Sun Position Sensor

Long tube fixed on universal fulcrum, and if sunlight is passing on the other end of the tube mean sun is on the line of tube exis.An auto adjustment device is needed, that will sense the light at the end of tube and adjust the tube in the absence of light there.

You will also need some polaroid sheet, this will have to be cut to fit the tube, and will find the sun on overcast days.

It depends how accurate you want it.
An electro mechanical 'clock' mechanism might be good enough, once it is set it would be good for a while.
I've toyed with the idea of buidling one myself, a pair of photosensors (mounted in suitable tubes (maybe with slots), a couple of motors and a microcontroller should do the job, you'd probably need to duplicate it for elevation too if you wanted accurate tracking.
It would take some clever (for clever don't read 'complicated') software to make it re-synchronize every morning and in case of dense cloud/eclipse/squirrels etc.
Not sure how to cope with cloud cover, but if it's well designed it would pretty much track on it's own with the software only making minor corrections.
(E.G get the software to follow yesterdays track if there isn't a good signal today. Only store 'good' track data, ok, you may want add another photcell at the bottom of a tube to detect 'goodness')
Del

(I'd have thought a search for 'solar tracking' would bring up some schemes)

Do you think an annual log table of sun position (sunrise to sunset) can be used for this? This can avoid cloud issue and also no sensing is needed.This way one can program things for one year and forget it.as simple as coordinate geometry.

Sounds good to me, maybe a minor adjustment once a year on it's birthday...an excuse for cake too>
Del

sir i need a help from you....... I am doing project on solar tracking system. I wanna use RTC-Real Time Clock{DS 12887}.But my guide said to use sensors ! so i go for sensors. I use two LDR for it. I need a circuit for this! if sun li8 falls,the two sensors produce some li8 intensity. by comparing tat two li8 intensity, i give input to microcontroller.... for tat i need circuit dia clearly showing abt the function of ldr......

Some friends of mine in Brisbane who are involved is solar research have told me they use a green LED as the sensing element. I don't have the circuit, but I was shown how it tracks a parabolic dish.

To the best of my knowledge it was a basic amplifier circuit as they were trying to design and make cheap reliable stuff for third world aid projects. Expensive items like microprocessors were not applicable due to cost and complexity.

From memory the green LED develops a voltage roughly proportional to the illumination it recieves, the fall in voltage being the error.

I agree with you completely, a clock mechanism/Real Time Clock chip would actually be good enough as the sun is always in the same position (just higher and lower according to the season) every day. Even if it is seen less often/lower in winter, its still at the same horizontal angle to where its located.....

For the elevation correction over the year, I would think that a manual correction "Winter" and a "Summer" position would probably suffice fully......

I personally would never ever consider an optical tracking system as you yourself pointed out, even clouds might cause errors......

A PICAXE Basic PIC should be man (and cheap) enough for all the controlling needed, an I2C Real Time Clock will supply the time really accurately....and moving the solar collector only 4 times an hour will probably be even more accurate than needed.

Use the PIC to simply drive a well geared down small stepper motor......speed is simply not required.....over a toothed belt and aluminium toothed wheels.....

No need to have an encoder, just put the mechanism in a "home" position, press reset to align the controller chip and the stepper and you're off!!!

Or limit switches could also be used if NOT mechanical ones, Hall effect for example are better weather sealed of course.

Keeping things simple that are out in the weather is a very good idea.....optics that get the full sun's UV rays on them will probably fail more often than not!!! Or simply need cleaning very often.....

You only need to pick a time in the evening to rest the position after the sun has set no matter which day of the year, then turn it back to a position that will start to track the sun, even if the sun is "unseen" in the winter time, to maximise the output for any day of the year....

Simply said, you pick the start & end angles required from the longest day (21st June in the northern hemisphere, 21st December for the Southern) of the year for the start and end of any day......

K.I.S.S. (Which I do believe you also posted some time ago in a previous blog!!) is always needed.....

