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Converting torque to electricity

  1. Apr 5, 2016 #1
    We have a solar tracking device that uses phase change of paraffin wax when heated inside a solar receiver. With a helical slot in a torque tube we can translate the expansion into rotational motion. We use this rotation to point solar panels at the sun, thus generating more electricity. Look us up at << Link removed by Moderator >>

    We have a unit that generates 3,000+ ft lbs of torque. Strong, but only one slow rotation per day. Could this torque be used to directly generate electricity?? How much would we need to make this drive a generator?
    Last edited by a moderator: Apr 6, 2016
  2. jcsd
  3. Apr 5, 2016 #2

    Simon Bridge

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    Probably not as good as the solar panels... it may produce a lot of torque but how much power?
    Demount a solar panel, attach a pulley, see if you can get it to lift a weight.
    You could, in principle, gear one up to rotate a generator shaft quite fast...
    I suppose ##P=\tau\omega##, at a constant speed.
  4. Apr 6, 2016 #3
    Thanks Simon..We've done the weight test, that's actually how we tested the device before connecting it to solar panels.
    Question remains whether at 3,000 ft lbs rotating essentially only 90 degrees per day whether it would even be possible to gear it up to created the speed (and torque) that a generator requires.
  5. Apr 6, 2016 #4
    Power = force X distance / time. Let's assume the "driving arm" is exactly one foot long. The available force is 3,000 pounds. The distance is (twice the radius times pi / 4) (because of 90 degree rotation). So the distance is (2 X pi)/4 or 1.57 feet. Let's assume this happens during daylight hours, say 8 hours. The work is the force times the distance. Divide by seconds and you get a horsepower value. It's pretty small, 0.0003 HP. You should check my numbers, I have the flu and I'm not thinking 100% clearly. Note that you get exactly the same power regardless of the length of the "driving arm"
  6. Apr 7, 2016 #5

    Simon Bridge

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    What he said: though if you've done the weight-lift test then you have a measure of the average available power ... it is P=mgh/t ... the mass lifted, how high you lifted it, and how long that took, and the gravity factor.
    When you run a generator offof it, you cannot get more power than that.

    If a generator with that capability is worth it to you is another story.
    Gearing up will add load due to the nature of gears... which is outside my capabilities sorry.
  7. Apr 7, 2016 #6
    Good stuff. Correct me if I'm wrong, but I think the horsepower would be (3,000x1.57)/(8*60*60)=0.16. Still pretty small. So I read on a generator website that 2hp can generate 1kW of electricity. So, 0.25hp would generate 250W or about the same an one solar panel. So at 0.16, we'll need 2 (rounding up) of our devices to generate the same electricity as 1 solar panel. Solar panels cost about $300. No way (yet) we can build 2 of our devices + the generator for that.
    Thanks for your thoughts!
  8. Apr 7, 2016 #7


    Staff: Mentor

    You are asking about a heliostat. Look up Arduino or Rasberry PI heliostat projects. I'm sure you'll find lots of them, and the discussions may include power requirements, and gear reduction schemes. You may also be able to post your question on forums where heliostat hobbyists hang out.

    A roller bearing on the panel mount would help reduce rotation power needs a lot.

    By the way, don't forget wind when estimating the power required. It may take a lot more energy to rotate the panels on high wind days. If your device is to be reliable 365 days/year, then it must be designed for the worst case day. It may also be smart to design it to "feather" the panels (rotate them to near zero wind resistance position) if winds exceed design.
  9. Apr 7, 2016 #8
    Jeffb47, you forgot to divide by 550 to get horsepower. Do a dimensional analysis on your units and you'll see where your error is.
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