Naked Science Forum
Non Life Sciences => Technology => Topic started by: Adam Murphy on 01/05/2020 15:46:39
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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?
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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.
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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
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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.
https://spam.com
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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
(https://www.alternative-energy-tutorials.com/images/stories/heating/parabolic.jpg)
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.
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I think, if we curved down the solar panels their efficiency will be reduced and this is what we all don't want
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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.
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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.
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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.
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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
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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.
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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.
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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.
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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]
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Fortunately, a solar panel which reflects light is usually aimed so that the reflection hits the Sun- technically this warms the sun up slightly.
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This would indeed be the case for a plane mirror with "infinite focal distance", but the OP was asking about a curved one.
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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.
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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
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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!
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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.
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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?
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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".
The spec would be " a sphere".
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Note that a practical tunnel has an Ω cross-section, not a circle - that is called a pipe!
Best tell the people who bore tunnels.
They think that circular cross sections are wonderful.
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Even the best solar panel reflects some of the incoming radiation. The curved office building at 20 Fenchurch Street has caused serious problems
Those aren't solar panels, it's just window glass, mounted almost vertically along a curve. In the UK, and similar latitudes, solar panels are nearly always angled at less than 40 degrees to the ground, which reflects the sun back into the sky, nor is there any reason to architecturally arrange them to cause focusing.
See:
https://blog.spiritenergy.co.uk/contractor/best-angle-solar-panels-uk
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Best tell the people who bore tunnels.
They think that circular cross sections are wonderful.
Best tell the guys that built the one in your picture! Modern boring machines like to make circular tubes because rotation is easy to generate and control, but you then have to fill or cut out the bottom to accommodate the flat road - and even the track that supports the boring machine. Hand-dug tunnels like the one shown can have an omega section right from the start, so the hydrostatic forces compress the brick lining but the diggers are always working from a flat surface.
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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".
The spec would be " a sphere".
Are you seriously suggesting that the earth is not flat? Begone, heretic!
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Rather mundanely, I'm suggesting that a Dyson sphere is a sphere- though , technically, other shapes could work, with less efficiency.
Best tell the people who bore tunnels.
They think that circular cross sections are wonderful.
Best tell the guys that built the one in your picture! Modern boring machines like to make circular tubes because rotation is easy to generate and control, but you then have to fill or cut out the bottom to accommodate the flat road - and even the track that supports the boring machine. Hand-dug tunnels like the one shown can have an omega section right from the start, so the hydrostatic forces compress the brick lining but the diggers are always working from a flat surface.
Well Damn it.
Why didn't someone mention the flat bit before.
Oh, I did.
, since he's talking about a curved surface, we can ignore the floor of the tunnel.
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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.
Also, the rotation would be effective, if your roof (or any receiving area) is some acres. Other wise each plate would hardly need any rotation. And automation cost will be significant compared to the outcome.
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Is that the tunnel that you could go time travel or in the other parts of the galaxy?
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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.
Thanks for the suggestion
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I've looked into this a bit further. Angling the solar panels so that they point directly at the sun at all times gives the maximum electricity for any given amount of solar panel, and fairly flat power output from sunrise to sunset. However the mechanism to do it is expensive.
But apparently around 2014 the solar panels themselves had dropped in price enough that it became cheaper to simply use more fixed solar panels oriented at different angles and lose some of their potential production, It's actually more economic to do that in many cases than just using a south facing panel, particularly if you're using the power directly rather than exporting it (where you'd want to be replacing electricity at ~20p/kWh with solar power at ~6p/kWh.)
For example you could point them south west and south east at about 90 degrees to each other and you'll get pretty much the same effect as a solar tracker. Or East and West facing sloping roofs work really well in summer (winter sucks though a bit unless you add a south facing panel as well.)
There's a few more interesting wrinkles as well that make it particularly worthwhile in some cases.
If the panels (or strings of panels) are the same voltage, then you can parallel them up and connect them to a single inverter and the power will add. Obviously you can't get more power than the inverter can handle, but the inverter won't take more current than it can use, so it's safe and you'll get more power than normal when it's cloudy because the light scatters and gets absorbed by the more shaded panel as well.