For Sun Angle Charts for any position on the earth, go here, they are free and needed in designing such a system correctly:-

http://solardat.uoregon.edu/SunChartProgram.html

For a full explanation go here:-

http://solardat.uoregon.edu/AboutSunCharts.html

For an example chart go here:-

http://www.californiasolarcenter.org/pdfs/ssh/sun-chart-example_38lat.pdf

This looks promising, at least the guy isn't charging for the info.

http://www.iwilltry.org/b/projects/build-a-heliostat-for-solar-heating-and-lighting/

The previous answers explain different techniques to track the Sun, but none actually answer the question, 'is there a sensor that can track the Sun even if it's cloudy?'.

That's a difficult question to answer because clouds obscure the Sun due to scattering, and to know what wavelength can see through the clouds you'd have to know the particle size of the water vapor drops in clouds. The particle size is not well established. But, it's certain that no inexpensive sensor covering the visible to infrared spectrum would work. You'd probably need two sensors, one for visible light and one for long-wavelength IR in the range of a few microns.

"The previous answers explain different techniques to track the Sun, but none actually answer the question, 'is there a sensor that can track the Sun even if it's cloudy?'." Actually the question should be "Is there a sensor which provides positioning information to ensure maximum output of power at all times?" with the footnote "If, because of cloud cover, there is no sharply defined maximum, the sensor does not hunt for an output". I would suggest a calculation based on 2 fixed sensors, one directed towards the East horizon, one to the West, to detect sunrise and sunset. The times of the previous day's sunrise and sunset, together with the current day's sunrise, will give you all the information you need, though I suppose you will want to guard against small boys shining torches at the sensors.

You are re-interpreting his question -- which is OK. That's what others here have done in various ways to address the overall concern about maximizing the collected power.

My response, though, was aimed directly at the question posed about sensing the sun even through cloud cover:

"Is there an electronic device that can be used to sense the sun through both clear sky and cloud cover?"

And WHY have so many responders suggested other ways of tracking the sun? Because, as I suggested in my reply, the answer to the question is no, there is no electronic device that can do that -- not one you can buy at a hardware store or order via the internet and then connect to your solar water heater.

Most radio-telescopes operate at wavelengths unaffected by clouds, and certain long-wavelength regions of IR are not affected by clouds. So a sensor could be made, but it wouldn't be simple and it would not likely be cost-effective.

Afaik polarized light sensors would be the key to tracking in cloudy weather.

Check out this robot direction sensing design, based on the polarized light sensing used by insects: http://adb.sagepub.com/content/6/1/131.abstract

The stone iolite is thought (by some) to have been the 'sunstone' or compass used by vikings for navigation, because it is pleochroic and naturally polarizes light, so gives the direction of the sun even in cloudy weather.

The stone iolite is thought (by some) to have been the 'sunstone' or compass.

It is also called optical quality calcite. While studying ancient navigation methods I came across references to this viking method. I obtained a cubic inch sample of the calcite stone and it does work. Two photocells could be used to compare the real and the refracted image seen through the stone. That would upgrade it from tenth century to twentieth century technology.

hey elnav,

yes it's pretty cool eh. I have some iolite which I've seen in action, but hadn't read about the use of calcite until I clipped that link last night.

Elnav:

Anyone who studies ancient navigation techniques is going to have some great ideas.

Could you tell us a bit about the iolite; and how the Vikings used it in navigation.

Its a bit off topic but it sounds really interesting.

Also; can you be a little more detailed on how it could be used in combination with photo cells to step a motor?

Thanks

Gavilan

The iolite is new to me but the optical calcite is what I found out about. I was intrigued anough to find a rock shop that had a piece in stock. It measures 1" thick by roughtly 3/4" X 1-1/4" long. When you hold it above you ot looks similar to a piece of plexigalss or ice. Fairly clear but slightly fuzzy.

The instructions I read said to place a black mark on one of the clear sides which is along the clevage lines of the crystal planes. Some of the surfaces are crazed from fracturing across the grain. dont use such a side.

When you view the mark through the crystal you see two marks due to the refraction index. The thicker the piece, the further apart the two marks appear. Rotating the crystal around a axis parallel to your sight line shows the two dots changing in density of darkness. When the density appears equal the, long axis of the crystal is pointing towards the sun. Even when it is hidden behind a 10/10 cloud cover. This was the part that really intrigued me.

I was speculating that some form of light sensors comparing the darkness of the two marks would serve as a photometer and enable the observer to see when equal light hit the two sensors. At that point the edge or axis of the crystal is pointed toward sun. (Coupling a conventional qaudrature photo sensor / tracking circuit would then be relatively simple).

