Mixing solar panel sizes

[Trackrig]

On a MH roof you have some large spaces and some smaller spaces or spaces with possible shading issues that you would want to avoid. Can you mix panels of different physical sizes / wattages, but of the same Mfg, voltages, etc?

Bill

[MDKMDK]

A portable can more easily wander off, if not properly secured or watched. Another minor drawback.

[Almot]

Portables are a lot more trouble. They become inconvenient in sizes bigger than 200W, and storing them in a bus is more inconvenient than in a truck. One benefit I can see is that you can (sometimes) get a portable out of the shaded spot where your rig is parked.

[brulaz]

BFL13 wrote:

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BUT you cannot mix voltages such as add a 12v 100w panel to a "24v" 255w panel.
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But you can put two 12V 36 cell panels in series, and if their combined Vmp is close to that of a 24V 72 cell panel, you can parallel the series pair with the 24V 72 cell panel.

Haven't done it actually, but it makes sense, I think. The two 36 cell panels are just a 72 cell panel split in half.

[brulaz]

time2roll wrote:
1000w is maybe 60 amps into the battery. You need storage to go with that much power. This would be 6 to 8+ batteries.
...

Sadly, 1000W will only happen under the best conditions.

The OP should consider a portable array if possible. We have 690W ~flat on the roof and 340W portable/adjustable. Very often we get as much or more power from the portables as from the rooftop because of shading and angles.

But the portables are definitely more trouble so only go out when boondocking more than a couple of days. Over shorter stops we drag down the batteries and charge up on the road.

The OP may not "need" big storage, but it would definitely be nice for those non-optimal days.

As for matching panels, 36 cell (12V) panels are more expensive than the big 72 cell panels but can be made to fit in smaller places on the roof. Also, I have a pair of 36 cell (12V) panels that when run in series almost exactly match the Vmp of my bigger 72 cell (24V) panels on the roof. So running them in series/parallel to my MPPT controller would work well.

Agree about running the batts at 24-48V. Makes life a lot easier.

[Almot]

48-12 converter is one more piece of hardware, but I like this idea.

Even with 12V bank, 60A TS MPPT controller could be all he needs, and there aren't many good MPPT that are smaller.

In Wa/BC weather, 1000W under constant rain would get ... I better won't say how much it would get ;)... Wintering in Southwest the bus will be self-sufficient.

[pianotuna]

At 1000 watts use either a 24 or 48 volt battery bank and a dc to dc converter for the 12 volt loads.

[Lwiddis]

More reading, Bill, before you buy anything.

[time2roll]

1000w is maybe 60 amps into the battery. You need storage to go with that much power. This would be 6 to 8+ batteries. Since you are starting from scratch consider going 24 or 48 volts on the battery. Especially if you are buying a large inverter for 120v power. This cuts down on wire size, easier to balance the battery, and a smaller controller can be used. A DC/DC converter can supply 12v to existing accessories.

[Almot]

1000W will not be an overkill. Some places are warm but cloudy and/or rainy, and then 1000W works like 200W.

With 1000W it is often easier to use MPPT controller and series connections, or series-parallel, for higher voltage and lower amps.
Ex, one string 4*120W series, and the second same string in parallel to this.

In such a string you can replace 2*12V panels 120W each with one 24V panel @240W-250W, with some loss of efficiency.

1000W array is (potentially) 70-75A output post-controller. In this range it will be likely MPPT, not PWM. I recall Midnite Solar have some 90A units. You might also get away with Morningstar TS MPPT 60, from what I hear it's a better value than Midnite. Input voltage of array MUST not exceed the controller limit.
In Wa you won't need more than 60A controller.

Make cardboard templates the size of 100 or 120W panels, - won't be easy because they are often different shape, some long and some square. In 24V panels there is more order, 240-280W panels are mostly 65" by 40". Go on the roof and play with those pieces.

One thing to be careful with, if you like high elevations in winter (I don't). High voltage in series could spike dangerously high when it's cold and sunny.

[Trackrig]

time2roll wrote:
What controller do you plan to use?

Generally in parallel you need to match Vmp as best you can while in series you want to match Imp.

I don't know which controller yet, have just been up on the roof measuring the open spaces a couple of times to see what I might fit in. I would like to be around 1,000W so I don't have to redo anything later. That could be overkill, but I know it will take care of me.

Bill

[brulaz]

Yes try to match Vmp in parallel for mppt, or more generally just match the # of cells (36, 60, 72).

[time2roll]

What controller do you plan to use?

Generally in parallel you need to match Vmp as best you can while in series you want to match Imp.

[BFL13]

Yes you can parallel eg, a "12v" 160w panel with a 12v 100w panel for an array of 260w. BUT you cannot mix voltages such as add a 12v 100w panel to a "24v" 255w panel.

Better not to mix mono and poly either--they act a little differently in low light. Can be done though.

You can have a 24v set of panels with its own MPPT controller and another set of 12v panels with its own PWM controller, set both controllers to the same high set point voltage 14.8v eg, put both controllers on the same battery bank, and they will add their amps.