charged--the Apollo may cut the voltage back to "float" which would be around ~54.4 volts.

You need to understand your loads (Watts, Amps, Watt*Hours, Amp*Hours, etc.) so you can size your solar array (and battery bank) appropriately.

The rules of thumbs that we use here are just estimates--but if followed, you will probably have a well functioning system with long life. You certainly can go outside the recommendations, but you have to understand the specific issues if you do.

Can you charge your batteries with a genset or utility power and get them back to near fully charged? Do you know how much power you are using (Watt*Hours or Amp*Hours per day)? Do you know how much power (Watt*Hours or Amp*Hours per day) the solar charge controller is putting back into the battery bank every day?

If this is a "serious" use off-grid solar system... Please look installing a Battery Monitor. You will very quickly identify how well your system is operating. One of the readings a Battery Monitor will give you is State of Charge (xx%). Very easy and quick to see how things are going with your batteries and very useful for non-technical users (spouse, kids, guests). The Tri-Metric unit is a very good, low cost unit.

-Bill

BB. · May 2009

Re: adding pannels

By the way, can you give the exact model number for your Sharp Panels and how they are wired (2 in series, etc.).

The panel Vmp of the string needs to be >~62 volts to fully charge your battery bank. If the Vmp of the string is less than ~62 volts, you will have problems fully charging the bank.

-Bill

oglethorp · May 2009

Re: adding panels

Sharp 165 w panels
Short Circuit Currant 5.4A
Rated current 4.72A
Open Circuit V 44.5
Rated V 35.0
Are there any options for the budgeteer other than Golf Cart Batts?
Also I d like to put in a bank switch to get the most out of the old ones before turning them in.
As before I appreciate your patience with those of us out there that are getting off the grid and encouraging others to do the same despite the cost (pay now or pay to much later)

icarus · May 2009

Re: adding panels

Don't mix old batteries with new. Run the old ones until they drop,, checking individual cells Specific gravity frequently for dead or dying cells. Fully charge from a genny and equalize often,, watching the water. As batteries die,, cull out the bad ones until the bank is too small to be of use. Even at 1/2 size,, if you run them down to 50% routinely, there really is no harm, no foul if you are just trying to get the last drop(s) out of them.

Tony

BB. · May 2009

Re: adding panels

Assuming they are similar to Sharp NT 165 panels:

Max Power Voltage - Vmp 34.6 Vdc
Open Circuit Voltage - Voc 43.1 Vdc
Voltage Temp Coeff - Vtoc -0.144 V/°C
STC Rating - Pmp 165 Wstcdc
Max Power Current - Imp 4.77 Adc
PTC Rating 144.8 Wptc

Assuming you are somewhere Temperate--32F to 95F--a first cut on Voc (cold) and Vmp (hot) works out to:

Voc = 46.7v @ 32F
Vmp = 28.12 v @ 95F ambient...

2x Voc = 93.4v
3x Voc = 140.1v

2x Vmp = 56.24v
3x Vmp = 84.36v

Assuming your 48 volt battery system needs ~58v to charge (battery at 77F) and the controller voltage + wiring voltage drops are ~2 volts... You need (on a hot day) Vmp:

Vmp>58v+2=60 volts

You may be charging your batteries (again on a hot day at):

Vbatt-charge = 56.4v - 2v = 54.24v (equivalent to 13.56 on a 12 volt battery bank)

At that voltage, you are no longer really charging the battery bank--but just "floating" it (long term storage). And, you would not be able to "equalize" the battery bank on a hot day.

So, look at three panels in series instead:

Vmp=3 * 28.12v = 84.36v -- so this would be fine for charging your battery bank.

But, when you put three panels in series--you have to look at what happens at cold temperatures (when panel voltage rises)--and specifically Voc (voltage open circuit).

2x Voc = 93.4v
3x Voc = 140.1v

When you put 3 panels in series in cold weather (32F for this example)--you are very near the maximum input voltage for the controller.

From the Apollo website:

Wire PV modules in series up to 72 VDC nominal (140 Voc max)

You are probably exceeding the Apollo's maximum input voltage range...

And this is a problem with "high voltage" solar panels, 48 VDC battery banks, and Off-Grid Charge Controllers... Most them (right now) max out at around 140-150 VDC.

The Sanyo "44 volt/35 volt" panels are not a good fit for this system.

You would be better off if you could get standard "12 volt" panels (really Vmp~17 volts). You can pick a series string Vmp/Voc that does not run up to (or over) the controller's voltage limits (maximum input, and minimum input for 48 volt battery charging).

Does this make sense to you (is sort of confusing)?

More Disclaimers: And there are some NEC required "safety margins" that I did not take into account here--so more detail work is actually needed (actual minimum temperatures, do I have the correct solar panels, wiring voltage drops, etc.).