It should be remembered that viking navigation was not that precise. They used a kamal for latitude. Plus/minus a couple of degrees was high precision in those days. When above the arctic circle the sun literally danced circles around them. In fact this was used as a clock ashore when north was fixed and known.

The crystal is obviously capable of a 180 degree ambiguity. Much the same as the old WW2 gnomiometers on radio compasses. But any navigator worth the name would be good enough to be able to resolve the difference. Like the polynesian navigators they also used ocean swells, bird flights and such like to help determine direction and eventually position. It was often a case of dead recogning.

The fact viking trade with a scheduled cargo run year after year tells me the navigators had sufficient expertise to feel confident about over the horizon and out of sight of land navigation.

I misplaced the crystal when I moved, but if I find it again I intend to mount the crystal on a turntable with a mirror below it for easier sighting. An azimuth scale will allow me a more precise reading of horizontal angle. To use the crystal you must place it between the sun and your eye. Otherwise you do not se the refracted image and the polarized light in the correct relationship.

High latitude sailings means a low sun angle at the best of times. I am not sure what happens when you use this at latitudes below 45.

As for making a sun sensor for use in a modern machine, see the comment by xanasax #24 replying to #1. Polarizing sheet can be used to construct a sensor on the same principle as calcite or iolite.

Every photographer I know uses a polarizer filter at some point or other. Under full cloud cover it is not as obvious as a pointer that the calcite is.

Pretty sure that will work elnay, you could also used a redundant system, your proposal when the weather does not obscure the sun rays and the other one, basing from the systematic computed data of sun position that can be predicted by the calendar.

Thank You all for your comments.

I am leaning towards a 15 degree per hour tracker with a photocell based calibration technique. The motor will track at 15 degrees per hour unless overridden by the calibration cell(s).

Again; Thank you for your time and comments.

Gavilan

Here is a chart from that free chart maker I posted a few days ago. Its for the whole year and shows the sun's elevation at any time of any day.....

This shows that "tracking" the Sun, even when possible is simply not needed as you can predict the position, day in day out for the whole year.......just build a mechanism that slavishly follows that.....KISS!

Sensor? None that I've seen. I have however seen software that tracks annual sunrise/sunset and azimuth angle. That would do what you want but it isn't a "sensor".

Why not just stick a small photovoltaic panel in the shade behind the reflector so that when the sun shines on the panel it drives a motor which is then geared down to move the reflector. OK it will not work when there is cloud cover but it will catch up pretty quick when the sun comes out:-

There are already I am sure of it - programs which track stars in the sky... & that should include our own wonderful sun. If a telescope can be programed to follow a star why can't the same program be modified to control some other swiveling contraption? Carlos

Hello,

Here is an article from Science Buddieswhich outlines how to build a Sun sensor device built from common electrical components bought at the local Radio Shack store of their online store, or another electronics parts store. (CR4 Admin: replaced broken URL).

Enjoy the build if you should choose to undertake it! It was fun for us to build and only took a few hours worth of effort for non-EE's! [BTW, you can also purchase factory assembled sun-tracker devices if you should desire to do so.]

do you mean something like this

http://www.mtmscientific.com/solartracker.html

it wouldn't be too difficult to modify the output & the sensor panel to control a larger drive unit

Exactly!

Great link - thanks

The original post asked for some means ( preferably electronic) that can track the sun even if it is cloudy. Evidently no one bothered to follow through on the optical calcite. Because the calcite does sense sun position even when cloudy. It was used to determine sun position when cloudy. I made the point that a simple photocell arrangement can be used to detect the changes in density of the real and refractedd image in the calcite. Only when the two images are of equal density is the crystal aligned and pointing to the hidden position of the sun behind clouds.

Clock works using sidereal time would also drive a PV array but it is not a sensor and has no means of detecting if the assumed position of the sun agrees with real life. In other words it cannoy correct for any clock error. One further point about telescope clock drives. The PV aray would have to be mounted in an equitorial mount not a standard vertical mount.

Bingo......the mount would have to tilt for full sun 90'.

Great going with the calcite refraction navigation. Just can't get that Sirius out've your system can ye...........

I was going to try the Polynesian method of navigation but my wife wouldn't allow it.

