relo over Los Alamos, series panels in shade

Got my errands done and

the drive

The relo was ~60 minutes at my pokey pace¹, a pleasant drive with nice scenery. When I got within 10mi of the proposed camping area Google tried to route me through the Los Alamos National Laboratory main campus security checkpoints; no thank you! I manually rerouted. The reroute showed signs about LANL property and spontaneous searches, but there were no checkpoints there and locals drove through. I followed and it turned out to be the right course of action.

I found the turn-in and started to explore on foot with Muffinbeast, who was ready to be out of the vehicle.

campsite

The campsite is at 8,200ft and is noticeably cooler.

My criteria, in rough order of importance

1. passability during monsoon, at least during drier intervals
2. sun exposure for solar – I use Sun Surveyor for this
3. sun exposure to dry out the campsite
4. usable data
5. nice view I don’t think about this much. I enjoy it when I have it but nice view often equates to lots of people.

Muffin and I walked the trails and did not bother going down anything that was sloppy – it will only get worse. The spot in the 3rd pic up there had max solar (~7 hours) but the trail was rutted and would get iffy when wet. Another spot had 6 hours but was not in a packed-down established site and extraction would not be guaranteed.
The spot I chose, in the 1st pic, has about 5 hours of clear, high sun, and maybe 1.5hours of partial shade. The partial shade, while unfortunate, affords an opportunity to debunk a solar myth, namely that panels in series make 0w when one is shaded.

There is only one worrisome spot in the road (pic #2) which has standing water in it. It’s on a slight downslope and is straddleable (?) by the wide Promaster so I don’t think it will be a problem getting out. Plus there are trees conveniently placed which I could use for use with the recovery strap and “come-along”.²

solar harvest amongst the trees

Like a mountain oasis in an arid land, mixed conifer forests of Douglas fir, white fir, and spruce generally thrive at higher elevations where it is cooler and wetter. Compared with the ponderosa pine forests, these communities are more diverse and lush. A rich undergrowth of forbs, grasses, and shrubs makes this a popular zone for foraging by wildlife. Black bears and elk are common. – source

The conifers are, I’d guess, 40-50ft tall. There are open spaces but it’s hard to find any that aren’t grossly affected by shading. There are also some live oak stands but they are scrubby at this elevation. ~8ft max so they aren’t causing problems..

theoretical max

In the pic above the rearmost panel is shaded. With zero shade the 90.9v, 750w string could be capable of 596w (750w x 0.7945 cosine of solar zenith angle). The myth predicts zero watts; let’s see if we get zero or more than zero.

actual series harvest

• At the time of the pic the system was making 185w @ 62.92v
• a little later it was making 232w @ 32.0v out of a calculated max of 604w (750w x .8059)

Are these great numbers? No. Are they greater than zero? Yes.

what is happening?

MPPT controllers don’t know anything about the panels other than what wattage they put out at Vpanel points across the curve. Max power is being found at some odd spot here and the reason may not be immediately obvious: reducing string voltage can allow shaded panel substrings to contribute again. This is not always going to make Pmax but sometimes it does.

a longer explantion including a link to an example w/math.

theoretical parallel harvest

Let’s compare this outcome to the same panels wired in parallel. Two panels would be functioning normally and one would not contribute.³

Using our early 596w example, each panel would be making ~199w and two would be active. So 199w x 2 = ~397w.

conclusion and future plans

Is 397w > 185w? Yes it is. With my panels in my configuration and my controller parallel config would make about 2x the power during those 1.5 hours of partial shade.

Am I going to climb onto the roof and rewire the panels in parallel for this 14d stay? Nope, not as long as the present config meets the daily requirement. I won’t really know until tomorrow, because during this morning’s drive the alternator was getting a rare chance to contribute. My estimation is that is contributed +20Ah I will not have during my emplaced camping.

updates

• Thursday afternoon: the system held Vfloat 13.4v until ~1630.
• Thursday evening: went to bed ~2330 after watching a scary movie. SoC = 85%.
• Friday 0700: woke up with SoC 71% and system barely net positive (+10w) from indirect light. Made coffee and breakfast on the lab hotplate.
• Friday 0900: solar making >200w
• Friday 1000: bright overcast, down to ~300w from a peak of ~450w around 0930. Theorectical max 568w (750w x 0.7574 cosine)
• Friday 1145: went on a hike with Muffin, still overcast. By the time we got back at 1145 Vabs 13.8v had been reached and Absorption completed. Bank in float.
• Friday 1800: because of diffraction from the overcast conditions the system was able to hold Vfloat until a little after 6pm. The effects of partial shading can be greatly reduced by diffuse lighting.

This suggests that, assuming fair-to-good conditions, under this canopy the system will have excess power between noon and 4pm.

comments

mastodon comment thread for this post

1. if you want to enrage locals then drive the speed limit ↩

2. ie, manual cable puller / winch ↩

3. due to undervoltage when one or more of the substrings goes offline ↩