[Adam Murphy (OP)]

Paul wonders:

"Why are solar panels not made in a tunnel shape so the sun rises in the morning and lights up the first part of the solar panel and as the sun passes over the top  (I know the Earth is revolving. I am just using the common terminology) , the top of the solar panel is receiving the full sunlight, and as the sun sets on the horizon, it's beams are  landing on the other side of the "tunnel"?"

What do you think, why don't we curve solar panels?

[alancalverd]

The proposal is inefficient because not all the elements will be optimally irradiated at any time.

The daily arc of the sun varies (from none to 360 degrees at the arctic circle!) depending on the time of year. The maximum elevation varies with season.  So you need to adjust the alignment of any receptor to maximise its yield.

If you can move the receptor, then a flat plate can always be 100% covered at optimum angle (i.e. perpendicular to the sun). If you aren't going to move the plate, aligning it to the average midday sun will give you the maximum yield for a given area of cells, over the year. 

Depending on the use of the electricity, it may be better to angle the plate a little lower, to maximise winter yield. 

[evan_au]

the top of the solar panel is receiving the full sunlight, and as the sun sets on the horizon, it's beams are  landing on the other side of the "tunnel"?"

Each solar cell produces very little voltage - around 0.7V.
- Very many cells are placed in series so that they add up to around 900V DC for input to the inverter (this electronic circuit converts DC into AC).
- A solar cell that is in the dark does not put out a voltage, but acts as a resistance to the flow of electricity (reduces the voltage)
- So if you have half the cells in the dark, you would get less output than if you just had half of the cells.

You want all cells in the solar panel to be similarly illuminated, so they put out a similar voltage, have a similarly low resistance, and the inverter can efficiently convert the total DC voltage (whatever it adds up to) into AC.

Why are solar panels not made in a tunnel shape

There are some solar collectors that are built in a trench shape, with a parabolic cross-section.
- These collectors have a pipe which runs down the focus of the parabola, so the Sun's rays are collected from a wide area and are focused on the thin thermal collector in the middle of the trench
- Something like oil or water runs through the pipe, collecting the heat
- The disadvantage of this type of collector is that they are mechanically more complicated - a motor has to follow the Sun across the sky; if the motor (or the Sun-following sensor) breaks down, it only collects sunlight for perhaps 30 minutes of each day
- In larger solar farms, motors keep the flat solar cells pointed at the Sun; at least, in this case, if the motor breaks down, the flat solar panel will still collect power for several hours of the day, even if it is pointing in the wrong direction.
- The advantage of flat, stationary solar cells is that they are mechanically simple; on cloudy days, the sunlight comes from all directions across the sky, and flat panels can collect solar energy from across the sky

See: https://en.wikipedia.org/wiki/Solar_power#Concentrated_solar_power

[Harryobr]

By the way, I disagree with you. In our time you can find so many flexible panels in the market. I also saw an article where describe solar tree.
newbielink:https://spam.com [nonactive]

[CliffordK]

There are parabolic trough mirror designs of "heat" solar panels.

https://www.parabolicsolartrough.com/
https://www.alternative-energy-tutorials.com/solar-hot-water/parabolic-trough-reflector.html



They generally need to track the sun on one axis, but not two axes. 

They have the advantage of making hotter temperatures than flat panels, but less volume heated.  But, for example, it is easier to reach boiling temperatures with a parabolic solar panel.

Paradoxically, a solar adsorption refrigeration system also benefits from the high temperatures of a parabolic reflector.  But, I don't believe any have been put into commercial use yet.

[Danny056]

I think, if we curved down the solar panels their efficiency will be reduced and this is what we all don't want

[CliffordK]

There are also reflector electric generating solar panels, and I believe have some of the highest efficiencies per square foot.

The would generally require 2 axis solar tracking.

[wolfekeeper]

Most solar panels are made from a slice of silicon. The slices are universally made flat, it would be very difficult to cut curved shapes and turn them into solar cells.

[Petrochemicals]

They are curved, due to the gravitational attraction of the sun. I am unsure if the curvature is sufficient to follow the curve of a 300m km circle though.

[evan_au]

They are curved, due to the gravitational attraction of the sun

The Earth has a much greater gravitational force on your roof (or the Solar panels on your roof) than the Sun or the Moon.
- So the Solar panels will sag slightly between their supports, attracted by the Earth

[CliffordK]

Most solar panels are made from a slice of silicon. The slices are universally made flat, it would be very difficult to cut curved shapes and turn them into solar cells.

