Concept idea - Feedback desired - Solar Dish

[weblife]

Hello,

I'm new to these forums and indeed this is my first post as well.

I live in Copenhagen, in Denmark, in Europe.

The weather here is relatively cloudy and with temperatures mostly around 20o Celcius in summer and down to -10o C in winter.

Generally solar panels are not used much here, due to the weather being as it is.

I have not worked with solar panels before, but have had an interest in the area for years. I am pretty much starting from scratch when it comes to practical implementation, but lets see.

My hopes is that this can eventually become a prototype that I can build or put together. It would be fun to see if it will work or if it becomes too expensive to produce compared to just more plain panels. I also worry about maintenance, it must be sturdy and relatively self-contained.

Here is my idea. Please feel free to comment and point out flaws:

A dish construction with a centrally mounted arm. This placed on a structure that can pivot to make the dish face the sun.

The inside of the dish would be lined with reflective material.

At the end of the arm of the dish, there would be placed a solar panel pointing inwards, towards the mirrors. It would ideally be circular.


I'd like to break up the construction in each of the elements as each of them have their own challenges:

A. The solar tracking pivot mount.

B. The reflective dish.

C. The solar panel.

D. The central arm.

Chapter A - The pivot mount

A.1. The Mount
- The mount will be determined pretty much by the size and scale of the dish and panel.

A.2. Tracking the sun:
- How is this done best? - Is there a piece of equipment you can get off the shelf for this sort of thing?


Chapter B - The reflective dish

B.1. The physical dish
- Do reflective dishes exist already? - If I have to find a way to order one, do you have any leads to where?

B.2. Reflective surface
- The coating has to be reflective enough to get the job done, yet not too reflective as that will simply heat up the panel to a degree where any material will melt. Ideas?

B.3. Secondary input
- Is there a way to harness the excess energy that will be absorbed in the dish material?

- Placing a coil of water pipes on the shadow side for a water cooling system for the central solar panel? (Running along the arm to the panel's backside.)

B.4. Keeping it shiny
- It rains quite a bit here. Making sure the water can run off the dish in the middle and that nighttime parking position allows water to run off and avoids bird droppings.

- Is the weak light reflected from the moon and over the horizon strong enough to be collected at night? - We are so far north that really dark night is not something that happens unless it is also cloudy. (Which of course it is...)


Chapter C - The solar panel

C.1. Panel
What kind of panel should I look for to do this? - The mounting will get very hot. I need a sturdy panel that can handle it. A circular overall shape would be easier to target for the dish.

C.2. Cooling
- Some kind of cooling device could be hooked up, using the excess heat to evaporate water to cool down the panel? - I recall some tricks from my days as a scout, we'd make a basic refrigerator with dark plastic and water. Could that be adapted and used?

C.3. Piping
- Running a pipe with a water circulation system should be possible with the amount of heat there is going to be around. Using the warm water's evaporation to power the cooling and circulation. Anyone with hands on ideas for this? - My only frame of reference is PC cooling systems for overclocking.


Chapter D. The central arm

D.1. Placement and shadow
- I figured placing the arm in the center would minimize it's shadow as the dish will always be aiming at the sun. Correct?

D.2. Wires
I need to read up on the type of cable needed for the specific installation, do you know any good sources for that? - Cable durability; from both the environment and capacity from the wattage.

D.3. Pipes for the water system
- Maybe the water pipe can double as the structural carrier of the arm?

[weblife]

When you reply, if you could please use the chapter references it will be easier to keep track of what part your replay is towards. Thanks!

[Mike90250]

For solar (thermal or electric) to be effective (actually work, work often enough to be useful, and be affordable) you need to have good bright sun.

Look around and see all the solar panels in your area, ask the owners if they are happy. You will still need a water heater, and a electric meter for the grid.

[weblife]

Hi Mike, thanks for the pointer. The whole mirrors idea is to alleviate that part of that problem, at a cost that is lower than simply more panels.

