Large solar array support beams

[s/v Jedi]

Originally Posted by Dirk01

Okay,

then my idea about the combined electric/thermal power panel isn't anything making sense for you. Maybe it makes sense for others...
TBO, I don't know yet enough about temperatures and effort to get the heat from the panel into my hot water tank and how big it should be to get out enough warm water for two short showers a day and the typical dish washing of course..

However, I wouldn't change to a gunboat 60ish also. Not because I don't like it or I wouldn't have the money to run it (which I defintively have not), but for only 2 people it's just overkill

Cheers

We have an Isotherm basic 40 liter water heater which has been great. It’s 20 years old and keeps going like new.

I did add a thermostatic mixing valve; I think you can order these with one nowadays.

I think you also need a circulation pump. You can find these on Amazon… some in stainless steel and temperature rating up to well over boiling point of water.

[CaptainRivet]

Have a look at this guy, he has slide out solar panels on his off-road RV:

https://m.youtube.com/watch?v=cM5s4F-7AOk

Perfect solution for your need too.

[RaymondR]

I decided that one of the better ways of piping the solar collector into the existing hot water system was to form a closed circuit into the calorifier inlet and outlet at the storage tank.

The problem with including the collector into the cold water inlet and hot water outlet is that this puts any circulating pump in a circuit which is under water system pressure all the time and I could not locate a circulation pump which was suitable at a reasonable price. The relatively low pressure the engine cooling solution circulates at would allow a cheaper packerless pump to be utilized.

[Lee Jerry]

Originally Posted by s/v Jedi

Very surprised that this lamination, 0.72 mm thick skins around foam core which is at its thickest point maybe 2” but much thinner for most of it.

Supported at both ends (1.5 meter apart?) it took 1,200kg to break it.

The skins were formed from 3x 210g regular weave plus an 88g finish skin, so total 718g which translates to 0.718mm layup thickness.

That seems a little thin, I'd guess more like 1.1 mm, but it's not that important.

The projected strength for regular weave carbon fiber is 600psi ...

If you mean tensile strength of the laminate, this seems really low. The company in the video gives values in the range of 500 to 600 MPa, or 72,500 to 87,000 psi for their laminates. This is important; see next post.

...and we have to assume the skin on one side broke before the other side did so let’s estimate the too of the wing to be 12” wide…. 12 x 0.718 = 8.6mm high at an inch wide. 25.4 / 8.6 = 3 so the projected strength is a third of 600 pounds = 200 pounds or 100kg.

So the other 1,100kg of strength was all due to the core and the skin on the other side. The compression strength is a bit less, 570psi so the skin in compression must have failed first?

More important is the deflection. At 100kg there was only a 6mm deflection while the single skin would have bent like a rubberband.

It's unusual to look at the components that way. The whole sandwich functions as a unit to provide the strength. Kind of a "more than the sum of the parts" thing. The core doesn't provide much strength. Its purpose is to increase the moment of inertia of the "beam" by keeping the skins separated and in-plane. The skins take "all" of the load.

[s/v Jedi]

Originally Posted by Lee Jerry

That seems a little thin, I'd guess more like 1.1 mm, but it's not that important.



If you mean tensile strength of the laminate, this seems really low. The company in the video gives values in the range of 500 to 600 MPa, or 72,500 to 87,000 psi for their laminates. This is important; see next post.



It's unusual to look at the components that way. The whole sandwich functions as a unit to provide the strength. Kind of a "more than the sum of the parts" thing. The core doesn't provide much strength. Its purpose is to increase the moment of inertia of the "beam" by keeping the skins separated and in-plane. The skins take "all" of the load.

Yes, it’s 600 MPa, but the math is correct. I keep converting units, it’s madness

I was under the impression that the core increases stiffness and for strength it provides a moment as a multiplier of fiber strength, which is why a thicker core makes for a stronger part.

I find it interesting that this wing was designed to cope with 100kg downforce and the skins turn out to have a 100kg tensile strength. I’m starting to think this isn’t a coincidence…

[Lee Jerry]

Originally Posted by s/v Jedi

The new cassettes need support at the very end of the panels because of the sliding mechanism and those panels are much longer: 209.5cm. The cassettes can stick out a bit, but side wall and sliders add another 4cm at each end, for a total length of 217.5cm. I think the supporting beam should be 210cm long with the cassette sticking out less than 4cm each end.

