Solar panel project

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  • #1
Wolst73
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Have built a small solar panel system to power some garden LED lights. However, I am having trouble with charging the battery. Lights work for 1 night then off for 2-3 days.
System is: 20w solar panel, 12v 30a pwm solar charge controller, 12v 18ah battery powering 6x3w LED Cree lights with 700mA flex block buck-boost DC driver. Is the solar panel too small to charge the battery in one day? Panel is in a location where it gets sun most of the day. Panel specs say it produces 1.23A but I've never been able to measure. Voltage shows 19v in full sun.
Any help greatly appreciated.
 
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  • #2
Wolst73
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Oops, forgot that the lights are set to stay on for 3hrs.
 
  • #3
OmCheeto
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Have built a small solar panel system to power some garden LED lights. However, I am having trouble with charging the battery. Lights work for 1 night then off for 2-3 days.
System is: 20w solar panel, 12v 30a pwm solar charge controller, 12v 18ah battery powering 6x3w LED Cree lights with 700mA flex block buck-boost DC driver. Is the solar panel too small to charge the battery in one day? Panel is in a location where it gets sun most of the day. Panel specs say it produces 1.23A but I've never been able to measure. Voltage shows 19v in full sun.
Any help greatly appreciated.
Let's see:
18 watt lights, used 3 hours per day = 54 watt hours/day
216 watt hour battery
20 watt panel

So if the battery were fully discharged, you could charge it in 10.8 hours, if the panel is producing 20 watts.
And a fully charged battery would power the lights for 4 days, at 3 hours per day.

It should work.

Without further details, we would just be guessing what's wrong.
How old is the battery? How many times have you fully discharged it? Do you have any 10 ohm resistors? How old is the solar panel?
 
  • #4
russ_watters
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On a perfect summer day, a 20 watt solar panel will produce about 120 watt-hours. On an average day, it should produce the 54 needed to charge the battery.

However, I suspect that the vast mismatch between charge controller capacity and panel output is a big source of inefficiency. If your total electrical system efficiency is only 50%, then you'd need an average of 2 days of solar power to get one night of light.
 
  • #5
Wolst73
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Battery is brand new. When first hooked up, it powered the lights every day for 4 or 5 days. Thought all was good so never bothered to check if the battery was discharged in the morning. Assume now it wasn't. Then it took several days to charge up the battery. Solar panel is new although I bought it off eBay so not sure of quality.

No resistors, just using multimeter to measure voltage. Haven't been able to measure amps with it using a couple of hookups scenarios I found online.

Also read that the amp rating of the charge controller didn't matter, was good to have more just in case you happened to need more. Not true?
Thanks for the replies
 
  • #6
sophiecentaur
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It could be worth while mentioning that the panel needs to be in full Sun, without obstructions and pointing in the appropriate direction for it to perform to the seller's spec. I set up a similar system but without the 'timed' load (I use a motion sensor to turn my lights on) so my total charge draw over 24 hours is probably less. I did some pessimistic sums and came up with a 40W panel and a 14Ah battery. That seems to work in practice. I have a 'tong' Hall Effect Ammeter and have never measured the claimed maximum current output of the panel - even with full Sun (UK location). The charge controller (cheap far eastern version) seems to imply 'some' degree of charging even with low illumination but a few mA really can't make much difference to the overall charge equation.
The lesson seems to be that my pessimistic approach to the system design was the way to go. If you want to find out how well your system is really doing then you should think in terms of actual measurement (unloaded Volts are not the whole story) - it's very easy to do an Ah calculation in your head when you read 0.25A (or whatever) on your meter and to decide whether it's supply or storage capacity that you need to increase. Those sealed Lead Acid batteries are very good value and panel prices are coming down on an almost monthly basis.
 
  • #7
anorlunda
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On a perfect summer day, a 20 watt solar panel will produce about 120 watt-hours.
That's a silly thing to say without knowledge of the OPs latitude, and the particulars of the installation. Latitude is a dominating factor.

On an average day, it should produce the 54 needed to charge the battery.
For reliable lighting, the panels/batteries must be sized for the worst case, not the average day. My own system uses 205 watts of panels and 440 AH of batteries to reliably provide 40 amp-hours per day of load.

