frames/stands for solar panels

[Simon]

I'm looking to build a frame for my solar panels, currently I have 6 250W panels just dumped on my lawn propped up on a wood pile and I could do with lifting them and fixing them at the right angle.

My main concerns are how to fix them to the ground in a way that won't need constant replacement and how to make sure the whole thing is safe against the wind. I'd also like to be able to tilt them if possible as here is the UK the sun is rather horizontal in the winter so I don't know if tilting the panels more upright will help or if that will add more complication than it is worth.

[fourtytwo42]

Hi Simon,

Mine are fixed at 52deg inclination as that happens to be both my roof angle and latitude.
There is a really useful website http://re.jrc.ec.europa.eu/pvgis/apps4/pvest.php that allows you to easily twiddle things and see the results.
If I was able (planning restriction) I would probably go for tweaking the inclination twice a year.

As for wind loading there is loads of stuff available such as http://www.nef.org.uk/knowledge-hub/view/wind-loading-on-solar-pv-panels

J

[Simon]

I am at 51 degrees but in winter I think 70-80 degrees inclination is probably more like "perpendicular to the sun". Unlike you mine won't be going on the roof, they will be on a frame in the garden. I may put a shed underneath later.

So my main problems are that they will be fully open to the wind (one has already taken a tumble but fortunately was ok) and as I'm putting them on ground wood posts won't last the longest but I don't want to make the whole thing out of metal although that might be an idea - price dependant really. I want to get them up without spending too much but doing a good job.

[fourtytwo42]

Frankly in the depths of winter nothing makes a huge difference anyway, see the various calculators.
For mounting there are many products intended for flat roofs held down by weights (sandbags etc) or you could use hollow concrete blocks (resting on the ground) with steel tube cemented in then at least you can move them if required.

[Simon]

yes I was thinking of weighing them down, I was hoping I could built a frame that stood on the ground and not with posts sunk into it and weights to stop it being blown over. The other thing though it I want to make it reasonably High so that I can still walk under it and it escapes shadow for longer.

[Ian.M]

You need professional advice from a metrologist to determine the peak 50 year or 100 year gust speed  that can be expected at your location.   Then as a rough check plug it into this calculator:
http://www.engineeringtoolbox.com/wind-load-d_1775.html to get the force on a vertical flat panel.

e.g. if you are on the south coast in an exposed area, 60m/s wind speed (peak gust recorded for the Great Storm of October 1987) and 10m² of panel area gives 21600N.  Assuming a frame as wide as it is tall, that means you need 4.4 Tonnes of ballast equally distributed on the front and back legs to prevent toppling, or (assuming your local soil weighs 1200Kg/m³), ground anchors that effectively engage with 3.66m³ of soil.

Don't assume a tilted panl will experience less force than one normal to the wind direction.  Lift-drag calculations get *really* complex . . . .
You can probably assume you aren't going to have to cope with 60ms gusts unless you live on a coastal cliff and wind speeds are supposed to be measured  10m above ground level.   At a height of a couple of meters they are typically 1/3 less.  Plugging in a more reasonable peak gust of 40m/s and reducing it to ground level gives 4267N force and a far more reasonable 861Kg ballast mass.  Assuming densely compacted soil, that could be ground anchors into as little as 0.6m³, which may be within the capabilities of multiple screw-in ground anchors.

[radar_macgyver]

Use perforated steel tube or perforated angle. These are relatively cheap, and can be bolted together into a sturdy frame. If you know how to weld, regular tubing or angle would work as well (and is cheaper). To keep them from blowing away, you can get mounting feet for perf tube. Put a few anchor bolts into concrete with a hammer drill and you'll be fine. If you don't have a concrete base, you can do the same but into a few heavy cinder blocks (as suggested by fourtytwo42). Alternately, get a bag or two of concrete mix from a hardware store, dig a small trench, pour it in and let it set with a piece of perf tube embedded in. The lower you make the panels to the ground, the lower the wind loading. In the US, most jurisdictions have a height threshold above which one is required to get a building permit. There may be similar laws in the UK.

