Need the solar/power pros to weigh in

[luthj]

Not all panels have bypass diodes. A couple quick experiments will show you which config works best.

 

[TantoTrailers]

Back to solar. I’m preparing for my trip to UT in a couple of weeks and I ran my heater and fridge for 10 hours yesterday to simulate a night of use. I consumed 16% battery and today I am trying to regain all of that with solar. It’s early morning but the sun is out and my panels are on the roof. I’m only generating 8w though from my 2 120w panels. I have some shade from a scraggly tree without leaves but is that normal output or do I have some sort of problem somewhere?

 

[luthj]

Shading can reduce panel output by %80 or so. If the output comes up to normal levels when the shade clears, you are fine.

 

[TantoTrailers]

“Normal” is a funny term...I have never seen over 108w from this system! I will have no shade at around 1pm so I can report back.

 

[luthj]

A good test may be called for then. A 240W system should make 0.7*240=168W with direct sun (directly overhead). This assumes sufficient loads of course.

 

[luthj]

Switching the panels to a parallel arrangement can provide more power in a partial shading situation. It depends on the shade type and panels internal wiring. Some folks use a rotary switch to toggle between parallel and series.

 

[TantoTrailers]

I will give this some testing...I will try each panel on its own and in parallel to see whats up....more to come in a bit.

 

[TantoTrailers]

Ok so quick test. Left panel, right panel, series, parallel.



Left


right


series


parallel


clearly parallel is optimal for current lighting/shading. I will test again when I have no shade a bit later today. However numbers are still weak sauce!

 

[TantoTrailers]

Not quite out of the shade yet, still hooked up in parallel. Bluebird skies.

 

[luthj]

Looking better. They battery will be pretty full soon, so you will need to put a momentary load to get pull panel output once the charger goes to absorb.

 

[TantoTrailers]

I have my little water heater that I can hook up to the MPPT directly, it draws 100W

 

[TantoTrailers]

Unshaded tests are complete and results are pretty much identical for both parallel and series. Odd part is, adding the water heater load didn’t result in any higher wattage from the panels/controller. It basically 0’ed out the charge to the battery.

I’m not sure what I can do to maximize the output but 7A to the battery was achieved from both setups.

Parallel without Water heater


Parallel without water heater


Parallel with water heater


Showing the 0 effect while heater is on


Series without water heater


Series with water heater


What voltage should my battery be at when full from solar charging?

 

[luthj]

Whatever your absob voltage is (14.4V about). That will be held until the return current is met. Then it will float around 13V.

Obviously there is a lot of variables, but typically you should get at least 50% in direct sun in lower temps. Though low sun angle has a big impact. There is a quite a variance between panels though, with some MFGs fudging the numbers a bit.

 

[TantoTrailers]

Yea these are not the most expensive panels on Amazon haha...I get what I pay for! It seems as though I may have regained most of what I used in my 10 hour run test yesterday.

 

[dwh]

Whatever your absob voltage is (14.4V about). That will be held until the return current is met. Then it will float around 13V.

Haven't been keeping up with this thread. But...my Victron by default sets absorb time as a multiple of bulk time. And there is a max on that timer as well.