However, I suspect that the vast mismatch between charge controller capacity and panel output is a big source of inefficiency.
A PWM charge controller does absolutely nothing when the voltage is below 13.8. The controller is not a big source of inefficiency, it doesn't contribute inefficiency at all as long as the battery is undercharged.

@Wolst73,
Is your battery the deep discharge type? I assume it is lead-acid.

I find that long-lived systems with daily cycles should not plan to use more than 30% of the claimed amp-hour capacity of the battery.

If your system has been running a long time undercharging a lead-acid battery, the battery has probably become sulphated. You can rescue it with a so-called "equalizing" charger. Otherwise you need to buy a new battery, and keep it fully charged every day to avoid sulphation.

Although your panel gets sun all day long, it won't make much power when the sun is low in the sky. Rated watts times 5 hours per day at latitude 25 degrees is a fair assumption.

I have no idea how efficient that 700mA flex block buck-boost DC driver is.

Cheap self-contained solar garden lights often have just one AA battery, meaning that they run at 1.5 volts. I suspect that they run the LEDs at less than rated voltage. That gives less than maximum light output, but it saves a lot of energy. Can you adjust the output voltage of the 700mA flex block buck-boost DC driver?
 
  • #8
russ_watters
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That's a silly thing to say without knowledge of the OPs latitude, and the particulars of the installation. Latitude is a dominating factor.
I don't see how that can be true. The best day for any solar panel is the day that the sun is, at noon, directly perpendicular to the panel (or at its highest)...+- a few days if it isn't clear outside that day.

Yes, I'm assuming the solar panel is reasonably well aimed.
For reliable lighting, the panels/batteries must be sized for the worst case, not the average day.
Agreed. My point was to explain why it might sometimes work and sometimes not: it will vary with the weather and season.
The controller is not a big source of inefficiency, it doesn't contribute inefficiency at all as long as the battery is undercharged.
I don't see how a charge controller could not use any power itself. But I readily admit to not having any idea how much loss there is in the charging process.

But yes, I do get that when the battery is undercharged (as it is in this situation) the charging efficiency would be at its best.
 
  • #9
Wolst73
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After 3 days of "charging" green light on charge controller was on when I got home. Does green light mean battery is fully charged or just has enough charge to be over the minimum allowed? Have had nights where the green light was on but lights only stayed on for 1/2 hour. The fact that it worked everyday for the first 4-5 days when the new battery was installed leads me to think it is not being fully charged.

Is your battery the deep discharge type? I assume it is lead-acid.

Not sure if it's deep discharge. Sealed lead acid. New battery.
image.jpeg


Panel is leaning against fence. Not rotating with the sun but never in shade most of the day. I live in British Columbia, Canada. This time of year we rarely have completely cloudy days so charging should be at its best. Winter months are unfortunately cloudy every day. Do you think I need a different panel? Would like to have this work everyday in the winter months as well.

Anything in my system you would swap out?
 
  • #10
Wolst73
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Lights just went out. On for 1 hour 35 minutes. Aargh.
 
  • #12
anorlunda
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That's a silly thing to say without knowledge of the OPs latitude, and the particulars of the installation. Latitude is a dominating factor.

I don't see how that can be true. The best day for any solar panel is the day that the sun is, at noon, directly perpendicular to the panel (or at its highest)...+- a few days if it isn't clear outside that day.

Yes, I'm assuming the solar panel is reasonably well aimed.

You didn't have your thinking cap on Russ. It has nothing to do with the aiming of the panel. But this relationship between power and latitude is widely misunderstood, so I'll elaborate.

Here are two graphics from http://earthobservatory.nasa.gov/Features/EnergyBalance/page2.php
sunlight_angle.png

solar_insolation_time.png


So we see that independent of panel aiming, the watts/m^2 of sunlight at the Earth's surface varies enormously with latitude, approaching zero at the poles.

You may not have traveled to equatorial latitudes, and thus don't fully understand the saying "only mad dogs and Englishmen go out in the midday sun." The midday sun at the equator is much more intense than in Pennsylvania.

You may also not have traveled to high latitudes where seasonal variations become predominant, and where the hours of daily sunlight vary as much as 0 to 24 hours per day.

