Automatic Photovoltaic Tracker

[pontiosf1]

Mr Bernie, answering your question i have to say that the deviate from the true position of the sun is almost 1 degree. To be exact, three times a year the constructor of the tracker would have to change a little the right angle of the panels. These are only for the azimuth, the elevation is another matter.
Mr Milldrone, the site was very useful as i decided to continue the program of PLC likewise.
If i have the sunrise of every morning, i can program the PLC to make steps, until the west terminal will be hitted.
In case of an electrical cut, what should i do? Establishing a movement sensor, is a solution to ensure the correct position of the tracker?

 

[milldrone]

In case of an electrical cut, what should i do?

This is the best reason to have a "real timeclock"

 

[rguimond]

Just for curiosity
1. Why are you doing this when this equipment is already on the market?
2. I have difficulty understanding how you are going to do this without a real time clock - either integral in PLC or external and then triggers PLC to start.
3. What is your allowable or desired error in tracking the sun movement.
4. Why not control for both axes to get best performance? Granted you can adjust vertical weekly or so for seasonal variation?

Seems to me the best is to have both axes controlled.

You can get tables from US Naval Observatory like Mildrone did, or from US Dept of Energy EREN group, or from local astrologer society or local library.

For simplicity I like Bernies idea of using photo detectors. Not only would they have to be shaded but they would need either to sight down a long tube to get best accuracy. Start and stop times could be done with these detectors or by an independent pair (one East for sunrise and one West for sunset). This just might work provided you are willing to readjust and calibrate once a week say.

Dan Bentler

I agree, two axis control would be ideal. I'm currently planning on converting an old 12-foot aluminum mesh satellite dish into a solar heater for my swimming pool. Screwing segments of mirrored lexan to the frame and replacing the old C-band feed horn with a tightly-wound copper coil inside a cap to circulate water through.

This contraption will require super-accurate positioning in order to concentrate reflected sunlight to the focus. I'm guessing, based on the unlikely event that the lexan will conform precisely to a parabolic shape and focus all the light on the focus, that the effective diameter of the focus will be about 12".

For horizontal movement, I'll be attaching a linear actuator to a quadrant (arm) off the vertical shaft. The shaft will be mounted in bearings. I reason that determining the exact location of the sunrise and sunset at summer solstice will allow me to determine the maximum stroke of the actuator and length of the quadrant. The range of horizontal motion won't change throughout the year - I'll return the dish to the "sunrise" position every night and start the actuator at the same time every day...

For vertical movement, I'll use another actuator in conjunction with a look-up table. The actuator will be able to move the dish from the horizon to the azimuth. The look-up table should, throretically, only include the sunrise time (start moving the dish upwards at this time). I haven't research this a lot, but I'm guessing there's a direct relationship between the sunrise time and the angle of the azimuth for every latitude, so the rate of vertical motion should be easy to calculate.

Shouldn't need any "sensors" at all, other than those in the actuators.

 

[milldrone]

I agree, two axis control would be ideal. I'm currently planning on converting an old 12-foot aluminum mesh satellite dish into a solar heater

I have heard that the solar power available in a typical C band satellite dish can vaporize pets and garage doors. Just be careful!

 

[leitmotif]

I have heard that the solar power available in a typical C band satellite dish can vaporize pets and garage doors. Just be careful!

Went thru one of those stations. From having done some radiated energy on military radars it had enough power to fry almost anything when transmitting.

As far as the solar goes - when concentrated there is lots of energy also. Two examples
Broken glass can start a forest fire
Magnifying glass and fire starting (non PC to mention ants)

Dan Bentler

 

[rguimond]

I have no doubt that there'll be plenty of energy at the focus of the dish, but unless a lens was installed at the focus to concentrate the light into a narrow beam, I don't think there's any possibility of vaporizing everything. The focus is about 6' from the surface of the dish. If the reflected energy missed the focus, it would dissipate to the original concentration by the time it travelled a further 6'. No fear of burning holes through low-flying aircraft! Birds landing on the focus, however, could be barbequed.

 

[pontiosf1]

I agree that the two axes control should be perfect but it is not allowed by the budget. My client can handles only one axle. I will do the project with a real time clock from the PLC and the tables, like these that mildrone suggested. The equipment from the market are way too expensive.
Thanks again everyone. When i finish my project i will post the problems and the details i will meet.

 

[diat150]

are you going to put a feedback transmitter to verify position of the array? like that you could put a deviation alarm that would let someone know if the alignment gets out of whack in relation to what it should be.

 

[pontiosf1]

Yes a pulse generator will give the exact position anytime. By this means i can restore the system, in possible electrical cut or wrong position, send alarms by gsm modem etc.

