Which MPPT Controller?

[Poecheng]

That's daft! Putting panels in series halves the current available from the two panels. ie the OP will in effect just have one 100watt panel with (potential) 24v charging ability.

Er .... no it's not.

a) he will have 200w (max) whatever voltage you want to consider; The power (Watts) of the panel in the same conditions remains the same whether you extract it as 24v, 12v or whatever. The amperage, however, will alter in inverse proportion to the voltage. In your last phrase quoted, 100W has simply gone missing.

b) You are quite correct it halves the available amperage into the MPPT but not correct if you are suggesting it halves the amperage into the battery. The whole purpose of the MPPT is it can take a large range of voltage above a certain level and step it down it into a 12V charging current (ie about 14 point whatever). It doesn't somehow throw that extra 12v away (24v in and 12v out) but converts it into current.
The advantage is that, in series, you will always have voltage above that certain level and thus can take advantage of whatever sun/light is around. In parallel and in poor conditions you just have two 12v panels struggling to reach that voltage.

 

[Poecheng]

Deleted post (emphasis added):
"I recommend you read Victrons document. It clearly shows how a 24v 100watt panel only provides 66w into a 12 battery. If your claims that an MPPT controller is a dc to dc converter and can reduce the voltage and double the current are true, then I can't see anywhere Victron make that claim.
Indeed, if only 66w is available from a 24v 100watt panel, then they are 'throwing away some of the extra 12v', though I agree in duller condition, having 2 in series might maximise charging, but at the expense of more rapid charging in brighter conditions."

I now have done:
http://www.victronenergy.com/upload/documents/White-paper-Which-solar-charge-controller-PWM-or-MPPT.pdf

and it says precisely what I suggested (again, emphasis added):

3. The MPPT charge controllerAs shown in figure 6 the voltage Vm corresponding to the Maximum Power Point can be found bydrawing a vertical line through the top of the power-voltage curve, and the current Im can be foundby drawing a horizontal line through the intersection of the Vm line and the current-voltage curve.These values should be equal to the values specified in table 1.In this example Pm = 100 W, Vm = 18 V and Im = 5,56 A.With its microprocessor and sophisticated software, the MPPT controller will detect the MaximumPower Point Pm and, in our example, set the output voltage of the solar panel at Vm = 18 V and drawIm = 5,56 A from the panel.What happens next?The MPPT charge controller is a DC to DC transformer that can transform power from a highervoltage to power at a lower voltage. The amount of power does not change (except for a small lossin the transformation process). Therefore, if the output voltage is lower than the input voltage, theoutput current will be higher than the input current, so that the product P = V x I remains constant.When charging a battery at Vbat = 13 V, the output current will therefore beIbat = 100 W / 13 V = 7,7 A.

That really is why they are so good. A (probably theoretical rather than measurable) advantage is that it is better to move higher voltage around rather than higher amps (as per the National Grid) as amps come up against resistance. Better to shift it as high volts/low amps and convert it to lower volts/higher amps locally.

 

[ianj99]

Er .... no it's not.

a) he will have 200w (max) whatever voltage you want to consider; The power (Watts) of the panel in the same conditions remains the same whether you extract it as 24v, 12v or whatever. The amperage, however, will alter in inverse proportion to the voltage. In your last phrase quoted, 100W has simply gone missing.

b) You are quite correct it halves the available amperage into the MPPT but not correct if you are suggesting it halves the amperage into the battery. The whole purpose of the MPPT is it can take a large range of voltage above a certain level and step it down it into a 12V charging current (ie about 14 point whatever). It doesn't somehow throw that extra 12v away (24v in and 12v out) but converts it into current.
The advantage is that, in series, you will always have voltage above that certain level and thus can take advantage of whatever sun/light is around. In parallel and in poor conditions you just have two 12v panels struggling to reach that voltage.

After further consideration, and especially for UK waters, I agree that series connection is the way to go and will also avoid the issue with the required 5v differential between vbat and panel output.

 

[Poecheng]

In my last post I suggested a possible advantage re resistance. In fact, reading on in the Victron document, section 6, they refer to this as a real consideration before drawing the following conclusion:

Conclusion:When using an MPPT charge controller there are two compelling reasons to increase the PVvoltage (by increasing the number of cells in series):
a) Harvest as much power as possible from the solar array, even at high celltemperature.
b) Decrease cable cross sectional area and therefore decrease cost.