I am told if you know the latitude and longitude of a point on earth all the rest is a formula which will give you the exact position of the sun relative to that point in real time. So all you guys need is a PLC feed it with the formula and you got your positioner. Best positioner that will work regardless of the weather. The PLC must have a real time clock.

I think the world cannot do anything without unnecessary complication. I can explain a simple (and working ) system my son made for a high school science project some 25 years ago. The real challenge is a robust tilt mechanism for the PV cells or solar absorber. JP

"I can explain a simple (and working ) system my son made for a high school science project some 25 years ago"
Then maybe you should?
Del

Royalty issue involved,

I think the bigger challenge is a robust and reliable tracking (frame) mechanism itself. Do you have one now? JP

If you track something that only varies in elevation each day, which elevation change could probably be effectively covered with probably two fixed positions of the solar cells, you are too my mind complicating the whole build. Many do this, but I do feel they haven't really thought the problem right through.

If the solar collector is sized for the worst days in winter, it actually may be too large/effective in summer. So angling for the best collection in winter and leaving it there all the year round, will also probably do the job required.....

Remember that the earth is tilted by 23° to the Sun. When rotating around the Sun, you get a 2 x 23° change in sun elevation, no matter where you are on the planet. Eg. The difference between the mid winter sun position at midday is exactly 46° lower than the mid summer position......everywhere.....

I am a great believer in K.I.S.S.

Did you look at the links I posted for a solar chart (free) for your exact position on planet earth? Post #21.

Also, an accurate clock tracks the sun exactly, which is why sundials also work of course without electricity, but not when its cloudy!!! All these things make the job even more compliicated.....

Check the links carefully in my post #21. I think you may be in for a pleasant surprise!!! I printed my chart out and its very pretty and easy to understand. Only in leap years it might be a day out, which will make no difference whatsoever......

Best wishes.

Solar heating for water and space would involve piping. Not to mention which the weight of such a panel is considerably more than a typical PV panel. Are you sure this really makes semse? How much heating will you get on a cloudy day. The power needed to drive a high power tracker is going to be considerably more than for a PV array. On a cloudy day wher is this power coming from?

The evacuated glass tubes are designed to collect sun heat from all angles without using a tracker mechanism. Might this not be a better solution?

You are so right. Without any details of the proposed unit(s), I am sure that the challenge of making an affordable drive mechanism far outweighs (or outwits) the requirements of a sensing system. With tracking, how much improvement is expected? There was a tracking solar HWS sold many years ago in Australia but its popularity wained even though the sensing was simple and non electronic. JP

If you are using a tubular solar water heater it is nonsense to use such a device . the heating elements being cylindrical it doesn't matter at what angle the sun rays fall. all you have to do is position it north to south.

See reply #40 and #41; the OP already agreed a tracker did not make sense just go with the circular tubes.

An asimuth/altitude mount(horizontal disk with a vertical axis ) is enough for tracking the sun.They are easy to make and can be driven by astro-tracking software.By clicking on the sun on a free downloaded star program (stellarium forex.) the system "senses" where the sun are at any time of the day,month and year. You don't have to find the exact gearing ratio as long as you are inside some given min and max ratioes. The software calculates the precise speeds and commands two servo-motors too simulate an ecvatorial trajectory ,or for the moon,stars or the sun. 12 volt are very common current supply for the most of astro amateurs mounts. You can choose a medium prized system because you don't need the extreme precision requiered for astro photo. I have such a system myself and have some knowledge about the gears & weight and so on. Lars J.

Why are we fixating on the mechanics of tracking a sun hidden by clouds when he solution is to use a solar heat absorber that does not requires a complex tracking mechanism?

In a way, I completely agree with you, but do remember that those evacuated glass tube systems cost a lot of money and if fixed in position (depending upon the angle), say at due south for example, will not give much of an output till 09:00 at best, even in summer, as the first tube will block the light partially to the others......

I personally (God knows what the OP himself thinks!) like the idea of tracking the sun from morning to evening, although I do believe that elevation tracking to be mostly a waste of time no matter what the system is. As the energy collected will be at a low in winter, I would fix the elevation for winter time and then just leave it alone, as in summer, even though the angle may be wrong for summer, the amount of energy collected may still be many times the winter value.

