Solar panels in series

Please ignore the couple of sentences at the end - started to expound, realised I was waffling but failed to delete them! Oh for an edit function!

Cheers

John

"The flip side though is that partial shading of one panel will reduce total output to virtually zero as Boobook says."

Not if the panels have bypass diodes installed, I believe.

Bypass diodes will work sometimes when one panels output is almost zero, but a partially shaded panel will still reverse bias the diode and hence the series current will be reduced. Try it.

Parallel will totally address the shading issue however.

Al see vanners and campers getting sold MPPT controllers with claims of 30% more power and they are not told the complete story. To get anywhere near the extra power requires specific conditions and panels need to be tracking at correct angle.

MPPT controllers are no benefit with flat mounted panels.

MPPT controller should have maximum efficiency on 12V panels charging 12V battery. If you go to 24V panels charging 12V battery efficiency drops. The higher the panel voltage charging 12V batteries the lower the efficiency.

"MPPT controller should have maximum efficiency on 12V panels charging 12V battery. If you go to 24V panels charging 12V battery efficiency drops. The higher the panel voltage charging 12V batteries the lower the efficiency."

I don't believe this statement.
Please educate me further.

Marty,

No, No and No!
With a simple controller the current drawn by the battery while charging pulls the panel voltage down to the voltage required by the battery, which is about 25-30% below the panel's maximum power voltage. But...An MPPT controller accepts the higher panel voltage and converts it into the voltage required by the battery. This process is very efficient, so although the voltage is dropped 25-30% by the controller, the current delivered to the battery by the controller is actually close to 25-30% higher than the current arriving from the panel/s. Simple switchmode "magic" trades off excess voltage for increased current.

This applies regardless of panel orientation (including horizontal), though obviously it's always better to be aimed directly at the sun in order to maximise capture. Your final paragraph is correct for simple controllers, wrong for MPPT.

Lex - I'll concede your point regarding panels fitted with a bypass diode, but they aren't always there, so let's keep it simple!

Cheers

John

Hi John,
Tony the engineer at the 12 volt shop in Perth advised me that MPPT controllers don’t have an advantage in normal Australian conditions but are used to best advantage in Europe. Under ideal conditions my 130 watt panels, with a simple PWM controller, will put out 140 watts, which seems to confirm what he says.

Hi Dennis

Lets assume those panels are outputting 140 watts into an almost fully charged battery at 14 volts. Then they're outputing 140/14 amps = 10 Amps.

If you had a MPPT controller operating at the best efficiency of the panels at about 18 volts and still about 10 amps then you would be getting 180 watts out of the panels with (say) a 90% efficiency of the MPPT controller would give you 90% of (180/14) = 11.57 Amps into the battery. and increase of 15%

If however your battery was somewhat discharged say 13 volts The pwm current into the battery would still be 10 Amps and the output reduced to 130 Watts.
The MPPT controller would still extract 180 watts from the panel and the battery would be getting 90% of (180/13) = 13,8 amps into the battery.
An increase of over 30%.

The lower the state of charge of the battery the greater the advantage of the MPPT over the PWM.

Is the cost and complexity worth it?
That's up to the user.

Dennis,

Your "engineer" is wrong! With efficient switchmode technology, an MPPT controller will trade off excess voltage to increase charging current anywhere. This applies while the laws of Physics apply!! even in the southern hemisphere!!!

I have no argument with your 130W panels putting out 140W - it sometimes happens, but with a non-MPPT controller you cannot put those watts into your battery. The panel's maximum output occurs at about 18 volts. Your battery can't accept more than about 14 volts. Much the same current (amps) comes from the panel, but you can only use 14, not 18, volts. Watts = volts x amps, so you are losing a significant wattage. I'm not knocking simple controllers, indeed I still use one myself, but you will get more power into your battery with an MPPT one.

Cheers

John

John yes yes yes. Marty is right. Post a graph or specification from MPPT manufacturer that demonstrates improved efficiency of 24V charging 12V battery.
Whenever you convert voltage up or down efficiency is lost. It is so otherwise you would have invented perpetual motion.

John
This engineer knows his stuff - been in the industry for years.

Lex
180 watts out of a 130 watt panel – don’t be silly.
I don’t care what controller you’ve got connected, it’s never going to happen.
Read your panel specs.

William,

You are right of course about inefficiency of any energy transformation. I said above that MPPT controllers are very efficient - they are not 100%, but most are over 90%, and some manufacturers claim 97%. If only we could ignore the laws of thermodynamics!

Marty is not right though.

He says
1)"Al see vanners and campers getting sold MPPT controllers with claims of 30% more power and they are not told the complete story. To get anywhere near the extra power requires specific conditions and panels need to be tracking at correct angle."