 

[kamenges]

Originally posted by leitmotif:

1. Why are you doing this when this equipment is already on the market?

Dan, you realise this can be said of 99.975% of everything produced? And yet we have hudreds of models of cars from tens of different manufacturers and a huge homebrew market in the US alone. My company makes the same items as several other companies do. So just because something is currently available off the shelf is not a compelling reason reason to stop doing it. Where would we be if Peter Nachtwey said others already made motion controllers?

Keith

 

[pontiosf1]

Exactly!

 

[OkiePC]

Okie, were you considering ordinary cadmium sulfide photo detectors as part of a Wheatstone bridge? Then using the resulting imbalance as a bipolar output?

I never actually have worked on a solar tracking application, it is just one of my re-occurring daydreams.

When I was a 22 year old green tire sorter, I lived in a decent little brick house in Duncan, and about a year after we moved in, the 30 gallon electric water heater cracked. It just seeped, so no damage to the utility room wall.

So when I picked up the new heater, I bought some garden hose to 1/2NPT adapters and about 100' of black garden hose which I installed “in series” with the tank inlet. I ran the hose out the widow right behind the tank, and zig-zagged it across the garage roof, getting east and west exposure on a pretty low angle roof.

It was only up there about three months, but I bet it saved me $50. My wife complained about the smell of rubber at first, but I assured her it would go away and it did after a couple of loads of laundry...my work clothes smelled like rubber anyway.

I never really sealed up the window, and so in the early fall, mice started moving in. So I took it down long before the first freeze. I always wanted to set that up again, with a little PLC and an air purge system for freeze prevention.

The last water heater explosion I had to deal with four years ago resulted in the purchase of a $450 Bosch Aquastar tankless gas water heater. That thing rocked, and knocked $25 off my monthly gas bill at least. Infinite hot water (no savings if you have teenagers). It was cool to open the kitchen faucet hot and watch the burner fire up in proportion to the flow. Tankless is the bomb.

Back on the subject. If the target installation is not too harsh, I would put in a simple HMI. The Red Lion G304, or 306K would be great. They boot fast, so you would only need to apply power to set up the parameters, and adjust the clock. Heck, you could probably put the math in the Red Lion as a program, and only need the operator to input his latitude, longitude, direction, date and time..or whatever parameters make sense.

Is this a portable or fixed application?

Then put in an aiming feature, to let the operator or setup technician to manually jog the thing to perfect alignment, and push a touchscreen button to “calibrate”. In the PLC you just save offsets to your raw data table or recalculate it in the Red Lion if you choose that route.

I would think that on a clear day, perfect aiming would result in a voltage peak from the cells. If you add an HMI, a solar battery voltage meter would be a must have item, especially if your customer is going to be adjusting the vertical (seasonal) by hand. That, with the Jog/Calibrate function would make setting peak efficiency most user friendly.

You might want to use something absolute for position feedback, and of course end of travel limit switches, which could be used as home signals with an encoder. A string pot is an inexpensive absolute feedback device that only requires an analog input.

Just my humble okie opinion.

 

[leitmotif]

Dan, you realise this can be said of 99.975% of everything produced? And yet we have hudreds of models of cars from tens of different manufacturers and a huge homebrew market in the US alone. My company makes the same items as several other companies do. So just because something is currently available off the shelf is not a compelling reason reason to stop doing it. Where would we be if Peter Nachtwey said others already made motion controllers?

Keith

Good answer. I wanted to hear it from him but he already answered affirming yours.

He could have said I know there components on the market but I want to do it. Would have been a good answer too.

Dan Bentler

 

[danw]

A solar tale.

Up the road, is a solar installation on a farm. 10 'panels', each the area of a big SUV vehicle, each mounted on an 8" steel pipe, with a tracking system, sensors, actuators and control.

Two weeks ago I was at the place and it was overcast, so much that I could make out the presence of the sun through the clouds, at 1400 hrs. The trackers had the panels almost 'flat', parallel to the earth.

The panels have a digital display showing their instantaneous output in watts. It isn't clear whether that is 'net' watts after local power consumption for running the inverters and controls, but let's assume it is. Each panel was producing 300 watts. 3000 watts total for all ten.

An hour later the overcast cleared, open sky.

The production leaped to 600 watts per panel and the trackers accurately positioned the panels, at the appropriate angles.

600 watts per panel. 10 panels. 6000 watts total.

Here we pay $0.10 USD per Kilowatt hour (KWH). According to the owner, the power company pays $0.05 per KWH for power fed back into the grid.

So the sun's out at 3PM on an early summer day, and he's getting a $0.30/hour return on a $150,000 investment.

For a year round, 12 hour day on average, at $3.60/day, the break even on a $150,000 investment in 4167 days, or 114 years.

 

[longshanks]

This is a little late, but you might take a look at www.redrok.com He has a tracker that uses green LED's for the sensors, listed under the LED3x unit. Might be worth a look. One of his designs is set up for a 24vdc input PLC..... I plan to try it myself.