Duel axis tracker foundation

I discussed the options with a builder friend and we came to the conclusion that a pipe dropped 2m into the ground encased in around 3T of concrete is going to be more stable and enduring than 76mm screws. I have commissioned a local to me steel fabrication company to manufacture the drop pipes. Price is £740 the pair delivered. I've bought in £140 of primer and enamel to paint the poles and the tracker metalwork.

I've designed the pipes to have a 400mm circular mounting plate (12mm steel) with the 8 tracker post holes plasma cut and also one additional 30mm hole for 25mm flexible conduit pipe that will run the DC out and AC in cabling plus RS485 comms. The overhang from the 220mm pipe will be supported by four 90mmX150mmX10mm ribs.

There is a 300mm (5mm steel) base plate on the 220mmx 2600mmx5mm pipe, making it water tight. The base plate will also spread the down force over just having the pipe wall bearing down. The buckle force for the pipe is 450psi (using an online calculator) and I determined a strong wind on a solar sail will yield 14psi lateral force (using an online calculator). So the pipe with a 3T concrete anchor should be sufficient foundation.

I'll be digging an East to West trench to drop the pipe into leaving 2m underground and 600mm above ground. The top metal plates have lifting slits for forks and straps. This will allow me to lower the pipe that'll weigh in at around 100kg in a controlled way into the trench by mechanical means, using my digger arm or telehandler. The slats which will be welded in line with the pipe will also be an aid in the unloading and painting processes. The top of the lifting brackets are 600mm below the base plate so will provide a ground level guide when it is being installed.

I've added a substantial lower bracing plate 1000mmx300mmx10mm which will sleeved onto the pipe once a 222mm hole is cut out. This is intended to provide lateral bracing support to the pipe length that will be encased in concrete.

The pipe option with paint will cost around £450 per installation. I have a 2.5T digger and telehandler and cement mixer so there will be no equipment rental costs to add in to the project. the concrete will cost around £150 in stone, sand and cement (ready mix is available but that would cost around £600)

I continue to receive deliveries almost daily with all things I'll be needing from cabling, AC meter, in line fuses, to crimping tools to PV surge protectors to glands and boxes. The list is extensive with lots more left to buy in. Deliveries of components, mainly from China have been fast; generally within 7 to 12 days.

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The pipes arrived yesterday and I'll begin the prime and paint exercise tomorrow. I'll take around 10 days to finish the pipes in a olive green coach enamel paint.

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This month, March, I've painted the ground pipe and all the galvanised metalwork from the trackers. All in 2l of primer and 2.5l of coach enamel paint. I felt dark green would blend into the orchard setting better than bright galvanised metal.

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The tracker comes with self tapping metal screws but I have abandon those having had two break on the shaft when fitting and then required drilling out. Instead, I've elected to enlarge the holes for mounting various things on and around the tracker using blind rivets. The will make the final setup with the addition of the axis controller and electrical cabling easier some 10 foot off the ground than trying to work with self tapping screws through medium gauge steel. I've used M4 rivets for the conduit ducting clips and M6 rivets for the controller mount.

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I'm ready to go to the digging stage next as soon as the ground dries. We had the wettest February on record and it has rained every day since so I'm going to be taking a few days off the project awaiting a spell of drier weather. The remainder of the forecast for March isn't looking good, snow has been forecast.

Very nice. Bruce Roe

It's still raining every day, proper monsoon weather. So no chance to get to the digging stage for the short term.

I've been busy adding more M4 blind rivets to the tracker poles, both trackers now have metal earth connection blocks screwed on and also the mounting rivets for the cable enclosures have been added. The last thing to bolt onto the tracker pole is the line run for the earth cable down the length of the pole from the earth block sited near the top of the pole. I'll be fixing cables of a variety of sizes to the trackers and also fixing lengths inside the battery shed so I wanted to make my own to bespoke for each cable size. To this end I purchased a 300mmX200mm 1mm sheet of aluminium and cut clamp strips where the eye size can be varied to the cable size being catered to. The pictures I have added show the clip making process.