I did google "solar dish" and I can see that I'm not the fist to think of this, although most seem to be using just the heat and not the photons to produce their power. (Or in some cases they simply melt stuff for industri)

http://www.solarpaces.org/CSP_Techno...solar_dish.pdf - Article about similar concept, but using heat instead of solar panels.

http://greenpowerscience.com/ - Website that sells various stuff. Their concept seems to be using a large Fresnel lens in place of mirrors. Same basic concept, heat something up and harness the power.

I was mostly looking for a way to make ordinary solar panels feasible in low light areas at a low cost. I want a unit that has a fixed focal point and is self-contained once deployed, giving the output as electricity to be placed in battery or inverted into the grid.

Imagine something the size of a camping stool, that you place on the ground and voila, camping electricity. The mount would in that case contain the battery and the dish would orient towards the light.

Scaling that concept becomes a problem when the reflected mass of rays to the central area exceeds a certain temperature. (Depending on the panel placed there and cooling available) Moving the panel closer to the dish if the temperature grows too high could be a way to help that.

Some kind of rollers on the bar?

Inverted umbrella with reflecting insides for the low-budget version? - Collapsible for transport. Durability?

[Sunking]

Will not work work for Solar PV. The clouds and low sun angle remove the light which PV panels react to. There is nothing to magnify

[russ]

Not the first by 30 or 40 years? People have always wanted to increase the amount of light striking the cell - but to date it has never worked out - even for the companies that should know what they are doing.

At present several are using a parabolic trough to make a combination of hot water and electricity from PV. Still expensive - the water is used to cool the cells to keep the from frying.

[weblife]

Thanks for the replies guys. I have looked up some information from the providers of solutions here in DK. - They use efficiency rates of 13% for monocrystallic and 6% for amorph panels. These appear lower than what I can read of their use elsewhere. - Indicating that two things:

1. There is enough sun here, in general, to use solar panels.

2. They run at lower than maximum capacity due to low levels of sun available.

I would hazard the guess that with additional collector mirrors or fresnel, it should be possible to get higher efficiency. I've begun looking at what shapes this "booster array" should take to make this feasible.

Moving a mirror around by hand is not an option that looks desirable. Turning the panel upside down facing a dish has two weaknesses, the first being that the m2 exposed to light is now fully on the dish, the second that dishes have a focal point that can get way too hot to handle.

There is a treatment you can put on glasses to make them opaque when exposed to sunlight. Putting something like that on the booster array to control the additional output might be a way to deal with that.

The troughs are a good idea. Placing two rows of cells in the target area, one facing each side in a down slanted "V" shape.

- There would be air cooling for the panels, as they are suspended on a bar in the air and not flat against the ground.
- The panels can collect both he collected light and a bit from the side angles.
- The troughs can be placed on a pivot mount.
- It might be possible to make a triangular bar with a third panel facing conventionally upwards, closing the V over.
-- The output of that would be the lowest of the three though, as it would be unboosted. Having access to the back will increase cooling options for the other two.

Calculating the curve of the "optimal" trough is on the list.

Have you seen panels sold in a single column anywhere?

EDIT: Double-sided solar panels. http://www.treehugger.com/files/2005/05/double_sided_so.php

I began wondering, since I saw an article mentioning the back material of a panel being reflective. And lo and behold, it has been done. The article promises efficiency boost of 30% compared to single sided cells. Of course many things factor into that, that are not available in the article.

But since my project is about increasing the yield/optimizing cells to run at near max capacity this is good. I can drop the V shape and go with a single vertical panel placed in a trough or even just between a simple "V" shaped mirror.

That alone will also optimize the angles from where the sun will deliver good output. - Even if placed in a static setting.

[russ]

See -

http://www.absolicon.com/

[weblife]

Brilliant!