If a system is constructed so that the winter energy collected is the minimum required, the same collector(s) may be FAR too big for the summer, some might even need to be covered up in a good summer to stop "over cooking" things......

A far cheaper system could be built using scrap radiators, maybe only 50% of the effectiveness of the evacuated glass tube system, but for a tiny amount of the cost and a lot of DIY. It would not need to be moveable if it was built so that some collectors pick up any early morning Sun and some collect midday and some early evening.

Oversize the system (as its not as efficient) and see what happens.......

Although I haven't got the time now to build it, at least this year, I have often spent many hours planning such a build in my head and how I would control the pumps and how I would also install some method of stopping the Sun's energy for say when an error occurs, as working with hot/boiling water is just not my thing!!! And working at night also not!!

I guess the OP must decide for himself what he wants, both in price and complexity. but tracking is a costly way to go as the units are heavy and at the mercy of any high winds and storms......If mounted fixed on a roof, they are easily attached and are then as strong as the roof is......also no problems of flexible water connections.....The panels just need to be bigger for the same energy collection levels......

So this blog (and you personally as well, thanks!) have just now convinced me that tracking the Sun is NOT the best way to go, though I would have enjoyed the building and development of such a system, I do now believe that the financial returns are simply not worth it......nor the upkeep either.....many thanks, you helped me and probably the OP too. I now know just how I will proceed, if I ever actually make one!!!

Andy wrote:

I completely agree with you, but do remember that those evacuated glass tube systems cost a lot of money and if fixed in position (depending upon the angle), say at due south for example, will not give much of an output till 09:00 at best, even in summer, as the first tube will block the light partially to the others......

REPLY

Thamks for the reminder about early and late sun. I tend to overlook that because I know I can't count on any sun until about 9:30 - 10:00 in the morning. High cliffs to the east of use blocks the sun. According to the website you supplied ( thanks!) I now have documented proof to those who doubt me that in winter the sun barely reach 30 degrees above a flat horizon before noon which explains why the charts say we only get 1.9 sun hours in winter here.

With the vacuum tubes a simple means of elevating one end of the rack during first four hours would prevent one tube from shadowing the adjacent tube. Like wise reversing this tilt for afternoon would help.

At latitude 54 North we simply do not get much sun in winter so the focus is on other means.Frtunately being situated in the middel of the nothern boreal forests we have lots of pine beetle kill not to mention slash from logging operations. Consequently free fire wood can be had for the cost of chainsaw fuel and trucking the wood home.

We live within a few hundred kilometers of huge hydro-electric dams in the north so we currently enjoy what is reputedly one of the lowest electricity rates. It so cheap it cost less to heat electrically than with natural gas. And wood is even cheaper. Hyro power is green being renewable. Solar and wind has a hard time being cost effective around here. ROI calculates out to around 50 years by which time the equipment is way past its normal lifetime and would have needed replacement already.

Biggest need for electric alternate power is as backup when storms take out the power lines. Due to remoteness it may take days and even a whole week for repairs to be effected.

I am at around 50°N, but no big cliffs.......

The solar charts I posted are really good to work out how much sun you get (ignoring big cliffs!) anywhere on the planet....and for free!!

Its a neat idea to push up one end of the tubes and then the other, but this will involve flexible connections for the water and a weakness in the design with regard to high winds, as well as complicating the design somewhat.....I still don't think its worth doing that....

My daughter's Grandparents-in-Law had a system with glass tubes put on their roof about 2 years ago, with the cost of €15,000 that I could have built a fixed system from scrap rads for at worst €3-5,000.......for €1,000 more with a heat pump.....easily repairable and not moving at all.....

Mr gavilan asked for some kind of tracking and sensing equipment. if that's not the agenda anymore, i assume the problem has found a solution by the other's comments! May be a new question arise: How to maximize his sun-energy device?

OP: "sense the sun through both clear sky and cloud cover? The application for a tracking solar collector used for water and space heating?"

see also reply #43

A tracker only makes sense for PV not heat collection where flexible water line must be accomodated.

"not heat collection where flexible water line must be accomodated"

Not in a parabolic mirror system

But I agree the tube system you recommended is by far the best domestic and light commercial water heating technology

now you get me curious. How does a parabolic mirror system perform under heavy cloud cover? the clouds disperse and diffuse the light considerably

My comment refers to the 'flexible pipe' assertion you made.

