Microhydro planning, 1200 ft transmission cable

[mbryner]

Hello guys,

I don't have any experience w/ microhydro and I know most of you don't either, but many of you are experts w/ electricity so you can answer my question!  I'll give some background first, especially for any newcomers.

I'm in the planning stages of my microhydro project.   As most of you know, I live off-grid in the mountains of Southern Oregon.   We have about 3 kw of solar panels, 16 x L16 batteries in 48 VDC setup @ 700+ amp-hours.   The 6/1 Listeroid running WMO at ~2000 watts maximum charge capability is my backup.   Through winter we've had to run it about 2 hours/day (?) average.  

There is a fairly substantial creek, Powell Creek, that cuts through the middle of our land, but I don't have water rights.   A dairy down in the valley has water rights dating back almost 100 years.   I've tried a few times to get non-consumptive use rights, but the county watermaster, BLM (Bureau of Land Management), ODFW (Oregon Dept Fish & Wildlife), etc. are not interested.   Powell Creek runs year-round, but the paved BLM access road is right next to it.  That BLM access road is not just for access to our land -- it continues up into the mountains as a gravel road and is a secondary fire escape road for our area.   Locals drive on it to check on their pot-grows up in the mountains, 4x4'ers, ATV'ers, hunters, etc. all drive on it.   I don't have control over it, even though it runs through my land.   The BLM and watermaster check the creek regularly so they'd see a pipe and I'd have to put a transmission line under the paved road -- therefore, using Powell Creek for a microhydro site is out of the question.

I have another option though:  there are numerous seasonal tributaries to Powell Creek and there's one that is mostly on my property.   We call it Bear Creek (because of the bear we saw up there a few times).   Bear Creek is fairly steep and seasonal, so there are no fish in it.   I'm figuring on bootlegging a small microhydroelectric system on it.   Permits around here are quite a pain, and what I'm going to do won't affect the flow in Powell Creek and I'll be putting the water back in before the creek enters the neighbor's land, so no one will be the wiser.  (Besides, he has a fairly substantial cannabis operation -- look for several in the map picture.)    Right now it's running probably 100's of gal/minute.  (Look at the video link.)   When it's rainy, wintery, cloudy is when we need the extra power, so this will be perfect.  My penstock would be about 1500-1600 feet long through 2" polyethylene pipe.   I picked polyethylene over PVC because of it's flexibility and freeze tolerance.   Also, burying it is out-of-the-question.

The general equation for microhydro average power output, assuming about 50% overall efficiency and including voltage loss of transmission lines, is:

        Vertical Head (ft) x flow (gal/minute) / 10 = watts

Guesstimating for my proposed site:

        Shoulder seasons:  250 ft x 15 gal/min / 10 = 375 watts
        Higher water:        250 ft x 30 gal/min / 10 = 750 watts

These are *very* rough estimates.   I got the vertical head and pipeline length estimates by hiking the area and looking at the elevation data from Google Earth.

On the map picture, the red line is the penstock near Bear Creek.   It would terminate near the 5000 gal water holding tanks.   From the water tanks to the well house is about 400'.   From the well house to the power house (where the batteries and Listeroid are) is about 800'.   So, about 1200' total for transmission line from hydro turbine to the powerhouse.  It was a very expensive cable pull to bring power from the powerhouse to the well house, and on to the water tanks.    IIRC, it was #4 cable,  2 hots, 1 neutral, and a ground.  (Cost about $7k for cable and labor!)  It's all buried in 2" conduit.   It would be difficult to get more cable into that conduit.

