Sun hours

[bcroe]

As the good weather ends, I finally got the new foundation concrete finished. 6 supports for 6 bearings, for a
variable tilt array. The 12 L bolts are in place for above ground attachment. Since I don't want it to emulate
the HOLLYWOOD sign (like the original), a full size 66' X 5' fixture was built to hold the L bolts at exactly the
right location and orientation: straight and square, but sloped to my 10% grade.

They certainly are in a straight line; will be easier to do the final shimming for bearing alignment. That is my
yellow laser on the side. Bruce Roe


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[AzRoute66]

So, this is all East facing right?

[SunEagle]

Looking good bruce

[bcroe]

So, this is all East facing right?

Correct; will double my East facing panels. With the tilting top and below ground done,
am working on the middle (above ground bearing supports).

If this array proves out, will do a West facing mate, start removing the worst shadowed
South facing panels. Bruce Roe

[DanS26]

Bruce, Just wondering how your strings are attached to your Fronius inverters? Specifically.....do you combine strings at the arrays then send a single DC home run to each inverter? I'm just curious how the inverters handle strings of different powers. In other words if you have East and West facing strings combined then the MPPT for each string is vastly different over the course of a day, but the strings are combined. Just curious how the Fronius inverters handle that from an MPPT standpoint?

I know that the Fronius inverters that you have can each handle 6 individual strings each with a different MPPT....but when you combine strings and use a buss bar in the inverter it appears to me that differential capability gets lost. If that analysis is correct......how much is lost if any?

[sensij]

In other words if you have East and West facing strings combined then the MPPT for each string is vastly different over the course of a day, but the strings are combined.

The mpp voltage is not vastly different for the array orientation more directly receiving the sun and the one that is not, so combining the two orientations in parallel does not cause unacceptable loss. A lot of the effect is thermal... the array getting direct sun will be hotter, and have a lower mpp voltage than the cooler parallel string, but I think the effect won't be as bad for ground mounted panels as it might be on the roof. The mppt will seek whatever voltage maximizes power, so it will tend to follow the mpp voltage of the array in direct sun.

[DanS26]

The mpp voltage is not vastly different for the array orientation more directly receiving the sun and the one that is not, so combining the two orientations in parallel does not cause unacceptable loss. A lot of the effect is thermal... the array getting direct sun will be hotter, and have a lower mpp voltage than the cooler parallel string, but I think the effect won't be as bad for ground mounted panels as it might be on the roof. The mppt will seek whatever voltage maximizes power, so it will tend to follow the mpp voltage of the array in direct sun.

Well he**, lets just point these arrays all over the place as long as they are connected in parallel.......money should be no object. Yes I'm being sarcastic.....but in reality arrays should be designed to produce the maximum power for the least cost. Bruce's experiment, although noble, does not appear cost effective to me.

In defense of Bruce's design....it appears he is locked in on the AC side of things so he is maximizing the DC side of things without regard to payback.

[sensij]

Well he**, lets just point these arrays all over the place as long as they are connected in parallel.......money should be no object. Yes I'm being sarcastic.....but in reality arrays should be designed to produce the maximum power for the least cost. Bruce's experiment, although noble, does not appear cost effective to me.

I don't know enough to evaluate whether or not the system represents the pinnacle of cost-effectiveness. If parallel strings of east and west facing panels are the biggest problem, the design must be pretty darn good. Here is Fronius's white paper on the losses that those parallel strings might experience, relative to independent mppt. (<1% difference in annual output, by their model)

[DanS26]

I don't know enough to evaluate whether or not the system represents the pinnacle of cost-effectiveness. If parallel strings of east and west facing panels are the biggest problem, the design must be pretty darn good. Here is Fronius's white paper on the losses that those parallel strings might experience, relative to independent mppt. (<1% difference in annual output, by their model)

Thanks sensij, that white paper was most helpful.

[J.P.M.]

I don't know enough to evaluate whether or not the system represents the pinnacle of cost-effectiveness. If parallel strings of east and west facing panels are the biggest problem, the design must be pretty darn good. Here is Fronius's white paper on the losses that those parallel strings might experience, relative to independent mppt. (<1% difference in annual output, by their model)

I don't know enough about Bruce's arrays either, but given his installed orientations and particularly tilts, I'd question whether his annual output for his arrays in their current configuration couldn't be matched by a single array using the same panels and equipment with the same tilt adjustable features in a more southerly orientation but with a lower surface area.

