solar upgrade

[Starburst2]

On my RV roof I presently have 2 Kyocera 135 W panels, flat mounted, hooked in series, feeding to my Blue Sky Solar Boost 3024iL charge controller. I want to add more panels to my array. The simplest seemed to me to be to add a Kyocera 215 W panel or a 245 W panel but I do not want to owerpower my charge controller.
The two 135 W panels have the following specs: Vmp 17.7 , Imp 7.9 A, Voc 22.1, Isc 8.7A
The 215 W panel has the following specs: Vmp26.6, Imp 8.1A, Voc 33.2, Isc 8.8 A.
The 245 W panel has the following specs: Vmp 29.8, Imp 8.2 A, Voc 36.9, Isc 8.9 A.

The Charge Controller specs are: Output Current Rating 30A/40A, the Nominal Battery Voltage is 12/24 VDC, and the PV input max is 57VDC.

Since the two 135 Watt panels are hooked in series I am not sure how that affects the load on the charge controller.
Can someone who understands all this give me some guidance as to what maximum size panel I can add without exceeding the capacity of the controller?
Thanks for your feedback folks.
Regards,
Lloyd

[time2roll]

Delete

[time2roll]

I would probably end up with 4x 135w with 2 series 2 parallel.
However it is probably best to go 4 parallel.

If the shade for one panel is expected to be that bad I might go with just 3 in parallel. Hard to know unless I could see the roof/panel layout.

[Salvo]

It's a good test, but it won't look pretty. The two strings are 5V apart. Plus, when the newer panel gets shade it will get worse.

Here's what you want. 20A, $20-

Sal

[HiTech]

Salvo wrote:
I don't see any good way to combine all 3 panels. To make matters worse, your shading issues could degrade your entire setup.

I would connect the 2 Kyrocera panels to a pwm controller. You can get a pretty good 20A pwm controller for $20 at ebay. You'll connect these panels in parallel. Use your Blue Sky controller for the new higher volt panel.

Sal

Probably right but pretty easy to test. Connect the new panel in parallel to the old series panels and measure amps into battery. Disconnect the old panels from controller and direct hook them in parallel to the battery, parallel to the controller output. Measure total amps into battery. If it is significantly better, get a cheapie PWM controller for the 12v panels.

It is possible that buying the higher Vmpp new panel and paralleling it to the Vmppx2 of the old panels may not be too far from the max power point for either when it optimizes the system to a voltage in between. It all depends on the specific IV curves and how far the new panel drops off a couple of volts above, and how far the old panels drop off a volt or two below Vmpp.

Jim

[HiTech]

If you run the 12v panels in parallel and then series in the new panel, it's hard to know how far from the maximum power point all your panels will be running, MPPT can potentially maximize the single system voltage, but where in that range the different panels would run is a wild guess.

Jim

[Salvo]

I don't see any good way to combine all 3 panels. To make matters worse, your shading issues could degrade your entire setup.

I would connect the 2 Kyrocera panels to a pwm controller. You can get a pretty good 20A pwm controller for $20 at ebay. You'll connect these panels in parallel. Use your Blue Sky controller for the new higher volt panel.

Sal

[2oldman]

Starburst2 wrote:
maybe I am better off to run 4 x 135W panels in parallel.

You'll be pushing the 30a limit of your controller if you add another 270w. It's going to be close, but i'll bet the controller will get hot.

Does the 30/40 spec on your controller mean 40a@ 24v?

[Starburst2]

Smkettner, maybe I am better off to run 4 x 135W panels in parallel. That way, for those times when one is partially shaded, I will still have the full, output from the remaining 3 panels. I think I will have to modify the wiring by placing a joiner box on the roof then run big cable (#4) from the joiner box down to the controller to minimize the drop in voltage. The main reason that I originally connected them in series was because I could run from the panels all the way to the controller via the #10 gauge MC4 leads with a 24 vdc supply. Since I am transferring the panels to my new coach, now is the time to make the wiring upgrade. With #4 from the roof top down to the controller I think I preserve all my options. Your opinion?
Regards,
Lloyd

[time2roll]

From link above:

57VDC maximum (Recommend Maximum VOC at STC <= 45.6 VDC)

Current panels are at 44.2 Voc, no way would I go additional series on the 3024iL.

[2oldman]

Starburst2 wrote:
I read an artcle on the Nortern Arizona Wind and Sun forum which convinced me that partial shade is a non issue when you have an mppt controller. What say you?..

I have not read that article, nor is there any knowledge among us on the board about MPPT being any 'cure' for shade.

The only way I know to deal with shade is let the panel diodes do their jobs. During shade they make all or part of the panel inoperative, effectively making it a 'pass thru' board until the sun reappears.

I can provide many threads about shade for you if you like. It's discussed often on here, with no real consenus about what's "good" and "bad" because we all seem to experience different results. I'm a series guy, many swear by parallel. Personally, I think if you have good quality panels with properly installed diodes, it will not matter how they are connected.

[HiTech]

Starburst2 wrote:

HiTech wrote:
Does your controller find multiple power points? With those voltage specs it looks like the new panel would have to parallel to the other 2 that are in series to stay in spec for what the controller can handle.

The second panel you are looking at has a closer Vmpp to 2x your existing panels. Closer MPPs means the system will make better power across the different spec panels because each can run closer to its optimum voltage when run together.

Jim

Hi Tech, why would l need to run them in series? With the two 135'sin series giving me a nominal 24 VDC plus a 245Watt additional panel (nominal 24 VDC), hooked in series would give me 48 vdc, NO.?
Lloyd

I believe you need to keep the Voc total for the solar string under the controller limit. As the PWM switches on and off the input circuitry is subjected to the open circuit voltage, not just the voltage under load. In addition in cold weather and with cloud effect, panels will actually put out a higher voltage than Voc.

Jim

[time2roll]

Starburst2 wrote:
SMKettner, see my response to 2oldman. Is the article that says partial shading on your array is a non issue with mppt controllers, valid or a pipe dream.?
Lloyd

Depends. In the OP's case he will in effect have two panels in parallel. Moderate shade on one set will probably put them out of production.

Depends on the shade also. OP is concerned about shade from roof items which is the worst. Uniform shade from a distant object or thin clouds I understand is not as big of a deal and you just lose in proportion to loss of irradiance.

MPPT is far from exempt from shade issues.

[Starburst2]

Westend, thanks for the feedback. My thought was to parallel the 245W 24 volt panel with the existing pair of in series 135's which would still give me two 24volt modules feeding the 24 vdc controller. I may be able to find space for another pair of Kyocera 140's but as I mentioned to smkettner I will encounter partial shading of one of the panels caused by the AC. If the mppt controller negates the adverse affect of this shading then maybe that is not an issue.
Regards,
Lloyd

[Starburst2]

HiTech wrote:
Does your controller find multiple power points? With those voltage specs it looks like the new panel would have to parallel to the other 2 that are in series to stay in spec for what the controller can handle.

The second panel you are looking at has a closer Vmpp to 2x your existing panels. Closer MPPs means the system will make better power across the different spec panels because each can run closer to its optimum voltage when run together.

Jim

Hi Tech, why would l need to run them in series? With the two 135'sin series giving me a nominal 24 VDC plus a 245Watt additional panel (nominal 24 VDC), hooked in series would give me 48 vdc, NO.?
Lloyd