I'll end with a fun puzzle that does involve aiming the panel, but that sounds like a riddle. "For a solar panel located at the North Pole on midsummer day, how should the panel be aimed for optimum energy production?"
 
  • #13
anorlunda
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Not sure if it's deep discharge. Sealed lead acid. New battery.

That is a motorcycle battery. It is not the deep discharge type, and it is inappropriate for your application. It is probably heavily sulphated by now, and beyond rescue. Throw it away.

Perhaps NiCad batteries might be best for you, but you already own a charge controller, so it might be best to buy a new deep discharge lead-acid battery. Those are the types sold for marine and RV use.

How big should the battery and panel be? You have not told us your requirement. What is the worst case weather where you require the garden lights to work? If you live in a cold place, it might be a 4 foot snow storm and you don't shovel off your panel for a week. If you live in a warm place, it might be the number of consecutive days when you have thick stormy clouds and thus little or no solar power. Or perhaps you are happy when your garden lights work only after a sunny day.

Finally, what is your latitude?

You might also check out your local garden store. They might have a panel/controller/battery/light packaged solution appropriately sized for your location.
 
  • #14
OmCheeto
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That is a motorcycle battery. It is not the deep discharge type, and it is inappropriate for your application. It is probably heavily sulphated by now, and beyond rescue. Throw it away.
No!
We still haven't figured out why, even though all the numbers match up, the system doesn't work.
The battery may still be viable.
I'm currently doing an experiment, with two x 2 watt thin film panels(my preliminary analysis, is that they are garbage. The screws holding the plastic together are worth more than these pieces of...), and one of my dad's 25 year old 50 watt polycrystalline panels.

Dad's panels are still kicking butt!
Perhaps NiCad batteries might be best for you, but you already own a charge controller, so it might be best to buy a new deep discharge lead-acid battery. Those are the types sold for marine and RV use.

How big should the battery and panel be? You have not told us your requirement. What is the worst case weather where you require the garden lights to work? If you live in a cold place, it might be a 4 foot snow storm and you don't shovel off your panel for a week. If you live in a warm place, it might be the number of consecutive days when you have thick stormy clouds and thus little or no solar power. Or perhaps you are happy when your garden lights work only after a sunny day.

Finally, what is your latitude?

You might also check out your local garden store. They might have a panel/controller/battery/light packaged solution appropriately sized for your location.
I'm guessing his latitude is about 49.3°N, based on the population densities of British Columbia.
Not far from me, btw. (45.5°N)
 
  • #15
sophiecentaur
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This conversation is interesting as far as it goes but he really needs to be measuring things. I got my Hall Effect DVM for only about 30GBP and it is useful for so many other things. The non- invasive current measuring capability is a godsend. All you need is a length of single conductor and mine will measure tens of mA repeatably
 
  • #17
OmCheeto
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This conversation is interesting as far as it goes but he really needs to be measuring things. I got my Hall Effect DVM for only about 30GBP and it is useful for so many other things. The non- invasive current measuring capability is a godsend. All you need is a length of single conductor and mine will measure tens of mA repeatably
I was going to say that...
Not sure if you have a "Harbor Freight" type company in England.
Ours gives away meters for free.
My younger brother goes there, just to harvest the batteries from them.
Why do you say no? The picture says CYCLE on the side. It is a starting battery.
I think I was upset that you said; "Throw it away".
But I am with you 100%.
I've only ever had two of these little sealed Pb batteries.
One lasted quite a while, as it was designed for the system I used it in.
The other, lasted a week.

ps. Science!

2016.06.30.its.all.about.the.amps.png
 
  • #18
Wolst73
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You have not told us your requirement. What is the worst case weather where you require the garden lights to work? If you live in a cold place, it might be a 4 foot snow storm and you don't shovel off your panel for a week. If you live in a warm place, it might be the number of consecutive days when you have thick stormy clouds and thus little or no solar power. Or perhaps you are happy when your garden lights work only after a sunny day.

I would like them to work for 3hrs per day every day. Worst case weather is November to March where it is cloudy and rainy most days. Rarely below freezing or snow. Just cloud with little direct sun.