If you design a hinge into the bottom support, you may be able to use telescoping rails and adjust the angle depending on season. It helps to have a steeper angle in the winter to help snow slide off.

[Simon]

well my back garden is in a bit of a dip but yes it can get windy. I sounds like i would need to sink the legs into the ground. presumably with the panels at 45 degrees they will deflect some of the thrust, wind on the top is less of a problem at the air will deflect upwards, I'd be more worried about the air from underneath but i expect the air will deflect down.

[Simon]

Use perforated steel tube or perforated angle. These are relatively cheap, and can be bolted together into a sturdy frame. If you know how to weld, regular tubing or angle would work as well (and is cheaper). To keep them from blowing away, you can get mounting feet for perf tube. Put a few anchor bolts into concrete with a hammer drill and you'll be fine. If you don't have a concrete base, you can do the same but into a few heavy cinder blocks (as suggested by fourtytwo42). Alternately, get a bag or two of concrete mix from a hardware store, dig a small trench, pour it in and let it set with a piece of perf tube embedded in. The lower you make the panels to the ground, the lower the wind loading. In the US, most jurisdictions have a height threshold above which one is required to get a building permit. There may be similar laws in the UK.

If you design a hinge into the bottom support, you may be able to use telescoping rails and adjust the angle depending on season. It helps to have a steeper angle in the winter to help snow slide off.

Yes I think I will need to sink it into the ground. Rules about heights here are about how close you are to a neighbours fence, you have a maximum height right beside the fence and can go up by as much as you distance yourself, simply to about towering over your neighbour. I'm thinking 2m and I'm lower than the neighbour on the other side. No I can't weld, might be time to learn.

[fourtytwo42]

Gotta be careful here, it's not the same rules as a shed or extension, according to https://www.planningportal.co.uk/info/200130/common_projects/51/solar_panels/3 standalone systems must be >=5M from any boundary, that's why I didn't install a pole mounted tracking array I was thinking of. Of course if the installation is unobtrusive (ground level) it is unlikely anybody would complain or find this out. Also your wind loading problems will increase with height due to leverage on the foundations and being able to walk under them may not be much use among a confusion of guy's and or angled support poles, but I am sure the more you consider this a suitable solution will arise

[Simon]

oh for goodness sake, I can put in a 2m tall shed by the fence but not solar panels.... what a joke, our planning laws obviously hate solar panels, Easy to get round just put them on a shed! but they talk of 4m high so that might be why the distance from the boundry. to be fair I don't think anyone round here would care and a shed underneath was a consideration as it adds weight and wind shielding.

[Ian.M]

Take care you don't fall foul of planning regulations for permanent structures. Significant ground works for foundations *may* be an issue, and if you then add a shed under the frame is likely to count as a permanent structure.  If you intend to 'fly under the radar', get a friend who lives in the same area to enquire at the local council planning department . . . .

[Simon]

Here wooden structures are not a problem if they are not too tall. You can have a single story shed as large as you like.

[fourtytwo42]

oh for goodness sake, I can put in a 2m tall shed by the fence but not solar panels.... what a joke, our planning laws obviously hate solar panels, Easy to get round just put them on a shed! but they talk of 4m high so that might be why the distance from the boundry. to be fair I don't think anyone round here would care and a shed underneath was a consideration as it adds weight and wind shielding.

I know it's sick, turbines are even worse but I have been caught out by a local jobsworthy before so I just wanted to show you how bad it can get!

[Simon]

most people don't have a garden more than 5m wide, solar panels are only for post knobs. I do h\ave a wide garden but it would be a silly pace to put them smack in the middle.

[fourtytwo42]

most people don't have a garden more than 5m wide, solar panels are only for post knobs. I do h\ave a wide garden but it would be a silly pace to put them smack in the middle.

