combiner box for solar

Two panels do not need a combiner box. Combiner boxes are used to avoid daisy chaining three or more panels.

thanks ralphnjoann

OP-

It would be to your benefit to wire those 12v 100w panels in serial for the MPPT controller. Check the Vmax for the controller. Also, you would probably use less wire, could be smaller diameter and you would not need a combiner box.

Bend, while I fully agree with you, I was hoping to do parallel for the benefit of one might get some shade, I still have the other to pick up the difference, in series, if one gets shaded, the other will drop accordingly. I'll have to look into this more, as you do have a point well taken.

If the panels have MC4 connectors just use an MC4 parallel connector to combine them.
Then MC4 wire down to the controller is plug and play.
No need for fuse but a switch would make cutting power for service easier.

Need a fuse close to the battery on the controller to battery connection.

Yosemitebobr wrote:
Bend, while I fully agree with you, I was hoping to do parallel for the benefit of one might get some shade, I still have the other to pick up the difference, in series, if one gets shaded, the other will drop accordingly. I'll have to look into this more, as you do have a point well taken.

Some MPPT controllers have problems with the lower voltages of single/parallel 12v panels, Morningstar for instance. Might want to test prior to installation. And, remember that MPPT is only in bulk, abs and float are bucked PWM.

Could be back to a decision on the panel buy. However, the Bogart SC2030 PWM monitor & controller system would fit nicely with the paralleled panels if you don't have a battery monitor yet.

No combiner needed.

Also, If you have not make the MPPT purchase.. I would suggest a larger PWM (for the same amout of money, or less than the MPPT)

The reason as mentioned above by Bend is that MPPT do not perform well on a small system. Also they do not proform very well with a hotter climate, or when the system will normally be in a charged state. (this may or may not be your case, for me it would be because for at least the next year I'll be camping 1 week at a time)


Below is information from MorningStar's site about their own MPPT vs PWM controllers.

"1. Low power (specifically low current) charging applications may have equal or better energy harvest with a PWM controller. PWM controllers will operate at a relatively constant harvesting efficiency regardless of the size of the system (all things being equal, efficiency will be the same whether using a 30W array or a 300W array). MPPT regulators commonly have noticeably reduced harvesting efficiencies (relative to their peak efficiency) when used in low power applications. Efficiency curves for every Morningstar MPPT controller are printed in their corresponding manuals and should be reviewed when making a regulator decision. (Manuals are available for download on the Morningstar website).

2. As explained in the Environmental Considerations section, the greatest benefit of an MPPT regulator will be observed in colder climates (Vmp is higher). Conversely, in hotter climates Vmp is reduced. A decrease in Vmp will reduce MPPT harvest relative to PWM. Average ambient temperature at the installation site may be high enough to negate any charging advantages the MPPT has over the PWM. It would not be economical to use MPPT in such a situation. Average temperature at the site should be a factor considered when making a regulator choice (See Appendix).

3. Systems in which array power output is significantly larger than the power draw of the system loads would indicate that the batteries will spend most of their time at full or near full charge. Such a system may not benefit from the increased harvesting capability of an MPPT regulator. When the system batteries are full, excess solar energy goes unused. The harvesting advantage of MPPT may be unnecessary in this situation especially if autonomy is not a factor.

Thank you all for your input, it is very useful, now to put it all together. I'll be back I'm sure :)

Well, I'm back, different RV now a Super C and doing the solar install all once again. This time I'm going with 400w - and I believe the PWM controller over the MPPT. Once again, I need a better set up than I had last time. Last time I had two 100w panels for 200 w with a MPPT controller.

400+ watts is getting in the zone where 24v panels in series with MPPT controller start to make sense.

$468 gets 520 watts of panels (2)
$350 for 30a Morningstar controller.