steering controller for solar panels

[marktinkerman]

Hi we need to make several controllers for photovoltaic panels. what we guess is needed is 2 light sensors (or small pv's)set at 90 deg to each other and a circuit to compare the outputs and when one is greater than the other by a setable amount to switch a relay controlling a smallish 12 volt reversable motor which steers the panel until voltages are equal when it switches of and is capable of doing the same in the opposite direction depending on where the sky is brightest. the actual 12v motor and related engineering I can see how to arrange it's the control system I have little idea about. We have 3.5 kw of panels assembled in arrays of 4 x 120 watt 7.5 amp panels giving us 30 amp per array on axial mounts so we only need 2 axis control ie. east to west. several of our friends also need the same circuit as we work around the festivals during the summer. see www.samssauna.com or sams sauna on facebook for who we are. thanks mark

 

[betwixt]

There is a simpler way!

The cost and complexity of light based tracking systems makes it rarely worth the effort. The position of the Sun is very predictable and has been for many centuries!
If you mark the panel mount with an arrow in the center position and use a compass to aim it toward the midday Sun (directly north or south depending on where you are)
all you need to do is move it a fixed number of degrees from east to west per minute. If you use a constant stepping speed rather than measuring light intensity it is FAR easier to control, all you need is a geared motor or a stepper motor running at constant speed. Also bear in mind that a tracker may not function in early morning if the panels and sensors were left facing the sunset. You still need a reversing system to set the sunrise angle anyway.

Brian.

 

[siongboon]

Yes I agree that you should just make it simpler.
Anyway it is only one axis, 2 sensors in your system.

Best Regards,
Siong Boon

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[marktinkerman]

There is a simpler way!

The cost and complexity of light based tracking systems makes it rarely worth the effort.

been steering the panels by hand and quite often the brightest part of the sky isn't where the sun is and with 3.5 kw of panels a little bit of expense is worth the extra power mark

 

[betwixt]

Point taken - and I did say 'rarely' !

Your array is larger than mine and I based on it's power capability I would guess it is very heavy. I would still have doubts about the advantage of exact tracking giving you an overall gain when you take into account the amount of motor power needed to rotate all that mass.

If the 'brightest part of the sky' is variable because of cloud cover I would worry about running motors almost continuously as they search for small light level differences.

If you really do want to track max illumination, use two LDRs, close together, both facing directly out from the panel face. Place a divider between them so its shadow is cast to completely cover one or the other LDR at extreme search angles. The difference between their resistances will give you a proportionate control signal.

Brian.

 

[marktinkerman]

Point taken - and I did say 'rarely' !

Your array is larger than mine and I based on it's power capability I would guess it is very heavy. I would still have doubts about the advantage of exact tracking giving you an overall gain when you take into account the amount of motor power needed to rotate all that mass.

If the 'brightest part of the sky' is variable because of cloud cover I would worry about running motors almost continuously as they search for small light level differences.

mass is balanced with the axial mount we use .... tripod with panels mounted on long leg - been steering by hand and do get large gain

thats why we need setable sensors so it can be set to only respond when difference equals..?
Brian.

 

[betwixt]

Interesting- you managed to edit the quote!

The route I would go down would be the two LDRs with their resistance measured by a microprocessor. This way you can easily reprogram the parameters until you find the best levels to use. You can do it without a microprocessor but as you need some timing element to return the panels to east overnight and some sort of motor control, doing it all in software would be much easier than discrete components.

Brian.

 

[marktinkerman]

Interesting- you managed to edit the quote!

The route I would go down would be the two LDRs with their resistance measured by a microprocessor. This way you can easily reprogram the parameters until you find the best levels to use. You can do it without a microprocessor but as you need some timing element to return the panels to east overnight and some sort of motor control, doing it all in software would be much easier than discrete components.

Brian.

had thought of microprocessors but no idea of how to go about it... knowing it's possible and doing it very different, those words "easily reprogram" make me cringe
Ive had 3.5kw of solar panels for about 9 months now and ran two arrays of 4 x 120 watt panels each last year steering them by hand towards max brightness and metering output. Ive realised arrays of 4 are a bit heavy for moving from festie to festie (see www.samssauna.com for what we do) so smaller arrays of 2 or3 panels which mean more arrays to steer and therefor more steering units. can't afford to buy this many at professional price and the supposedly competent electronic engineers I've spoken to haven't done anything to help except blind me with tech speak. have found several designs on various forums and am following up a couple that I can sort of understand. Be very happy if you can come up with suggestion that I can follow. mechanics electrics plumbing etc I'm very good with but computers just about work for me and electronics seems like magic ....string beads together and things happen???Know what I want panels to do but not how to get them to do it. Another thing I want to do is have a light sensor (or read panel output) and when voltage drops below 12v approx trigger 3 pole change over relay (or similar) to reconnect panels in array to 24v to cope with dawn/dusk or heavy overcast and because enough charge controllers to run the amperage Ive got cost a fortune I'm planning on using voltage sensor to switch on dump load using a water filter and uv steriliser on our hot tub as dump load and possibly a washing machine for towels if I have that much excess power although thats unlikely as we have been asked to power stages and lighting and when we not at festies a loud noise will be enough to tell me its time to get the power tools out (we're offgrid at our workshop)

any suggestions in language a mechanic can follow appreciated. mark