Solar panel mixing again

[BabaYaga]

I partly renewed the solar set up on my 29 foot sailing boat at the beginning of this season. As I am not convinced that I am getting best possible yield, I would be grateful for some advice.
This is what I have:
On the hatch garage is a (new) 45 W panel which is permanently connected. It has 39 cells and the values are as follows: Maximum current (Imax) 2.10 A, maximum voltage (Umax) 21.43 V, voltage open circuit (Uoc) 26.5 V and short circuit current (Isc) 2.17 A.
I also have two foldable 50 W panels which only come out when the boat is used, generally when at anchor or moored. They each consist of four small interconnected panels in a fabric ‘briefcase’. I have had these for a few years. The specification I can find for them gives only the following values: Maximum current 2.78 A, maximum voltage 18 V.
So 145 W of solar in total, but sometimes I may only use one of the roving panels. And when under way normally only the 45 W panel.
When more than on panel are in use, they are connected in parallel into a Victron Smartsolar 75/15, which is also new. The 12 V house bank being charged consists of 3 x 90 Ah AGM batteries.
My basic question is are the two panel types involved compatible to run into the same controller? If not, what would be the best solution to maximize the yield? Connecting in series seems unpractical with my usage pattern.
I am well aware that similar questions have been asked before, but I have not found answers relating exactly to my type of setup.

 

[Baggywrinkle]

 

[B27]

A solar panel has a V/I curve.

A typical small panel will have something like open circuit volts ~21, max power volts ~18 and a max power current and a short circuit current.
So long as the max power voltages are 'similar' you can combine panels in parallel without losing much efficiency.
Your controller will set the panel volts and the current will be whatever each panel contributes at those volts.

If you want absolute highest efficiency, you need separate MPPT for each panel, because the panels may have different angles o the sun, partial shading etc.

The OP mixing a 45W which has a max power voltage of 21V with 100W of panels having a max power voltage of 18V (round numbers) will lost a bit of efficiency, the system panel volts might end up about 19 so each panel will be close to, but not at, its optimum.

If you look at the V/I curve for a panel and multiple V by I to get power at different voltages, changing the voltage away from max power by a volt or so does not make a huge difference.

If the panels face different directions, then you get more hours of power and the system volts changes according to which panel gets more sun.

If your battery is well charged and you don't need all the power, the panel volts will rise to match the current drawn.

 

[BabaYaga]

Thank you for the video link, some interesting and striking examples there, but as I mentioned I cannot really see any practical way of connecting my current three panels in series even if I wanted to, given how they are being used.

The OP mixing a 45W which has a max power voltage of 21V with 100W of panels having a max power voltage of 18V (round numbers) will lost a bit of efficiency, the system panel volts might end up about 19 so each panel will be close to, but not at, its optimum.

Thanks for your reply. Going by what was taught in the video, it seems that I should only expect the lower of the two voltage levels when different types of panels are connected together in parallel, so in this case 18 V. That still makes almost 138 W, if I have got the numbers right, out of the total nominal 145 W 'installed'.
So it seems getting a second controller, for the two lower voltage panels, would perhaps be my best bet for increasing the yield, but the improvement would not be significant.

 

[Boathook]

I tried adding a portable 100W portable panel to my fixed panels and it made no difference to power output according to my victron smart controller.
I've therefore use the portable panels via an old pmw? Controller that I plug into a 12 volt socket. Seems to work and adds extra charge to the batterys.
This mild weather has meant that I have used the boat more but the shorter daylight hours means my fixed panels don't develop enough charge during the day to cover usage. Another winter project coming up to beef up fixed panels.

 

[B27]

I don't think you want to connect different panels in series.
Or even identical panels if they will see different amounts of sun at any time.

Exactly what happens may vary a little bit with how the solar controller tracks the maximum power point.
There are 'MPPT' chips about which don't actively find the optimum panel voltage, they just load the panel to 18V because that's usually near enough, and convert it to whatever voltage is wanted.

I don't think you can do any damage paralleling panels so long as they each have a reverse blocking diode and the wiring is adequate gauge. So try it and see?