I appreciate the idea that he seems to feel spreading/shifting more output more over the day and thus getting more production earlier/later in the day is useful, and may result in some savings via smaller inverters, etc., I also sure don't know any demands/particulars his POCO or distribution equipment may make to limit his max. output at mid day, but, aside from those things, and maybe some others, if he's on some form of NEM grid tied billing arrangement, he'll get more annual production per m^2 of panels with a more equator facing orientation, and probably spend less to do it.

But, all that said, he's got a hell of a system and seems to be having fun. What's not to like ? We all have our hobbies that wind up as holes down which money disappears. Hail the freedom. I doubt his system is optimally cost effective, but neither is mine. Hang in there Bruce. Enjoy.

BTW, on panel temps. I'd SWAG that in the same orientation(s), ground mounted arrays will probably have a lower operating temp. than similarly oriented roof mounted array(s). But I'd also be pretty sure arrays in different orientations in the same environment (ground or roof) will have different panel temps., depending on orientations, as f(energy balance) and additionally tend to be somewhat f(time of day). One perhaps practical outcome/consideration of that, particularly for way off south, high tilts, would be that white backed panels at off south azimuths and high tilts would probably tend run cooler than black backed panels in the same orientation, and so be more efficient in a given orientation.

[bcroe]

Bruce, Just wondering how your strings are attached to your Fronius inverters? Specifically.....do you combine strings at the arrays then send a single DC home run to each inverter? I'm just curious how the inverters handle strings of different powers. In other words if you have East and West facing strings combined then the MPPT for each string is vastly different over the course of a day, but the strings are combined. Just curious how the Fronius inverters handle that from an MPPT standpoint?

I know that the Fronius inverters that you have can each handle 6 individual strings each with a different MPPT....but when you combine strings and use a buss bar in the inverter it appears to me that differential capability gets lost. If that analysis is correct......how much is lost if any?

There is an OUTBACK PV12 dual feed combiner box at the end of the arrays closest to the
2 inverters, each 7.5KW. The combiner normally takes 6 (lower voltage) circuit breakers, or
4 (higher voltage) fuse holders, on each side. Each side has a pair of 6 gauge wires running
the 230' to an inverter. At this voltage losses hardly exceed 1%. However, by turning around
the top bus bars, 6 fuse holders may be fitted to each side, my configuration. This is no
where near any components capacity.

The Fronius inverters have 6 fuseable input positions; I buss 3 together with fuse positions
shorted for the 6 gauge feeds. I am not aware that the inverter has any multiple MPPT
capability. Every string is made up of 720 series cells, either 10 panels of 72 cells or
12 panels of 60 cells. As Sensij points out, the voltage doesn't change much for varying
sun, and the curve isn't that critical, so they seem to play nicely together.

I haven't made any cost effective claims here; terms like "mad scientist" and "science
experiment" have been heard. I've already shown that the basic standard design can
be improved on here. Still being in the experimental stage, we shall see. It will always
be more expensive to generate PV power under the clouds than in the SW desert, but
I'm not that far from breaking even. Bruce Roe

[AzRoute66]

[... from Post #167] Assuming the snow has a place to go, there will be motorized vibrators attempting to shake it off on the next round. Bruce Roe

And did we strap a Jumping Jack soil compactor to a vertical or a Home Depot style paint shaker to the top rail? Pictures of the front are good for magazines, pictures of the backs are better for me... Also want to hear your current thinkings on large ground mount with tilt. Thanx.

[bcroe]

And did we strap a Jumping Jack soil compactor to a vertical or a Home Depot style paint shaker to the top rail? Pictures of the front are good for magazines, pictures of the backs are better for me... Also want to hear your current thinkings on large ground mount with tilt. Thanx.

The vibrator may not make this version; I have one from getting bubbles out of home panel
days. It would probably take a lot of testing to optimize, to get the axis, frequency, and perhaps
waveform right. The worry is cracking panels, or difficulty extending to multiple panels.

I will show you a rear picture of a tilting array just as soon as its together (may be impeded
by season and weather). Bruce Roe

[Jim Jakosh]

I have a new 6 panel array and I think I must be losing about 30-40% by not having the panels track the sun east to west. I have been taking measurements of the angle to hit the panels perpendicular north to south to figure the best time to set them at a new angle- maybe 6 times year. But I started measuring the east to weast angle too and there is a vast angle change from east to west during the day. I am now looking for a tracking system for a 4 panel array that I might build next spring.
Inetdog, do you remember who was selling the tracker for $155. I;m not a computer guy much at all and I was thinking of making a tracker for both directions with 7 to 9 presets and the unit would click to an angle based on the most energy hitting the small solar panel at that angle. I'm gong to try to get help from our high school robotics class.

[littleharbor]

You can find lots of single and dual axis tracker electronics and rams on eBay. Stuff like this..
Solar tracker.jpg