If you have a flat roof or the panels are on the ground, then you can manually re-angle the panels differently a couple of times a year. That really improves the energy output, maybe 35% extra kWh per year, mostly in the mornings and evenings and particularly in winter, because you can point the panels south.
It turns out that the extra panels are relatively cheap, the panels and frames are only about 20% of the cost of the system or something so that's why it's a net win (at least sometimes particularly when you're self consuming the electricity and want a relatively even output curve). Of course if you're looking for total maximum output kWhs and you're only being paid per kWh and there's no limits on power output, then pointing all the panels due south may be superior, but then you'll have to scale the inverters and everything else.
Nevertheless some solar farms now do this, particularly if they're limited by their grid connection (which is often the case) and so they want a relatively flat power output.
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If you're interested in the field of sciences of materials, you must seriously consider the perovskite solar cell (PSCs)! They're a cool and rapid-moving technology. Since the beginning of their development in 2009, they've been able to increase their efficiency from 3% and up to 22% of efficiency which makes the technology one of the fastest-growing technologies available today. The most interesting thing about perovskites (and the reason they wrap into tandem cells so well) is that you are able to "tune" the band gap of the absorption layer in many different ranges dependent on the quantity of bromide or iodide present in the mix. They're also semitransparent and behave like an optical splitter. This makes it possible to create customized tandem cells based upon the characteristics of your "bottom layer" absorber (oftentimes silicon wafers, though other organic cells have also been utilized).
PSCs are easy to create, however they can be difficult to master since they can be sprayed with a coating on the glass, or on any surface with electrodes and voila! You've created a solar cell (see transparent solar panels for sky scrapers, super amazing technological advancement!). The issue is that they have many stability issues in PSCs that are present in the present and require addressing before they can be marketed as an actual product for sale however, given the rapid technological advancements, I believe we'll be there in the next 10 years!
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Hi, everyone here I can tell why are solar panels not curved?
Because most of the radiations are captured by the plane surface, solar does not need to have a curved shape.
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Hi, everyone here I can tell why are solar panels not curved?
Curved the mirror will concentrate all the energy in one point. No photovoltaic cell could withstand this intensity. For proof you have the solar oven of Odeillo
Odeillo solar furnace (https://en.wikipedia.org/wiki/Odeillo_solar_furnace)
(https://upload.wikimedia.org/wikipedia/commons/a/ac/Four_solaire_001.jpg)
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(https://upload.wikimedia.org/wikipedia/commons/2/27/Four_en.svg)
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Solar panels do not need to have a curved shape. Maximum radiation is captured from a plane surface. Curved shapes as seen in solar thermal plants are used to focus the radiation to a single point, thus magnifying the local energy density. Focusing is not necessary in PV, therefore you don't get to see curved panels.
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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.
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In operation, solar panels are more or less constant voltage, largely independent of illumination. The current depends on the illumination. Because of that, panels with different illuminations work well in parallel, less so in series. You want panels in series to all have similar illuminations, to all be at the same angle to the sun.
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You want panels in series to all have similar illuminations, to all be at the same angle to the sun.
Half of my panels face east, half face west.
- One side active in the morning
- One side in the afternoon
- both semi-active at noon
- The inverter has two inputs, one for each string of solar panels.
The ideal would be to have them all facing north, but my house doesn't have a large north-facing area - and there is apparently some local regulation that discourages solar panels on the road-facing side of the house (but I'm sure I've seen other homes doing it...)
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The best angles to have your solar panels at is complex. Since about 2014 the cost of the panels are low enough that having more solar panel capacity than inverter capacity became cost effective. I believe I'm correct in saying that you would ideally want your panels facing north-east and north-west in your case; the cost of the extra panels is a small proportion of the cost of the system. When I ran the numbers on a system I was planning here, it was something like the cost went up by 15% and the productivity went up by 20%.
East-west systems approximate solar tracker outputs and may be optimal near the equator, and if you're not on net metering where the feed in tariff is small compared to the normal usage tariff if you're doing any significant self usage of the electricity.