SOLAR TRACKING SYSTEMS

On Mon, 2 Nov 2015 22:07:32 -0800 (PST), snipped-for-privacy@gmail.com wrote:

No, because such a device will only work for elevation. For azimuth, a "tilt meter" (also known as an inclinometer) will not show any change in output for any change in azimuth.

What is "back tracking"?

I'm beginning to notice a pattern. It doesn't matter what advice or information we provide, you reply with a completely irrelevant question that usually has nothing to do with the problem you're allegedly trying to solve. To me, this indicates a severe lack of fundamentals in how the sun travels across the sky, the required positioning accuracy, circuit fundamentals, and solar power, all of which you'll need to build a functional tracker.

I've made it a point of asking at least one question in each of my replies to see if you are actually reading what I wrote. You're not and have ignored all my questions.

You're also seriously lacking in the ability to ask a proper technical question that can actually be answered. Personally, I'm tired of this game and will not attempt to answer any more of your overly general one-line questions in the future. I suggest you get some help as you've been at this for at least 12 days and have yet to even mention an electronic circuit or component.

I also suggest that you pick a tracking technology, ANY tracking technology, and study how it works, what's needed to make it work, and what are its limitations. It doesn't matter which technology you pick, they all have their problems and limitations. Then try to define what you are working with. How big and heavy are the panels? How far do they need to move? How much power do you need to move the panels? How much power can you steal from the panels to run the system? How will it work (gear ratios, traverse, elevation correction, optical distractions, clouds, etc). Just ignore the other methods of tracking and concentrate on the one you guess might be best for what you're doing. Don't invent a complicated system that will probably not work. Be prepared to compromise some performance in order to keep things simple. Then, when you have all the parts of the puzzle at least partly defined, throw together a first attempt on paper. Calculate how it might work under various conditions, seasons, and positions of the sun. Check the limits of travel to make sure it doesn't break. When you have it designed on paper, build a scaled cardboard, stick, string, and glue model of the tracker. Whether big or small, it should follow the sun in the same manner. See what it does and adjust things as needed. If you have electronics at this point, that's fine, but simulations with a clock are good enough for cardboard. When you're model is working, then you can think about designing and building the real thing.

Good luck and don't worry if it doesn't work. My senior project in college only half way worked and my first real design project was a total flop. I survived.

NEMA is amen backwards. Say your prayers when you search for one of those.

On Mon, 02 Nov 2015 23:09:03 -0800, Jeff Liebermann Gave us:

Silicon solar cells do not like concentrated (i.e. multiple solar images) light. Instead of producing electrical output, the light heats the cells which lose efficiency when hot. If you must build a concentrator, use the heat to run a boiler and steam turbine generator.

On Tue, 03 Nov 2015 14:51:07 -0800, Jeff Liebermann Gave us:

Even better.

You lose out if the PV array ends up hotter due to concentrating the sunlight on it, but if you want to charge something a bit faster then a concentration factor of 2x can be had with a couple of plane mirrors that fold out to form half a hexagon. a la \_/

The current isn't quite doubled but unless the location is very hot the output of a small solar panel is enhanced at minimal extra cost.

Moving parts and so much less reliable.

as in other silicon diodes and transistors ?

drop by 300 mV. With cell nominal output voltage of 600 mV at room temperature, the output voltage as well as the efficiency will drop by

If mirrors are used, the back side of the solar cell should be protected against direct sunlight. Also ample heatsinks on the back side of the cell will help keep the cell temperature down and hence maximize the cell output voltage and efficiency.

What about overcast days? That's when "efficiency" is more important.

It might be instructive to consider the situation where you can't "see" the sun. Less light is coming from all angles. What's the math describing that? Does tracking help?

What's the physical arrangement of a huge solar panel with tracking mirror concentrators?

It might make sense to track some of the mirrors off target if the cell temperature gets too high. Are mirrors cheaper than more solar cells for the times of lower insolation?

I assume that the solar cells are pointed downward into the trough. That means the light is all reflected from the walls of the trough. Besides keeping the mirrors clean, there are some reflection losses involved. The problem is that even with 100% reflection efficiency, one cannot concentrate more light than is collected by the trough. That means that a conventional rooftop solar panel array, and a trough type arrangement of the same rooftop area, will produce the same amount of power. Of course, the solar panels involved will be smaller with the trough, but you still end up with a big ugly mess on the roof.

Another problem with the trough arrangement is that unless it's a perfect parabolic shape, the 3 sides are going to have some unwanted reflections that could end up going in unwanted directions, such as through the neighbors windows. With sheet metal, a parabolic cross section is easy enough to make.

Note that none of the parabolic trough collectors in the photos are for illuminating solar cells. Mostly, they're boilers, heat exchangers, and steam generators.

