Community Off-Grid Living in a SHTF scenario

This design and the Bolivian unit in post 20 use jet nozzles, which convert pressure head (due to elevation difference) to velocity head which is then absorbed by the impellers. Both are small scale machines and simply would not do for a community supply, tho' they could be ganged. Bear in mind that the output of the machines is dependent on the mass flow rate (gpm, if you will) regardless of elevation difference. If you have the flow, you can get the power. These two little turbines above are completely unsuitable for the river, the delta h is simply too low to convert to any useful velocity head.

Which brings me back to the river: That floatation tire thing by G_f has some potential, with a lot of ifs.
-Gotta keep the trees off it, needs upstream barrier.
-Completely independent of river stage, a good thing.
-Wants a really positive and permanent anchor.
This bag operates by converting the speed of the river mass (velocity head due to existing stream speed, not converted from differential height ) at the surface. Very inefficient, but possibly usable on a small scale, dunno. The same sort of speed principle is used in some of these experimental tidal power units, except that the tidal turbines are completely submerged where they can take flow across the entire surface of the blades, sim to melbo's windmills. To harness the river directly without a dam would require a similar low head propeller submerged with all the attendant PIAs with anchorage and physical protection from logs (and oh!! the poor salmon!!)

One of those little impulse units showed operating info at 50 hz, not the 60 that we use. Re-rating for 60 hz is easy, but needs to be done, and the issue of speed control isn't well addressed. AC wants very close speed control, most household stuff isn't too sensitive, but if you get too far off design (say out side the range of 58 to 62 hz), things start failing (i.e., burning up or out.)

There's also the problem of synchronizing multiple units that might be running in parallel, not a trivial task with AC. It is MUCH easier to match voltages between multiple machines in DC, which is one reason I advocate for DC generation and battery storage and buffering in small scale operations like household size. Inverters can (not all do, it depends on how many steps they take in the digital approximation of what is a naturally analog wave) provide a much "cleaner" AC sin wave than the most sophisticated synchronizing gear.

Speed control then: Backing up a bit for readers that might be curious. Think of your foot on the accelerator in your car. You raise and lower your foot to hold a speed over the road, regardless of how steep (or not) the hill is, you are governing the speed. Now, engage cruise, and the machine takes over the governing, and does a much better job of it than you can. (Pays better attention to the task at hand than you do.) The analog to cruise control on the turbine is a governor that throttles water flow to hold a very precise speed on the output shaft. When you plug your hair dryer, fridge, or power saw in, it expects to see AC at 60 hz, and if they don't, bad, expensive, things can happen. To dodge the bad expensive things, the controls on the generators are good (but expensive) things.

 

Ghrit has some very good information in his post. I would like to bring up another subject that would need to be addressed in this discussion. If you generate DC, then you are seriously limited, in the distance from the Generator Site, you can move the Electrical Power to the Electrical Load. This is the reason AC was able to take over the Market in Electrical Distribution, back in the early days of electrification. With AC, you can use a Transformer to change the Generated Voltage to a very High Voltage, and reduce the I2R losses in the Transmission Lines between the Generator and the Load. Just by jumping the voltage from 120 Vac to 480 Vac drops the I2R losses, and wire sizes for the same transmitted Power Levels, significantly. The only issue that needs to be considered in how high the Transmission Voltage can go, is the Insulators used to isolate the wires from each other, and Ground. I have built 2 mile Transmission Lines at 480 VAC, just using tree limbs, and #12 Stranded Wire, that can move up to 10 Kw. Going higher in voltage, increases the Distance, and Power handling capability, but requires Glass insulators, and better transformers, that are harder to find, laying around in Junk Yards. This means, you do not necessarily have to LIVE, next to your Power Source, and still have good, and significant Power available. 10 Kw will run a Subsistence based Outfit, of three or four families easily. Many of my neighbors run their complete outfits on 3 Kw, and with Battery/Inverter/Charger systems at each local User Location, you can easily use higher Peak Power, for short lengths of time, and then recharge your batteries off the MiniGrid during times of lower power usage, from the MiniGrid, as your Power Source. I have always said, MicroHydro is the absolute CHEAPest Alternative Energy Source you can have. It runs 24/7, and with storage local at each of Multiple User Locations, it can be a very useful community based Power System. .... YMMV....