The well house mainly just needs 240 V AC for the well pump, and the water tanks don't need much power except for the microwave link for internet.  The main question for this group is: can I cannibalize the neutral and ground wires for microhydro power transmission?  I would disconnect the neutral and ground wires at their ends, and pound in new ground stakes at the well house and the water tanks.   The well pump would then be on the 2 hots coming up from the powerhouse and the new ground.  For CFL lights in the well house, I would use a smallish 2:1 transformer.  One of its output leads would be 120 V hot, and the other would be neutral, bonded to the new ground.  (Acts as an isolation transformer with floating ground, anyway.)   Same idea for the microwave antenna up by the water tanks, except up there  the transformer can be very small because it only draws 20 (?) watts.   Then I could use those nice big ground and neutral wires for transmission of 120 V AC or DC power from the hydroturbine back to the powerhouse.   Would save a lot of money.    Should still be safe, correct?   Everything would still grounded and isolated via transformers, but I'd have multiple grounds in the system.   Bad?   Thanks for any input.

The other option is to use small (i.e 12 gauge wire) in a new conduit, transformed up to 480 V AC at the turbine, and back down-transform at the powerhouse.

Either way, it's going into a MPPT Midnight Solar Classic charge controller.   Don't know what the dump load will be yet.

Marcus

Video of Bear Creek (watch my Australian Shepherd almost slide down the falls.)

In this picture you can see the dwelling and powerhouse in the middle, well house on the far right (just the white speck of roof), and the canyon where Bear Creek is behind it.



Map picture:  


Cables I'm referring to on the line between well and water tanks.   The extra blue wires in the 2" conduit are the water level sense wire loop for turning the well pump on/off.  The 1" conduit contains the CAT5 cable for internet/VOIP phone.

[David Baillie]

Hey Marcus,
Electical is not my specialty but even I know that here competing grounds is a code no no.  I run into the same problem; everything is up to code spec and inspected but now I want to add all sorts of cool stuff that will never see an underwriter's lab.  Are you allowed direct burial cable in your area?  No conduit just a depth of 18" or more like this: http://electrical.about.com/od/typesofelectricalwire/a/directburialcab.html . Thant's one hell of a run whichever way you go. 
Best regards, David

[mbryner]

Hi David,

Thanks for the reply.  

Yes, we can do direct burial.   It's more the size of wire and length required and labor to do that that I'm trying to avoid.    With or without conduit, trenching 1200 ft is a lot of work.

Yes, I realize it wouldn't be completely code compliant.   But I think it should be safe the way I'm proposing.   In the course of internet research, I've seen multiple grounds on alternative power projects, especially on long distance transmission.   I've even seen people advocating no grounds on some projects.   There won't be any inspections on this.   The house is brand new, code compliant, and inspected.   The barn that I'm building this summer falls under agriculture permit, so it doesn't have to go through building permit process either, and everything electrical in it will be totally code compliant.    I don't plan on having any inspectors anywhere near the area in the near future.

Marcus

[Tom Reed]

I'll 2nd that that on messing with the neutral and ground wires. BUT lets talk about how your pump house is wired. Perhaps there might be a way to back feed your power in to that circuit. So tell us, or give us a schematic there.

Looking at your the debris in your stream a hydro-screen will probably be necessary on the intake to the pentstock. Do you subscribe to Home Power Mag? They often have good hydro articles.

But the first thing to do is choose your intake area, make a small dam and measure the flow with a weir. http://www.engineeringtoolbox.com/weirs-flow-rate-d_592.html Then you know what you've really got there for your resource.

While the poly pipe may seem like a good idea, the fittings are huge flow restrictors because they fit inside the pipe. Also the black poly will break down in the sun much more quickly in the sun. Freeze will be a non issue if there is flow in the pipe or there are no dips in the pipe to collect water.

[mbryner]

I'm working on the schematic right now.   It should be ready sometime in the next few hours.

Yes, the intake will have a coanda type filter.   Planning on taking water out of the creek w/ a culvert pipe with a small dam, then over the coanda screen.   See hydroscreen.com.   Not sure where to get the screen though because it looks like those guys are wholesalers.   

Just bought the polyethylene pipe today.   300 ft rolls of 2" diam x 5.   I could cancel the order probably still.   You would pick PVC?   It breaks down in the sun too.   Bell ends on PVC are easy to work with.   

Thanks for the reply.

