Project planning

[blakester]

I hope this is the right place for my questions. I want to build a micro hydro plant near a spring. The head is 40 meters and I can get about 80 l/s constant all year round. I was thinking about a PAT because I have heard that they are a lot cheaper then Pelton or Turgo. I would like to hear some ideas from anybody. No matter how many times they have been repeated. Thanks ahead. I posted an image of the spring around here somewhere

[wpowokal]

Link to your "spring"

http://www.otherpower.com/images/scimages/13518/springs.jpg

I don't know how to put your pick up so post a link, oh $#|+ just jealous, I see much power.

allan down under

[TomW]

[blakester]

thanks for posting the image...still waiting for ideas

[hiker]

http://www.otherpower.com/otherpower_hydro.html

[blakester]

thanks but it doesnt cover my numbers (head, flow). I still appreciate it though

[SeanR]

With that much head Turgo or Pelton is probably the easiest.

This guy seen to have done a not to expensive set-up.

http://h-hydro.com/turgo_drive.html

Good luck

Sean

[hydrosun]

PAT or using a pump as a turbine can work but will only be efficient if properly matched with the head and flow. A pelton or turgo are a lot more adjustable. Your numbers indicate that you could produce 12 kilowatts or more depending on the efficiency. Are you on grid or off? What kind of generator are you thinking of using?

Chris

[Ungrounded Lightning Rod]

Yeah.  And tapping the water right at the spring means no leaves and junk to clog the turbine.

Jealousy squared:  I not only don't have a power source like that, I have to burn a bunch of power to pump my (stinky, staining, unsuited-for-swam-coolers, pH water out of a well and pressurize it.

[Ungrounded Lightning Rod]

Or a Banki.

According to this chart from the wikipedia article on water turbines your head/flow combo is nicely in the high-head region of Banki/crossflow turbine practicality and right at the low-head end for Turgo and Pelton.

Bankis are easy to fabricate and self-cleaning.

[Ungrounded Lightning Rod]

Also a Francis might work if you were feeling ambitious.  B-)

In your place I'd go with the Banki for full-on homebrew or buy a prefabbed Turgo rotor.

[blakester]

I plan to connect to the grid, and I dont know about the generator.

[hydrosun]

The simplest generator would be an appropriate sized induction motor and motor starting relay. And you would need a water deflector to shut off the water when the grid goes down. Of course this all depends on the requirements that the utility puts on you. It may take you years to get the permits, if at all. That's if you go the legal route. That's why more of these are done quietly off grid. Good luck.

Chris

[Ungrounded Lightning Rod]

Why shut off the water when the grid goes down?  The spring water has to go away anyhow.  It's not like you're saving stored water behind a dam, giving you an advantage to holding it unless needed.  An automated valve and its controls (which would have to work during power problems) are extra cost and extra failure points - and grid failure is rare.  So you'd like to avoid the device (and depending on it for safety) if you can.

You can let the motor spin at 2x normal RPM until the grid comes back and let the un-decelerated water spray around a bit as it leaves the mill with most if its momentum intact.  (You'll want to have something like a pebble bed to keep it from eroding the tailrace.)

The motor won't generate significantly, even if spinning, unless the grid island has a significantly capacitive power factor - which is unusual.  But if it does it would be enough to electrocute linemen.  So if you're grid-tied you should have a frequency-selective relay driving a cutout contactor, just in case (and to satisfy the power company).

The contactor would be line-side powered so it would pull in as soon as the line comes back and stabilizes.  Turning on the excitation when the motor is spinning near 2x will produce a generation surge roughly equivalent to the startup surge of a motor driving a pump - just feeding power the other way.  You dump the slowdown inertia of the rotor and the generation picks up as the rotor slows from 2x to 1x, a mirror image of a motor starting from stall with a pump load.  So the contactor should be happy with the current surge.

You won't need anything special if you're fed by a 3-phase line.

(Not sure if you need "start" excitation for a single-phase feed to make the motor do the right thing if it happens to be spinning over 1.5x or near 2x the synchronous RPM when the contactor closes.  Note that if you're using a run cap on the third phase with a single-phase feed you may be providing enough capacitance to keep it generating if the grid islands - which would be a problem both if you don't have a cutout and when your cutout closes on grid restoration unless the cutout also unhooks the cap.)

[hydrosun]

The one system I've seen doing this had an electromagnet holding up a weighted lever that when released lowered a paddle to deflect the water away from the pelton. It had to be manually pulled back up to restart. The idea is the same as always having a load on a wind generator when it's turning. That's why a diversion load is used instead of controlling the voltage like you do with solar panels.  I don't even like to have my small Harris units freewheel for too long. I've seen voltage spikes destroy diodes that way. An induction motor may work differently but I'd rather have it shut down for safety.

Chris