-Bill

PS: There are a few folks around hear that have had good experiences with using old Fork Lift batteries. Search for user "adas"--He is in Hawaii and has built a large system for his commecial metal fabrication business (I think that is his business).

oglethorp · May 2009

Re: adding panels

Thanx so much everyoner,, I ll be back with more info/questions in the days ahead.
Azalways,,,

oglethorp · June 2009

Re: adding panels

If I were to add 2 Kyocera KD210 GX-LP panels to my setup would thos give me the needed power to charge my 48v bank properly
Pmax 210W
Vmpp 26.6
Impp7.90
Voc 33.2
Isc 8.58
Thanx,,,

icarus · June 2009

Re: adding panels

By my quick calculations adding those two panels would put you,, in total to about 17 amps into 48 volt battery bank,,, still way under the 5% low recommendation,,, but closer. If you re-read Bill's post # 6 I believe,, he spells out in detail why you need ~ 1400 watts of panel,, adding the 2 more give you somewhere in the 1080 watts, note counting any derating for differing Vmp of different panel specs.

Icarus

oglethorp · June 2009

Re: adding panels

4panels ? Obviously I m no good with the calculations and I do very much appreciate your patience

BB. · June 2009

Re: adding panels

And you have to look at your Vmp (hot) / Voc (cold) numbers. I like to use the Xantrex Sizing Calculator... There is one for their Grid Tied inverters, and another for Off-Grid/Solar Chargers (XW-60 line).

Using the XW calculator--there is really only one good solution for the KD210 panels... Strings of three. Assuming -30F in winter, and 100F in summer (min/max).

Gives you Vmp (hot)=63 volts and Voc (cold)=121 volts.

That will work for both your Apollo T80 or other Xantrex/Output type MPPT controller.

You are sort of between a rock and a hard place here... You have one set of panels that can easily exceed the min/max for any charge controller (too few panels, less than 3, battery is not properly charged on a hot day. Too many panels, more than 2, controller is over voltaged on a cold =30F day).

With the panels you have/are looking at--you are pretty much locked into using the Sharps in 2 per series string on one controller.

And using the KD210's in 3 per series string on a separate MPPT controller.

If you could find a use/another person who needs 12-24 volts -- the Sharps in groups of 2 on the Apollo T80 should be fine (and more parallel strings can be added nicely for a larger array).

-Bill

oglethorp · June 2009

Re: adding panels

Next possible option, Would the addition of these(4) , 2 together and in series
Solarworld 165 Mono/P
Recomended by a up and coming solar electrician

Peak Power (Pmpp) 165 W Cell Type: Mono-crystalline
Peak Power Voltage (Vmpp) 35.3 V Cell Dims: 125mm x 125mm
Peak Power Current (Impp) 4.68 A Length: 63.39 in.
Open Circuit Voltage (Voc) 44.5 V Width: 31.89 in.
Short Circuit Current: 5.10 A Depth incl. jbox: 1.34 in.
Max. System Voltage: 600 V Depth excl. jbox: 1.34 in.
Weight: 33 lbs. Nominal Voltage: 24 V
Box Quantity: 4 Limited Warrantee: 25 years
Max Series Fuse: 15 A

Thanx again,,,

BB. · June 2009

Re: adding panels

Using the Xantrex XW string sizing tool--The SolarWorld SQ-165 panels are also very close to not working over full temperature range too.

Even using the default temperatures with 3 panels in series, the 14F cold temperature will run the Voc to 149 volts -- Above the Apollo T80 input maximum voltage of 140 volts.

And two panels in series is not really high enough voltage either to optimally charge your batteries on a hot day. Vmp=56.6v (at 95F)--(minus two volts, give you 54.6 volts).

If you assume your average hot weather is 80F, then the Vmp=59F(hot)... Two in series would probably work. You would just have to equalize your banks on a cool day (or use a genset once or twice a month in the hot summer).

The Solar World panels have basically the same Vmp as the Sharps you already are using.

So--if your measurements with your existing Sharp NT 165 panels are showing that your batteries are getting the correct charging batteries on a your "average" warm day... I guess, just stay with two panels in series and keep adding them in parallel to the array.

Your system design (with the Vmp=35 volt) panels is very close to working/not working on warm days. If your measurements of battery/array voltage show they are properly charging your battery bank and you just need more panels--then use more of the same.

At least, you will save the expense of redoing your existing panel+charge controller setup.

Solar panels, if you don't run them at exactly Vmp--but a a bit higher (or lower)--they still produce pretty nearly their full output (in your case, probably within 95% of what the power would supply anyway).

So, I am going to back off my "gloom and doom" warning about your existing array. Two of your existing panels in series is probably "close enough" to give you a reasonably functional system assuming your average highs are closer to 80F than 95F for your region.

-Bill

Solar Guppy · June 2009

Re: adding panels

One might conclude from these posts that harvesting energy just stops if the true vmp is below the battery voltage, that's not that case, for a real measured example:

A typical 48V system, the 2 Volts above the true vmp point might only have a 10-20 watt reduction on a 4kW array ( measured I might add, not hypothetical )

So for the hour or two in the day or a few days a year the vmp might be to low to havest at true vmp, better than 99% of the available energy can still be harvested.

This would be automatic on any Mppt controller, they would track to the Vin/Vout minimum and as the battery voltage rises with the charge would just maintain the differential ( maximum duty cycle typical 97-98% on mppt controllers )

48V nominal configuration for solar will work fine, even in hot climates. Even if one had to take a percent or two of the peak heat of the day in harvest, its really in the noise compared to the battery efficiency when storing this energy.

adding panels

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