Street Light turning on Charge Controller

wagoneer

A bit of anecdotal info here:
Under a full moon, my charge controller will actually click on and try to charge the batteries - but there isn't enough power so it shuts down again. The moon can actually cause enough rise in the open circuit voltage to trigger the controller. This may be where rumors like "works in moonlight" get started.

Hello all,

I was doing some research and came across this bit of info by Cariboocoot. However my situation is somewhat different. Be weary, this is somewhat heavy on the Mathematics side.

My panels are located in such a way that the street light shines on them at night. Now this turns on the MPPT CC and it sees an input of ~30 Volts and 0.1 Amps. It then does its conversion and gives out 12.2Volts and 0.5Amps.

Now I have a bank of 2volt lead acid batteries configured for 12V reading ~12.5V.

Q1 )My first question, will the CC low 12.2V output acutally charge my battery bank and not cause any harm to either CC or battieries?


Q2) Secondly one cell is rated at 2V 500AH and reads 2.07V ( 80% DOD). Does this mean it still has 400AH (500*0.8 ) remaining, thus has used(100AH)?

Now, with my small system, the CC logs ~ 30AH per day. Would it be safe to say that i need aprox 3+ days to bring the battery to fully charged state (ie 30AH *3.3days to put back the used 100AH)

Sorry if the math is not clear.

Thanks in advaance
Wagoneer

BB.

Re: Street Light turning on Charge Controller

wagoneer wrote: »

Q1 )My first question, will the CC low 12.2V output actually charge my battery bank and not cause any harm to either CC or batteries?

What brand/model/date of manufacture Charge Controller do you have... There is one (Outback FM series from a few years ago) that had a problem where it "turned on" at night. I (am guessing) that it would discharge the battery bank some because it turned on.

Q2) Secondly one cell is rated at 2V 500AH and reads 2.07V ( 80% DOD). Does this mean it still has 400AH (500*0.8 ) remaining, thus has used(100AH)?

[stupid mistake on my part--see answers below--delete to save more embarrassment. ]

Now, with my small system, the CC logs ~ 30AH per day. Would it be safe to say that i need aprox 3+ days to bring the battery to fully charged state (ie 30AH *3.3days to put back the used 100AH)

It may take ~110 to 120 AH to fully recharge the battery bank.

By the way, what is the size of your system (500 AH @ 12 volt battery bank?; XXX watts of solar panels, approximate location of system, etc.)...

I do not believe that a full moon or simple city street lamp will generate enough power to turn on most MPPT type charge controllers. There is simply not enough energy in the light to do that.

There is a good chance that you have an issue with your charge controller.

-Bill

wagoneer

Re: Street Light turning on Charge Controller

Sad news...The Charge Controller is an Outback FM80 Q4-2008. I had it for some time now but just decided to use it temporarily, to get my feet wet and gain some"solar mileage".

A) Now ... how do i deal with this issue of Night Triggering by the Charge Controller? Is there some adjustment to be done in the settings? Or do i turn it off when night sets in? Solutions please.

The reason why i said the 2.07V was 80% DOD was basd on this http://www.windsun.com/Batteries/Battery_FAQ.htm

Can you direct me to your source of the battery voltage chart?

C) The system was setup as i mentioned to gain some solar mileage, so its nothing outstanding.
-> 2 Banks of 6 (2V 500AH ) batteries configured for 12V.
-> FM80 Outback Charge Controler
-> Location is ~13.1' N 59.3 'W
-> ~ 160watts of Panels

zeuspaul

Re: Street Light turning on Charge Controller

The reason why i said the 2.07V was 80% DOD was basd on this http://www.windsun.com/Batteries/Battery_FAQ.htm

The table in your link indicates 2.07V is 80% charged, not 80% discharged.

Zeuspaul

BB.

Re: Street Light turning on Charge Controller

Zuespaul is correct...

I miss-read your number as 12.07 volts, not 2.07.... 80% state of charge/20% depth of discharge. Using the same chart you are.

Regarding your system... We would normally recommend solar panels based on 0.77 system derating, and 5-13% of the battery bank 20 Hour Amp*Hour capacity (1,000 AH @ 12 volts?):

• 1,000 AH * 14.5 volts charging * 1/0.77 * 0.05 min charge rate = 942 watts minimum array

The 5% is just a rule of thumb based on several assumptions (mixing of electrolyte in battery, rate of self discharge as battery gets old, usable power from system,etc.).

With a 160 watt panel, you are, more or less, just trickle/maintenance charging the battery.