Maybe I missed something here, but it seems you said the supports (connections) have to be at the ends of the beam, but then specify a beam length less than the cassette length. I don't see how that works.

I can lower the hinge point for the dinghy lift arm about 10cm, but I would prefer to also make that arm 10cm longer, so I want the beam and support strut to work for the current position with the dinghy hoisted up fully. The dinghy lift arm comes up to the same height as the lower tube, but the too of the arm is bent out so there is horizontal distance of about 30cm. The strut must clear this.

So, considering all the above, the beams will be 210cm long. Starting from the inboard end, we have the following attachments:

- at 10 cm the first 1.5” diameter arch tube.

- at 50 cm the second 1.5” diameter arch tube, with 15cm below that another 1.25” arch tube which can connect the strut.

- at 100cm the strut to beam attachment. As the beam and strut will be one continuous part, it may extend much further, but for the simplified diagram for calculating strength, this is what I plan to ise.

- beyond the strut a 110cm span, which would become the cantilevered beam.

I am thinking to make the beam core 10cm high above the arch tubes and I haven’t decided on the width yet. A 5cm width foam core feels right and allow good lashing to the arch tubes and cassette.

I think you want to make it just a little bit bigger. I'd recommend a minimum of 12.5 cm height. I like the 2:1 aspect ratio (don't know why), so 6.25 cm width. With the material properties described below and a 50 kg load at the end of a 110 cm beam, I estimate 5.7 mm deflection and a factor of safety (FoS) of ~15 on bending stress. If you increased to 15 cm x 7.5 cm, the deflection drops to 3.3 mm and FoS increases to >20. These were for a straight beam; deflection would increase (slightly) with a taper.

There are tons of variables that go into the final performance (i.e. mechanical properties) of a laminate. So figuring out what they actually are is tricky. What method are you planning for construction? I assume not pre-preg (do you have or plan to build an oven?). I also assume you won't vacuum bag. Therefore, it will be standard manual layup (I've assumed).

The company in the video above (Easy Composites) reports a range of material properties for their parts, but it looks like reasonable values are: 500-600 MPa (72,500 - 87000 psi) for tensile strength and ~32 GPa (4.6E6 psi) for modulus. They vacuum bag, so get a higher fiber to resin ratio then I expect you will. Thus, I WAGed values by reducing their values by 20% and used 400 MPa (58,000 psi) and 25.6 GPA (3.7E6 psi), respectively. (This probably isn't that critical because I also assume thicker skins, so it offsets.)

I used 2 mm skin thickness on the top / bottom and 1.5 mm on the sides. To get this, I envisioned a 4-layer layup:
- cloth all around
- 45 bias all around
- uni tape top/bottom
- and finally another cloth all around

The best (only?) way to confirm properties is to build and test a sample (of the skin at least).

Now here comes my problem. With the support strut almost reaching halfway down the beam, it would carry the full weight if it was long enough to life the beam off the upper arch tube. I think I want to distribute the load.
Besides making patterns for each beam to deal with variations of the arch tubing, how can I fine tune this so that the beams sit in the same plane and the load gets distributed?

With the previous frame, the fittings I used were for tubing with an 1.67” O.D. and I used a deck anti-skid tape around the tubing to make it a tight fit. I guess I can do something similar for fine tuning these beams, using a tape that doesn’t compress, like UHMW tape?

Using a "large" beam as described above could / should eliminate the need for a strut. However, if you still want one, you could build the tube connection, and then two possibilities are:
- turnbuckle or jack screw that allows you to tweak the length
- a rod that allows shims to be added to adjust the length

[Lee Jerry]

Originally Posted by s/v Jedi

Yes, it’s 600 MPa, but the math is correct. I keep converting units, it’s madness

I was under the impression that the core increases stiffness and for strength it provides a moment as a multiplier of fiber strength, which is why a thicker core makes for a stronger part.

A thicker core increases the inertia of the sandwich; it makes a taller I-beam. (It also increases the shear in the core, so the core has to be stronger.) Inertia is in the denominator of both the deflection equation and the bending stress equation. Thus higher inertia decreases both deflection (i.e. is stiffer) and bending stress (i.e. is stronger in bending, but weaker in shear).