[dogsbody]

I must say having a lot of experience of thermal collectors, I too have been thinking....
One of the problems as I see it is that the sun rises in the east and sets in the west. Even after dawn there is a lot of power in the sun, but most system optimise for midday collection. The obvious answer is a system which tracks the sun, and the obvious answer to that is the cost. Further in areas of the world where wind is a major problem Denmark included, is that most of the time it is OK but very occasionally it is very strong, which means the tracking solar array must be very robust. It is quite easy to firmly attach a plate panel to a roof, but a tracking system is very much more difficult, and in some way not dissimilar to the mast of a wind turbine.
My conclusion therefore, is that flat panels are cheap and cheerful ( and getting cheaper by the day) and that they will win the day due to their simplicity to manufacture and to install.

[axis11]

[QUOTE=weblife;30546]Thanks for the replies guys. I have looked up some information from the providers of solutions here in DK. - They use efficiency rates of 13% for monocrystallic and 6% for amorph panels. These appear lower than what I can read of their use elsewhere. - Indicating that two things:

Efficiency ratings are often times based on conditions that very seldom occurs in actual situations.

1. There is enough sun here, in general, to use solar panels.

Near the equator where I live, there is more sunlight and more sunhours. But the time for investment recovery is at least ten years. How long it would take on your location?

2. They run at lower than maximum capacity due to low levels of sun available.

You could use mirrors, concentrators, trackers, cooling etc to increase your harvest. Would the increase in power gain be worth the additional cost?

[russ]

Even after dawn there is a lot of power in the sun, but most system optimise for midday collection.

I agree with your conclusion but not all the steps to get there - Sun rise here today is at 0655 hours - hourly insolation readings for the day are
0800 42
0900 200
1000 379
1100 544
1200 673
1300 750
1400 764
1500 718
1600 617
1700 462
1800 280
1900 75
2000 3

90% of the available watts are between 1000 and 1700 - My solar thermal system is producing 50

[dogsbody]

Very interesting readings, the first that I have ever seen. Your conclusion that 10 am to 5pm is the optimal collection timeframe, means that they must be tied into a bearing relative to due south, and then the solar collector optimised to the bearings over the period 10.00 am to 5.00 pm. In addition of course there must bea seond parameter, that is the change in azimuth from summer to winter.
A fixed plate collector, will have to "collect" insolation at a series of oblique angles during the day, and hence the reflectivity of the "glass" substrate will throw another variable into the mix. Anybody done any comparative readings with different makes of panel, and does the substrate itself vary on oblique angles tothe amount of energy converted?
Put simply any collector, fixed or tracking must be a series of compromises, as to angles of incidence, reflectivity, efficiency and of course cost. The more information that is available the better the decision as to what to install, and even to specify

[russ]

The reading is really not exactly what the solar thermal collector sees - it is referred to in the Davis manual as Global Solar Radiation. The sensor is aimed upwards - from the manual 'This irradiance includes both the direct component from the sun and the reflected component from the rest of the sky'.

Even if the panels were facing East for the morning sun there would be little gain before 0930 as there is not much to collect - same for evening. There would be a gain between 1000 to 1100 possibly - very little between 1200 to 1600 - a bit from 1700 to 1800.

UV radiation readings more or less track the insolation readings.

I maintain a log of the hourly readings, daily maximum and daily totals for insolation and UV just for my future reference.

[Mark-in-Seattle]

Single Axis Trackers Typically Harvest Approx 30% More than Fixed PV Mounts

The title is my brief point.

When solar PV panels were more expensive it was easier to cost justify a well engineered single-axis tracker to gather 30% more energy (for the average situation). I should know I'm still evaluating several of my own designs for our residential solar project (yes I've got way too much time on my hands). As panel prices have dropped thru 2011 and into early 2012 the design cost budget is much tighter; the extra cost required to pivot 2 panels should not be more than the cost of the "saved" third panel (30% more energy harvested) plus the cost of the saved third micro-inverter, assuming a string inverter was not appropriate due to shadowing issues.

This is an over simplification, due to posting constraints, but I think it conveys the central truth. I do not wish to discourage anyone's design efforts in this area. The industry and the world would enjoy a creative breakthrough around this difficult problem, hence my own modest efforts with the aid of friends with advanced degrees in materials science and 8 patents between those involved....but it is still quite a daunting challenge.

Best of luck !