How can this happen?

[V8Ian]

About three years ago I bought a 24V solar panel to keep my coach batteries maintenance charged.
The coach has four N70s, two in series, two in parallel resulting in 24V.
On checking the output of the panel, in good sun it was making 40V and slightly overcast skies 36V.
171562 171563 171564

Due to the limitations of the panel, no regulator is required. How can the panel produce ~150% of its capacity?

[Hogarthde]

Ian,
I have just submitted your name to the Nobel Prize Committee,(physics) for nomination.

Whilst we poor plebs have trouble keeping the smoke in.....you my esteemed colleague , have managed to make smoke.

Pity the Queens Birthday Honours is over for 12 months

[Blknight.aus]

depending on how and where you measured what...

it cant...

it can make a certain amount of power, the total number is watts.

you can have X volts and Y amps and when you multiply x by y you should ideally wind up with a number in close proximity to the number of watts the panel can produce.

if you had really thin wires, id expect the voltage at the panel itself to be high, the amps to be low and when you get down to the battery side of the wire the voltage would be a lot lower and the amps the same.. The missing volts being converted to heat in the wire (the very simple version)

but yes, some panels do infact make more power than they are rated to. this is because some panel manufacturers rate their panels at a lower solar intensity than others. Its a bit like car salesmen or winch salesmen.

which is the better winch the 12000lb winch or the 8000lb winch? 12000lb yeah, but what if.... 12000lb is only available while the motor is cool you're on the bottom layer of the drum with a solid 14.4v being delivered compared to the 8000lb winch that will put down 8000lb of pull with the motor near red hot, the batteries putting 10.2v into the motor and on the top layer of the drum...

So it is with solar panels, the panel thats rated to 120w at 15 degrees c with a perfect sun angle with high intensity sunlight is not as good as the panel thats rated at 120w at 35 degrees c with a 15 degree offset to a milder sunlight.

You can also pick up extra solar effort with additional reflected light, If youve got direct light on the panel from the sun and you're picking up an additional reflected source you get some more free ergotrons.

[Blknight.aus]

depending on how and where you measured what...

it cant...

it can make a certain amount of power, the total number is watts.

you can have X volts and Y amps and when you multiply x by y you should ideally wind up with a number in close proximity to the number of watts the panel can produce.

if you had really thin wires, id expect the voltage at the panel itself to be high, the amps to be low and when you get down to the battery side of the wire the voltage would be a lot lower and the amps the same.. The missing volts being converted to heat in the wire (the very simple version)

but yes, some panels do infact make more power than they are rated to. this is because some panel manufacturers rate their panels at a lower solar intensity than others. Its a bit like car salesmen or winch salesmen.

which is the better winch the 12000lb winch or the 8000lb winch? 12000lb yeah, but what if.... 12000lb is only available while the motor is cool you're on the bottom layer of the drum with a solid 14.4v being delivered compared to the 8000lb winch that will put down 8000lb of pull with the motor near red hot, the batteries putting 10.2v into the motor and on the top layer of the drum...

So it is with solar panels, the panel thats rated to 120w at 15 degrees c with a perfect sun angle with high intensity sunlight is not as good as the panel thats rated at 120w at 35 degrees c with a 15 degree offset to a milder sunlight.

You can also pick up extra solar effort with additional reflected light, If youve got direct light on the panel from the sun and you're picking up an additional reflected source you get some more free ergotrons.

and looking at your panel data sheet on the edit.....

your 24v panel is a folding panel which is made of 2 identical 12v rated panels in series, the clue is in the Voc section of the label, the open circuit voltage is only 21 V,

[NavyDiver]

The Suns energy on the surface of the earth is known as "The solar constant"

It is approximately 1370 watts per square metre (W/m2).

The solar constant actually varies by +/-3% because of the Earth's slightly elliptical orbit around the Sun.

Your in Qld right[bigwhistle]


Now I made my self a smart ass I admit I have N.F.I. sorry [thumbsupbig]

[PhilipA]

If the two panels are rewired in series rather than parallel then the voltage is doubled.

I do this with my folding panels to get maximum amps out with an MPPT regulator.

The downside is if any one cell is covered then there are no amps , while in parallel there are still half the amps.
Regards PhilipA

[V8Ian]

and looking at your panel data sheet on the edit.....

your 24v panel is a folding panel which is made of 2 identical 12v rated panels in series, the clue is in the Voc section of the label, the open circuit voltage is only 21 V,
They're not folding panels Dave. It's two panels attached on the same plane. I had it made to specificly keep the batteries charged. The fellow who made it is a solar specialist who I came across at a caravan and camping show.
The measured voltages were at the alligator clips, with a high end multimeter.

[BradC]

About three years ago I bought a 24V solar panel to keep my coach batteries maintenance charged.
The coach has four N70s, two in series, two in parallel resulting in 24V.
On checking the output of the panel, in good sun it was making 40V and slightly overcast skies 36V.
171562 171563 171564

Due to the limitations of the panel, no regulator is required. How can the panel produce ~150% of its capacity?

It can't.
A panel has 3 variables.
- Open circuit voltage
- Short circuit current
- Maximum power voltage.

- Often short circuit current is relatively close to maximum power current.

You can't get maximum current at the open circuit voltage, so that's a no-go.
You can get close to maximum current at the maximum power voltage. For a 12V panel that's often around 17V. (Yours is 17.8V).
The maximum power current for your panel is 560mA. 560mA at 17.8V is 9.968W.

If you connect that to a charged battery directly you get ~560mA @ ~13.8V (or 7.73W).

An MPPT regulator tries to run the panel at the voltage where it delivers max power, so it'll drop the 17.8V down to 13.8v using a switching converter and result in closer to ~710mA into the battery.

[Blknight.aus]

They're not folding panels Dave. It's two panels attached on the same plane. I had it made to specificly keep the batteries charged. The fellow who made it is a solar specialist who I came across at a caravan and camping show.
The measured voltages were at the alligator clips, with a high end multimeter.

its still 2 panels connected in series, or its got the wrong sticker on it.

IMHO there are very few solar specialists who attend camping and caravan shows. Salesmen definately but not specialists.

[mikegf]

While I understand the “no regulator required” mantra (as the output current is physically limited by the wattage available), I’m a bit skeptical. I’ve used small panels (5-10W) on the farm (usually with batteries past their diesel use by date from tractors, utes etc) and they seem to die more quickly than expected. Even though the current is low, 17+V (from a 12V panel in full sun) is still much higher that the nominal 15V (ie 2.65V per cell) max.

I now use a charger on all panels (even the tiny 5W ones). For the smaller panels PWM charging is fine. Jaycar/RTM has a tiny and inexpensive ($16) 3A PWM controller that I use. Stick it on the back and seal it up with silicone. I now seem to get much better life - though the relatively small sample set may just mean I’ve been using old batteries in better condition and the charger has done nothing[bigwhistle]

Edit: in your case you may need more $$ for a 24V capable charger (starting about $40).

[Hogarthde]

Quick question Mike, Did you mean to type ‘charger’ ?

[PhilipA]

I repeat. It seems to me that they are series to give 24v.

If they were in parallel the controller could not reach 24v .
Regards PhilipA