The closest approximation of solar concentrator was the ill fated Solyndra design: It would have worked and possibly been profitable had Solyndra been able to reduce costs, remove toxic substances, and figure out a way to keep the cylinders clean. In the end, they couldn't compete with lower cost per watt Chinese panels.

That's correct for a 2:1 concentration. However, higher concentrations are going to start melting things. More entertaining was what happened when some friends tried to build a solar concentrator. The focused spot was smaller than the solar cell, resulting in uneven heating. The solar cells cracked.

Water cooled solar photoelectric panels are the "hot" ticket in solar these daze. The collectors float on water and track the sun with the water providing cooling:

Yep, but there's one really big advantage to NOT using photovoltaic cells. The problem is that to consume electricity, the power must be generated simultaneously. When I turn on a house light, the generator load at Hoover Dam goes up a tiny amount. There's no intermediate storage system, except for peak load leveling schemes and the traditional home power battery pile. I'll take the unreliability of moving parts over the costs and hassles of maintaining a battery pile.

However, with steam, the means of storing heat are well known and fairly simple. On one extreme, if you happen to live over a salt dome, you can pump in into the ground and retrieve it later. On a smaller scale, the heat energy can be converted to other forms, such as compressed air or pumping water uphill, and used when needed. You can also do those with electricity, but it's so much easier with steam power.

Hint: The future of power will not be in who can generate electricity the most efficiently, but rather who can store the generated electricity in the most efficient manner for later use.

Why does the trough have to be parabolic. You're not focusing an image on the collector. As long as the trough is close enough to a parabola that the reflected rays fall on the collector, good enough. The difference between a circular section and a parabola aren't all that great.

So what? They got their hands deep enough into our pockets. They didn't have to actually work.

Steam lines tend to be small and narrow to reduce the danger of an explosion. As the ratio of the reflector aperture to collector area increases, the requirement for something close to a parabola increases. However, you are correct for collectors that are about half the diameter of the reflector, such as in the Solyndra design. However, for big trough collectors, it's going to be a parabola.

I'm going to resist the temptation to jump into the quicksand of yet another political discussion. All I care about is the technology and the economics, but of which were problematic, because Solyndra was the closest approximation to a trough concentrator for driving solar cells instead of a steam plant.

Nice. 1000mm x 22mm tube that puts out 4 watts. 4 watts / 1m * 0.022m = 4 / 182 watts/sq-meter Assuming a science fiction solar insolation of 1000 watts/sq-meter for high noon, this thing is: 182 / 1000 = 18% efficient Not bad, but I don't believe it and probably not worth driving 50 miles to pickup a few for my rooftop experiments.

I thought we were talking about PV, as well. With only a 2:1 concentration, the target is pretty big so a parabolic reflector is way overkill.

How can you separate Solyndra from politics? ...or any solar project, for that matter.

It was simply a graft concentrator.

Yep, I just wanted the avoid the usual progression: Tech discussion -> politics -> Obama bashing -> global warming -> conspiracy theories -> personal insults -> character assassination -> one-line comments -> discussions about what to discuss -> ad absurdum

Agreed. For 2:1 on a parabolic reflector, the area of the solar cells would be 1/3 the area of the reflector aperture. It's 1/3 because the solar cells block quite a bit of light from reaching the reflector. If it takes out 1/3 of the parabola, then what's left is twice the area of the solar cells or a 2:1 concentration. That's going to be a rather odd looking reflector with such a big center target.

A trough reflect is better, but with 2:1 has the same problem. The diameter of the pipe down the middle is going to be 1/3 the diameter of the trough or another ugly design.

How? I just ignore the political aspects and concentrate on the technology. Others might be more interested in the politics, and are certainly welcome to engage in such a discussion. It's just that I'm not interested.

Incidentally, history is written by the winners, except in cases where people lost money. There, it's written by the losers.

Four watts, for that huge tube, with multiple layers of stuff, filled with silicone oil, looks insane to me. You need 250 of them per kilowatt peak power. Only a fraction of the active material gets used.

Even at a junk store, it's $2.50 per peak watt.

Halted is one of the original, and few remainining, electronic surplus stores around here. Most couldn't survive the rising real estate values.

Steve and Woz offered them Apple stock for parts once; Halted turned them down.

"Even at a junk store, it's $2.50 per peak watt."

Than really puts it in prospective, doesn't it. And they can't even ship it. Any guess how much it cost the taxpayers?

We really got screwed.

It's a souvenir, a collectable, not sensible as a solar cell. Well, maybe if you live on a planet with multiple suns.

There is no reason the solar panel has to shade the reflector. Of course the reflector isn't perfect, either.

Are you really going to try to do a solar boiler with only a 2:1 concentration? If it's PV, what's the pipe do?

But that's the only reason the projects are even started.

Interesting point of view. OTOH, there are a fair share of books written about Carnegie, Vanderbilt, Morgan, and Rockefeller, Jobs, and Gates.