Nancy, I agree this is a great project. PIC processors are used a lot of places. I have played around with their development kits. It's always nice to see/read about the different projects people develop.
@kf2qd: You probably never measured the output of a solar panel when a cloud appears. It is simply actually - the output power is linear with the amount of light.
Since it does not get pitch dark when a cloud appears, the solar panel does not stop delivering power. It may be half the amount and on very severely overcast (dreadful dark grey rainy days as there are in The Netherlands) the output may be in the order of 10%, but they still deliver power.
Since the tracker should consume a minuscule amount of power, it has a very large gear reduction since it does not move fast, so it can be powered by a small motor and even that motor needs to operation only part time, there is no reason to stop tracking when "the sun disappears" behind a cloud. The power consumed by the tracker should be in the order of 1% of the array output and it has the potential to double the daily energy output - depending on latitude and shadowing.
At the end of the day the panels are typically parked in more or less horizontal position anyway, which is safety in case a storm comes at night.
Note that the tracker will not lose the sun even when it is clouded for a long time, since the sun has a predictable path. So, as long as you do not completely reset your tracker and it has either a clock or knowledge of the previus sun position it can continue to point the panels to the correct position even when it has no good measurements for some time (or ever - it may be completely based on time and latitude to calculate the sun position).
I wonder why so many sensors were used. I know that it is in theory possible to make a tracker with a single photo sensor, but the simplest systems I have seen always use two pairs of sensors, one in X and one in Y direction to find the sun when starting from any orientation.
It's me, the author again. Does anyone have a good circuit for Gadget Freak that finds the sun with analog comparators? I tried using several op amp comparators all voting on who had the brightest signal. It didn't work very well. Show me where I went wrong. Maybe you used your method for some other purpose.
The aestetics are not only depending on the whim of the home owner, but often also simply required by local ordinance or even by law. and then also on technical feasibility. I installed a solar system on my 40 deg sloped roof (which was pretty ideal) in The Netherlands, while the roof was pointing S-W, which was not idea but even for that relative large error in orientation, the reduction in total output was less than 10%. Besides that it was not allowed to mount the panels any other way than parallel to the roof and it would also be rather infeasible to mount panels at an angle on a sloped tile roof, while it is trivial to mount panels a few inches above the tiles in an array. The array covered the majority of the roof surface and I already had to appear in front of the commission judging the aesthetics of the neighborhood because they did not like my design (after a neighbor complained - probably jealousy). When I showed a cleverly taken picture with the blue sky reflecting on both the (blue) panels and the 3 windows in the roof as well as the hot water collector, so they all appeared in the same surface and matching color, nicely contrasting to the yellow brick of the walls, they saw the idea of the complete surface and no longer applied the standard law that you have to stay away from windows with solar panels and approved my design. Pfoei. (This was a 3kWp array plus a solar hot water panel of 6x6ft embedded between 3 tilting windows of 3x6ft)
Hi, Gregarious2. Aloha, Brah. I lived in Hawaii for 22 years.
It's fun to see people think of all the alternative solutions. There is no one right way. It depends upon your application and design goals.
My problem with analog quad cell was that the motors were constantly being nagged, "this way; oops cloud; this way." The MCU could be programmed with some hysteresis / forgiveness and sleep to save energy. Again, if you are using a parabolic channel to focus along a water pipe, you need high accuracy. In Hawaii, you have solar power to waste. Here in Montana we want that boy aimed as accurately as we can.
Hey, Dudes: anybody want to comment about applications for multiplexing apart from the solar application?
I've used the quad cell method ( both analog and digital ) with concentrator systems and it works quite well as part of a servoed tracker. Digital was a bit easier to cope with the sun behind clouds, sunset vs sunrise positions, etc... conditions. Hamamatsu once sold a photodetector array ( S9132 ) that output XY position of a bright spot using an on board row column multiplexer scheme. You clocked the chip and looked for maxval on the x and y data streams. I think it was under $30.
One thing I've noticed here in Hawai'i with a huge boom on PV systems. ( we currently pay .45 / kwh ) Most of the installers seem to go for aesthetics rather than efficiency. Driving through any neighborhood, you will see most PV arrays are flat to the roof pitch in whatever direction the house is pointed. The lucky folks face south.
zomeworks, a company in new mexico has a totally non electrical solution to the tracking problem thats quite popular with cattle ranchers with desert watering holes that uses 2 canisters of freon (or similar) connected with piping so that when the panels shade one it becomes heavier tilting the panels appropriately. there's lots of ways to skin this cat !
to kf2qd, I agree that the MCU program should include inputs and logic to stop tracking when the sun is dim. BTW, I've messaged the editor to include my source code in the link. There should also be a hysteresis in searching, i.e., consider letting the MCU and motors sleep for 2 or 3 minutes before making a correction. Hysteresis is more important for a small collector than a big array. And let's remember that not all collectors are flat panels. If we use a parabolic channel to focus light along a pipe, we need high aiming accuracy -- and we need to stop tracking when ambient conditions or temperature say it's a waste of energy.
I have thought about a solar tracker - say you have a day when it starts out sunny, but gets heavy overcast. Do you keep tracking, hoping for sun, or do you shut down your tracker because there isn't enough power coming off the panel to replace wha the tracker uses? Or the day starts off cloudy and the sun comes out at noon. If 2 of these days some in sequence it was cheaper to quit tracking when the sun faded, and start tracking when the sun reached some minimum intensity.
For solar power you really need to consider the total power budget of every component. If a given component uses too much power, and a tracker running when there is no sun is a total waste of power, then it means you won't have power for other, possibly more important uses. If I don't run the tracker on a day with no sun, I have power for lights that night so a disabled resident can see their way to the restroom.
So - on a day with plenty of sun, solar tracking is a plus. An a day with no sun, tracking the "non-existant" sun is a total loss.
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