BTW, Coosa board is probably a good option for the core in these beams.

I find it interesting that this wing was designed to cope with 100kg downforce and the skins turn out to have a 100kg tensile strength. I’m starting to think this isn’t a coincidence…

I don't think it is equal; I think the tensile strength is a lot higher. Sorry, but I don't follow your calcs.

[Lee Jerry]

Originally Posted by Lee Jerry

I think you want to make it just a little bit bigger. I'd recommend a minimum of 12.5 cm height. I like the 2:1 aspect ratio (don't know why), so 6.25 cm width. With the material properties described below and a 50 kg load at the end of a 110 cm beam, I estimate 5.7 mm deflection and a factor of safety (FoS) of ~15 on bending stress. If you increased to 15 cm x 7.5 cm, the deflection drops to 3.3 mm and FoS increases to >20. These were for a straight beam; deflection would increase (slightly) with a taper.

Also, FYI, I get 11 mm deflection and FoS of 10 with your proposed 10 cm x 5 cm beam.

[s/v Jedi]

Originally Posted by Lee Jerry

Maybe I missed something here, but it seems you said the supports (connections) have to be at the ends of the beam, but then specify a beam length less than the cassette length. I don't see how that works.

The cassette end plates are angles that go under the panels, allowing overhang. I found ready-made 20’ lengths of 1/4” thick angle online that I can have cut in 4’ lengths and shipped standard ground. These have equal sides so I could use a 4” x 4” angle which fits the slider plus fixed panel and allows a small 1.5” overhang on each side, leaving 2.5” to sit on the beam.

I think you want to make it just a little bit bigger. I'd recommend a minimum of 12.5 cm height. I like the 2:1 aspect ratio (don't know why), so 6.25 cm width. With the material properties described below and a 50 kg load at the end of a 110 cm beam, I estimate 5.7 mm deflection and a factor of safety (FoS) of ~15 on bending stress. If you increased to 15 cm x 7.5 cm, the deflection drops to 3.3 mm and FoS increases to >20. These were for a straight beam; deflection would increase (slightly) with a taper.

So this is for a 110cm overhang, with the first 100cm supported at both ends (strut at 100cm) ? I’m confused because you write 110cm and further down that this is without the strut.

There are tons of variables that go into the final performance (i.e. mechanical properties) of a laminate. So figuring out what they actually are is tricky. What method are you planning for construction? I assume not pre-preg (do you have or plan to build an oven?). I also assume you won't vacuum bag. Therefore, it will be standard manual layup (I've assumed).

I’m thinking I will need to make the step and start using vacuum. I built a nice 4’ x 8’ assembly table last year with this in mind. I need to start buying the gear for this and wonder if my refrigeration vacuum pump will work. Also, I see I can use a gadget in combination with my air compressor.

The company in the video above (Easy Composites) reports a range of material properties for their parts, but it looks like reasonable values are: 500-600 MPa (72,500 - 87000 psi) for tensile strength and ~32 GPa (4.6E6 psi) for modulus. They vacuum bag, so get a higher fiber to resin ratio then I expect you will. Thus, I WAGed values by reducing their values by 20% and used 400 MPa (58,000 psi) and 25.6 GPA (3.7E6 psi), respectively. (This probably isn't that critical because I also assume thicker skins, so it offsets.)

I used 2 mm skin thickness on the top / bottom and 1.5 mm on the sides. To get this, I envisioned a 4-layer layup:
- cloth all around
- 45 bias all around
- uni tape top/bottom
- and finally another cloth all around

What material weights for these layers?

The best (only?) way to confirm properties is to build and test a sample (of the skin at least).

Using a "large" beam as described above could / should eliminate the need for a strut. However, if you still want one, you could build the tube connection, and then two possibilities are:
- turnbuckle or jack screw that allows you to tweak the length
- a rod that allows shims to be added to adjust the length

Yes, the UHMW tape would function as the shim material.

[Dirk01]

Originally Posted by RaymondR

I decided that one of the better ways of piping the solar collector into the existing hot water system was to form a closed circuit into the calorifier inlet and outlet at the storage tank.

...

Raymond,

why don't you use the Isotemp Water Heater - Basic TWIN 40L with Double Coil & Mixer?

