Sizing of Sonotube for mounting a solar panel tracking system

I have four ET Solar ET-M572175 Solar Panel 175 W panels that I want to mount. The panels are several years old, but they are brand-new, actually still in the original packaging and were quite inexpensive. Due to limited space, I think I'd like to use something like the ECO-WORTHY Solar Panel Kit Tracking System Dual Axis with Tracker Controller for mounting them. The panels should hopefully do a reasonable job at keeping the Eco Flow Delta Pro battery generator I plan to purchase topped up.

The Eco Worthy web site doesn't specify the size of the mounting plate at the base of of the main pole, but it has eight bolts and I'd guess is 6" square. Assuming that's correct - I will obviously measure once I have the parts in hand - what diameter Sonotube would be recommended for the mounting base? For deck supports, the rule of thumb is 3 time the size of the post. That would mean 18" if my assumption about the 6" size of the base plate size is correct. About right? Or overkill for something that won't need to support anything like the weight of a deck?

A bolted plate has considerable leverage to pull up on bolts, and their retention strength is what holds it upright.
I would put "L" bolts through the base or something with holes in same location and hook under rebar prior to pouring concrete.

Or, I would use a post cast into the concrete, rather than bolted on top.

Not overkill, tall array with wind on it will get huge force.

Do you already have the tracker?
20 years ago, a tracker to produce extra kWh/day cost as much as additional panels (at $5/W) to produce the same extra power. And was expected to break down in 5 years (vs. 25 to 40 years for the panels.)

Today, PV panels are $0.20 to $0.40/W. Tracker mount makes no financial sense.
Buy additional panels and parallel strings oriented SE with panels oriented SW to get extended hours of production. Using fixed mounts.

Thanks @Hedges.

I don't yet have the tracker, but at $370, the cost is not much greater than the hardware for a static mount. I realize that the cost of solar panels is now down in the range where it is more cost-effective to add panels rather than optimize your array with tracking. My issue is one of space and marginal cost however.

I have only a small area that gets anything close to direct sun due to very extensive tree cover everywhere else on the property. The house design is a chalet-style oriented so that the steeply pitched roof faces E-W and is in any event, well-shaded by large trees. The tree felling and trimming needed for a roof mounted solar system, or a larger ground mount, is extensive, with the estimates I've gotten all running to nearly the same cost as a complete typical household solar system. With roof mount too costly, a typical ground mount not really feasible, and the sunny area relatively small, the tracker system seemed to make the most sense.

To provide some hopefully helpful detail, what I've tentatively decided to do is to add an Eco Flow Delta Pro, a manual transfer panel and those 4 solar panels to keep things reasonably charged up. The plan is to put some specific circuits via the transfer panel on the Delta Pro system, things like the refrigerator, router, modem & some motion lights, and let the battery system power things when we're not there (this is a vacation house). Since we loose power frequently, the battery generator will come in handy when we are there, and though our outages are usually quite short, in the event of an extended one, the hope that the panels will provide us with at least some ability to ride things out,

Hard for anyone to answer your question without more details. The proper size of the concrete post will depend upon the wind and snow loads on the panels, and your soil type (e.g. how much force the soil can take). It is NOT just make a pier that goes down to below frost line the minimum size of the plate you are attaching. You likely will need to go quite a bit deeper and likely wider too, again depending upon these other details.

Just as an example, some 30 years ago I put in a Two-Seas top of pole mount for 720W of panels. Their mount specified that the steel post (which was set in concrete) needed to go 6' down in the ground to take the forces. Your numbers will no doubt vary, but take this as an example.

Four 175W panels is fairly small.
Try to find wind speeds for your area, and an on-line calculator for forces.
Bending moment will depend on height of mount, and that determines pipe diameter and depth & width of footing.

I favor triangles (all members under tension/compression, not torsion), and a 3 or 4 footing base. It could be a single larger column, braced by two others.

A mount could have these four panels facing one way, and additional panels facing another, taking up the space a tracking mount would have rotated through.

I understand that the question is difficult in the absence of more detail, and I appreciate all of the advice and suggestions.

While the tracker system has a wind sensor will tilt the array to horizontal, even assuming that works quickly and reasonably well, the bending moment can still be substantial, In any event, the sensor and actuators are unlikely to be able to engage quickly enough in the case of sudden wind gusts. And I don't for a second believe the hype on the Eco Worthy website that states " . . . by drilling the expanding screws to ground, the base can firmly stand in hurricane or storm without problem."

BTW, I do not intend to use the "expanding screws" that are provided in the kit to attach the base (they look like typical lead shields). Instead, I plan to sink galvanized bolts in the concrete base when poured.


What I'm now thinking is that it may be better to have a base with a larger area than something like a 12" Sonotube would provide. A concrete square, perhaps 18" or even 2 feet in each dimension, with a rebar matrix embedded. That would spread the load from the supporting pole during windy conditions over a relatively large area. I don't know the how much force the mounting pole in the Eco Worthy kit can take before failing, but I'd think it would be the weak point in the system if mounted on a an 18-24" inch concrete base.

Thanks again to all for the replies.