There are both flexible as well as semi-flexible solar panels.

I believe the quality of the flexible and semi-flexible panels has been improving over the years.  They would certainly be worth considering for mounting on an automobile or trailer.

[Bored chemist]

I think the best shape is spherical.
https://en.wikipedia.org/wiki/Dyson_sphere

However, for Earth based ones they need to be "square on" to the sunlight, and that means very nearly flat.

[CliffordK]

I think the best shape is spherical.
https://en.wikipedia.org/wiki/Dyson_sphere

However, for Earth based ones they need to be "square on" to the sunlight, and that means very nearly flat.

Good point.

Ideally one would add a curvature equal to Earth's orbit.  But, for a 3' or so wide panel, that would be awfully close to being flat.

[alancalverd]

Even the best solar panel reflects some of the incoming radiation. The curved office building at 20 Fenchurch Street has caused serious problems

During the building's construction, it was discovered that for a period of up to two hours each day if the sun shines directly onto the building, it acts as a concave mirror and focuses light onto the streets to the south.[28] Spot temperature readings at street-level including up to 91 °C (196 °F)[29] and 117 °C (243 °F) were observed[30] during summer 2013, when the reflection of a beam of light up to six times brighter than direct sunlight shining onto the streets beneath damaged parked vehicles,[31] including one on Eastcheap whose owner was paid £946 by the developers for repairs to melted bodywork. Temperatures in direct line with the reflection became so intense that City A.M. reporter Jim Waterson managed to fry an egg in a pan set out on the ground.[32] The reflection also burned or scorched the doormat of a shop in the affected area. The media responded by dubbing the building the "Walkie-Scorchie"[33][34][35] and "Fryscraper".[28][36][37]

In September 2013, the developers stated that the City of London Corporation had approved plans to erect temporary screening on the streets to prevent similar incidents, and that they were also "evaluating longer-term solutions to ensure the issue cannot recur in future".[28][38] In 2014, a permanent awning was installed on the south side of the higher floors of the tower.[39]

The building's architect, Rafael Viñoly, also designed the Vdara hotel in Las Vegas which has a similar sunlight reflection problem that some employees called the "Vdara death ray".[40] The glass has since been covered with a non-reflective film.[41]

[Bored chemist]

Fortunately, a solar panel which reflects light is usually aimed so that the reflection hits the Sun- technically this warms the sun up slightly.

[alancalverd]

This would indeed be the case for a plane mirror with "infinite focal distance", but the OP was asking about a curved one.

[Bored chemist]

This would indeed be the case for a plane mirror with "infinite focal distance", but the OP was asking about a curved one.

There was something that always annoyed me about the book "The Lord of the flies"

Well, the OP says

a tunnel shape

OK Here's a Tunnel.

Tunnel..JPG (93.02 kB . 648x416 - viewed 9448 times)
Now, since he's talking about a curved surface, we can ignore the floor of the tunnel.
And there are two ways you could "tile" the tunnel with solar panels- they could face in, or they could face out.

If they faced in, they would never see the Sun, so we can assume the OP meant that the solar panels faced outwards.

That gives you a convex mirror- and you can't focus the Sun's rays with a convex mirror.
It's like Piggy's glasses.

On the other hand, I did talk about a concave structure- albeit a big one.
It's not flat but it does focus the Sun's rays back onto the Sun

[alancalverd]

On the other hand, I did talk about a concave structure- albeit a big one.
It's not flat but it does focus the Sun's rays back onto the Sun

Only if its focal distance is 7.5 x 10¹³m, giving its radius of curvature of 1.5 x 10¹⁴m - what most engineers would call "flat within spec".

However a practical fixed curved solar panel simply needs to subtend about 180° (or whatever the economic maximum solar arc may be)  with whatever radius is convenient. The idea of a convex collector is interesting if you don't want to set fire to passing cars but the efficiency of the non-perpendicular elements will be lower at any point because they won't be collecting scattered radiation from the perpendicular one.

Note that  a practical tunnel has an Ω cross-section, not a circle - that is called a pipe!

[alancalverd]

There was something that always annoyed me about the book "The Lord of the flies"

I had the same problem. Two story lines that couldn't possibly coexist. Turned me into a teenage skeptic.

[vhfpmr]

They are curved, due to the gravitational attraction of the sun.

Haven't you asked yourself why anything that's not bolted down like solar panels doesn't take off, and fly to the sun all by itself?