Marcus

[mbryner]

OK folks.  Here's a schematic.   Now I think I've found a solution.   Since the hydro turbine has DC output, the negative cable is bonded eventually to ground anyway, so I can use the same cable for negative of the hydro turbine and ground.  (Still "code OK".)   And, I know that the 2 hots of the 240 from the inverters can be transformed to 120 w/ one output lead as hot and the other as neutral, correct?  But can the well pump function correctly w/o neutral from the panel at the powerhouse?   So disregard the separate grounds as drawn on this schematic and tell me what you think.

[mbryner]

Here's a better schematic.  Now I'm just taking the neutral and converting it for use as (+) cable for DC from the hydro turbine, and not having 120 V AC unless from a transformer.

[KeithO]

My first  thought from your video is that its a perfect spot for an overshot waterwheel ,but thats just me 

A dumb question from a foreigner : with so much water sloshing around and such a good roof for gathering rain water , why do you need a well and pump ?

cheers
Keith

[SteveU.]

Hi MarcusB
I have one of those seasonal "creeks" bisecting my back yard. Unfortunately only ~10 foot drop in the ~600 feet.
Stick with your poly pipe for the freeze resistance, impact durability and proven 30+ year life. These can and are melt jointed commonly in industry and construction. Check the Internet for how.
But only 2" diameter in 1200 feet I think the flow resistance will kill your power. Be sure and use a calculator for this factor.

Regards
Steve Unruh

[mbryner]

@KeithO:  that amount of water sloshing around only happens in winter & spring.   In summer it's dry here.   That creek will be dried up sometime in June.   Harvesting enough water off the roof to last through summer w/ irrigation would take a gigantic holding tank or pond.   The pond would need all kinds of permits and I don't have any space for it on a hillside.   The holding tank would cost $$$$$$$.

@SteveU.:  Volume makes up for head height.   If your creek is flowing fast enough, you could potential have a site.    Yes, I know about the melt joining of poly pipe.  But where do I get the machine?   More research necessary.   I just bought 2" diam poly pipe in 300' rolls.    Even if there is a joint every 300', it can't be worse than a PVC joint every 20'.  Plus, I could always go back and melt join the joints later.   This thing isn't going to be buried.   According to calcs, the 2" pipe should be about 90% efficient, which is in the ballpark.   Here's a very good calculator: http://www.powerspout.com/advanced-calculator

[BruceM]

Hi Marcus,
I can confirm that even at my elevation (5600 feet) exposed black irrigation tubing lasts for over 20 years without failing from UV exposure.

Re: Your electrical plan.  I think it's unwise to use the safety ground for the microwave line, pump safety ground and the 120VDC current carrying ground.  You are likely to get enough DC bias on end of the line to cause problems, especially for the microwave link at the far end.  The DC noise from the microhydro generator head would also be a concern for the microwave link safety ground.

Instead, I would liberate that wire (existing safety ground for pump and micrwave link) for the DC ground use only.

The well pump head is grounded and in the water typically, and non-grounded pumps were used for 100 years until the last 20.  For the safest setup, the well pump  could be on a ground fault interrupting breaker.  This completely eliminates the need for the safety ground to carry sufficient current to clear a fault, at the expense of some parasite load and nuisance tripping during lightning storms. For myself, I would just provide an earth ground for pump controller, etc, connected to the pump head ground wire (a 4 wire submersible pump cable I assume) and check the resistance of the pump hot wires to that ground annually.  If it gets below 5 Megaohms, I'd think about replacing the pump, as the insulation is starting to fail.  I have configured many pumps in this manner for people who need to reduce ground current magnetic fields at their rural homesites, since with Wye power, the neutral is not transformer isolated, and a good earth connection like a well diverts current into the aquifer, causing net current problems at the site, and elevated magnetic fields.