Well it's a tough call I have been disappointed several times to not be able to implement what I thought was a sound plan due to planning restrictions (is that a pun) BUT where there is a will there is a way! Perhaps you could re-organize your garden to have an island in the middle ? If you can do that and if your >=5M from the boundary then its definitely worth considering a pole mounted dual axis tracker, just bury a huge block of concrete (you can sub sequentially grass over) and go to welding school

Even her indoors may be coaxed into realizing it makes a suitable talking point among friends

[Simon]

I think I will be doing a lot of "shed building", I have 9sqm now, I want to add more although I could use the roof now that prices are coming down.

[floobydust]

I think you have to worry about frost-heaving moving things around, if you put anything into the ground. Frost line (depth) I am not sure for your locale. So It might be easier to have things "float" on the surface.

This is a triangle-frame with wood (heavy) posts base, in a pilot project.

[Simon]

well it does not get too cold here and gets warmer every year (you know that global warming thing). With a shed it would sit on top but foundations can be a pain.

[mtdoc]

A few points:

If you have any winds at all, you WILL need to have posts or a pole sunk into concrete buried in the ground.  How deep and large the footing(s) need to be depends on how large the surface area of your panels and max wind speeds.    You can find resources on the web to do the exact calculations to minimize footing size or you can just overengineer - using deeper holes and more concrete than you think you need. Concrete is cheap and digging holes is labor intensive but inexpensive.

You have 2 choices - Pole mount or ground mount with several posts.  Single large footing versus several smaller footings. I have done both.

Pole mount has the advantage of taking up a smaller footprint and potentiallly easier adjustments of array angle (if desired).   Pole mount will mean buying a large steel pole (likely 6" diam. schedule 80 for your 6 panels) and metal racking hardware.  For the hardware there are commercial systems that are very well engineered but expensive - but you can also DIY. If DIY you can make it simpler by purchasing a premade bracket like this (Search UK ebay site for UK options).

If ground mount - you can use several treated wood posts sunk in concrete footers.  Use bigger wood than you think you might need - I know someone whose 4" x 4" wooden posts were snapped off in high winds.   For your 6 panels - a 2x3 panel array supported by 4  4" x 6" treated posts (or metric equivalent) each sunk into a 3' deep  x 1.5' post hole filled with concrete would likely suffice - unless if is high off the ground, in which case leverage would require more posts.  Array can be mounted on large diameter treated lumber rails or metal rails.  Avoid direct contact of  dissimilar metals or metal with treated lumber.

You can find some good (and bad) examples of DIY mounts by doing a search on the NAWS forum.  There are some UK based solar forums as well.

Below are pics of my 2 current arrays. My pole mount required a very large concrete footing because it is moist soil. It has a 2 axis tracker. This was put in several years ago before PV prices dropped so at that time the extra expense of a tracker made sense.

My second, larger array is on a wood shed. I initially planned to just build a large ground mount - but considering the very high wind gusts we get here - I decided taking the time and expense to build a large shed meant less forces directly behind to panels and the added bonus is a large shed!  It is supported by 9  4x6" treated posts - each in 3' x 1.5' concrete filled holes

Next summer I plan a 3rd large array. It will be a pole mount array without tracker.

[Simon]

Well I could probably get away with a maximum height of 2m considering I'm lower than those I border with and be able to have as many as I like (sod the 9sqm limit), that will mean that at 45 degrees I can get in 3m of panel making the lot 3m wide and probably room for as many again. A back wall on the frame would mean that although getting the full force of the wind (whilst being in a sheltered spot) it would force the front of the frame into the ground instead of lifting it up into the air. and look like the back of a shed. The idea of putting them on a shed becomes a bit redundant as that is a big shed and i don't really want a huge shed although with a back on that is some storage space, I also plan to move out one day so I'd have to either take them with me or make them an asset to the house.

[Simon]

The panels would face into my garden so no one can complain of the eyesore.

[DenzilPenberthy]

Some ideas here:

http://www.windandsun.co.uk/products/PV-Mounting-Structures