 

[noelex]

I partly renewed the solar set up on my 29 foot sailing boat at the beginning of this season. As I am not convinced that I am getting best possible yield, I would be grateful for some advice.
This is what I have:
On the hatch garage is a (new) 45 W panel which is permanently connected. It has 39 cells and the values are as follows: Maximum current (Imax) 2.10 A, maximum voltage (Umax) 21.43 V, voltage open circuit (Uoc) 26.5 V and short circuit current (Isc) 2.17 A.
I also have two foldable 50 W panels which only come out when the boat is used, generally when at anchor or moored. They each consist of four small interconnected panels in a fabric ‘briefcase’. I have had these for a few years. The specification I can find for them gives only the following values: Maximum current 2.78 A, maximum voltage 18 V.
So 145 W of solar in total, but sometimes I may only use one of the roving panels. And when under way normally only the 45 W panel.
When more than on panel are in use, they are connected in parallel into a Victron Smartsolar 75/15, which is also new. The 12 V house bank being charged consists of 3 x 90 Ah AGM batteries.
My basic question is are the two panel types involved compatible to run into the same controller? If not, what would be the best solution to maximize the yield? Connecting in series seems unpractical with my usage pattern.
I am well aware that similar questions have been asked before, but I have not found answers relating exactly to my type of setup.

Connecting these different panels to a single MPPT controller will not do any damage, but the solar yield will be compromised by the disparate maximum power point voltage between the two solar arrays.

You can roughly estimate the expected loss by assuming the Vmp of the total array will be equivalent to the Vmp of lowest contributor. In this case, if we assume a Vpm of 18v the new 45w panel will be limited to 45x18/21.43 = 32w. Thus thus the 45w panel will behave (very roughly) as if you have added a 32w panel.

The maximium output would be install seperate MPPT controllers to controll the disparate solar panels, but the gain in output may not be worth the extra cost and complication.

 

[Baggywrinkle]

Thank you for the video link, some interesting and striking examples there, but as I mentioned I cannot really see any practical way of connecting my current three panels in series even if I wanted to, given how they are being used.

Thanks for your reply. Going by what was taught in the video, it seems that I should only expect the lower of the two voltage levels when different types of panels are connected together in parallel, so in this case 18 V. That still makes almost 138 W, if I have got the numbers right, out of the total nominal 145 W 'installed'.
So it seems getting a second controller, for the two lower voltage panels, would perhaps be my best bet for increasing the yield, but the improvement would not be significant.

Yep, that calculation is correct, you will only lose just over 7W of capacity from all panels combined compared with having everything nicely matched. Not worth the expense of another MPPT IMO.

Adding additional temporary panels in parallel is easier than in series, and in your case, connecting in series would only give 120W - so it really doesn't make any sense at all to wire in series.

 

[BabaYaga]

I tried adding a portable 100W portable panel to my fixed panels and it made no difference to power output according to my victron smart controller.
I've therefore use the portable panels via an old pmw? Controller that I plug into a 12 volt socket. Seems to work and adds extra charge to the batterys.

Interesting, that is broadly in line with my experience from this first season with the new solar setup. I might try something similar.

Thanks all for the further replies.

 

[B27]

I tried adding a portable 100W portable panel to my fixed panels and it made no difference to power output according to my victron smart controller.
I've therefore use the portable panels via an old pmw? Controller that I plug into a 12 volt socket. Seems to work and adds extra charge to the batterys.
This mild weather has meant that I have used the boat more but the shorter daylight hours means my fixed panels don't develop enough charge during the day to cover usage. Another winter project coming up to beef up fixed panels.

To me, that suggests the Victron controller is regulating the current and doesn't 'think' the power from the extra panel is needed.
I could speculate why that might be, but it might be more useful to get in there with a multimeter (and the Victron manual...)

 

[Boathook]

To me, that suggests the Victron controller is regulating the current and doesn't 'think' the power from the extra panel is needed.
I could speculate why that might be, but it might be more useful to get in there with a multimeter (and the Victron manual...)

I originally thought that, but the battery voltage was down a bit so I was expecting more power going in. The portable panels are a slightly different voltage (lower) which possibly was the issue.