Twin Coil:
The Basic Twin as the name suggests has two heat exchanger coils installed. The double coil can be used to extract heat from two separate sources, such as twin main engines or from a main engine and a generator. It can also be used to deliver a second source of hot water supply, for instance as to radiator heating system.

Cheers
Dirk

[MVDarlin]

I recommend 1" ss bar stock.

[Cpt Mark]

I just built a bimini/dodger out of this stuff. Super strong, lightweight,easy to work with. I used 2 in material and can walk anywhere on top. Bimini is 10'x10'. Might be worth looking into

https://www.carbon-core.com/products...els/composite/

[Lee Jerry]

Originally Posted by s/v Jedi

So this is for a 110cm overhang, with the first 100cm supported at both ends (strut at 100cm) ? I’m confused because you write 110cm and further down that this is without the strut.

You're right, those values are for the 110cm length so would include the strut. I'll add a table with more cases below. You'll see that you can still go without it but will need a little beefier beam. Or perhaps a shorter strut that doesn't go out as far on the beam as you've described above, say to 75-80cm with a better angle and less interference with dinghy tube.

I’m thinking I will need to make the step and start using vacuum. I built a nice 4’ x 8’ assembly table last year with this in mind. I need to start buying the gear for this and wonder if my refrigeration vacuum pump will work. Also, I see I can use a gadget in combination with my air compressor.

For this application, vacuum bagging is nice if you can do it, but I wouldn't say is required. IMHO, it's primary advantage is weight savings (in using less resin), since most of the strength comes from the fibers (which is the same). There are secondary benefits to structure (a little, via better inter-layer bonding) and (potentially) appearance.

What material weights for these layers?

Ha. Is that an important detail? It was a bit late last night when I posted...

I was using 300-350g per cloth (including bias), so ~1000g total cloth plus the uni. You could use more layers of lighter cloth, such as the 210g used in the wing. That would have minor strength benefits (less distortion of fibers, for example), but requires a bit more work in construction (and maybe cost). I'll just specify total cloth weight below to be made up as desired.

Yes, the UHMW tape would function as the shim material.

I was thinking you were looking for more range, like several mm whereas the tape is probably good for <= 1 mm.



Here are some performance numbers for a 50 kg load at the end of a straight beam for various beam sizes with various layups.
Beam Size (cm) / Deflection (mm) / Bending FoS

110 cm long beam (with strut) with ~1000g of carbon fiber (plus uni):
100 x 50 / 11.0 / 10
125 x 62.5 / 5.7 / 15
150 x 75 / 3.3 / 22

160 cm long beam (no strut) with ~1000g of carbon fiber (plus uni):
125 x 62.5 / 17.5 / 11
150 x 75 / 10.2 / 16
175 x 87.5 / 6.4 / 22

160 cm long beam (no strut) with ~1200g of carbon fiber (plus uni):
125 x 62.5 / 13.6 / 14
150 x 75 / 7.9 / 20
175 x 87.5 / 5.0 / 28


Do note that the carbon weight is a bit of an estimate on my part in trying to relate it to a laminate skin thickness and associated properties. And obviously, there are other arrangements possible, but hopefully these give you an idea of what's possible or where you're at. I can look at others if you want. I may try to improve the calcs.

[RaymondR]

Originally Posted by Dirk01

Raymond,



why don't you use the Isotemp Water Heater - Basic TWIN 40L with Double Coil & Mixer?



Twin Coil:

The Basic Twin as the name suggests has two heat exchanger coils installed. The double coil can be used to extract heat from two separate sources, such as twin main engines or from a main engine and a generator. It can also be used to deliver a second source of hot water supply, for instance as to radiator heating system.



Cheers

Dirk

Hi Dirk, I already have a fairly new HWS with engine and electric heating and when I rebuilt the solar farm included an allowance for later inclusion of a collector for water heating and was seeking a modification which would include solar at least cost. Using the engine cooling system to implement it is the simplest and most economical solution.

[s/v Jedi]

Originally Posted by Lee Jerry

You're right, those values are for the 110cm length so would include the strut. I'll add a table with more cases below. You'll see that you can still go without it but will need a little beefier beam. Or perhaps a shorter strut that doesn't go out as far on the beam as you've described above, say to 75-80cm with a better angle and less interference with dinghy tube.