Using PV Watts website; picking Puerto Rico (closest to Barbados?), 0.52 system derating (flooded cell batteries, AC inverter), a 1,000 watts (1 kW) of solar panels will generate:

"Station Identification"
"City:","San_Juan"
"State:","Puerto_Rico"
"Lat (deg N):", 18.43
"Long (deg W):", 66.00
"Elev (m): ", 19
"PV System Specifications"
"DC Rating:"," 1.0 kW"
"DC to AC Derate Factor:"," 0.520"
"AC Rating:"," 0.5 kW"
"Array Type: Fixed Tilt"
"Array Tilt:"," 18.4"
"Array Azimuth:","180.0"

"Energy Specifications"
"Cost of Electricity:","11.9 cents/kWh"

"Results"
"Month", "Solar Radiation (kWh/m^2/day)", "AC Energy (kWh)", "Energy Value ($)"
1, 5.16, 74, 8.81
2, 5.58, 72, 8.57
3, 6.08, 87, 10.35
4, 5.97, 83, 9.88
5, 5.50, 77, 9.16
6, 5.62, 77, 9.16
7, 5.75, 81, 9.64
8, 5.78, 81, 9.64
9, 5.85, 80, 9.52
10, 5.40, 76, 9.04
11, 4.85, 66, 7.85
12, 4.77, 67, 7.97
"Year", 5.53, 922, 109.72

Around 66-87 kWH per month--or if we assume 76 kWH per month minimjm during sunny portion of the year:

• 77,000 WH * 1/30 days per month = 2,567 Watt*Hours per day average

If you have 160 Watts of solar panel, that would be (at best, ignoring self discharge):

• 2,567 WH per day * 0.160 kW/1.0 kW of panels = 411 WH per day of AC power

If you have a 30 watt computer and a 13 watt CFL:

• 411 WH / (30+13 watts) = 9.6 hours of "useful power" per day...

But, that is assuming the battery does not self discharge (who knows, perhaps 10-100 watt*hours per day self discharge?). And if you discharge the battery, it will take you a long time to recharge the battery bank.

• 160 watts * 0.77 derating * 1/14.5 volts charging * 5.4 hours per day of "full sun" = 46 AH per day
• 1,000 AH * 80% discharge / 46 AH per day = 17.4 days

Leaving a battery below ~75% state of charge for days/weeks/months will cause sulphation and the battery bank will die sooner than later.

Regarding the Outback--Call their support number (or your retailer) for information... There is a thread here about the problem--but I never saw the solution (firmware upgrade and/or something else?).

I am not in anyway connected with Outback or the solar industry--So, these are just guesses from my readings here.

-Bill

dwh

Re: Street Light turning on Charge Controller

wagoneer wrote: »

Be weary, this is somewhat heavy on the Mathematics side.

I realize that was probably a typo, but it's so funny it almost made me spew coffee from my nose when I read it!

Hang around this place awhile and you'll realize how utterly apropos that statement is.

mike95490

Re: Street Light turning on Charge Controller

I want to know what brand PV panels those are ??

wagoneer

Re: Street Light turning on Charge Controller

Ok guys!!!

I have found some info on Outback's Forum relating to system producing power at night

Apparently as B.B stated it was a known issue from back in 2008.

• The permanent fix is to send the FM80 back for a firmware upgrade.
• While the work-around is to use Auto Restart Mode 2 (in Advanced menu).

dwh - sorry for almost causing you to spew your coffee with the typo

Thanks to all for your support. This is truely an amazing forum.

RCinFLA

Re: Street Light turning on Charge Controller

The fact that you are developing 0.1 amps from the PV panel at such low light is a good thing. Low light performance is primarily determined by the amount of leakage resistance the cells have.

Poor quality cells have low leakage resistance which shunts away any low level illumination generated current keeping the PV panel voltage low.

Good quality, low leakage cells, take very little illumination to reach near Vmp to Voc of panel's series cell stack.

The primary question is whether you have any net positive current going into batteries.

Some charge controllers use the battery side to run their electronics, some use the PV side power which is a bit tougher since it is a unreliable power source based on PV light level.

If the charge controller runs from battery side power it can get into a situation that the controller electronics is in sleep except for input sense trigger circuit and the PV input voltage level reaches the trigger to wake up the controller buck switcher which takes more power to run (from the battery) then the PV is producing.

This would result in a net loss on the battery. The controller should recognize this and immediately shut down its buck switcher, wait for perhaps several minutes to try again.

Another way is for the controller to put an intentional leakage resistance across the PV panel which would ensure the PV is producing more then enough power to run its buck switcher before waking up controller. It releases the leakage shunt when switcher is active.

Putting a 200 ohm power resistor across PV connection terminals on controller would likely make the night time wake up problem go away but it should be fixed with controller software change.