# COMMUNITY : FORUMS : GREEN

## Movable Solar Panel:- Sizing limits.

Hi folks looking to build a tracking solar panel for North and South directions. I have a few drawings made up but im stuck for the maths side of things as I have a size limit I need to stick to in. I need the panel to move by 15° towards north and towards south. So a 30° movement in total. What I have in mind if an arch where the panel will sit on which can be moved with a single piston placed on the South end of the panel. This is to contract and expand to move 15° up and 15° down. My size limit is the panel must not exceed 200mm or 20cm in real money when at its maximum positions. I have assumed a 2 meter long panel (or array of panels in a frame) So because of this im a bit unsure about how to tackle the maths side of things to work out the arch's profile to meet this criteria. Anyone got any words of wisdom? The 200mm limit is the max UK law allows me to play around with the panels maximum position.

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apmaman (author) 2 years ago

Ok, so I've made some substantial progress however im a bit stuck again. thanks for the help so far!

I have gathered enough data to show the cumulative yearly solar radiation on my panel as 190054 W/m2....

Now, I am trying to convert this figure into kWh's as the UK will pay you a rate for generating the electricity, and another rate on top of that for selling it back into the grid.
Generating 13.88 pence per kWh
Export 4.77 pence per kWh.

I have the ratio set at 60% of the electricity will be on the generating tariff and 40% will be exported. (more money but using the electricity I generate in my home)

The solar array is 4kW peak and covers 28m2 in area.

Any help?

NRG4UandMe2 years ago

u could always ground mount or pole mount ...

DavidN713 years ago

Not worth the effort. For those in the US the allowance [200mm] is less than the length of an adult hand [>8 inches]. If these panels are roof mounted the extra energy collected isn't worth the risk of having them lift off or lift the roof off in a gale. There is a best angle for mounting is based of latitude, but you aren't going to be allowed that much tilt because of wind loading. If they were ground mounted, then you would be allowed the best latitude angle.

http://www.solarpaneltilt.com/

apmaman (author) 3 years ago

Anyone good at maths? Ahaha!

What I have now is the length on an arc and the Sagitta....

As S would be the maximum it would sit off the roof I will assume a 4cm thick rail and bolting mout, so 160mm to play with. The half cord length is the width of a solar panel, so roughly 900mm which needs halved 450mm, depends but I'll take that as a guestimate.

Soo... 160mm and 450mm gives me 713mm radius. All good.

Just slightly confused about how to calculate the length of the minor arc... I think it would be something like this.
Radius = 713, so diameter = 4479

Length = X?
angle would be 180° as its flat?
2 pi raduis / 360° = X/180°
x = ((2 pi r) * 180) / 360
(4477.64 * 180) / 360
= 2238.82mm?

Anyone else good with circles?

apmaman (author) 3 years ago

The 200mm limit is the UK law for roof mounted solar panels, they cannot protrude at any point more than 200mm from the roof.

Yeah I have been planning on using an arduino to control the system with a few LDR's to track the sun. This is going to track the changes in the season so its a North South adjustment of 30° in total I'd like. Enough to get a good face on for the sun throughout the year.

I've not got around to the maths part of the "banana bracket" but I have done some for the stepper motor one.. I've got an assumption of 4cm thick rack system so leaving me 160mm of play (0.16m) Right angle triangle.

a = 0.16m
b= 0.28m
c = 0.32m (this is the breadth of the panel, with an "unlimited" length depending on how many panels I hook together)
A being 30° and B 60°

With an assumed 30° roof pitch I was going to have the panel pre-set in one maximum (60°), say winter where the sun would be at its lowest so the most vertical to allow the most light to hit the panel, and then just adjust over the year season to the other size of flat against the roof 30°

Downunder35m3 years ago

You might be overthinking the problem here.
As you only need a change in one direction a simple hinge at the bottom and a screw drive to adjust the angle is far easier.

I assume you want to track the sun with it, so a small stepper motor with a threaded rod attached can be controlled with an Arduino.

For less science a normal motor and some limit switches will do just fine.

Kiteman3 years ago

When you say "must not exceed 200mm", does that mean "200mm away from the surface of the roof", or "200mm above the roof line"?

(In fact, if you post a link to the rules, somebody may be able to find a workaround.)