For this application, vacuum bagging is nice if you can do it, but I wouldn't say is required. IMHO, it's primary advantage is weight savings (in using less resin), since most of the strength comes from the fibers (which is the same). There are secondary benefits to structure (a little, via better inter-layer bonding) and (potentially) appearance.



Ha. Is that an important detail? It was a bit late last night when I posted...

I was using 300-350g per cloth (including bias), so ~1000g total cloth plus the uni. You could use more layers of lighter cloth, such as the 210g used in the wing. That would have minor strength benefits (less distortion of fibers, for example), but requires a bit more work in construction (and maybe cost). I'll just specify total cloth weight below to be made up as desired.



I was thinking you were looking for more range, like several mm whereas the tape is probably good for <= 1 mm.



Here are some performance numbers for a 50 kg load at the end of a straight beam for various beam sizes with various layups.
Beam Size (cm) / Deflection (mm) / Bending FoS

110 cm long beam (with strut) with ~1000g of carbon fiber (plus uni):
100 x 50 / 11.0 / 10
125 x 62.5 / 5.7 / 15
150 x 75 / 3.3 / 22

160 cm long beam (no strut) with ~1000g of carbon fiber (plus uni):
125 x 62.5 / 17.5 / 11
150 x 75 / 10.2 / 16
175 x 87.5 / 6.4 / 22

160 cm long beam (no strut) with ~1200g of carbon fiber (plus uni):
125 x 62.5 / 13.6 / 14
150 x 75 / 7.9 / 20
175 x 87.5 / 5.0 / 28

Do note that the carbon weight is a bit of an estimate on my part in trying to relate it to a laminate skin thickness and associated properties. And obviously, there are other arrangements possible, but hopefully these give you an idea of what's possible or where you're at. I can look at others if you want. I may try to improve the calcs.

Thank you! I think many others will follow with the wish for large solar arrays and this thread will really help for diy

I have looked at materials that I can easily source from a local shop and Jamestown Distributors and have this proposal:

Beam with integrated stud for the first 1000mm, then unsupported for the next 1100mm.

For the core I plan to use three layers of 3/4” thick Coosa board, so 57mm wide. Keeping the 2:1 ratio you like (I normally use 1.618, anyone guess why? but that’s not enough height for this application) then the core height is 114mm.

But I want to taper the beam. Starting at 114mm I would like to taper that down to 57mm at the end (so the end is square).

With the fiberglass skins added, this approaches 60x120. The Coosa tensile strength is insignificant; it can barely carry itself.

The glass/carbon fiber layup schedule, I’m trying to compensate a bit for the tapering as well as core dimensions:

1. 1708 (equals 650gsm carbon fiber biax)
2. CF twill weave 203gsm
3. Extra layer like 4
4. Extra layer like 4
5. E-glass cloth 6oz equals 145gsm carbon std weave

Total layup equals 1400gsm of carbon fiber. I selected a twill weave to get it to form nicer over roundover edges and I see it has the same strength properties as regular weave.

For unidirectional CF on the edges, I can easily source 318gsm from Jamestown Distributors/ TotalBoat and I wouldn’t mind using two layers instead of one. Where in the laminate schedule would it be best to add these two layers? Separately or together and between layers 3 and 4?

Also, I plan to use a 1/2” round-over router bit for the edges and think I can put the unidirectional very neatly over the edge. I wouldn’t mind to use one layer 100mm wide and lay it over the top so coming down 20mm each side and the second layer 120mm wide to overlap the first layer by 10mm on each side. This would almost double the unidirectional CF at the top.

For the bottom edge I plan to only cover the roundover itself, making it flush with the sides. With CF a bit weaker in compression, should I add another layer to compensate? The top would get a total of 220mm width unidirectional and three layers on the bottom would total 180mm width.

The factor of safety >10 is mind blowing. Does this really mean it would take 500kg to break it? This means testing is relatively safe, as I would only be testing deflection without risking breaking it.

I am really curious where these proposed beam dimensions and layup schedule would get me and if you can do the math for the tapering :-) I think the tapering doesn’t matter for strength because it follows the load curve but it will have a big impact on deflection. I hope to have countered that with more unidirectional primarily and a little more for the rest to balance it out, although I have a feeling it may need another layer of 200gsm CF…