Pelton wheel generator

[expat]

This coming week I'll be helping a buddy install a Pelton wheel and generator at his house. They are not on the electric grid, and rely, at the moment, on Solar (charging batteries for an inverter) and/or a Diesel generator.
They want to cut down on the use of the Generator during the winter months by installing a Pelton wheel to charge the batteries (Solar, in the winter is insufficient)
He has water rights to a small lake about 200 feet above the house, so I figure he can draw on about 80psi to the Pelton wheel (depending on flow rate and pipe friction)
Anybody here with any experiance with these things?

 

[XS650]

Originally Posted By: expat
This coming week I'll be helping a buddy install a Pelton wheel and generator at his house. They are not on the electric grid, and rely, at the moment, on Solar (charging batteries for an inverter) and/or a Diesel generator.
They want to cut down on the use of the Generator during the winter months by installing a Pelton wheel to charge the batteries (Solar, in the winter is insufficient)
He has water rights to a small lake about 200 feet above the house, so I figure he can draw on about 80psi to the Pelton wheel (depending on flow rate and pipe friction)
Anybody here with any experiance with these things?


You should be able to find some design guidelines online. They have been around for over 130 years...and are still great turbines when matched to the job.

He needs to find out the characteristics of his wheel and design the feed system to provide enough water. Think in terms of flow and velocity, pressure is meaningless without flow.

 

[Shannow]

They need to be matched with regard to turbine inlet pressure and turbine operating speed.

(Optimum efficiency is when the water hitting the blade is travelling at twice the bucket speed. Your water velocity is related to the inlet pressure. Your blade velocity is radius times speed.

Flow (power) then comes from available flow rate and nozzle size.

A shallow dam up high is perfect for pelton wheels (properly sized)

 

[expat]

Thanks guys!
The design of the wheel 'is what it is' (it is a horizontal wheel with facility for up to 4 jets, mounted slightly above. It appears the water would divert possibly 90 degrees as it passes through each paddles dish) Head pressure is not changeable, all I can d o is minimise pipe friction, we will use a 3" PVC delivery pipe, to bring the water about 450feet to the wheel. At the wheel I will construct a manifold to feed the jets. jet size (and number) seems to be the only variable.
When the batteries become fully charged it will be necessary to Dump power, it's been suggested we use a heating element for this. But I prefer the idea of shutting off the water supply to the wheel to conserve head water!
I have thought about Lawn sprinkler type solenoid valves at the jet manifold, but fear that they may not be efficient at preserving water pressure when open. A valve at the Dam would be better, but would mean a larger (more expensive) solenoid valve far removed from a power source.
Still scratching my head on this one, because the site is rural, I want to work out and obtain as much stuff as possible before I get out there.
Just looking for Ideas

 

[Shannow]

Shutting it off sounds sensible.

However you decide to do it, ensure that it shuts slowly you'll have the equivalent mass of a car (around 1300lb) column of water running down the pipe, and it won't stop on a dime.

Will need a slowly operating valve, plus some sort of full flow relief.

Don't underdesign, as even 80psi water can hurt and do damage.

Also, a final isolation at the dam would be good for if it all goes wrong.

 

[expat]

Thank you.
I was thinking of a one way valve to bleed air into the pipe immediately after the shut off valve/solenoid (because the solenoid may close too quickly) this could also prevent syphoning if there is a leak.

All my pipe and fittings are rated 200 psi.

 

[XS650]

One possibility for flow control would be a solenoid valve at each jet. Controlling power by shutting one or more jets down would maintain or slightly increase head and the remaining operating jet's efficiency wouldn't take a hit. Check specs on some lawn irrigation type valves, some manufacturers give pressure drop vs flow and they don't look too shabby.

Shannow point about not making major instant changes in flow is right on

 

[expat]

My fear now is with solenoid (irrigation) type valves at the jets closing too quickly.
Perhaps a Blow Off valve to protect against water hammer?
Or an Air tube as a Damper?

 

[XS650]

Originally Posted By: expat
My fear now is with solenoid (irrigation) type valves at the jets closing too quickly.
Perhaps a Blow Off valve to protect against water hammer?
Or an Air tube as a Damper?


