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re: hydro electric questions.
4 jul 1997
norman goetz  wrote:
>craig hull  wrote:

>>i have been thinking about putting in a micro-hydro system if and when we
>>build a house in the mountains...

could make for inexpensive and reliable electrical power.
how will you heat your house and hot water?  

>>given a site with sufficient head and flow i would think that the biggest
>>issue with ac would be keeping the turbine turning at a constant (or
>>nearly constant) speed. given today's prices of micro-controlers, i would
>>think that this could be done through a combination of solenoid operated
>>diverters to regulate water flow and a variable power sink (such as
>>electrolyzing water) to provide rapid load balancing and adjustments. 

if there's lots of water power available, or no way to store water uphill,
varying the load on the alternator to keep the frequency constant seems to
fit better than solenoid operated diverters. the cuttyhunk windmill used to
work this way, with a one-byte output from a trs-80 controlling 8 binary-
weighted 1 kw to 128kw air-cooled resistors with series switches in parallel
with the alternator. water cooled resistors can be simpler and smaller. the
control algorithm was simple: if the frequency is too high, increase the
binary output count to increase the load; too low, decrease it. 

>you guess correctly that speed control is the problem.  it is essentially
>unsolvable, so charge diversion is indeed what's done...

i'd call this power diversion, watts vs coulombs.

>it can be done with fairly simple relays rather than microprocessor control.

a microcontroller with commercial "lightning-proof" solid state relays sounds
faster (better frequency control), less expensive, and more reliable to me.
digikey (800) 344-4539 http://www.digikey.com sell microcontrollers, eg the $49
parallax basic-programmable bs2-1c and its accessories, and blue earth and
micromint make similar things. an old pc might work fine... all electronics
(800) 826-5432 http://www.allcorp.com sells inexpensive used solid state
relays, eg teledyne 615-8500 cat# ssrly-14u relays for $8.50 each, ul and csa 
listed, which can control up to 10 amps at 250 vac. a dozen might control an 
18kw alternator. herbach and rademan (800) 848-8001 http://www.herbach.com
sells new tm93hvc2525/6/7 600/1000/3500w 240 vac chromalox immersion heaters
for $3.50/3.95/6.95 each.

>very few sites are built this way any more, unless they are also connected
>to the grid to make money with the "excess".

and reduce air pollution. water heating seems a good load as well. it takes
2.3 kwh to boil away a gallon of water. the cuttyhunk people had plans to heat
island houses electrically with dynamic load switching as a less wasteful
alternative to their desk-sized resistor bank under the windmill...

>one situation in which ac is still considered, is where the generator
>is located more than about 300 feet from the house. then a rough
>unregulated ac of 110v or more is sent to the house, run through a
>transformer to get down to say 24 or 12v, and rectified to dc.  this
>avoids the need for huge and expensive copper cables which would be
>needed otherwise to go the distance without losing a significant
>percent of the current to resistance losses in the cables.

if there's lots of water power available, and the alternator rpm changes
relatively slowly, it seems better to send well-regulated 120/240vac, with
the shunt regulator inside the house, with a lightning arrestor in series,
but no batteries or inverters, and use the excess power for heating water,
etc. some water wheels are more controllable than others. a pelton wheel
with no load might run 6 times faster than under full load, but other types
might only run 20% faster.

nick



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