No - the improvement is there regardless of panel orientation. Correct orientation provides optimum capture area.

2)"MPPT controllers are no benefit with flat mounted panels."

No - The improvement is there regardless of panel orientation. Horizontal mounting is not optimal for most locations in Australia. For maximum sun capture the panel should be mounted perpendicular to a line drawn to the sun. At solar noon in midsummer on the Tropic of Capricorn, horizontal is in fact optimal.

3)"MPPT controller should have maximum efficiency on 12V panels charging 12V battery. If you go to 24V panels charging 12V battery efficiency drops. The higher the panel voltage charging 12V batteries the lower the efficiency."

No - What we speak of as 12V panels actually produce their maximum energy output at about 18 volts, which is too high for directly charging a 12V battery. When a panel is connected DIRECTLY to a partially discharged battery, the battery draws sufficient current to pull the panel voltage down. An equilibrium is established where the panel voltage is sufficient to maintain the charging current. Once the battery is fully charged and draws less current the voltage rises - this is when we need a controller (even just a simple one) to turn off charging and prevent the panel delivering excessive voltage to the battery.

With a SIMPLE controller and a "12V" panel charging a 12V battery we are losing about 30% of the available energy. With a "24V" panel and a 12V battery we lose far more. Marty is quite correct in saying that, BUT, an MPPT controller overcomes this by converting the voltage at better than 90% efficiency. There is benefit too in using the higher voltage panel, since current (and hence resistive loss) is halved in the wiring from panel to controller. This is not a function of the controller so no manufacturer's graphs or specs, just simple application of Ohms Law.

I respect your opinions, and Marty's too, but I don't share all of them!

Cheers

John

Dennis

"180 watts out of a 130 watt panel – don’t be silly.
I don’t care what controller you’ve got connected, it’s never going to happen.
Read your panel specs. "

You claimed 140 Watts out of 130 Watt panel with a PWM.
I didn't claim anything to do with a 130 watt panel.

My figures applied to a panel with an output into a battery of 140 Watts with a PWM.
If you can get 140 Watts with a PWM then my MPPT figures stand.
I only took the 140 Watt figure as an example.


Maybe I should have said - don't be silly. Read YOUR panel specs.
130 watt panel with a PWM controller- I would expect max about 7.5 Amps. Charging an almost fully charged battery at 14.5 volts - 14.5 X 7.5 = 108.75 Watts
Charging a low battery at 12.5 Volts - 12.5 x 7.5 = 93.75 Watts

140 Watts out of a 130Watt panel with a PWM. Don't be silly. It's never going to happen.

Lex,
If you have good quality panels – in ideal conditions you can achieve a little more than 140watts out of a 130 watt panel. I was blowing 7.5 amp fuses with 130 watt Sharpe panels and when I took measurements to find a fault I found the panels were putting out over 10amps/140 watts. Sharpe’s specifications confirm that this can happen - you should get a copy.

Dennis

Since most solar panel specifications are at a standard sunlight energy level, (1 kW / sq metre) it is quite possible to get more than the specified output current under better than specified conditions. This applies to any solar panel correctly specified.

So if you're getting a measured 10 Amps at 14 Volts out of those panels with a PWM controller then my previous figures regarding the advantage of a MPPT stand. You should get better than 11.5 Amps or 160+ Watts into the battery.

If you and your engineer don't follow this I suggest you find another engineer.
One who understands Solar technology.

This whole Wattage thing with solar panels is quite irrelevant with anything less than a MPPT controller. The Amps out of the panel is what you get into the battery. Wattage varies dynamically with state of charge (Voltage) of the battery.

With a MMPT controller you will get more Amps. How much more depends on many factors

Lex,
MPPT controllers give a greater output but not to the extent you are quoting for good light levels. You give simple wattage calculations, but it’s not that easy, you have left out a lot of other parameters needed to evaluate the differences in the outputs of the two controllers - other than measuring them of course.
But we are just going around in circles and I think the best we can do is to agree to disagree.

12V, Solar, MPPT, Amps, and Amp Hours?

I Only have one Question.

Where's Mainey?

Dennis

"you have left out a lot of other parameters needed to evaluate the differences in the outputs of the two controllers "

Thought that's what I said here.
"With a MMPT controller you will get more Amps. How much more depends on many factors"



Boobook
"12V, Solar, MPPT, Amps, and Amp Hours? "

We didn't get to Amp Hours (or is that "Amp hours" or "Amphours"). :-)

Mainey must be on holidays. ;-)

Lex M (Brisbane) posted:
.....
Mainey must be on holidays. ;-)

Or morphed perhaps Lex, he hasn't appeared as "Mainey" since a large 12V thread blow up in about September that has been moderated (dissapeared).

Strange but true........ Perhaps he is a buddhist, and come back as another being.