Cut 100mmX20mm strips with metal cutters
Straighten the curled strips in a vice
Bend the strip around a drill bit of the appropriate size
Pinch around the bit in a vice
Tap the eye level with the clip so it can be surface or edge mounted
The edges were run over on a grinding wheel to remove any burring on the edges
I still have to drill a 4.5mm hole in the clips to accommodate a M4 pan head screwed into the tracker pole rivet

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Using screw piles sounds like a smart move, especially with your equipment on hand. It's a bummer that off-the-shelf solutions aren't as available in the UK, but your trench idea sounds solid. I don't have any experience with screw piles, but maybe someone else here does. Your plan seems well thought out, considering wind loads and the site's natural shelter.

The weather is showing fare for the weekend so I am hoping to start groundwork with the easy part first, the base for the high security metal battery shed. I put together the base mould today ready for if the weather does improve as promised. If the weather holds I could be pouring the base on Monday.

Constructing the base mould is a lot easier having a variable height platform to work on and around as offered up by our telehandler forks.

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Do you have footings dug and rebar going in before concrete?

I have a Volvo EC25 2.5t digger to do all the groundwork for the project. I have just purchased a trenching bucket to add to the many implements of the digger section. It's a narrow 3" bucket that I'll use to run conduit from the shed to each tracker and also to run a mains armour cable from the shed to the home. I'll be cutting in 60m of cable across my garden so a 3" bucket will make for less disruption compared to my previous smallest bucket which is 12".

I won't be adding rebar to the slab as the spec from the shed manufacturer is for only 2" of concrete or 2" paving slabs. I'll be doing 5" of concrete on a 1" stone base. The contents and shed will weigh in at around 400kg and a 1:2:4 concrete mix that I will lay down will have a load capacity of 1,600kg without reinforcement. If you can get away without mesh or rebar it makes sense as a concrete pad is easy to mechanically break up if anyone wants to do that in the future, far less so with steel reinforced concrete.

I got to break ground today. Forecast for a fine weekend and it was overcast with light rain. Still base frame for the battery shed is in the ground and ready to pour concrete after a bit more compacting of the sand/stone mix base. A few days of rain will likely sort that aspect form me. I have added an earthing rod into the frame area that I will take up through the shed floor to provide the earth for the battery shed electrical units that will range from the inverter, to generator infeed and consumer unit output. I will also add in a couple of power sockets into the circuit in case I need or wish to add an air conditioning unit to maintain the optimal temperature conditions within the shed.

Weather permitting the concrete will be laid down next weekend when a mate is available to assist in the making and laying process.

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Power outlets can be a great convenience, all my arrays have them.
Bruce Roe

I took advantage of the decent weather this weekend to get the solar tracker mounting pipes in the ground. So everything is now ready to backfill with concrete. I extracted 4m3 of soil, 2ft was topsoil and 4 foot was then boulder clay with the final foot being more sandy clay. The boulder clay took some digging effort, which should help give the tracker mounting pole a lot of support.

I have been in contact with a local ready mix company that specialises in batches up to 4m3 so good to go as soon as they can fit me in, if the weather holds. I'm hoping the concreting can be done before I go on holiday in May so everything would then be ready for the next stage of shed build and kitting out followed by trenching of electrics to the tracker sites and mains cable to the house.

If I can complete all the electrical side by the end of June then I should have the solar panels installed by the end of July in time for my original timeline to be up and running for August.

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New digger toy arrived today, a 3" trenching bucket that I'll use, probably in June, to cut the armour cable into the ground for the house run and to cut the conduit into the ground for the two runs from the battery shed to each tracker.

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Bucket is cool, looks like the max depth is preset? My own experience is a trencher digs as wide as the chain, but a backhoe bucket adds some inches to its width, more dirt to deal with. The standard here is 24in deep, so I am not required to use conduit. Bruce Roe

There were two trench bucket max depth options of 400mm (16 ") or 700mm (28") . I purchased the shorter 400mm option. The company I used was the Rhinox Group who ship Worldwide. I could just have used my 12" bucket but this will give a much neater cut across my lawn with a fraction of the spoil to reinstate after the cable is laid.