For the micrwave link, I would use a small step down toroidal transformer to generate 120VAC from the 240VAC, use an appropriately small fuse, and ground the secondary side to earth ground as in the delta distribution system.  In your case you would ground one leg of the secondary to create a neutral and a safety ground.   I've used this arrangement with a non-grounded floating secondary for several  satellite dish setups for 20 years with not problem.  In my case, it was so that I could used a balanced  power filter without creating ground current problems.  Filters with lots of capacitance to ground will cause excessive ground current unless they are balanced, either 240V or 120V with floating or +-60VAC.  When the filter has balanced inputs, the AC current to ground through the matching capacitance per leg is self canceling.

It's fun to see 120VDC listed on someone else's schematics besides mine.  


Best Wishes,
Bruce

[mbryner]

Hi Bruce,

Exactly the input I needed!   Thank you very much!   

So basically you would go back to the 1st wiring schematic I posted, w/ a separate ground wire at the well casing and another up at the internet hardware.   The pump is a 3 wire pump, w/ 2 hots and ground (I think).   I set the pump myself, but I don't remember exactly.   I'll go up and look after work today.   

Marcus

[sailawayrb]

Hi Marcus,

Wow, I missed this thread until now.  Your overall hydro plan sounds good.  I didn't check your penstock head loss and you had best double check that...  As long as your flow rate is relatively small and you are mainly using the site head (i.e., pressure from elevation) to generate the power, you should be OK.  Yes, 120 VDC is nice to work with.  Bruce is dead on correct.  You may want to read this:

http://en.wikipedia.org/wiki/Single-wire_earth_return

Bob B.

[BruceM]

Marcus, Yes, your 2nd schematic, with the ground wire used only for the 120VDC ground is what I'd use.    

BobB-
What I'm proposing is in no way a single wire system, there will be no current flowing through the earth.  That is not something that the homeowner should do.

I believe the single wire systems are bad news from a health perspective (human or livestock).  They inject ALL of the return current through the earth and aquifer. This is even worse than Wye systems, which do not use transformer isolation due to their "ground tie" connecting the distribution neutral to each transformer secondary center tap. Wye systems have about 25% of the total return current to the power plant (as measured on the main cooling pond pipe) flowing in parallel to the neutral wire and through the earth and aquifer. (This according to a power engineering text.) The Wye system grounding practice is an unfortunate outgrowth of Edison's DC distribution system, which of course could not use transformer isolation.

In my opinion, Delta distribution (every transformer set up to provide isolation) is vastly superior from a human and livestock health perspective.  There is no current flowing through the earth for Delta systems because of the transformer isolation/grounding practice. Earthing a transformer at a single point on the secondary side only causes no current flow through the earth. Residential areas with Delta secondary power distribution typically have background magnetic fields below 0.006 milligaus, even with overhead (air insulated) wires (which are another anachronistic mistake). This is less than 1/100th of the typical Wye residential power line frequency magnetic field levels.

We all evolved with the earth's Schuman resonance (biological frequency magnetic fields in the very low microgauss to 100 nanogauss range caused by ringing of the earth from lightning strikes around the world).  Without these fields, in just 2 generations, all fish were born blind. By injecting large amounts of mixed frequency AC current through the earth, my theory is that we  interfere with the Schuman resonance and create a health stressor for ourselves and livestock.  The problem is totally fixable, even in Wye systems, by just changing to the single point grounding practice that has been well known in electrical engineering for much over 50 years. There are such hybrid Wye systems in CA, called "uni-grounded Wye".

End rant. Sorry!
Bruce

[sailawayrb]

Hi Bruce,

I wasn't suggesting that you were proposing a single wire system.  I was just suggesting that Marcus might want to consider a single wire system at the distances he will be running wire.  It has reportedly been accomplished safely in many places if done properly.  There is apparently a huge savings in wire cost and it could be good approach if done properly.  However, I don't have any first-hand experience with single wire.  BTW, I found your rant to be very interesting and certainly something to consider.

Marcus, Wild Blue now has 12Mbps download satellite service for $49/mo.  It is 4 times faster than DSL and works for streaming Netflix and VOIP.

Bob B.