Finally, what is your latitude?

Latitude is 48.4.

I got my Hall Effect DVM for only about 30GBP and it is useful for so many other things

Is that the same as a digital multimeter? Have that but can't get any amp reading.
 
  • #19
Wolst73
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Ok, so I have the wrong battery, easy fix...does that mean that's the problem or do we still have a charging issue that needs solved no matter the battery?
 
  • #20
OmCheeto
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...
Is that the same as a digital multimeter? Have that but can't get any amp reading.

Actually, there is a way around that.
Simply hook your panel directly to the LED system, without the battery.
Then let us know what the voltage is.

18 watt lights, used 3 hours per day = 54 watt hours/day
216 watt hour battery
20 watt panel

As I said earlier, theoretically, the system should work.

Ok, so I have the wrong battery, easy fix...does that mean that's the problem or do we still have a charging issue that needs solved no matter the battery?

That's what we're trying to figure out.
edit: One thing I noted from the image of your battery, is that it has a rated charging capacity of 0.3 amps.
Is your charging system limiting the amperage to that rate?
If it is, then you're only getting about 24 watt hours of charging a day, which is half of your requirement.

If your charging system is ignoring the 0.3 amp limit, then you may have damaged your battery. per post #22.
I'm not really familiar with sealed lead-acid batteries.

ps. I would share the results of my experiments from this morning, but they make absolutely no sense.
hmmm... Ok, I'll share them, just for entertainment value.

Code:
initial conditions:
__________________no load voltage_____rated watts
black panel____________11.72____________1.5
red panel______________22.7_____________2.0
both panels in series__34.1_____________3.5
dad’s panel____________17.5____________50.0
battery(1265 wh)_______12.29(<-- indicates 50% charged)

charging with both red and black panels in series
time(min)____amps____volts____watts
_0___________0.085___12.35____1.05
10___________0.085___12.38____1.05
conclusion: these panels can charge the battery in about ... 600 hours.

charging with dad's 35 year old 50 watt panel
time(min)____amps____volts____watts
_0___________1.677___12.96____21.73
10___________1.530___13.47____20.61
20___________1.527___13.61____20.78
50___________1.519___13.63____20.70
conclusion: an hours worth of charging should add about 20 watt-hours.

So, what doesn't make sense?

7 hours later, after only charging the battery for an hour, the battery's voltage reads 12.47, which indicates that the battery is 75% charged.
(75%-50%)*1265 wh = 316 watt hours.

20 watt hours ≠ 316 watt hours.
I'm guessing that my battery, sitting idle for the last 6 months, suffered from stratification.
I doubt you have this problem.
But come November, you will.
 
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  • #21
OmCheeto
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Also, I interpolated "state of charge(SOC)", from voltage, via a list at Battery University:

BU-903: How to Measure State-of-charge
Code:
SOC__Volts
100% 12.65
_75% 12.45
_50% 12.24
_25% 12.06
__0% 11.89

Mainly because I'm too lazy to measure specific gravities and temperature.

Btw, did anyone mention, that this is complicated?
 
  • #22
Tom.G
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is that it has a rated charging capacity of 0.3 amps.

That battery marking in the CURRENT column, 0.3 CAPACITY, indicates a constant-current charging rate of (0.3 x 18AH), 5.4Amps until the battery voltage reaches that listed in the VOLTAGE column, 14.4 to 15V for cyclical use, then switch to a constant-voltage maintenance charge. If the battery is used as essentially standby power, such as emergency lighting of an EXIT sign during a power outage, then you would switch to constant-voltage charge at 13.5 to 13.8V, EDIT prolonging battery life.
 
Last edited:
  • #23
OmCheeto
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That battery marking in the CURRENT column, 0.3 CAPACITY, indicates a constant-current charging rate of (0.3 x 18AH) 5.4Amps until the battery voltage reaches that listed in the VOLTAGE column, 14.4 to 15V for cyclical use, then switch to a constant-voltage maintenance charge. If the battery is used as essentially standby power, such as emergency lighting of an EXIT sign during a power outage, then you would switch to constant-voltage charge at 13.5 to 13.8V.
Thanks! I was worried that I might have misinterpreted what that meant.
I wonder why they mark them like that, when a "Do not exceed 5.4 amps" would be much more clear to a layman.
 