Blow off valve sounds good to me, but my experience with systems like that is limited.

Air tube design would be trickier.

 

[IndyIan]

What are hot water tank blow off valves set for? Maybe a few of those plus an air tube or heavy duty well water pressure tank to absorb the hammer?

Sounds like a fun project, we've got about 150' of elevation change by my house I did rough numbers on levelling an area at the top of the hill to collect water and then generating electricity with a water turbine but it didn't work out...

 

[Shannow]

We've got all sorts around the power station.

There's a pelton wheel installation, and rather than blow offs, they've got power open spring close butterfly valves, with the butterflies timed to close slowly. Works good.

Simple relief valves don't work well in water hammer situations, and are typically specialised diaphragm valves with sensing lines.

Depending on the flows and pressures you have, a Tee piece full of tennis balls could help on the closing of the very last valve.

Need lots more information on power outputs and flows 'though.

 

[XS650]

Originally Posted By: Shannow
We've got all sorts around the power station.


There is lots of Pelton history around here. They were invented in the 19th century in Camptonville California, a mining town about 60 miles by twisty road from where I live. I was in some small mining town museum a few years ago and they had a small Pelton wheel that had been used to direct drive a sewing machine in the 19th century.

 

[DKT]

I think the lawn sprinkler solenoids would probably work well on the header. They will handle the pressure, and I don't think they restrict flow that much. Also if you use 4, one for each jet, you can probably just turn them off one at a time over a couple of minutes and aleviate the water hammer possibilities.

I went to the rainbird website and they have residential valves rated at 150 psi. Home Depot has just your basic 1" valve (rated for 40 gpm max) for $16.

Just a thought.

 

[XS650]

Originally Posted By: DKT
I think the lawn sprinkler solenoids would probably work well on the header. They will handle the pressure, and I don't think they restrict flow that much. Also if you use 4, one for each jet, you can probably just turn them off one at a time over a couple of minutes and aleviate the water hammer possibilities.

I went to the rainbird website and they have residential valves rated at 150 psi. Home Depot has just your basic 1" valve (rated for 40 gpm max) for $16.

Just a thought.


He would still need something to handle the case where all valves close at once because of a power failure. Valves designed to close slowly like Shannow mentioned would be nice but probably expensive.

 

[DKT]

Redundent power might be cheaper, these small valves only draw 1/4 amp at 24V. Just trying to keep the cost down.

 

[DKT]

I did a little web searching and you might find this interesting:
http://www.pumpfundamentals.com/micro-hydro.pdf

 

[scurvy]

Stupid question here.

Why not go with manually operated valves, if cost is a concern? A big gate valve for the main flow and quarter turn ball valves for the individual jets, or something like that.

They're almost always cheaper than 'automatic' valves and more reliable.

 

[expat]

"Why not go with manually operated valves, if cost is a concern? A big gate valve for the main flow and quarter turn ball valves for the individual jets, or something like that."

The reason is, the batteries may get fully charged at, say, 10 O clock at night, would YOU want to go outside, in the Winter to turn valves off?
Dumping power is OK in November, But what about April, when the Dam will only get lower?

I am on the outside with this, I will not have to live with, or Pay for this installation. But I am getting an insight to the considerations (assuming you have a limited budget)
Do you put that extra money into your Battery pack? Better Electronics to monitor and charge those Batteries? Automatic valves to save some Head water, so you can get another weeks use from the pelton Wheel before the Diesel Gen set kicks in?
Bigger Better Solar panels to extend the time when you can get solar power? The list goes on, AND round and round.

 

[scurvy]

Originally Posted By: expat
The reason is, the batteries may get fully charged at, say, 10 O clock at night, would YOU want to go outside, in the Winter to turn valves off?
Dumping power is OK in November, But what about April, when the Dam will only get lower?

If it were me, yes, I would go outside to turn valves off. Or I would see the batteries approaching 90% charged in the evening and shut the valves off before going to bed.

But I don't know the customers' needs/wants/etc... which is why I asked. Thanks for the clarification.

 

[expat]

"If it were me, yes, I would go outside to turn valves off. Or I would see the batteries approaching 90% charged in the evening and shut the valves off before going to bed."

I could see how that could get tiresome, especially considering the location.