 

[ianj99]

In my last post I suggested a possible advantage re resistance. In fact, reading on in the Victron document, section 6, they refer to this as a real consideration before drawing the following conclusion:

Conclusion:When using an MPPT charge controller there are two compelling reasons to increase the PVvoltage (by increasing the number of cells in series):
a) Harvest as much power as possible from the solar array, even at high celltemperature.
b) Decrease cable cross sectional area and therefore decrease cost.

So the conclusion is that either 24v panels or 2 series connected 12v panels should be used, along with a reputable mppt controller such as the Victron ones. (or 3, 12v panels in series for a 24v system)

 

[Javelin]

OK,
Buy victron BlueSolar MPPT 75/10,
Link the panels in series,
Relax and have a cup of tea,
Thanks, I think.

 

[Tammany]

I've fitted a cheaper eBay controller and it seems to work well. The meter is handy too. It normally shows around 17-18v going in and 13.4-14v charging. I have 2 x 10w polycrystalline panels in series and one monocrystalline 20w in parallel although intend on adding another 40w too.

http://pages.ebay.com/link/?nav=item.view&id=280979967391&alt=web

 

[VicS]

I've fitted a cheaper eBay controller and it seems to work well. The meter is handy too. It normally shows around 17-18v going in and 13.4-14v charging. I have 2 x 10w polycrystalline panels in series and one monocrystalline 20w in parallel although intend on adding another 40w too.

You have a single 40w panel in parallel with two series connected 10 watt panels controlled at 17-18V ??

The 10 watt panels are 6 volt each then ?????

 

[Tammany]

20w + 2 x 10w . They are 12v panels but only produce high volts in full sun. Only fitted them a few weeks ago so weather hasn't been brilliant so haven't seen what they will be like in full summer sun yet.

 

[Tammany]

Monocrystalline produce next to nothing in poor weather too

 

[DannyB]

Just been looking on eBay at Sundely flexible panels and the state if connecting multiple panels to connect them in parallel not series. They even have a little diagram. I wonder why ?

 

[RichardS]

Just been looking on eBay at Sundely flexible panels and the state if connecting multiple panels to connect them in parallel not series. They even have a little diagram. I wonder why ?

If these are not expensive panels it is probably being assumed that the controller will not be a relatively expensive MPPT one.

Richard

 

[TonyMS]

If you have several panels, and one is in shade:

With a parallel set up, the shaded panel is presumable effectively disconnected (assuming a blocking diode)
With a serial setup, it is providing a resistance in the circuit, reducing the current produced by the other panels

I don't have any solar panels to test here in England. Can anyone tell what the resistance of a shaded panel is?

Tony

 

[aluijten]

If you have several panels, and one is in shade:

With a parallel set up, the shaded panel is presumable effectively disconnected (assuming a blocking diode)
With a serial setup, it is providing a resistance in the circuit, reducing the current produced by the other panels

I don't have any solar panels to test here in England. Can anyone tell what the resistance of a shaded panel is?

Tony

I've heard the same story. So unless you can make sure both get the same exposure at the same time it's better to put them in parallel.
When exposure is the same then series is more efficient (when using a proper MPPT controller)

 

[VicS]

If you have several panels, and one is in shade:

With a parallel set up, the shaded panel is presumable effectively disconnected (assuming a blocking diode)
With a serial setup, it is providing a resistance in the circuit, reducing the current produced by the other panels

I don't have any solar panels to test here in England. Can anyone tell what the resistance of a shaded panel is?

Tony

Dont bypass diodes solve the problem caused by shading ?

 

[Gypsyjoss]

I've fitted a cheaper eBay controller and it seems to work well. The meter is handy too. It normally shows around 17-18v going in and 13.4-14v charging. I have 2 x 10w polycrystalline panels in series and one monocrystalline 20w in parallel although intend on adding another 40w too.

http://pages.ebay.com/link/?nav=item.view&id=280979967391&alt=web

Hi Tammany
According to the spec, this appears to be a PWM controller , not MPPT.
Pete