  • #24
sophiecentaur
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If you want to take this further, measurement is the only answer. Clearly, this is a 'project' exercise as much as garden lighting so you want to learn as much as you can from it. If you don't know the actual charging rate under different conditions then you are working blind. This thread is on the Electrical Engineering Forum and what we advise and what you do should reflect that. It isn't a "Suck it and See" forum. If, like me, you are worried about justifying the expense of buying more gear then a good way of measuring current (Hall Effect Meter) is always worth having. Treat yourself and you will find that, within only a few months, you will find other uses for it. It will measure your mains supply current and also the charging rate of your car alternator without disconnecting anything. Knowledge is Power, remember.
To assess the real state of the battery, you could use other loads (several Watts of 12V car bulbs) and find (in an hour) just how much charge you can cram into it. Sad man that I am, I measure the state of my system nearly every time I go into my shed. :H
 
  • #25
anorlunda
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So, what doesn't make sense?

7 hours later, after only charging the battery for an hour, the battery's voltage reads 12.47, which indicates that the battery is 75% charged.
(75%-50%)*1265 wh = 316 watt hours.

It does make sense if the battery is sulphated (repeatedly suggested on this thread). A sulphated battery acts like a normal battery in terms of charge/discharge voltages, but that the amp-hour capacity is reduced. A18 AH battery when sulphated may act like a 6 AH battery.

Sulphation results from undercharging. That is why I suggested earlier that Nicad batteries would be better for you. They don't have the sulphation problem. Lithium batteries would also be good. Lithium performs better at cold temperatures (the nighttime temperature at your location hasn't been discussed yet)

Latitude is 48.4.
OK, if your latitude is about 48, then it needs about 2.5 times as much panel as at 30 degrees latitude. And in those rainy months with shorter days, you need about 4 times as much panel as on a sunny day in June. So take @OmCheeto's numbers and divide by 10 to get the expected performance in your case. If your battery is sulphated, then divide by 30.

By the way, sealed/not sealed flooded/gel/agm are not different battery types. Starting versus deep-discharge are the two major types of lead-acid battery design. The deep discharge ones have fewer but thicker lead plates. For solar energy storage, a deep discharge battery is needed.
 
  • #26
Wolst73
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mCheeto, post: 5510606, member: 103343"]Simply hook your panel directly to the LED system, without the battery.
Then let us know what the voltage is.[/QUOTE]

Solar Panel hooked directly to DMM showed 19.4V.
Panel hooked directly to Vin on led driver and DMM hooked up to Vout showed 40.4V

image.jpeg


Here is the LED driver

image.jpeg


This is the website I was using to plan my system.
http://www.ledsupply.com/blog/understanding-led-drivers/

Maybe this will shed some light on the problem?
 
  • #27
Wolst73
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the nighttime temperature at your location hasn't been discussed yet)

Average temperature in winter months is 5C. Summer average about 22C. Rarely below 0 and rarely above 30C. No nighttime extremes.
 
  • #28
jim hardy
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Oops, forgot that the lights are set to stay on for 3hrs.

What controls that ?

If you turn the LED's off using the Flexblock's "Dimming" pin provided for that purpose
its input current drops to ~6 millliamps
http://www.luxdrive.com/content/FlexBlock_A011_V1.pdf page 6
Connections
Where a manual on/off control is desired, the potentiometer in Figure 14 may be replaced by a
pushbutton or toggle switch. The output current will be zero and the input current will drop to the
quiescent level when the switch is closed. Figures 16 and 17 show external dimming control combined
with on/off control.

if instead you placed a timer switch in the DC output wire going to the LED's (which would be natural a enough assumption )
the output will rise to maximum voltage as the Flexblock spins its wheels trying to force current through the open switch,
and you measured 40 volts,
in that situation input current will be significant and will discharge the battery when you're not looking.
So -
where'd you connect your timer switch ?


Sorry to ask such a basic question
but it's the small things of the Earth that confound the mighty...

old jim
 
  • #29
Wolst73
56
7
What controls that ?

