Solar Panel Slew bearing, van hub?

Hello, I Have 5 solar panels for water heating which are doing a good job. As part of the experiment I intend making these into a pole mount so that I can rotate and track the sun. I have worked most details out like tracking electronics (arduino), pole and mounting frame.

I wonder if any of our readers has seen a suitable installation and can describe the slew bearing or bearing assembly?

Initial thoughts are to use a front wheel drive van rear hub which has taper rollers, probably, overkill but readily avalailable?

Thanks Peter

While the wheel hub provides a good bolting surface the back end is going to rely on some seriously stressed welding. Perhaps a rear drive gives a longer 'pole' to attach to.

A hub assembly from a trailer spares supplier might be cheaper. They come with a choice of stub axle etc.

Edited By Rex Hanman on 20/09/2021 18:32:59

Edited By Rex Hanman on 20/09/2021 18:33:49

Hello Peter,

From my experience over many years now, I think you might do better in terms of extracted energy by fitting a stainless steel sheet behind the tubes to reflect the light that passes between the tubes back onto the underside of them. I increased the output on my single panel of 20 tubes by about 25% in capturing that.

The sheet doesn't have to be mirror finish either, heating wavelengths are tolerant to a standard mill finish on cold rolled sheet.

Regards

Brian

Thanks for the reply. If I used a suitable rear hub complete with bearings etc I was going replicate the original stub but make the length reasonable as it would be inside the pole/tube to avoid over stressing the welds.

Is that what you mean?

I can't help wondering how big these panels are, and how exposed to the wind? Will they be out in all weathers? I would have thought that these details would dictate how robust the slew bearing must be and hence what type of bearing assembly might be suitable..? It's a good idea though.

Rod

Are these evacuated tube collectors with plumbing connection, to your hot water cylinder, or Photovoltaics with electrical connections to an immersion heater? I’m thinking it may well be the latter.

Thanks for the messages eveyone. They are Photovoltaic panel, 5 of them.Yes they will be out in all weathers and windage is an important consideration which is why I was asking in case anyone had seen or have experience of a commercial installation and could recall the bearings type or how it was made up?

A lot of the info out there does not really go into the detail I am looking for, I have seen plain plastic (for wont of a better word!) bearings advertised which is what I suspect the commercial installations use. I only picked on a rear hub type arrangement as an alternative as they are robust and readily available.

Peter

Have you considered a washing machine drum spider. Three legs as a tripod base, and fixings for a couple of substantial bearings. The one on my old Bosch is a substantial lump of steel. Try the local scrapyard for an old (or not so old) machine.

This could be an area of seven square metres, or more. I don’t think a washing machine component is built for the side forces which may be encountered.

With five photovoltaic panels, I would be grid tying them with an inverter and use the 240V 50Hz power, instead of from the grid, with only surplus going to an immersion heater. Seven panels is likely near 200V DC on open circuit and possibly well over 100V at full power (depends on how the panels are connected and the number of cells per panel, of course). High voltage DC is not a recommended route for me - lethal electrocution danger and increased risk of fire in the case of a fault condition within the circuit.

Is this a single or dual axis tracker ? I’m guessing again that it is single axis. Even so, I reckon four square metres is quite a large area to control from a single fulcrum post unless rotating at ground level (with possible support at the outer corners).

Flutter in a gale is going to be a serious problem, the OP has talked about having this pole mounted so it will be single point fixing. PV panels do not like being flexed so the whole thing needs a substantial frame to control that adding significant weight to an unstable system. I have seen small shed roofs torn off in windy conditions, gusting would make any structure the size of a garage door mounted centrally on a single support vibrate and suffer rapidly from feedback damage.

As others have said, I would have serious concerns about the stability and safety of something of this size in windy conditions. A heavy frame to support the PV cells is required and a single pole unless of substancial proportions is unlikely to work, or, be safe ! I would recommend surface(ground) mounting on small wheels, rotating around a centre point. the frame then gives also elevation, This then gives true tracking of the sun. Good luck Noel.

Edited By noel shelley on 21/09/2021 11:07:32

I'd looked at bearing like used on a washing machine etc but all are too small/flimsy. On the other hand there are "proper" slew bearings as used on 360 degree excavators etc but very pricy /large to experiment with.

Its a single axis tracker I was interested, single pole mount is quite popular around the world and even in the UK.

This is a similar size to what I am doing. The support is very much like a roof with the panels attached to the correct alloy rails with clips

However it is fixed, I want mine to rotate as the next step, hence the question in case someone has already done it or has practical experience of it.

I may end up with a grid ties inverter etc but it's heating water, matched to an imersion heater. At present its running at 156v and 312w in todays cloudy conditions, full sun is 1100w.

The link below is the controller I am using. It matches the impediance when the sun is not shinning fully. Works very well and the link gives comprensive data as well as a working project.

Peter

https://create.arduino.cc/projecthub/stevetearle/loadmaster-xp-a-smart-pv-mppt-solar-hot-water-controller-4a813f

How about a closed ended tube inverted over a fixed bar. Large single ball bearing at the top end to take the thrust and a ball race at the bottom to control side wobble. Basically to stop the outer tube flapping about. The top ball needs to run in a reasonably deep seating above and below. easy enough to provide a flange at the lower end of the tube with a couple of bolted down stops just cler of the flange to prevent any lifting during high winds. Control arm for slewing can be attched to the outer tube.

Suggest monitoring a sunflower to generate the gimble demand angle.

regards Martin

The brake on a van hub might come in handy when its windy! I'd be inclined to use the hub at ground level, pole on top (wouldn't need to be very high if you have a good horizon) and mount the panels on that.

To find people who have done it before I suggest you go to the Navitron forum.

Yes the tube idea is a possibility--thanks.

Tried Navitron previously on other things so maybe worth a go--thanks.

Rotation of PV arrays is not popular because of the obvious complications and its normally reccommended to install extra panels to compensate but dont want to do this!

Peter

Hi would this type of bearing be ok,only needs your tube cutting and flanges welding on ends.Flanges would bolt to either side of bearing.

This is from front of a Discovery 2

Maurice

Maybe the fairground equipment supply people have something larger that could be used as a slewing bearing, it does I think need to be broad to help with damping down the effects of "panting" of the structure in windy conditions

tAbout the size I was thinking of but that hub looks like it slides onto a splined drive shaft so the bearings are in a separate housing, if I'm looking at it correctly!

Did a bit more searching and slew bearings everywhere like elevating platform etc, often combined with a motor to rotate them, probably similar on fairground rides but I'll bet some of the ancient stuff used a lorry front hub.