 

All true regarding power transmission, AC vs. DC and I squared R loss. DC is totally impractical for small systems, community sized or way larger. There are some DC transmission lines that use extremely high voltage (in the range of 100s of kilovolts) DC between grid nodes. We won't ever see that at the scale we are thinking here. DC really is impractical from a loss standpoint, even for in-house use. Conductor size is expensive, yeddy?

All that brings up synchronization again between small sources (generators.) FWIW, Honda now has several small (under 5KW that I know about) gensets that will automatically synchronize themselves as they are added to the system loads. All that tells you is that it can be done. I have not priced Honda sets with against those without the feature, so can't say how much extra it costs. The convenience is peerless if you are locked into gas units. That said, I don't know if they could be used for peaking power; meaning I don't know if they have to communicate with each other to synchronize.

Just in case, and BTW, synchronizing means to get the AC source frequencies in phase with each other and at the same frequency (60 hz for our purposes.) If you synchronize two generators out of phase, it is remarkable how far they can jump. (Don't ask how I know this ---)

ETA - Link for info on power transmission. It doesn't say how HVDC is converted, but give you an idea of some of the concerns.
http://en.wikipedia.org/wiki/Electric_power_transmission

 

ALL the Honda built Inverter/Generators have the feature built-In. All that is required is the Sync Cable, which is sold separately. They do Peak Loading, and Load Sharing, via their EcoThrottle design. Nice units, and very rugged. I have a neighbor that uses a pair of the 2000i versions and one has over 15K Hours on it and still going strong. That is a HUGH LOT of hours on a Gasoline fueled Genset, in anybody's book. .... YMMV....

The classic DC Power Transmission Line is operated by Bonneville Power Administration, and goes from Celilo, Oregon to Slymar, California. This was made possible by development of Very High Voltage Silicon Control Rectifiers, back in the late 60's. The Inverter Station on the Receiving End of this 500KVdc Line is a Hugh Warehouse sized building, where the DC is inverter back into 60 Hz AC.

 

You'll really want a water fall, not just a flowing stream, methinks.

 

So the question becomes, is there a way to get enough power to keep the town bubbling if not perking without incoming utility? Specifically, you want to know if there it a way to harness the river with existing hardware. Well, I don't think so, unless there is a dam close upstream, or pretty high flow highland streams that have a goodly drop to the river. However, there is an alternative, if you have enough lumber to burn in a boiler to make steam, and if there is a really good fabricator/blacksmith around, one could build a piston steam engine. If there happens to be a motor rewind shop in town, he might be able to rebuild a motor to behave like a generator run by the steam engine. Bear in mind that would have to be a multi pole slow speed machine. Is the battery factory old enough to have slow speed motors?

There is such a wide range of unknowns in this scenario that it is at best difficult to speculate. I simply do not know enough about the area to come up with anything more than generalities. Before any real speculation takes place, some specifics are needed.

 

Ghrit, There is another Option, that just might be considered. If one had a SineWave Inverter, a 50 Hp Induction Motor, and a 50HP Source of Power to drive that Motor at 1800 Rpm. One could in Theory, Produce close to 25 Kw of 60 Hz AC Power at the design Voltage of the Induction Motor. You would use the Inverter, to supply the Excitation Voltage input, for the Induction Motor to Sync to, and the mechanical Input to supply the energy, to drive the Induction Motor to Generate the Electricity for the output. I have not tried this idea, but I see no electrical, or mechanical reason that this couldn't be done. I do know that if you drive an Induction Motor faster than its Sync Speed, it will push power back into a connected Grid. T he faster you drive the Motor, the more current it will push into the Grid and will always stay in Sync with that Grid. What is your Opinion? Just Ask'en... YMMV...

 

I don't see how you are going to establish excitation; you need it to get voltage to the inverter before it can provide excite. (Chicken or egg?) Other than that, you are good to go with something mechanical driving the motor as a generator. Digging into memory, generators have some kind of windings to make the field for the mag field to cut, with the exception of permanent magnet machines, which I believe to be pretty small. When you drive an induction motor at synch speed it will indeed generate power rather than use it, but it is excited by the incoming voltage, or so I think. Not really my baliwick.

Now, where it falls apart is that trying to drive the generator faster than synchronous is a fail. At worst, you'll get pole slippage if the machine is synched up, a mechanical fail. If not synched up, the freq goes high.

 

Will have a look at that link tomorrow. (I knew you have wood, that's why I mentioned a boiler --)

Snag some of that lead, we might be casting bullets before this is all over --