The pwm solar charge controller controls how long the load is on. You can set it from 1 hour or until battery is exhausted. Once the panel output drops below a certain level the charge controller switches from charging the battery to the battery powering the load. Dimmer wires are unconnected.
 
  • #30
jim hardy
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Dimmer wires are unconnected.

okay, that's clear.

The pwm solar charge controller controls how long the load is on.
How does the PWM controller do that ?
Does it open a switch that's between the battery and the Flexblock ?

Once the panel output drops below a certain level the charge controller switches from charging the battery to the battery powering the load.
So at that time the battery commences powering the Flexblock ?
3 hours later, something stops the battery from powering the Flexblock ?
How does whatever does that do that ?
 
  • #31
Wolst73
56
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How does the PWM controller do that ?
Does it open a switch that's between the battery and the Flexblock ?

I believe it does.
 
  • #32
mheslep
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..

So we see that independent of panel aiming, the watts/m^2 of sunlight at the Earth's surface varies enormously with latitude, approaching zero at the poles.

Russ was largely correct for a *clear* summer day in most of the US. The collector and the "earth's surface" are two different things. If the collector is tilted south at latitude, it corrects for the oblique angle of the Earth's surface which otherwise reduces power per area.

The factor that can't be removed by panel pointing is path length of attenuating atmosphere for solar radiation, which grows larger at higher latitudes. When the sun angle to Earth surface determined by time of day or latitude is 75 degrees, the path length is four times greater than at an angle of 0 degrees.

https://en.m.wikipedia.org/wiki/Air_mass_(solar_energy)#Definition

The measured effect of latitude can seen by looking up the NREL solar radiation data for collectors "tilted at latitude" against "flat plate". In mid summer, some US northern cities under good conditions compare well with southern cities.
 
  • #33
jim hardy
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Surely the charge controller is temperature compensated ,
and located so as to be at same temperature as battery ?
Looks like an uncompensated charger would undercharge a cold battery.
Surely nobody would sell such a thiing in Canada...
battV_vsT.jpg

http://www.tekrispower.com/pdfs/xantrex/Batteries%20-%20Temperature%20Compensated%20Charging.pdf [Broken]
 
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  • #34
anorlunda
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Russ was largely correct for a *clear* summer day in most of the US. The collector and the "earth's surface" are two different things. If the collector is tilted south at latitude, it corrects for the oblique angle of the Earth's surface which otherwise reduces power per area.

The measured effect of latitude can seen by looking up the NREL solar radiation data for collectors "tilted at latitude" against "flat plate". In mid summer, some US northern cities under good conditions compare well with southern cities.

What you say is correct, but there are other factors that can't be compensated by attitude tilt angle of the panel. The seasonal variation in daylight hours is one. The azimuthal variation in the sun's direction is another. Anyone who has lived in the far north knows that the sun does not rise in the east and set in the west, it goes around you in a circle. My daughter grew up at 65 degrees latitude. Later in life we moved to 42 degrees. She heard the phrase "the Sun rises in the East." and she said, "Says who?"

Heliostats are cool, they can follow both the sun's altitude and azimuth.

Nobody nibbled at my little riddle in #12 about a panel at the north pole. Up there, the panel's altitude angle should always be nearly 90 degrees, but the azimuth must swing 360 degrees in summer. But the riddle part is that all those azimuthal angles are South when starting at the North Pole. :wink:

Also, nothing in the OP limited the question to mainland USA or to summer months only. I always try to remind myself that PF threads can be googled. The posts can be discovered and read by anyone from any country at any time in the future. When posting on PF, I try to visualize that broad audience rather than a private conversation between the participants.
 
  • #35
Wolst73
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image.jpeg

When multimeter hooked directly to panel it shows around 19v. When I hook multimeter up to where panel goes into solar charge controller it shows 11v? That is also the reading you get when hooked up to the next terminals which are the battery connections.

A PWM charge controller does absolutely nothing when the voltage is below 13.8. The controller is not a big source of inefficiency, it doesn't contribute inefficiency at all as long as the battery is undercharged.

Is this the reason for the slow charge? Where/why is there a dropoff in voltage? I would have expected the first terminals to still show 19v and the battery terminals to show whatever the batteries current voltage is?
 

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