I'm puzzled how that then links to: "How does a parabolic mirror system perform under heavy cloud cover?" But if it's important to you - start here

My question and comments are directed to how a solar heat collector reacts to the very diffused and reduced light that finally penetrate through dense cloud cover. PV panels that react to UV does function even under cloudy conditions but it was my impression that heat collectors were more responsive to infra read and this is greatly attenuated by clouds more so than visible and UV light.

I am aware of the site you included a link to but all such tables refer to conditions when skies are clear and sunlight reaches the ground. Here the issue is when cloud cover is dense at 10/10 coverage. During winter if the sun is shining, the sun barely reaches 30 degrees over the horizon at noon. We often have cloud cover a week or so at a time. As illustrated by the diagram at 30 degrees we only get half as much energy from sun at the best of times.

It sounds to me that you might be better off investing in growing fire wood.

A tip when researching in Wiki is to follow the See Also links.

E.g

• Albedo
• Flux
• Power density
• Sunlight
• Sun chart

But also somewhere there will be information on cloud effect on such as AndaSol

Don't need to its free. besides I wasn't the one asking in the first place.

Im a dummy,,,but in the mid 90/s Uof California Berkley( Davis ?), physics and engineering students (i.e. with the help of a professor-forgot his name) built a solar panel car for the engineering students solar car race which runs across the US every year. Im sure you guys have seen or read about the competition. Berkley came up with a device in which the solar panels, or cubes on the car would stay aimed at the sun for peak performance, keep in mind the cars are constantly moving and changing orientation to some degree. The device at the time was kept under tongue and cheek due to the winning stradegy pursuits. However, by now the secret may be out of the bag, its been over 10 years. Maybe look in to that.........

On another note, the solar degree charts here do not take into consideration of your latitude, which would alter my angle of zenith from everyone else's....yes / no ?

Wow; thanks for all the great input.

The advantage of a circular reflector is the ability to increase the collecting area. The collector focuses the energy on the collecting pipe. The collecting pipe needs to have low reflectivity and good thermal conductivity to be effective.

I anticipate using copper pipe at the collector focal point and then pumping the fluid through well insulated pipe to a "decision tree" connection that will feed the fluid to either the space heating radiator or hot water heater.

In the case of a half cylindrical collector the collecting area is equal to diameter X length of the collector.

The design of the system avoids the need for flexible hose or rotating connections for the heat transfer fluid. I'll let you folks figure out how that is done.

I don't expect it to replace either my current hot water heater or space heater. I just want to take a little of the load off.

While reviewing the posts I notice there is some debate as to the advantage of using tracking collectors.

How does the sun angle affect the ability of a flat collector to absorb impinging energy?

A six foot length of an evacuated pipe collector, where the tube diameter is 4 inches will give me only 288 square inches of low efficiency collection; and will be quite expensive.

If I use a 12 inch diameter PVC as the mounts - split them down the middle I have two collectors of 12 inch cross-section. I line the PVC with reflective polished metal and design the system so that the center of the collecting pipe is at the focal point of the collector.

A six foot length collector of 12 inch cross-section will provide 864 square inches of collecting area. The potential collected energy will be proportional to the solar insolation rate and collector cross-section. The thermal energy collected will be some partial value of the potential collected energy.

When I sit down and crunch the actual numbers I will want to consider both the diameter of my transfer pipe and the thermal conductivity of the pipe material to determine if the pipe can handle the potential thermal flux presented by the collector. It may be that I can use a less expensive material for my collecting pipe.

The thermal conductivity and thermal capacitance of the transfer fluid will determine at what rate I must pump the fluid in order to optimize the system.

This all sounds quite complicated and it's probably not necessary to do the math and physics; but for me what I learn from my experience is of the greatest value to me. If I end up making my house a little more energy efficient in the process; or encourage others to do the same, then that is just an added benefit.

It's all gravy.

I will be going into travel status for the next month. I will be in Austin this week, with all the modern amenities and wishing I could see the stars. At this time next week I will be in route to a remote Indonesian Island, where I will stand in awe of the stars; but probably be wondering why I don't have any hot water to shower with.

AND - it will still all be gravy.

Gavilan